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The voyage to interstellar space.

Susannah Darling

Katy Mersmann

The magnetometer, the cosmic ray subsystem, the plasma instrument.

By all means, Voyager 1 and Voyager 2 shouldn’t even be here. Now in interstellar space, they are pushing the limits of spacecraft and exploration, journeying through the cosmic neighborhood, giving us our first direct look into the space beyond our star.

But when they launched in 1977, Voyager 1 and Voyager 2 had a different mission: to explore the outer solar system and gather observations directly at the source, from outer planets we had only seen with remote studies. But now, four decades after launch, they’ve journeyed farther than any other spacecraft from Earth; into the cold, quiet world of interstellar space.

Originally designed to measure the properties of the giant planets, the instruments on both spacecraft have spent the past few decades painting a picture of the propagation of solar events from our Sun. And the Voyagers’ new mission focuses not only on effects on space from within our heliosphere — the giant bubble around the Sun filled up by the constant outflow of solar particles called the solar wind — but from outside of it. Though they once helped us look closer at the planets and their relationship to the Sun, they now give us clues about the nature of interstellar space as the spacecraft continue their journey.

The environment they explore is colder, subtler and more tenuous than ever before, and yet the Voyagers continue on, exploring and measuring the interstellar medium, a smorgasbord of gas, plasma and particles from stars and gas regions not originating from our system. Three of the spacecraft’s 10 instruments are the major players that study how space inside the heliosphere differs from interstellar space. Looking at this data together allows scientist to piece together our best-yet picture of the edge of the heliosphere and the interstellar medium. Here are the stories they tell.

On the Sun Spot , we have been exploring the various instruments on Voyager 2 one at a time, and analyzing how scientists read the individual sets of data sent to Earth from the far-reaching spacecraft. But one instrument we have not yet talked about is Voyager 2’s Magnetometer, or MAG for short.

During the Voyagers’ first planetary mission, the MAG was designed to investigate the magnetospheres of planets and their moons, determining the physical mechanics and processes of the interactions of those magnetic fields and the solar wind. After that mission ended, the Voyager spacecraft studied the magnetic field of the heliosphere and beyond, observing the magnetic reach of the Sun and the changes that occur within that reach during solar activity.

Getting the magnetic data as we travel further into space requires an interesting trick. Voyager spins itself around, in a calibration maneuver that allows Voyager to differentiate between the spacecraft’s own magnetic field — that goes along for the ride as it spins — and the magnetic fields of the space it’s traveling through.

The initial peek into the magnetic field beyond the Sun’s influence happened when Voyager 1 crossed the heliopause in 2012. Scientists saw that within the heliosphere, the strength of the magnetic field was quite variable, changing and jumping as Voyager 1 moved through the heliosphere. These changes are due to solar activity. But once Voyager 1 crossed into interstellar space, that variability was silenced. Although the strength of the field was similar to what it was inside the heliosphere, it no longer had the variability associated with the Sun’s outbursts.

This graph shows the magnitude, or the strength, of the magnetic field around the heliopause from January 2012 out to May 2014. Before encountering the heliopause, marked by the orange line, the magnetic strength fluctuates quite a bit. After a bumpy ride through the heliopause in 2012, the magnetic strength stops fluctuating and begins to stabilize in 2013, once the spacecraft is far enough out into the interstellar medium.

In November 2018, Voyager 2 also crossed the heliopause and similarly experienced quite the bumpy ride out of the heliopause. Scientists are excited to see how its journey differs from its twin spacecraft.

Scientists are still working through the MAG data from Voyager 2, and are excited to see how Voyager 2’s journey differed from Voyager 1.

Much like the MAG, the Cosmic Ray Subsystem — called CRS — was originally designed to measure planetary systems. The CRS focused on the compositions of energetic particles in the magnetospheres of Jupiter, Saturn, Uranus and Neptune. Scientists used it to study the charged particles within the solar system and their distribution between the planets. Since it passed the planets, however, the CRS has been studying the heliosphere’s charged particles and — now — the particles in the interstellar medium. 

The CRS measures the count rate, or how many particles detected per second. It does this by using two telescopes: the High Energy Telescope, which measures high energy particles (70MeV) identifiable as interstellar particles, and the Low Energy Telescope, which measures low-energy particles (5MeV) that originate from our Sun. You can think of these particles like a bowling ball hitting a bowling pin versus a bullet hitting the same pin — both will make a measurable impact on the detector, but they’re moving at vastly different speeds. By measuring the amounts of the two kinds of particles, Voyager can provide a sense of the space environment it’s traveling through.

These graphs show the count rate — how many particles per second are interacting with the CRS on average each day — of the galactic ray particles measured by the High Energy Telescope (top graph) and the heliospheric particles measured by the Low Energy Telescope (bottom graph). The line in red shows the data from Voyager 1, time shifted forward 6.32 years from 2012 to match up with the data from Voyager around November 2018, shown in blue.

CRS data from Voyager 2 on Nov. 5, 2018, showed the interstellar particle count rate of the High Energy Telescope increasing to count rates similar to what Voyager 1 saw then leveling out. Similarly, the Low Energy Telescope shows a severe decrease in heliospheric originating particles. This was a key indication that Voyager 2 had moved into interstellar space. Scientists can keep watching these counts to see if the composition of interstellar space particles changes along the journey.

The Plasma Science instrument, or PLS, was made to measure plasma and ionized particles around the outer planets and to measure the solar wind’s influence on those planets. The PLS is made up of four Faraday cups, an instrument that measures the plasma as it passes through the cups and calculates the plasma’s speed, direction and density.

The plasma instrument on Voyager 1 was damaged during a fly-by of Saturn and had to be shut off long before Voyager 1 exited the heliosphere, making it unable to measure the interstellar medium’s plasma properties. With Voyager 2’s crossing, scientists will get the first-ever plasma measurements of the interstellar medium.

Scientists predicted that interstellar plasma measured by Voyager 2 would be higher in density but lower in temperature and speed than plasma inside the heliosphere. And in November 2018, the instrument saw just that for the first time. This suggests that the plasma in this region is getting colder and slower, and, like cars slowing down on a freeway, is beginning to pile up around the heliopause and into the interstellar medium.

And now, thanks to Voyager 2’s PLS, we have a never-before-seen perspective on our heliosphere: The plasma velocity from Earth to the heliopause.

These three graphs tell an amazing story, summarizing a journey of 42 years in one plot. The top section of this graph shows the plasma velocity, how fast the plasma across the heliosphere is moving, against the distance out from Earth. The distance is in astronomical units; one astronomical unit is the average distance between the Sun and Earth, about 93 million miles. For context, Saturn is 10 AU from Earth, while Pluto is about 40 AU away.

The heliopause crossing happened at 120 AU, when the velocity of plasma coming out from the Sun drops to zero (seen on the top graph), and the outward flow of the plasma is diverted — seen in the increase in the two bottom graphs, which show the upwards and downward speeds (the normal velocity, middle graph) and the sideways speed of the solar wind (the tangential velocity, bottom graph) of the solar wind plasma, respectively. This means as the solar wind begins to interact with the interstellar medium, it is pushed out and away, like a wave hitting the side of a cliff.  

Looking at each instrument in isolation, however, does not tell the full story of what interstellar space at the heliopause looks like. Together, these instruments tell a story of the transition from the turbulent, active space within our Sun’s influence to the relatively calm waters on the edge of interstellar space.

The MAG shows that the magnetic field strength decreases sharply in the interstellar medium. The CRS data shows an increase in interstellar cosmic rays, and a decrease in heliospheric particles. And finally, the PLS shows that there’s no longer any detectable solar wind.

Now that the Voyagers are outside of the heliosphere, their new perspective will provide new information about the formation and state of our Sun and how it interacts with interstellar space, along with insight into how other stars interact with the interstellar medium.

Voyager 1 and Voyager 2 are providing our first look at the space we would have to pass through if humanity ever were to travel beyond our home star — a glimpse of our neighborhood in space.  

Related links:

• Video: “NASA Science Live: Going Interstellar”
• Explore Voyager 2 data on “The Sun Spot” blog

By  Susannah Darling NASA’s Goddard Space Flight Center , Greenbelt, Md.

Interstellar Travel

These speeds are far beyond what current methods of spacecraft propulsion can provide. The energy required to propel a spacecraft to these speeds, regardless of the propulsion system used, is enormous by today’s standards of energy production. At these speeds, collisions by the spacecraft with interstellar dust and gas can produce very dangerous effects both to any passengers and the spacecraft itself.

A number of widely differing strategies have been proposed to deal with these problems, ranging from giant arks that would carry entire societies and ecosystems very slowly, to microscopic space probes. Many different propulsion systems have been proposed to give spacecraft the required speeds to cross interstellar space: these range from different forms of nuclear propulsion, to beamed energy methods that would require megascale engineering projects, to methods based on speculative physics.

For both unmanned and manned interstellar travel, considerable technological and economic challenges would need to be met. Even the most optimistic views about interstellar travel are that it might happen decades in the future; the more common view is that it is a century or more away.

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• The Contents
• The Making of
• Where Are They Now
• Frequently Asked Questions
• Q & A with Ed Stone

golden record

Where are they now.

• frequently asked questions
• Q&A with Ed Stone

Interstellar Mission

Mission Objective

The mission objective of the Voyager Interstellar Mission (VIM) is to extend the NASA exploration of the solar system beyond the neighborhood of the outer planets to the outer limits of the Sun's sphere of influence, and possibly beyond. This extended mission is continuing to characterize the outer solar system environment and search for the heliopause boundary, the outer limits of the Sun's magnetic field and outward flow of the solar wind. Penetration of the heliopause boundary between the solar wind and the interstellar medium will allow measurements to be made of the interstellar fields, particles and waves unaffected by the solar wind.

Mission Characteristic

The VIM is an extension of the Voyager primary mission that was completed in 1989 with the close flyby of Neptune by the Voyager 2 spacecraft. Neptune was the final outer planet visited by a Voyager spacecraft. Voyager 1 completed its planned close flybys of the Jupiter and Saturn planetary systems while Voyager 2, in addition to its own close flybys of Jupiter and Saturn, completed close flybys of the remaining two gas giants, Uranus and Neptune.

At the start of the VIM, the two Voyager spacecraft had been in flight for over 12 years having been launched in August (Voyager 2) and September (Voyager 1), 1977. Voyager 1 was at a distance of approximately 40 AU (Astronomical Unit - mean distance of Earth from the Sun, 150 million kilometers) from the Sun, and Voyager 2 was at a distance of approximately 31 AU.

It is appropriate to consider the VIM as three distinct phases: the termination shock, heliosheath exploration, and interstellar exploration phases. The two Voyager spacecraft began the VIM operating in an environment controlled by the Sun's magnetic field with the plasma particles being dominated by those contained in the expanding supersonic solar wind. This is the characteristic environment of the termination shock phase. At some distance from the Sun, the supersonic solar wind is held back from further expansion by the interstellar wind. The first feature encountered by a spacecraft as a result of this interstellar wind/solar wind interaction was the termination shock where the solar wind slows from supersonic to subsonic speed and large changes in plasma flow direction and magnetic field orientation occur.

Voyager 1 is escaping the solar system at a speed of about 3.6 AU per year, 35 degrees out of the ecliptic plane to the north, in the general direction of the Solar Apex (the direction of the Sun's motion relative to nearby stars). Voyager 2 is also escaping the solar system at a speed of about 3.3 AU per year, 48 degrees out of the ecliptic plane to the south. To check Voyager 1 and 2’s current distance from the sun, visit the mission status page.

Passage through the termination shock ended the termination shock phase and began the heliosheath exploration phase. The heliosheath is the outer layer of the bubble the sun blows around itself (the heliosphere). It is still dominated by the Sun’s magnetic field and particles contained in the solar wind. Voyager 1 crossed the termination shock at 94 AU in December 2004 and Voyager 2 crossed at 84 AU in August 2007. After passage through the termination shock, the Voyager team eagerly awaited each spacecraft's passage through the heliopause. which is the outer extent of the Sun's magnetic field and solar wind.

In this region, the Sun's influence wanes and the beginning of interstellar space can be sensed. It is where the million-mile-per-hour solar winds slows to about 250,000 miles per hour—the first indication that the wind is nearing the heliopause.

On Aug. 25, 2012, Voyager 1 flew beyond the heliopause and entered interstellar space, making it the first human-made object to explore this new territory. At the time, it was at a distance of about 122 AU, or about 11 billion miles (18 billion kilometers) from the sun. This kind of interstellar exploration is the ultimate goal of the Voyager Interstellar Mission. Voyager 2, which is traveling in a different direction from Voyager 1, crossed the heliopause into interstellar space on November 5, 2018.

The Voyagers have enough electrical power and thruster fuel to keep its current suite of science instruments on until at least 2025. By that time, Voyager 1 will be about 13.8 billion miles (22.1 billion kilometers) from the Sun and Voyager 2 will be 11.4 billion miles (18.4 billion kilometers) away. Eventually, the Voyagers will pass other stars. In about 40,000 years, Voyager 1 will drift within 1.6 light-years (9.3 trillion miles) of AC+79 3888, a star in the constellation of Camelopardalis which is heading toward the constellation Ophiuchus. In about 40,000 years, Voyager 2 will pass 1.7 light-years (9.7 trillion miles) from the star Ross 248 and in about 296,000 years, it will pass 4.3 light-years (25 trillion miles) from Sirius, the brightest star in the sky. The Voyagers are destined—perhaps eternally—to wander the Milky Way.

Galactic Association of Intelligent Life - GAILE

Earth branch - information for space pioneers, physics of space travel.

We measure the distances to the stars in units called “light years.” A light year is the distance that a beam of light travels during one Earth year. Though it makes a conveniently large measure of distance, approximately equal to 9.47 E 12 kilometers, it has little relation to travel time between the stars.

For more than two centuries, the physics of Isaac Newton explained all the observable phenomena in our Solar system. Yet by the end of that period, physicists had observed a number of things that didn’t fit Newton’s theories and how they relate to the physics of space travel. While trying to measure the speed of light, they noted that all observers measured the same speed, regardless of how they were moving relative to the light source. Newton’s theories said velocities add linearly. The orbit of the planet Mercury also exhibited perturbations that Newtonian physics could not explain.

Albert Einstein resolved these dilemmas by rejecting two ideas implicit in Newton’s physics; the existence of an absolute inertial frame and the notion that simultaneous events can be simultaneously observed. Einstein accepted the commonsense idea that the laws of physics can be formulated so they are the same for all observers, no matter how they are moving through space. After all, the Earth rotates on its axis and travels about the sun, and the sun orbits the galactic center, and the galaxy in turn moves through space along with thousands of other galaxies. Where then, is the absolute frame of reference that Newton postulated? Starting with these new assumptions, Einstein re-derived the laws of physics to arrive at some startling conclusions. His reasoning is too complex to describe here, but his conclusions are important to the physics of space travel. Einstein showed that an observer in motion relative to an object will observe that object to be shorter than he would if he were at rest relative to the object. Such differences can’t be detected when speeds are low relative to the velocity of light, but at the speeds of interstellar spaceships they become significant.

Let’s say that a space traveller gets into a space ship and heads for the planet Genesis about 44 light years away. If the ship accelerates to 95 percent the speed of light, Genesis now appears only 13.6 light years away. To travellers on board the ship, the trip appears to take just 14.3 years, but to observers watching from Earth or Genesis (all the planets have low velocities relative to each other), the trip appears to take three times as long. This simple example illustrates why travelers aboard a starship perceive that the trip takes less time than the people waiting for them on the planets. The effects of acceleration further complicate the computation of travel times, but the results, calculated by computers, are indicated in the data tables for each colony planet.

Unfortunately, Einstein’s theories went on to predict that no material object could reach or exceed the speed of light relative to another object. Einstein calculated that as the relative speed of an object increased, its mass and therefore its resistance to acceleration would increase too. Experiments with atomic particle accelerators in the mid-20th century verified his calculations with stunning accuracy. Thus as the space age opened, and people began to send their first feeble probes to the other planets of the Solar system, the distances to the stars still seemed overwhelming. Even if technology could have developed new propulsion sources that would enable ships to approach the speed of light, the nearest stars would still have taken decades to reach.

Despite this dismal conclusion, Einstein’s theories did much to advance the cause of space travel, for he predicted that matter could be converted into energy. The inefficient chemical rockets that powered early space vehicles could not possibly have reached the stars. Only direct conversion of large amounts of matter into energy could propel spaceships near the velocity of light. Before the next great breakthrough in physics, the theories of Einstein had formed the basis of the laser fusion drive that propelled Captain Jan De Wyze and the Freedom 4 to Alpha Centauri and the discovery of Wyzdom. The round trip of just 8.6 light years required more than thirteen Earth years of travel time. Yet to the crew of the Freedom 4, the trip seemed to take five years each way. During that time they aged three years and four months less than the people waiting for them on Earth! Thirteen years after the return of the Freedom 4, a young physicist named Raymond Krauchunas again rocked the scientific world with a new comprehensive theory of space travel physics that unified the previously discordant concepts of matter, electricity and quantum mechanics. His theories encompassed all data that supported the theories of Newton, Einstein, Maxwell, and Planck, and went on to explain new data gathered during the voyage of the Freedom 4 and other, early, nearlight-velocity spacecraft. The singularities of mass and energy predicted by Einstein’s theories bothered Krauchunas. Singularities are mathematical concepts of infinity or “infinitesimalness” that never in fact occur in nature. In the past, simple theories predicted the force of an elastic impact or the stress before a crack to be infinite. Yet more refined observation and analysis showed these predictions to be imprecise.

Krauchunas again reexamined the basic postulates of Einstein’s physical theories and found in them subtle, hidden assumptions. Krauchunas rejected the notion that space-time need be described by any finite number of dimensions and postulated the existence of hyperspace. He went on to show how a space ship, or any self-propelling matter, could travel between points in Einstein’s space-time continuum by taking a short cut through hyperspace. Since the object no longer transverses “real” space and time, no time need elapse during the course of the trip.

An analogy may be helpful in understanding hyper-light travel. Imagine two ants walking along a piece of cloth that has been dropped casually on the floor. The cloth is wrinkled and folded back on itself, and the ants are walking on the folded surface. As they walk, one ant makes a tiny hole in two overlapping pieces of the cloth and crawls through it. He emerges at another point on the cloth several inches from the other ant who does not pass through the hole but keeps walking along the surface of the cloth. The second ant doesn’t reach the point on the cloth that the first ant has reached until some time has passed. Meanwhile the first ant has continued along the cloth and remains several inches ahead of the second ant.

In a sense, the first ant traveled faster than the second ant, but in another sense, the first ant did not travel through the same space as the second ant; so it becomes illogical to speak of his velocity relative to the second ant. Einstein envisioned space as a multidimensional analogy of the folded cloth. Krauchunas envisioned a way that people could make holes in the cloth to cross vast distances of “normal” space in no time at all. The path through hyperspace relates in a complex way to both the acceleration and the first derivative of acceleration, known as “jerk,” at the instant of departure from real space-time.

Twenty-five years passed between the publication of Krauchunas’s unified field theory and the launching of the first starship capable of hyperspace travel. The Albert Einstein, launched in 2112, made the round trip to Wyzdom in only thirty-eight months. Time aboard ship measured less than eighteen months. After the Einstein’s return, the ICSE constructed a much larger vessel, the Christopher Columbus, to make a fifteen-year exploration of eight nearby star systems. Yet even though the concept of hyperspace flight was proven, the first pioneers used conventional sublight ships to transport the first permanent colony to Wyzdom.

Though the development of hyperspace travel (sometimes called “space warp”) brought the stars within reach, reducing travel times to a matter of weeks required a second major scientific breakthrough. Prior to this, interstellar travel had been limited by the fact that Humans can tolerate no more than 1.3 g of acceleration for extended periods. Consequently, it took almost nine months for space ships to accelerate to the near light speeds needed to make the jump through hyperspace and another nine months to slow down again. Thus despite the advent of space warp, the minimum interstellar voyage took one and one-half years of Earth time (though the time seemed shorter to the passengers). Development of the artificial gravitational field allowed starships to attain much higher acceleration levels than those achieved in the early days of interstellar travel. These higher acceleration levels shortened trip times appreciably, and the g-field protected passengers and crew from the large acceleration forces undergone in the transition to hyperspace. The g-field also gave ship designers greater freedom to design their vessels, since the field could be used to resist acceleration forces that would tear the ship apart.

Within the confines of the ship, the artificial gfield creates a gravitational field identical in all respects to the gravitational field of a planet. It maintains this static field despite wide swings in the acceleration of the ship itself. Therefore, the gfield generators are not static devices but highly complex automatic equipment. Adjustments can be made so that the amount of gravity felt within the ship varies. Many novice space travellers believe it would be fun to make their journey in a weightless state, but although most people enjoy the sensation of weightlessness for rather brief periods, the weightless condition becomes rather annoying for the extended periods required by interstellar travel. In addition, people inexperienced with weightlessness can easily injure themselves by bumping into walls and ceilings. The crew adjusts the g-field of the ship during the voyage from the Earth value of 9.8 m/s² to the value of the destination planet. This allows pioneers’ bodies to become gradually acclimated to their new planet’s gravitation.

AIR & SPACE MAGAZINE

Interstellar flight: a progress report.

When it comes to star travel, some people won’t take no for an answer

Damond Benningfield

Like many boys growing up in 1950s England, Gerald Webb dreamed of the stars. He followed the exploits of the British Buck Rogers—Dan Dare, “pilot of the future”—and was thrilled by the launch of Sputnik in October 1957. Unlike most boys, Webb followed his dream. He joined the British Interplanetary Society at age 16, earned a degree in physics, and was helping to build payloads for sounding rockets when the society asked for volunteers for a new project: designing an interstellar probe. The team met every few weeks at a pub, The Rising Sun, and in 1978 produced the world’s first detailed plan for a starship: Daedalus , a 60,000-ton agglomeration of spheres, disks, and cones with an engine nozzle big enough to cover Trafalgar Square.

After that, Webb lost touch with the stars for a while. He stayed in the space business, becoming an aerospace consultant and helping to start a company that brokered satellite launches on Russian boosters, but the scope of his work was limited to Earth orbit.

On an unusually mild afternoon last August in Dallas, though, the stars once again feel within his grasp. Webb has joined about 200 other attendees at Starship Congress, a conference dedicated to promoting interstellar travel. The discussions range from solar sails to distributed databases, warp bubbles to game theory, exoplanets to international monetary policy. Session chairs periodically call on Webb, a sort of minor rock star among the interstellar crowd, for comments or to lead off the questioning.

While the speakers in the hotel meeting room talk about future searches for extraterrestrial intelligence, Webb, taking a break from the presentations, sits just outside, fidgeting with piles of brochures on a display table. Starship posters line the wall behind him, while another table offers colorful postcards promoting “Sunny Gliese 581e: Only 22 Light Years.”

“There hasn’t been a lot of progress in the field—all the problems we talked about are still being discussed,” Webb says. “I’m not disappointed in the lack of progress though. Things have started to get better—the necessary conditions for a starship are being laid. It’s reached the point where I think it’s inevitable. It will happen.”

Most of the other conference attendees likely would agree. A surge in interest in the last few years, driven largely by the discovery of hundreds of planets in other star systems and a bit of money from DARPA—the Defense Advanced Research Projects Agency—has led to the creation of several star-travel advocacy groups trying to fan enthusiasm through conferences; Starship Congress is one of several in 2013 alone. “There are some serious scientists and engineers looking at this because they’re dedicated to the idea of interstellar travel,” says Les Johnson, a physicist, science fiction writer and editor, and deputy manager of the Advanced Concepts Office at NASA’s Marshall Space Flight Center in Alabama. “It’s not some hobbyists in their garage. There’s no serious funding, but…a lot of us continue to meet, gather, publish, and work on this stuff in our free time.”

At the turn of the century, Johnson led a project that was one of the first to actually pay researchers to study the idea of interstellar travel, and one of the first drivers (along with a similar effort at another NASA center) of the current increase in interest. He was managing NASA’s efforts to link spacecraft with tethers when the agency began looking for a “stretch” goal: evaluating whether it was possible to send probes or people to other stars. “I was the new guy in the group, and it sounded exciting, so I raised my hand and said ‘I’ll do it!’ ” Johnson recalls. “For about two years, I had the coolest job title in NASA: manager of the interstellar propulsion research project.”

Johnson’s team determined that the most practical path to the stars was via solar sails, which required fewer scientific breakthroughs than fusion-powered nuclear engines or exotic propulsion methods like warp drive. Ultra-thin sails would use the faint but constant pressure of sunlight or high-powered lasers to propel them to a few percent of the speed of light. (NASA plans to launch a 124-foot solar sail, called Sunjammer after a sail in an Arthur C. Clarke novel, in 2015, although it will stay well within the bounds of the solar system.) “Sailships are the only way we know to get to velocities that are anywhere close to the speed of light,” Gregory Benford, another physicist/sci-fi author, tells the Starship Congress attendees.

Yet even with this relatively reasonable-sounding technology, the problems are so vast that we won’t be sailing to the stars anytime soon. Johnson says that to propel a craft to Alpha Centauri, the nearest star system, a solar sail would have to be as big as the state of Alabama, and would need a millennium to travel the 4.3-light-year distance. Change the power source from solar radiation to terawatt-scale lasers and you could cut the travel time to a century. The big drawback? Such a system would require power “equivalent to the total output of humanity today,” Johnson says.

And that neatly encapsulates the challenge of traveling to the stars. Even if the science allows it, the engineering demands are monumental, the energy requirements stupendous, the distances unfathomable, the time scales...well, pick your own adjective. To understand the scale of the problem, consider that the most distant spacecraft yet launched, Voyager 1, recently exited the solar system—35 years after it left Earth. At that rate, if the probe were headed toward Alpha Centauri (it’s not), it would not arrive for another 75,000 years.

Those pursuing the idea of interstellar flight remain undaunted. “We have to keep pushing,” says Richard Obousy, an organizer of the Starship Congress and a director of Icarus Interstellar, the conference’s host organization. “It’s a long, hard road, but what humanity is capable of on long time scales is tremendous.”

The long-road, long-time-scale theme is a common one. It’s reflected in the title of the group that won this field’s equivalent of the lottery: a half-million-dollar grant from DARPA. The 100 Year Starship (100YSS) organization, which was created after a 2011 agency-sponsored conference, is charged with developing the infrastructure needed to make it possible to launch a crew-carrying starship within the next century.

“Our task is to push radical leaps in technology design,” says 100YSS director Mae Jemison, a physician and former space shuttle astronaut who once guest-starred on “Star Trek: The Next Generation.” “I’m sure that we can create the capabilities. That’s a rather radical and bold thing to say. But I always think about putting a human on the moon.... When President Kennedy proposed landing a person on the moon in 1961, we had barely gotten someone off on a suborbital flight.”

The group’s early focus has been less about leaps in technology than about the mundane tasks of running an organization: raising money, arranging conferences, setting up a research institute. Much of the emphasis so far has been on education, public outreach, and linking starship research to problems on Earth. That has led to some of the more technology-oriented folks in the interstellar community feeling mildly resentful. Icarus, an original partner in the DARPA grant, dropped out “to pursue our own way,” Obousy says.

Yet Jemison, who operates 100YSS from a small suite of offices in Houston’s eclectic Montrose neighborhood, says the challenges of building a starship go far beyond just designing the hardware. “Everything that we need to know to have a successful human trip beyond our solar system are the very same things that we need to know to survive as a species on this planet,” she says. “If we look around us, we’re already on a starship.”

If our goal is to escape this particular starship and head for a similar one orbiting another star, we’ll need some kind of advanced propulsion. The topic brings out, depending on your perspective, radical dreamers—or just radicals. Starship Congress offered ideas for fission-fragment rockets, inertial containment fusion power, magnetic sails, and FTL (faster-than-light) warp drives, among others. Some concepts, like gigantic solar sails, are allowed by the laws of physics, but require engineering well beyond today’s capabilities. Others, like matter-antimatter engines and warp bubbles, draw oohs from the faithful but mild snickers from the more skeptical, who say the plans require too many leaps of faith.

“If you really want to get something done, science fiction won’t get it built,” says attendee Philip Lubin, a professor of physics at the University of California at Santa Barbara. “In some of the presentations, it was ‘A miracle is required here, a miracle is required here, a miracle is required here.’ But there was no acknowledgment of that.” Lubin acted as conference contrarian, frequently asking presenters pointed questions about their proposed technologies. But he also offered up his own sci-fi-sounding project: a planetary defense system that could double as a solar sail’s power source, using beamed energy to propel an unmanned probe to the stars.

The system would collect sunlight with miles-wide solar arrays in Earth orbit and convert it to a beam of energy, similar to a giant laser. Lubin says that over a year, such a beam could completely vaporize a threatening asteroid a third of a mile (1,760 feet) wide at a range of one astronomical unit—the distance from Earth to the sun (93 million miles)—and deflect much larger ones. “It wouldn’t require any miracles, just a lot of hard work,” he says. Such a system could start on a much smaller scale—big enough to zap space debris, perhaps—then be expanded as engineering and funding allow.

If used to propel starships, the energy beam could boost probes to substantial speeds, Lubin says. A 100-kilogram (220-pound) probe with a 100-foot reflector to catch the beam could reach Mars in three days; with a much larger reflector, such a probe could hit three percent of lightspeed—up to 20 million mph—by the time it reached the edge of the solar system in less than a month.

Such a probe might not survive all the way to another star, and even if it did, communications would be a major challenge. But some suggest that the first destination for an interstellar probe need not be a star. A journey into interstellar space might do just fine, providing a technology shakedown and an incremental step toward the stars, just as the suborbital Mercury flights of Alan Shepard and Gus Grissom were the first steps toward Neil Armstrong’s “giant leap” onto the moon. NASA’s Les Johnson thinks that missions to distances of 250 to 1,000 astronomical units (two to eight times Voyager 1’s current distance) could be ready for launch within a few decades.

For most interstellar mission planners, the ultimate goal is to send people blasting across the cosmos in big honkin’ spaceships. Few expect that to happen for at least a century, leaving scientists and engineers plenty of time to work out strategies. Meanwhile, others are already considering what may be the most important element of star travel: the people who will make that long—and presumably one-way—journey.

Sheryl Bishop, a social psychologist at the University of Texas Medical Branch, has studied mountain climbers, cavers, teams that have wintered over in Antarctica, and others to understand the motivations and behaviors of those who operate in extreme environments. In 2005, she even participated in a simulated Mars expedition in the Utah desert, spending two weeks with an all-woman crew.

That work brought her to the attention of Danish filmmaker Michael Madsen, who is producing a documentary titled Odyssey about how we might select the crew for a “worldship”—a miles-long craft that would carry hundreds or thousands on a generations-long star trek.

“The limitless expectations we have on Earth don’t apply” to such a journey, Bishop says. “Columbus didn’t have to worry about breathing—he wasn’t going to suffocate if something went wrong with the ship. With a worldship, you’re through with everybody on Earth, and everybody on Earth is through with you. So what kind of person is both willing to go and sane enough to select? They’d have no family ties, they wouldn’t miss the skies and seas. After a while you start thinking, ‘Oh my God—I’m defining a sociopath.’ ”

Such is the state of interstellar-flight planning, circa 2013—separating the committed from those who perhaps should be committed, the visionaries from the daydreamers, the difficult from the impossible. Even the experts can’t always tell the difference, so they keep studying, keep advocating, keep pushing toward the stars.

Damond Benningfield is a freelance science writer and audio producer in Austin, Texas.

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Damond Benningfield is a science writer and audio producer in Austin, Texas. See more at damondbenningfield.com .

News | May 18, 2020

Cosmic distances.

By Preston Dyches

Astronomical units are a useful measure for distances in our solar system, while light years are more practical for distances to the stars. The nearest star system, Alpha Centauri, is seen from Saturn in this image from NASA’s Cassini spacecraft. Credit: NASA/JPL/Space Science Institute

The space beyond Earth is so incredibly vast that units of measure which are convenient for us in our everyday lives can become GIGANTIC. Distances between the planets, and especially between the stars, can become so big when expressed in miles and kilometers that they're unwieldy. So for cosmic distances, we switch to whole other types of units: astronomical units, light years and parsecs.

Astronomical units, abbreviated AU, are a useful unit of measure within our solar system. One AU is the distance from the Sun to Earth's orbit, which is about 93 million miles (150 million kilometers). When measured in astronomical units, the 886,000,000-mile (1,400,000,000-kilometer) distance from the Sun to Saturn's orbit, is a much more manageable 9.5 AU. So astronomical units are a great way to compress truly astronomical numbers to a more manageable size.

Astronomical units also make it easy to think about distances between solar system objects. They make it easy to see that Jupiter orbits five times farther from the Sun than Earth, and that Saturn is twice as far from the Sun as Jupiter. (This is because, technically, you're expressing every distance as a ratio of the distance from Earth to the Sun. Convenient!)

For much greater distances — interstellar distances — astronomers use light years. A light year is the distance a photon of light travels in one year, which is about 6 trillion miles (9 trillion kilometers, or 63,000 AU). Put another way, a light year is how far you'd travel in a year if you could travel at the speed of light, which is 186,000 miles (300,000 kilometers) per second. (By the way, you can't travel at the speed of light, as far as we know, but that's a whole other story...) Like AU, light years make astronomical distances more manageable. For example, the nearest star system to ours is the triple star system of Alpha Centauri , at about 4.3 light years away. That's a more manageable number than 25 trillion miles, 40 trillion kilometers or 272,000 AU.

Light years also provide some helpful perspective on solar system distances: the Sun is about 8 light minutes from Earth. (And yes, there are also light seconds !) And because light from objects travels at light speed , when you see the Sun, or Jupiter or a distant star, you're seeing it as it was when the light left it, be that 8 minutes, tens of minutes or 4.3 years ago. And this is fundamental to the idea that when we're looking farther out into space, we're seeing farther back in time. (Think about it: you're seeing all the stars in the sky at different times in history — some a few years ago, others hundreds of years ago — all at the same time!)

Finally, parsecs. This is the unit used when the number of light years between objects climbs into the high thousands or millions. One parsec is 3.26 light years. The origin of this unit of measure is a little more complicated, but it's related to how astronomers measure widths in the sky. Astronomers use "megaparsecs" — a megaparsec is 1 million parsecs — for intergalactic distances, or the scale of distances between the galaxies.

And at the point when distances between galaxies become so epic that even megaparsecs get unwieldy, astronomers talk about distances in terms of how much a galaxy's light has been shifted toward longer, redder wavelengths by the expansion of the universe — a measure known as "redshift." Now that's astronomical.

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These New Technologies Could Make Interstellar Travel Real

Long considered science fiction, leaving the solar system and speeding amid the stars may soon be within reach.

On October 31, 1936, six young tinkerers nicknamed the “Rocket Boys” nearly incinerated themselves in an effort to break free of Earth’s gravity. The group had huddled in a gully in the foothills of California’s San Gabriel Mountains to test a small alcohol-fueled jet engine. They wanted to prove that rocket engines could venture into space, at a time when such ideas were widely met with ridicule. That goal was disrupted when an oxygen line caught fire and thrashed around wildly, shooting flames.

The Rocket Boys’ audacity caught the attention of aerodynamicist Theodore von Karman, who already worked with two of them at Caltech. Not far from the location of their fiery mishap, he established a small test area where the Rocket Boys resumed their experiments. In 1943, the site became the Jet Propulsion Laboratory (JPL), and von Karman its first director. JPL has since grown into a sprawling NASA field center with thousands of employees, yet it has managed to retain its founding motivation: test the limits of exploration, convention be damned.

They’ve had many successes over the years. In the early 1970s, JPL engineers built Pioneer 10, the first spacecraft to reach escape velocity from the solar system. A few years later, they followed up with Voyagers 1 and 2, the fastest of the many objects aimed at interstellar space. From the beginning of the Space Age to the launch of the Voyager spacecrafts — a span of just two decades — rocket scientists more than doubled flight speeds. But in the decades since, only one more spacecraft has followed the Voyagers out of the solar system, and nothing has done so at such a high speed. Now JPL’s rocketeers are getting restless again, and quietly plotting the next great leap.

The consistent theme of the new efforts is that the solar system is not enough. It is time to venture beyond the known planets, on toward the stars. John Brophy, a flight engineer at JPL, is developing a novel engine that could accelerate space travel by another factor of 10. Leon Alkalai, a JPL mission architect, is plotting a distant journey that would begin with an improbable, Icarus-esque plunge toward the sun. And JPL research scientist Slava Turyshev has perhaps the wildest idea of all, a space telescope that could provide an intimate look at a far-off Earth-like planet — without actually going there.

These are all long shots (not  entirely  crazy, according to Brophy), but if even one succeeds, the implications will be huge. The Rocket Boys and their ilk helped launch humans as a space-faring species. The current generation at JPL could be the ones to take us interstellar.

Rocket Reactions

For Brophy, inspiration came from Breakthrough Starshot, an extravagantly bold project announced in 2016 by the late Stephen Hawking and Russian billionaire Yuri Milner. The ultimate aim of the project is to build a mile-wide laser array that could blast a miniature spacecraft to 20 percent the speed of light, allowing it to reach the Alpha Centauri star system (our closest stellar neighbor) in just two decades.

Brophy was skeptical but intrigued. Ambitious aspirations are nothing new for him. “JPL encourages people to think outside the box, and my wacky ideas are getting wackier in time,” he says. Even by that standard, the Starshot concept struck him as a little too far from technological reality. But he did begin to wonder if he could take the same concept but scale it down so that it might actually be feasible within our lifetimes.

What especially captivated Brophy was the idea of using a Starshot-style laser beam to help deal with the “rocket equation,” which links the motion of a spacecraft to the amount of propellant it carries. The rocket equation confronts every would-be space explorer with its cruel logic. If you want to go faster, you need more fuel, but more fuel adds mass. More mass means you need even more fuel to haul around that extra weight. That fuel makes the whole thing heavier still, and so on. That’s why it took a 1.4 million-pound rocket to launch the 1,800-pound Voyager probes: The starting weight was almost entirely fuel.

Since his graduate student days in the late 1970s, Brophy has been developing a vastly more efficient type of rocketry known as ion propulsion. An ion engine uses electric power to shoot positively charged atoms (called ions) out of a thruster at high velocity. Each atom provides just a tiny kick, but collectively they can push the rocket to a much greater velocity than a conventional chemical rocket. Better yet, the power needed to run the ion engine can come from solar panels — no heavy onboard fuel tanks or generators required. By squeezing more speed out of less propellant, ion propulsion goes a long way toward taming the rocket equation.

But ion engines come with drawbacks of their own. The farther they get from the sun, the more limited they are by how much electricity their solar panels can generate. You can make the panels huge, but then you add a lot of weight, and the rocket equation slams you again. And ion engines have such gentle thrust that they can’t leave the ground on their own; it then takes them a long time in space to accelerate to their record-breaking speeds. Brophy knows these issues well: He helped design the ion engine aboard NASA’s Dawn spacecraft, which just completed an 11-year mission to asteroid Vesta and dwarf planet Ceres. Even with its formidable 65-foot span of solar cells, Dawn went from zero to 60 in an unhurried four days.

Ion the Prize 

While Brophy was pondering this impasse between efficient engines and insufficient solar power, the Breakthrough Starshot concept came out, and it got the gears turning in his head. He wondered: What if you replaced sunshine with a high-intensity laser beam pointed at your spacecraft? Powered by the more efficient laser, your ion engine could run much harder while still saving weight by not having to carry your power source on board.

Two years after his epiphany, Brophy is giving me a tour of an SUV-size test chamber at JPL, where he puts a high-performance ion engine through its paces. His prototype uses lithium ions, which are much lighter than the xenon ions Dawn used, and therefore need less energy to attain higher velocities. It also runs at 6,000 volts compared with Dawn’s 1,000 volts. “The performance of this thing would be very startling if you had the laser to power it up,” he says.

There’s just one minor issue: That laser does not exist. Although he drastically downsized the Starshot concept, Brophy still envisions a 100-megawatt space-based laser system, generating 1,000 times more power than the International Space Station, aimed precisely at a fast-receding spacecraft. “We’re not sure how to do that,” he concedes. It would be by far the biggest off-world engineering project ever undertaken. Once built, though, the array could be used over and over, with different missions, as an all-purpose rocket booster.

As an example, Brophy describes a lithium-ion-powered spacecraft with 300-foot wings of photovoltaic panels powering a full-size version of the engine he is developing at JPL. The laser would bathe the panels in light a hundred times as bright as sunshine, keeping the ion engine running from here to Pluto, about 4 billion miles away. The spacecraft could then coast along on its considerable velocity, racking up another 4 billion miles every year or two.

At that pace, a spacecraft could rapidly explore the dim areas where comets come from, or set off for the as-yet-undiscovered Planet 9, or go ... almost anywhere in the general vicinity of the solar system.

“It’s like we have this shiny new hammer, so I go around looking for new nails to pound in,” Brophy says dreamily. “We have a whole long list of missions that you could do if you could go fast.”

Interstellar Medium Well 

After Brophy’s genial giddiness, it is a shock to talk to Alkalai, in charge of formulating new missions at JPL’s Engineering and Science Directorate. Sitting in his large, glassy office, he seems every bit the no-nonsense administrator, but he, too, is a man with an exploratory vision.

Like Brophy, Alkalai thinks the Breakthrough Starshot people have the right vision, but not enough patience. “We’re nowhere near where we need to be technologically to design a mission to another star,” he says. “So we need to start by taking baby steps.”

Alkalai has a specific step in mind. Although we can’t yet visit another star, we can send a probe to sample the interstellar medium, the sparse gas and dust that flows between the stars.

“I’m very interested in understanding the material outside the solar system. Ultimately, we got created from that. Life originated from those primordial dust clouds,” Alkalai says. “We know that there’s organic materials in it, but what kind? What abundances? Are there water molecules in it? That would be huge to understand.”

The interstellar medium remains poorly understood because we can’t get our hands on it: A constant blast of particles from the sun — the solar wind — pushes it far from Earth. But if we could reach beyond the sun’s influence, to a distance of 20 billion miles (about 200 times Earth’s distance from the sun), we could finally examine, for the first time, pristine samples of our home galaxy.

Alkalai wants answers, and he wants to see the results firsthand. He’s 60, so that sets an aggressive schedule — no time to wait for giant space lasers. Instead, he proposes a simpler, albeit still unproven, technology known as a solar thermal rocket. It would carry a large cache of cold liquid hydrogen, protected somehow from the heat of the sun, and execute a shocking dive to within about 1 million miles of the solar surface. At closest approach, the rocket would let the intense solar heat come pouring in, perhaps by jettisoning a shield. The sun’s energy would rapidly vaporize the hydrogen, sending it racing out of a rocket nozzle. The combined push from the escaping hydrogen, and the assist from the sun’s own gravity, would let the ship start its interstellar journey at speeds up to 60 miles per second, faster than any human object yet —and it only gets faster from there.

“It’s very challenging, but we’re modeling the physics now,” Alkalai says. He hopes to begin testing elements of a thermal-rocket system this year, and then develop his concept into a realistic mission that could launch in the next decade or so. It would reach the interstellar medium another decade after that. In addition to sampling our galactic environment, such a probe could examine how the sun interacts with the interstellar medium, study the structure of dust in the solar system and perhaps visit a distant dwarf planet along the way.

It would be a journey, Alkalai says, “like nothing we’ve done in the past.”

Catch A Glimpse 

Solar thermal rockets and laser-ion engines, impressive as they may be, are still absurdly inadequate for crossing the tremendous gulf between our solar system and exoplanets — planets orbiting other stars. In the spirit of the Rocket Boys, Turyshev is not letting absurdity stop him. He is developing a cunning workaround: a  virtual  mission to another star.

Turyshev tells me he wants to send a space telescope to a region known as the solar gravitational lens (SGL). The area begins a daunting 50 billion miles away, though that’s still hundreds of times closer than our closest stellar neighbors. Once you get far enough into the SGL, something marvelous happens. When you look back toward the sun, any object directly behind it appears stretched out, forming a ring, and hugely magnified. That ring is the result of our star’s intense gravity, which warps space like a lens, altering the appearance of the distant object’s light.

If you position yourself correctly within the SGL, the object being magnified from behind the sun could be an intriguing exoplanet. A space telescope floating at the SGL, Turyshev explains, could then maneuver around, sampling different parts of the light ring and reconstructing the snippets of bent light into megapixel snapshots of the planet in question.

I have to interrupt him here. Did he say megapixel, like the resolution you get on your camera phone? Yes, he really is talking about an image measuring 1,000 by 1,000 pixels, good enough to see details smaller than 10 miles wide on a planet up to 100 light-years (600 trillion miles!) away.

“We could peek under the clouds and see continents. We could see weather patterns and topography, which is very exciting,” Turyshev says. He doesn’t mention it, but he doesn’t need to: That kind of resolution could also reveal megacities or other giant artificial structures, should they exist.

Assuming the JPL boffins can solve the transportation issues of getting to the SGL, the mission itself is fairly straightforward, if enormously challenging. Turyshev and his collaborators (Alkalai among them) will need to develop a Hubble-size space telescope,

or a mini-fleet of smaller telescopes, that can survive the 30-year journey. They will need to perfect an onboard artificial intelligence capable of running operations without guidance from home. Above all, they will need a target — a planet so intriguing that people are willing to spend decades and billions of dollars studying it. NASA’s TESS space telescope is doing some of that reconnaissance work right now, scanning for Earth-size worlds around local stars.

“Ultimately, to see the life on an exoplanet, we will have to visit. But a gravity lens mission allows you to study potential targets many decades, if not centuries, earlier,” Turyshev says merrily.

A journey to the SGL would take us beyond Alkalai’s baby steps, well onto the path toward interstellar exploration. It’s another audacious goal, but at least the odds of catching fire are much lower this time around.

Corey S. Powell , a contributing editor of Discover , also writes for the magazine's Out There blog. Follow him on Twitter: @coreyspowell. This story originally appeared in print as "Boldly Go."

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The U.S.S. Enterprise , depicted here in the 2013 movie Star Trek: Into Darkness , relies on its warp drive to zip across the galaxy.

Inside the Quest for a Real ‘Star Trek’ Warp Drive

It may be a while before starship captains can race across the galaxy, but engineers and physicists have a few ideas for making it so.

Within the Star Trek universe, traveling across the galaxy is a breeze thanks to the famed warp drive . This fictional technology allows humans and other civilizations to zoom between star systems in days rather than centuries.

Such rapid travel times are impossible in the real world, because our best theory for the way the universe works, Einstein’s special relativity , says that nothing moves faster than the speed of light.

While current rocket propulsion systems are bound by this law, plenty of hopeful engineers and physicists are working on concepts that might bring us a step closer to Star Trek ’s vision of racing across the cosmos.

“Currently, even the most advanced ideas behind interstellar travel entail trip times of decades and centuries to even the closest stars, due to the restrictions of special relativity, and our abilities—or lack of—to travel at an appreciable fraction of the speed of light,” says Richard Obousy , director and founder of Icarus Interstellar, a nonprofit dedicated to making progress toward interstellar flight.

“Being able to build starships with the capability to travel faster than the speed of light would open the galaxy for exploration and possible colonization by humans.”

Nuclear Engines

Distances in space are so vast that astronomers usually measure them in light-years, the distance light can travel in a year’s time. A single light-year equals about six trillion miles.

The closest star to our solar system, Proxima Centauri, is 4.23 light-years away, so even traveling at the speed of light, a one-way voyage there would take 4.23 years. That may seem pokey, but it would be a huge improvement over current technology.

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Right now, the fastest spacecraft headed away from Earth is Voyager 1, which is puttering along at about 38,600 miles an hour. At that rate, it would take more than 70,000 years to reach Proxima Centauri.

Still, various teams have proposed ways to at least reach a fraction of light speed and hasten our exploration of interstellar space.

Back in 1958, researchers at San Diego-based defense contractor General Atomics came up with Project Orion , which involved a spacecraft driven essentially by nuclear bombs. A controlled series of nuclear explosions would propel the ship at high speeds, rapidly carrying a hundred tons of cargo and eight astronauts to places like Mars and even the outer solar system.

Faster propulsion technology would allow us to visit our galactic neighbors, like this satellite of the Milky Way known as the Large Magellanic Cloud.

Blueprints were also created showing how to adapt the technology for interstellar travel. However, all experimentation with this so-called nuclear-pulse propulsion came to a halt with the Nuclear Test Ban Treaty of 1963.

Announced earlier this year, the ambitious Breakthrough StarShot initiative represents a less explosive effort to undertake an interstellar mission. Run by a conglomerate of billionaires and big thinkers, including famed physicist Stephen Hawking, the project’s goal is to send a flotilla of postage stamp-size spacecraft to Alpha Centauri, a triple star system that’s 4.3 light-years away. (See “Is the New $100 Million ‘Starshot’ for Real?” )

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The tiny spacecraft would be attached to a thin light sail, a piece of technology that would allow mission managers to propel the probes with lasers shining from Earth’s orbit. The lasers would accelerate the craft to 20 percent the speed of light, and the probes would arrive at their destination in roughly 20 years.

While many of the tiny travelers may never make it to Alpha Centauri, a few of them should survive and may even fly past any planets orbiting the far-off stars , beaming back data about these alien worlds.

“I’m incredibly excited to see private money being used to explore breakthrough ideas that may advance the field of interstellar flight,” Obousy says.

“I hope to see more like this in the future. While there are engineering challenges associated with the Starshot Initiative, none appear insurmountable.”

Warping Reality

Of course, the real breakthrough would be a true warp drive, which requires technology to catch up with our theoretical designs.

In 1994, Trek fans got a glimmer of hope from Mexican theoretical physicist Miguel Alcubierre, who came up with a radical theory of hyper-fast space propulsion that doesn't break Einstein’s special relativity.

Instead of accelerating the spacecraft itself to light speed, why not bend, or warp, the fabric of space and time around the ship itself? Alcubierre presented calculations that produce a bubble in space-time in which one end is expanding and the other is contracting. A spaceship could, in theory, be carried along with the warp bubble and accelerated to velocities up to 10 times the speed of light.

While that sounds simple on paper, to make it work, we may need to harness exotic forms of matter, like antimatter, that for now are poorly understood. In addition, numerous unsolved issues plague the creation and control of a warp bubble, Obousy says.

“One such problem, for example, is the idea of causal disconnection, which implies that any spacecraft sitting within the bubble would not be able to ‘communicate’ with the exterior of the bubble, suggesting that a ship would not be able to ‘turn off’ the bubble once inside of it,” he notes.

As is often the case in space travel, developing true interstellar travel like what we see in Star Trek will require significant changes in the cost and energy requirements.

“Currently, the amount of energy and money required to entertain the notion of manned interstellar travel is measured in large fractions of global output—specifically, tens of trillions of dollars, and energy measured on the scale of what many large countries use annually,” he says.

Still, he adds, “the finest minds of the 15th century could not have predicted the technological wonders of the 21st century. Similarly, who are we to say what technology the humans of the 27th century will have mastered.”

Andrew Fazekas, the Night Sky Guy, is the author of Star Trek: The Official Guide to Our Universe and host of NG Live! " Mankind to Mars " presentations. Follow him on Twitter , Facebook , and his website .

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April 17, 2023 report

This article has been reviewed according to Science X's editorial process and policies . Editors have highlighted the following attributes while ensuring the content's credibility:

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Solar sails could guide interplanetary travel, says new study (Update)

by Peter Grad , Phys.org

Space travel has brought us to our next-door neighbor, the moon, and to the depths of our larger solar community inhabited by giants such as Saturn and Jupiter.

In 1982, Voyager 2 whisked past Uranus closer than any other spacecraft has since, and now is sailing—46 years after its launch—through interstellar space, some 133 AU (approximately 19.9 billion km) from Earth.

But there have been few comparable satellite missions in recent years. Cost is the main obstacle, but time frame is also a factor. The design for such long journeys takes years to calculate, and planning and construction of a space vehicle would take about a decade. Factoring in the time a satellite would require to reach distant targets means our next peek into the stars will likely not come any time soon.

A team of scientists led by Slava Turyshev of the Jet Propulsion Laboratory at the California Institute of Technology, which launched the Voyager satellites back in 1977, is anxious to get space exploration back on track. The team proposes a novel means of travel that could get us to the stars faster and cheaper.

In a paper released on the arXiv preprint server, Turyshev and more than two dozen fellow researchers from the United States and Europe proposed merging miniature satellite units with a solar energy process that would create a fast, inexpensive, lightweight mode of travel.

Solar sailing is a process by which the pressure generated by the sun's radiation is harnessed for propulsion. Recent innovations in this technology were demonstrated in a successful crowdfunded 2019 mission undertaken by the Planetary Society's LightSail-2 project.

The researchers explain, "Solar sails obtain thrust by using highly reflective, lightweight materials that reflect sunlight to propel a spacecraft while in space. The continuous photon pressure from the sun provides thrust, eliminating the need for heavy, expendable propellants employed by conventional on-board chemical and electric propulsion systems, which limit mission lifetime and observation locations."

They say that sails are far less expensive than heavy equipment currently used for propulsion, and that the ever-present continuous solar photon pressure from the sun makes thrust available for a broad range of vehicular maneuvers, such as hovering or rapid orbital plane changes.

Solar sails and miniaturization "have advanced in the past decade to the point where they may enable inspiring and affordable missions to reach farther and faster, deep into the outer regions of our solar system," the report says.

The researchers refer to the merging of these two technologies as the Sundiver Concept.

"Fast, cost-effective and maneuverable sailcraft that may travel outside the ecliptic plane open new opportunities for affordable solar system exploration," the report states, "with great promise for heliophysics, planetary science, and astrophysics."

With enhanced maneuverability, the spacecraft can easily deliver small payloads to multiple destinations if required, and can dock with related modular craft. The reliance on the sun and the miniaturization of the carrier, which requires no dedicated launch site, will prove to be significant cost savers, the researchers add: "A substantial reason for the high costs is our [current] reliance on slow and expensive chemical propulsion, operating at the limits of its capabilities, effectively rendering the current solar system exploration paradigm unsustainable. A new approach is needed."

The Universe Today web site observed this week that with the project gaining support from NASA, in a few years we may "begin to see a fleet of ultra-fast solar sailing probes zipping throughout the solar system. That would be quite a sight."

Journal information: arXiv

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Is Interstellar Travel Really Possible?

Interstellar flight is a real pain in the neck.

Paul M. Sutter is an astrophysicist at The Ohio State University , host of Ask a Spaceman and Space Radio , and author of " Your Place in the Universe. " Sutter contributed this article to Space.com's Expert Voices: Op-Ed & Insights . 

Interstellar space travel . Fantasy of every five-year-old kid within us. Staple of science fiction serials. Boldly going where nobody has gone before in a really fantastic way. As we grow ever more advanced with our rockets and space probes, the question arises: could we ever hope to colonize the stars? Or, barring that far-flung dream, can we at least send space probes to alien planets, letting them tell us what they see?

The truth is that interstellar travel and exploration is technically possible . There's no law of physics that outright forbids it. But that doesn't necessarily make it easy, and it certainly doesn't mean we'll achieve it in our lifetimes, let alone this century. Interstellar space travel is a real pain in the neck. 

Related: Gallery: Visions of Interstellar Starship Travel

Voyage outward

If you're sufficiently patient, then we've already achieved interstellar exploration status. We have several spacecraft on escape trajectories, meaning they're leaving the solar system and they are never coming back. NASA's Pioneer missions, the Voyager missions , and most recently New Horizons have all started their long outward journeys. The Voyagers especially are now considered outside the solar system, as defined as the region where the solar wind emanating from the sun gives way to general galactic background particles and dust.

So, great; we have interstellar space probes currently in operation. Except the problem is that they're going nowhere really fast. Each one of these intrepid interstellar explorers is traveling at tens of thousands of miles per hour, which sounds pretty fast. They're not headed in the direction of any particular star, because their missions were designed to explore planets inside the solar system. But if any of these spacecraft were headed to our nearest neighbor, Proxima Centauri , just barely 4 light-years away, they would reach it in about 80,000 years.

I don't know about you, but I don't think NASA budgets for those kinds of timelines. Also, by the time these probes reach anywhere halfway interesting, their nuclear batteries will be long dead, and just be useless hunks of metal hurtling through the void. Which is a sort of success, if you think about it: It's not like our ancestors were able to accomplish such feats as tossing random junk between the stars, but it's probably also not exactly what you imagined interstellar space travel to be like.

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Breaking space news, the latest updates on rocket launches, skywatching events and more!

Related: Superfast Spacecraft Propulsion Concepts (Images)

Speed racer

To make interstellar spaceflight more reasonable, a probe has to go really fast. On the order of at least one-tenth the speed of light. At that speed, spacecraft could reach Proxima Centauri in a handful of decades, and send back pictures a few years later, well within a human lifetime. Is it really so unreasonable to ask that the same person who starts the mission gets to finish it?

Going these speeds requires a tremendous amount of energy. One option is to contain that energy onboard the spacecraft as fuel. But if that's the case, the extra fuel adds mass, which makes it even harder to propel it up to those speeds. There are designs and sketches for nuclear-powered spacecraft that try to accomplish just this, but unless we want to start building thousands upon thousands of nuclear bombs just to put inside a rocket, we need to come up with other ideas.

Perhaps one of the most promising ideas is to keep the energy source of the spacecraft fixed and somehow transport that energy to the spacecraft as it travels. One way to do this is with lasers. Radiation is good at transporting energy from one place to another, especially over the vast distances of space. The spacecraft can then capture this energy and propel itself forward.

This is the basic idea behind the Breakthrough Starshot project , which aims to design a spacecraft capable of reaching the nearest stars in a matter of decades. In the simplest outline of this project, a giant laser on the order of 100 gigawatts shoots at an Earth-orbiting spacecraft. That spacecraft has a large solar sail that is incredibly reflective. The laser bounces off of that sail, giving momentum to the spacecraft. The thing is, a 100-gigawatt laser only has the force of a heavy backpack. You didn't read that incorrectly. If we were to shoot this laser at the spacecraft for about 10 minutes, in order to reach one-tenth the speed of light, the spacecraft can weigh no more than a gram.

That's the mass of a paper clip.

Related: Breakthrough Starshot in Pictures: Laser-Sailing Nanocraft to Study Alien Planets

A spaceship for ants

This is where the rubber meets the interstellar road when it comes to making spacecraft travel the required speeds. The laser itself, at 100 gigawatts, is more powerful than any laser we've ever designed by many orders of magnitude. To give you a sense of scale, 100 gigawatts is the entire capacity of every single nuclear power plant operating in the United States combined.

And the spacecraft, which has to have a mass no more than a paper clip, must include a camera, computer, power source, circuitry, a shell, an antenna for communicating back home and the entire lightsail itself.  

That lightsail must be almost perfectly reflective. If it absorbs even a tiny fraction of that incoming laser radiation it will convert that energy to heat instead of momentum. At 100 gigawatts, that means straight-up melting, which is generally considered not good for spacecraft. 

Once accelerated to one-tenth the speed of light, the real journey begins. For 40 years, this little spacecraft will have to withstand the trials and travails of interstellar space. It will be impacted by dust grains at that enormous velocity. And while the dust is very tiny, at those speeds motes can do incredible damage. Cosmic rays, which are high-energy particles emitted by everything from the sun to distant supernova, can mess with the delicate circuitry inside. The spacecraft will be bombarded by these cosmic rays non-stop as soon as the journey begins.

Is Breakthrough Starshot possible? In principle, yes. Like I said above, there's no law of physics that prevents any of this from becoming reality. But that doesn't make it easy or even probable or plausible or even feasible using our current levels of technology (or reasonable projections into the near future of our technology). Can we really make a spacecraft that small and light? Can we really make a laser that powerful? Can a mission like this actually survive the challenges of deep space?

The answer isn't yes or no. The real question is this: are we willing to spend enough money to find out if it's possible?

• Building Sails for Tiny Interstellar Probes Will Be Tough — But Not Impossible
• 10 Exoplanets That Could Host Alien Life
• Interstellar Space Travel: 7 Futuristic Spacecraft to Explore the Cosmos

Learn more by listening to the episode "Is interstellar travel possible?" on the Ask A Spaceman podcast, available on iTunes and on the Web at http://www.askaspaceman.com . Thanks to @infirmus, Amber D., neo, and Alex V. for the questions that led to this piece! Ask your own question on Twitter using #AskASpaceman or by following Paul @PaulMattSutter and facebook.com/PaulMattSutter .  

Follow us on Twitter @Spacedotcom or Facebook . 

Join our Space Forums to keep talking space on the latest missions, night sky and more! And if you have a news tip, correction or comment, let us know at: [email protected].

Paul M. Sutter is an astrophysicist at SUNY Stony Brook and the Flatiron Institute in New York City. Paul received his PhD in Physics from the University of Illinois at Urbana-Champaign in 2011, and spent three years at the Paris Institute of Astrophysics, followed by a research fellowship in Trieste, Italy, His research focuses on many diverse topics, from the emptiest regions of the universe to the earliest moments of the Big Bang to the hunt for the first stars. As an "Agent to the Stars," Paul has passionately engaged the public in science outreach for several years. He is the host of the popular "Ask a Spaceman!" podcast, author of "Your Place in the Universe" and "How to Die in Space" and he frequently appears on TV — including on The Weather Channel, for which he serves as Official Space Specialist.

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Initiative for Interstellar Studies

Working towards the achievement of interstellar flight through knowledge to the stars - Starships in our lifetime

Exploring Equations

Introduction.

Interstellar exploration requires many different skills sets and areas of knowledge. Those not comfortable with mathematics equations may find other areas of this website more relevant to their interests. However, for those who are familiar with basic mathematics, much can be learned from an understanding of some key equations that underpin the physics of interstellar propulsion. The material below is intended to help you explore these equations, by allowing you to investigate graphically how changes in important variables alter the result of the equation.

Initially, this page includes two equations: The Tsiolkovsky rocket equation, and Robert L. Forward’s equation for the acceleration of a light sail. We plan to expand the page with more equations in future. If you have any suggestions for the equations you’d like to see here, please email us at  equations@ null i4is.org , and we’ll do our best to add the most popular suggestions.

The Tsiolkovsky rocket equation

\[ \Delta v = v_e \ln \left(\dfrac{m_0}{m_f}\right) \]

This equation gives the velocity increase available from a single-stage rocket with initial mass \(m_0\) (payload, structure and fuel), final mass \(m_f\) (only payload and structure, as no fuel left) and rocket exhaust velocity \(v_e\).

How it works

The Tsiolkovsky rocket equation is one of the most important equations across the whole topic of spaceflight. It applies to any single-stage rocket which propels itself forwards by expelling material out of the back of the rocket. It works for any rocket, from the smallest satellite thruster to the huge engines used for the Apollo missions to the moon, and even the fusion rockets proposed for the Daedalus and Icarus interstellar probes.

For a given choice of propellants, the exhaust velocity will be a broadly fixed value, as it depends on the physics or chemistry underlying the propulsion approach. For example, when the fuel is liquid hydrogen and the oxidiser is liquid oxygen (as used in the Space Shuttle Main Engine), the rocket exhaust velocity is  v e  = 4,500 metres per second (approximately). The key feature of this equation is that the answer – the velocity increase in the rocket between ignition and when all the propellant is used up, known as the ‘delta-V’ and shown in the equation as  ΔV , using the Greek letter delta – depends on the logarithm of the ‘mass ratio’ ( m 0 /m f ). Those familiar with the logarithmic function (or its inverse, the exponential function) will recognise that delta-V will only increase slowly with the mass ratio.

The result is that, for any practically achievable rocket, where the mass ratio is typically between about ten (Saturn 1B) and forty (Ariane 5), the delta-V achievable will be between two and four times the rocket’s exhaust velocity. This is why the chemical propellants typically used in today’s rockets, to launch payloads to Earth orbit or within the solar system, won’t be of any use for interstellar journeys: because the delta-V we need, if we’re to get our payload to an interstellar destination in a reasonable timeframe (e.g. below a century) is much more than four times the exhaust velocity of any chemical propellants available to us.

That’s why those interested in interstellar propulsion focus on rockets using nuclear fission, nuclear fusion or even more advanced technologies, each of which promises much higher exhaust velocities than available from chemical rockets. However, the Tsiolkovsky equation still applies to them too!

Historical background

The equation was developed and published in 1903 by the Russian rocket pioneer Konstantin Tsiolkovsky (1857-1935). If you’d like to know more about this visionary genius, we published a biographical article on him by John I Davies in Principium issue 20 (February 2018), available elsewhere on this website .

See how the \(\Delta v\) depends on the initial mass \(m_0\) for a specific rocket exhaust velocity \(v_e\) (with units m/s) and final mass \(m_f\) (with units tonnes \( = 1000\) kg).

The mass ratio (\(=m_0/m_f\)) is plotted below for an exhaust velocity of \(v_e=1000\) m/s.

Light Sail Acceleration

Robert L. Forward provides an equation [1] to calculate the acceleration of a light sail given the mass of the spacecraft, reflectance of the light sail, and power of the laser.

\[ \alpha = \dfrac{2 \eta P}{Mc} \]

where \(\alpha\) is the acceleration of the spacecraft, \(\eta\) is the reflectance of the light sail, \(P\) is the incidence laser power, and \(M\) is the total mass of the spacecraft including payload, structure and sail. \(c\) is the speed of light.

A light sail is a propulsion technology that uses the momentum carried by photons of light to accelerate a large, thin and very light sheet of reflective material, plus its payload. The source of these light photons may be natural (a ‘solar sail’) or artificial (a ‘laser sail’). The key benefit of using a light sail, rather than a rocket, is that it does not need to carry its own propellant, so is not subject to the limitations encoded in the Tsiolkovsky rocket equation above. The main disadvantage of this form of propulsion is that the momentum carried by a photon of light is very small, so a successful light sail mission will require a combination of a strong source of light, a large sail area, and a light spacecraft (including both the mass of the sail and that of the payload).

Solar sails are already a practical technology: the Japan Space Agency (JAXA) launched IKAROS (Interplanetary Kite-craft Accelerated by Radiation Of the Sun) towards Venus in 2010, and received signals from it for five years, until 2015, while the Planetary Society launched their LightSail 2 spacecraft into Earth orbit in 2019, and it was still operating at the end of 2021, some 2.5 years after launch.

Laser sails, on the other hand, have not yet been demonstrated in space – but the i4is Glowworm project , and its target probe ‘Pinpoint’, aim to pioneer this. In the longer term, the Breakthrough Starshot team have the aim of launching small laser sailcraft to our nearest star beyond the Sun, Proxima Centauri, at 20% of the speed of light, using a giant laser.

Solar sails have frequently featured in science fiction, with one of the earliest examples being Arthur C. Clarke’s 1964 short story ‘Sunjammer’ (later renamed ‘The Wind from the Sun’). In the 1970s, Dr Louis Friedman of the Jet Propulsion Laboratory (JPL) proposed to NASA a solar sail-powered spacecraft to rendezvous with the 1986 return of Halley’s Comet, but the project was cancelled after a year’s design work. Interest in the practical possibilities of light sails grew after that, leading to Robert L. Forward’s 1984 paper on the potential use of laser sails in interstellar travel, from which the equation discussed on this page is taken (See ‘Roundtrip Interstellar Travel Using Laser-Pushed Lightsails’ ).

See how the acceleration \(\alpha\) depends on the properties of the spacecraft, light sail and incident light. Reflectance \(\eta\) is the percentage of incident light reflected (expressed as a decimal value between 0 and 1). Incident laser power \(P\) has units GW, and total spacecraft mass \(M\) has units kg. The units of acceleration are shown as m/s 2 .

You are designing a light sail mission! You want the acceleration \(\alpha\) of the light sail to be as high as possible.

• Which of the parameters \(\eta\), \(P\) and \(M\) have an effect on the acceleration \(\alpha\) of the light sail?
• When designing the mission, would you want to make the spacecraft as heavy as possible?
• Would you choose a material for the sail with a high reflectance or a low reflectance?
• Would you want a laser with a high power or a low power?

All of the three parameters have an effect on the acceleration. As the total mass of the spacecraft increases the acceleration decreases, therefore you would want the spacecraft mass to be as small as possible to maximise your acceleration. You would want the light sail to reflect as much light as possible. This is also important to prevent the light overheating the spacecraft. You would want the incident power on the sail to be as high as possible.

• Forward RL. Roundtrip interstellar travel using laser-pushed lightsails. Journal of Spacecraft and Rockets [Internet]. 1984 Mar;21(2):187–95. Available from: https://dx.doi.org/10.2514/3.8632 and https://pdfs.semanticscholar.org/25b2/b991317510116fca1e642b3f364338c7983a.pdf

Contact i4is

Initiative for Interstellar Studies 27/29 South Lambeth Road London, SW8 1SZ United Kingdom

info@ null i4is.org

Starship Blog

Measurement of mass by space sails, project lyra mission guide, project lyra: a solar oberth at 10 solar radii, swarming proxima, laser and sail in earth orbit with evolutionary neurocontrol, oits takes on evolution, how close did ‘oumuamua approach each of the inner planets, was loeb’s bolide interstellar, ‘oumuamua – a sci-fi story or reality, ‘oumuamua: the mystery unfolds, psyche: oits has something to say, project lyra: ignore the outlier and miss an opportunity, the case of fireball cneos 2017-10-09, project lyra: the mission to resolve a mystery, optimum interplanetary trajectory software: the secrets revealed, laser sails: trajectories using optimum interplanetary trajectory software, mars ride-share: an opportunity not to be missed, c/2014 un 271 the comet which will not collide with the earth, project lyra: falcon heavy expendable, project lyra: using an ariane 6, optimum interplanetary trajectory software (oits), music of ‘oumuamua, things to come, project lyra: using jupiter alone to get to ‘oumuamua, ‘oumuamua: the state of play, why the stars, exploring ‘oumuamua’s trajectory – further notes, exploring ‘oumuamua’s perihelion date, members newsletter – march, principium 44, members newsletter – february.

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Interstellar Travel: The Agony and the Ecstasy

Guest blogger Cam Potts

Interstellar travel. What is the biggest barrier?

“Space is deep, Man is small and Time is his relentless enemy.” —L. Ron Hubbard, To the Stars

Astronomical units and light-years are depressingly small units in describing the distances. Travel at the speed of light takes years, decades, centuries, even millennia to transit the space between neighboring stars, let alone galaxies.

Just to clarify an astronomical unit is 93.0 million miles—the average distance from the center of the earth to the center of the sun; and a light-year is the distance that light travels per year, which is about 6 trillion miles. Light travels 186,000 miles per second.

At lightspeed, it would be a four year trip from the Earth to Alpha Centauri, the star system closest to ours.

Even more extreme, to reach the galactic center of our own Milky Way would require 30,000 years of lightspeed travel. Interestingly, though, there is another galaxy closer to our solar system than our galactic center. The Canis Major Dwarf Galaxy is a mere 25,000 light-years from us and 42,000 light-years from the galactic center.

It just seems impossible for humans to boldly go where no one has gone before!

Or is it? Are there secrets of physics not yet known? Secrets that would allow faster than light speeds? What about creating wormholes? Or quantum effects where we could exist in two locations at the same time or at least transit from one place to another instantaneously? What about being able to act in the physical universe light-years distant from our presumed location?  Would that be travel or just projection? Would it matter?

Are there secrets not yet discovered?

If so, where and how do we find them?

Perhaps the pages of a science fiction or fantasy novel would be a good place to start—a place to “prime the pump,” so to speak.

“Science fiction does NOT come after the fact of a scientific discovery or development. It is the herald of possibility. It is the plea that someone should work on the future.” —L. Ron Hubbard, Battlefield Earth Introduction

Often, people scoff at the ideas and call them fiction. Science fiction. But others read the tale and become inspired.

The masters of science fiction have taken us to the stars through space opera books and in hard science fiction. They have explored this impossible challenge from different perspectives and inspired the real brainiacs to persist.

Here are some must-read sci-fi books that do just that—books that make you think and are catalysts in achieving space flight:

Jules Verne imagined a space voyage to our nearest neighbor in From the Earth to the Moon , written in 1865. Countless people across several generations were inspired by Verne’s story. And only one hundred and four years later, Neil Armstrong took one small step that realized the vision!

By the time of Ringworld by Larry Niven (which I just finished rereading), new ideas were introduced: hyperdrive shunts for use in hyperspace, fusion motors for spacecraft of various kinds for near lightspeed travel in known space, reactionless drives for maneuvering—but no more real substance. Getting to some useful fraction of lightspeed or achieving faster than light (FTL) travel, theoretically violating physics, was an increasingly thorny problem.

A breakthrough was needed.

Hence, hyperspace. Usually defined as space with more than three dimensions and any theoretical or fictional space, dimension, location, etc. thought of as affording out of the ordinary, exceptional, or supernatural experiences or capabilities.

Now that’s a breakthrough! Suddenly, anything is possible.

The 1969 Piers Anthony novel Macroscope combines physics, metaphysics, and a very permissive use of the term “hyperspace” to create an amazing technique for interstellar travel. The book is much broader than just an exploration of FTL travel and is worth a look.

Carl Sagan’s sci-fi novel Contact took another tack permitted by physics. This one involved a hypothetical SETI (Search for Extraterrestrial Intelligence) contact that revealed the plans to build a machine that could travel to the stars. Somehow, the device employed an alien technique for manipulating a naturally occurring phenomenon of the cosmos—a wormhole.

There are many other books and films that take a look at interstellar travel and space exploration. Of course, the most famous, and still the one with the best propulsion system, is Star Trek. With FTL speeds measured in warps, interstellar travel is a breeze, and intergalactic travel becomes merely a voyage. Dilithium crystals anyone?

How Close Are We to Space Travel ?

I think you would agree, the idea of interstellar travel is not new, so why aren’t we already offering cheap fares to the all-inclusive resorts on Proxima Centauri b in the Alpha Centauri system?

Because it is really hard to get there due to the distance and the many unknowns along the way. Physics does not prohibit the trip, so there might be a way. We just have to develop it.

And that means work … HARD work.

Doing this involves creativity, thinking out of the box, thought experiments, visualization, and filling in the blanks with creative ideas. Then, there are the material experiments with lots of trial and error.

How cool are the real options so far? Here are the best interstellar travel methods I have been able to find.

Light sails (solar sails): These sails are large thin sheets that would be propelled using sunlight. Probably the most likely for small probes but not man-rated due to size and the near impossibility of slowing down at the destination. (man-rated: meeting requirements for human-rated spaceflight).

Fusion: Merging atoms together to create energy. Two potential methods are the most likely for a crewed voyage.

• The sequential detonation of about 300,000 one-megaton hydrogen bombs over about a month. This process would provide 10% lightspeed and a voyage time of about 45 years with no deceleration.
• Contained thermonuclear reactors onboard the starship. The Daedalus Project looked at this and abandoned it due to cost (at least so far).

Antimatter: Fantastic fuel density (potentially) but expensive. This would be used to fuel rockets to interstellar space. Antimatter refers to sub-atomic particles that have properties opposite normal sub-atomic particles, thus the electrical charge of those particles would be reversed.

EM Drive: A NASA project on the border of reality. This is the physics-defying contraption that produces thrust by bouncing microwaves around inside a closed, cone-shaped cavity and requires no fuel.

Alcubierra Warp Drive: Another project on the border of reality, which would achieve FTL travel by stretching space-time in a wave, whereby the space ahead would contract while the space behind it expands. The idea is that a spacecraft inside would ride this wave and accelerate to velocities beyond the speed of light. This speculative idea was proposed by theoretical physicist Miguel Alcubierre based on solving Einstein’s field equations in general relativity.

Of course the most exciting news on space travel is the NASA and SpaceX successful trip to the space station. While this is a small jump in comparison to intergalactic travel, it IS progress.

  How would you approach interstellar travel?

And as a side note, multiple New York Times  bestselling author, Jim Marrs, notes in his booklet “Alien Invasion: Is Earth Prepared?”

“It has been noticed that every time a space launch is announced with some innocuous payload, such as parts for the space station or a communications satellite, the launch seems to go off without a hitch. Yet when there is a secret launch, usually only described as military in nature, these often explode or get lost.”

Download the full article  “Alien Invasion: Is Earth Prepared?”  by Jim Marrs.

A pilot for over 53 years with a BS in Aerospace Engineering, Cam is now retired from a 40-year airline and aerospace career. Copywriting allows him to pursue two of his favorite pastimes—the world of flight and storytelling.

He lives outside of Palmer with wife, Nan, and the best dog in the world, Brushy.

You can contact Cam on LinkedIn or at campotts.com

Other articles and resources you may be interested in:

L. Ron Hubbard Science Fiction Book List

10 Great Space Opera Books

Science Fiction’s Role in Space Flight

Space Opera Science Fiction and the Future

Brand New Science Fiction

References: National Geographic on NASA’s EM Drive , Science Alert on Warp Drive , How Stuff Works on Antimatter , Space.com on Solar Sail Spacecraft , and Mashable.com on Faster than Light Travel .

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Nice little essay. But those of us who are denizens of the internet (and it’s an attractive alternative in these pandemic times) know that this problem has already been solved, both out there (of course) and down here. While some insist the internet has become sort of giant misshapen SciFi novel, there are still a few left here who don’t suffer fools lightly. It has to do with how space is actually constructed and how to form a region (usually sphere-shaped) that disagrees with that construction enough to allow “travel” near the speed of thought.

Thanks for the comment. It is tantalizing to me.

While your thoughts on this are probably well developed, I may just be ignorant enough to occupy the “fools” subset. Still, it sounds like you may be describing a method of travel that bends space-time in such a way that the departure and destination locations are very close and connected by a generated wormhole.

In the interest of full disclosure, the bulk of my education on this came from a scene in the movie, “Interstellar.”

In the scene, two dots are drawn on a sheet of paper, one at the top and one directly below it, at the bottom. The sheet, representing space-time as the fabric of the universe, was then folded, so the two dots were facing each other. Finally, a pencil was pushed through the paper at the point of contact, producing a circle. Now, the paper is a two-dimensional representation of four-dimensional space-time (3-dimensional space + time), and the circle would represent what appears to be a sphere but is actually a wormhole, or rift in space-time, connecting the two locations. At least, that’s the physics idea as I see it.

Then again, I wonder if we may be missing something. Something in the realm of a mega-physics or what some might call ontology, the branch of metaphysics that studies the nature of existence or being as such. A coming together of the science of the physical universe and the philosophy of life existing within it.

Science lets us know enough about the physical universe to be proficient at whatever game we want to play in it. Philosophy helps us discover who we really are and how we want to play the game for the greatest good or even change to a different game.

So, how does that have anything to do with interstellar travel?

If we denizens of the physical universe are multi-part critters, say body-mind-spirit, would the diligent investigation of each part yield information that might, along with our understanding of physics, help us crack the interstellar distance barrier once and for all? Along the way, might we discover secrets of existence that allow us to overcome life’s evils, to flourish and prosper, and to pay it forward? Might discovering those secrets somehow turn out to be the key to realizing our dreams of interstellar travel? I don’t know, but I think it’s worth a look.

This idea was visited in “Contact.” It was not enough just to be able to go. We also needed to answer why we should be allowed to go. Once we know that, we may not even need starships or warp drives or wormholes.

Maybe we will just have to decide to travel at the speed of thought.

Sir, you are better-versed than you give yourself credit for. And I am, perhaps, less well-versed than I promoted myself as being. But that doesn’t mean that I haven’t been exposed to loads of data on the subject, only that most of that data would probably not stand up in the “court of science.” I don’t know that this is the proper forum to travel down that rabbit hole. But it’s true, you do have to be willing to explore the outer limits of consciousness or “spiritual perception” to corroborate the stories we see on the UFO sites. My point, I suppose, is that if you do that exploration, you find lots of corroboration. It’s almost a sure thing that a lot more is going on under our noses than what most of us are aware of.

When you were learning to SPELL YOUR NAME I WAS BEING TRAINED TO CONQUER GALAXYS!!!!

Interesting read. A book i just finished was Delta-V by Daniel Suarez. It is set only a decade or so from now and gives a pretty realistic description of what could be coming.

Hi, great blog, Battlefield Earth was my favorite. The transportation was an amazing concept, but I felt LRH’s Mission Earth and “Will Be Was” concept was the best and I think workable. Just sayin

I found your post very interesting Mr. Potts. I have read Battlefield Earth by L. Ron Hubbard 7 times and each time found it more fascinating than the time before. Teleportation was the a thrilling concept and I believe it can be done. I am not a physicist or an engineer. I am an artist. And I found this particular science fiction book to be very inspiring to me.

I loved Battlefield Earth having read it 7 times through and listened to the audio book twice. It is one of my very favorite books of all time. Of any and all genres.

I really enjoyed reading this article. Personally, I never say anything is impossible. In the beginning of a book by Arthur C Clarke, (Songs of Distant Earth), he said that most science fiction is fantasy because it’s impossible to go faster than light. Of course the same was said about breaking the sound barrier. One article stated that it would take all the energy in the universe to go faster than light. But then again, some scientists were saying the exact same thing about breaking the sounds barrier. So don’t say something is impossible. (and I really like the idea of teleportation in Battlefield Earth, which I’ve read several times).

I just read the blog here and forgot that I had read Battlefield earth some years ago. There was one problem with that book and that was that I couldn’t put it down ! I was working a full time job at that time and would read until 2 am often times and would wind up being tired the next day. Ugghh. One heck of a book I must say! I should read it again.

I liked the audio version very much. It’s a good way to “reread” the story if you have more time.

A device used in SF such as Star-Gate, Babylon-5 and The Expanse is gates. The Expanse has an interesting system where a gate allows passage from normal space to an artificially sustained bubble outside of the universe. This bubble contains a number of other gates that lead to far distant spots in normal space. (It is not clear whether this bubble connecting thousands of gates is the only bubble created.)

I just finished the 47 audible version of Battlefield Earth. It has been my pandemic friend – amazingly uplifting and hopeful during all of this, despite the battles and treachery, there is courage and friendship and leadership and competence that shines through! I loved it!!!!

That’s great, Lissa! I am glad this audiobook has been such a good friend for you! Please note, it’s a friend that you will enjoy multiple times!

Great article! I for one believe that FTL speeds are possible. I’ve been fascinated with the idea of hyperspace for decades. I view it as a shortcut through curved space. I mentioned this to a colleague of mine one time in a very lighthearted conversation. He went nuts! Something about hyperspace had seriously disturbed him. This went way beyond a dispute about the possibility of FTL speeds and hyperspace. I had to change the subject.

I found the science of travel as depicted in Battlefield Earth to be fascinating and unassailable. Perhaps Sheldon (Big Bang Theory) would find a theoretical hole, but I doubt it!

Love this so much!

This is an extremely interesting and intriguing subject, to be sure. Personally, I’d be truly excited to travel to outer space and beyond. In fact, my daughter and I were discussing this very idea the other day and she said she wouldn’t mind going with me. So, in the end, it all boils down to the same thing, doesn’t it? We will go wherever our loved ones are. And maybe that’s an adequate explanation of death for some.

Thank you. Pretty amazing that it is the Science Fiction writers who lead the future of technical developments on the planet!

Thanks for pointing out that there are many books and films that take a look at interstellar travel and space exploration. My husband and I have always known that humans can make space travel possible in the near future. With this, we are hoping to find an organization that can send our personal message to outer space in the next spacecraft to leave our galaxy.

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NASA's Ingenious Efforts to Restore Voyager 1's Interstellar Communications on May，2022

V oyager 1, the venerable space probe and humanity’s most distant emissary, has encountered a communication hurdle that has persisted for months, leading to a valiant effort by NASA engineers to comprehend and rectify the anomaly.

For over 45 years, Voyager 1 has been gliding through the cosmos, and in its lifetime, it has delivered invaluable data on planets like Jupiter and Saturn, as well as a solitary image of Earth from the outskirts of our solar system. Yet, as it cruises over 15 billion miles from Earth, it faces a unique challenge: a breakdown in the way it communicates its observations and status back to ground control.

In May 2022, NASA’s Jet Propulsion Laboratory (JPL) engineers noticed the glitch when Voyager 1 began transmitting nonsensical data. This data, meant to inform mission controllers about the spacecraft’s operations and scientific findings, is crucial for the continuous assessment of the mission’s health and objectives. A JPL spokesperson highlighted the efforts made to resolve the issue: “The team continues information gathering and are preparing some steps that they’re hopeful will get them on a path to either understand the root of the problem and/or solve it.”

The glitch appears to be a discord between the spacecraft’s flight data system (FDS) and its telemetry modulation unit (TMU). Normally, the FDS would collect and package data for transmission to Earth, but the TMU has been sending a repeating pattern of ones and zeroes, rendering the data unintelligible.

Despite this setback, the mission team has made a breakthrough. In March 2023, after sending a ‘poke’ to the spacecraft, a signal was received that stood out from the garbled data stream. A Deep Space Network engineer decoded this and found it contained a readout of the entire FDS’s memory, a potential treasure trove for diagnosing the problem.

The issue is compounded by the enormous distance signals must travel, taking approximately 22 hours each way, leading to a slow, iterative process of trial and error as engineers send commands and await the spacecraft’s response. It’s a process the JPL spokesperson described, noting, “After they do that, they spend a few days digesting the information they got, consulting old documents to see if they can make sense of the little bits of information they can glean from things (since the telemetry data itself is unusable), and then send another command.”

Despite the challenges, the mission team remains hopeful. The wealth of data collected before the communication breakdown continues to shed light on the conditions of interstellar space, and the Voyager probes’ ongoing journey into the cosmos is a testament to human ingenuity and curiosity.

As NASA’s engineers labor to parse the received memory readout and develop potential solutions, Voyager 1’s mission remains a symbol of human achievement. Although the issue remains unresolved, the data sent back before the problem began provides an extensive understanding of interstellar space, and the work to re-establish complete communication is evidence of NASA’s relentless pursuit of knowledge.

Relevant articles:

– NASA Is Still Fighting to Save Its Historic Voyager 1 … , Gizmodo, Mar 7, 2024

– Voyager 1 sends back surprising response after ‘poke’ from NASA , CNN

– NASA finds clue while solving Voyager 1’s communication breakdown case , Space.com

– How was contact restored between NASA and Voyager 2? Here’s all you need to know about the ‘shout’ across interstellar space which retrieved the spacecraft , economictimes.com