What are Some Proposed Means of Interstellar Travel?

Michael Anissimov
Michael Anissimov
US astronaut Buzz Aldrin walks on the Moon during the Apollo 11 mission in 1969.
US astronaut Buzz Aldrin walks on the Moon during the Apollo 11 mission in 1969.

Because the stars are so far apart, proposed means of interstellar travel either involve very long trips, or very fast means of getting there. We'll focus on the fast means, because nobody likes to wait a long time to get to their travel destination.

There are four possible means of interstellar travel that are taken seriously. They are nuclear pulse propulsion — one of the first proposed, fusion-powered rockets, light sails propelled by lasers, and antimatter-based propulsion. Of these, antimatter propulsion and light sails seem the most promising as they are the fastest. Antimatter or light sails could reach speeds similar to that of light, taking advantage of the relativistic effect of time dilation, which could make the interstellar trip to Alpha Centauri, which is four light years away, seem like less than a year in duration.

"Project Orion" investigated the possibility of using pulses from nuclear explosions to propel an interstellar spacecraft.
"Project Orion" investigated the possibility of using pulses from nuclear explosions to propel an interstellar spacecraft.

The remaining methods of interstellar travel, nuclear pulse propulsion and fusion rockets, are limited to speeds of about 10% of that of light at max, making them of less interest. However, nuclear pulse propulsion is interesting because it has been within our grasp since 1945. If an aggressive nuclear space program were pursued in the 1950s and 1960s, humanity probably could have sent manned expeditions to the outer solar system by the 1970s. However, nuclear explosions are forbidden by current international law, and the Outer Space Treaty forbids the deployment of nuclear weapons in space.

In theory, a generation or fusion-powered ship could be assembled in orbit, however it could take hundreds of conventional rocket launches to move the equipment needed for such a massive craft into space.
In theory, a generation or fusion-powered ship could be assembled in orbit, however it could take hundreds of conventional rocket launches to move the equipment needed for such a massive craft into space.

One of the biggest requirements for interstellar travel is being able to slow yourself down once you reach your target star system. At speeds close to that of light, the braking process has to begin about halfway through your trip. One of the most discussed possible methods of interstellar travel - light sails accelerated by huge space-based lasers - would need to pack some nuclear bombs, a fusion reactor, or antimatter, to ensure that they have a means to slow down upon reaching their destination. For probes, fly-bys may be sufficient, but for serious colonization efforts, the ability to brake is a must.

Interstellar travel will eventually be able to take humans to other planets.
Interstellar travel will eventually be able to take humans to other planets.

One of the dead but famous ideas for interstellar spaceships is the Bussard ramjet, which would suck in and then burn interstellar hydrogen with a gigantic scoop, allowing it to get around carrying its own fuel. However, subsequent calculations found that the scoop would not be practical - the drag on it would exceed its thrust.

Michael Anissimov
Michael Anissimov

Michael is a longtime contributor who specializes in topics relating to paleontology, physics, biology, astronomy, chemistry, and futurism. In addition to being an avid blogger, Michael is particularly passionate about stem cell research, regenerative medicine, and life extension therapies. He has also worked for the Methuselah Foundation, the Singularity Institute for Artificial Intelligence, and the Lifeboat Foundation.

Michael Anissimov
Michael Anissimov

Michael is a longtime contributor who specializes in topics relating to paleontology, physics, biology, astronomy, chemistry, and futurism. In addition to being an avid blogger, Michael is particularly passionate about stem cell research, regenerative medicine, and life extension therapies. He has also worked for the Methuselah Foundation, the Singularity Institute for Artificial Intelligence, and the Lifeboat Foundation.

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Discussion Comments

pastanaga

@irontoenail - You'd have to really make the ship worth living in, or you'd have to already know there was a planet to go to. I mean, I think we will end up with a combination of generation ships and fast ships. The fast ships might not even have people on them. They might just be basically like robotic scouts that go off and report back what they find so that we can send people out when we know there's something to visit.

irontoenail

@indigomoth - I think that's mostly because we don't put enough money into the space program to give them proper means to combat the difficulties. It's cheaper to just train the astronauts to withstand the physical hardships than it is to give them a luxury ride.

But we basically do know how to create gravity so if there was enough money we'd be able to combat that problem at least. Recycling food, water and air in a large enough area shouldn't be a problem either.

I actually think the biggest problems with interstellar operations are ethical ones. I mean, you can't ask the children of the travelers whether they are willing to go to another star before they are born. And few stars are going to have Earth-like planets, so the whole trip could be a waste in the end.

indigomoth

It's fun to speculate on quick means of getting from star to star but I do think that the slower means are more likely. And when you're discussing them it's more about how we deal with the passage of time rather than how we deal with the power and speed.

The most likely seems to be a generation ship of some kind, that is built to be a self contained city where people live over a long period of time and basically have kids and maybe even grandchildren who are the ones that are really intended to arrive in the next star system. They would consider the interstellar experience to be normal, because they had never experienced anything else.

But the technology needed for that kind of habitat isn't possible at the moment. You'd need to make sure they had enough food, air, energy and gravity to survive for a long time. At the moment even the astronauts that only go away for a few months have to be carried when they touch back down because their muscles become so atrophied in space.

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    • US astronaut Buzz Aldrin walks on the Moon during the Apollo 11 mission in 1969.
      By: Yuri Arcurs
      US astronaut Buzz Aldrin walks on the Moon during the Apollo 11 mission in 1969.
    • "Project Orion" investigated the possibility of using pulses from nuclear explosions to propel an interstellar spacecraft.
      By: The Official CTBTO Photostream
      "Project Orion" investigated the possibility of using pulses from nuclear explosions to propel an interstellar spacecraft.
    • In theory, a generation or fusion-powered ship could be assembled in orbit, however it could take hundreds of conventional rocket launches to move the equipment needed for such a massive craft into space.
      By: unclepodger
      In theory, a generation or fusion-powered ship could be assembled in orbit, however it could take hundreds of conventional rocket launches to move the equipment needed for such a massive craft into space.
    • Interstellar travel will eventually be able to take humans to other planets.
      By: Stephen Coburn
      Interstellar travel will eventually be able to take humans to other planets.