Energy for Space Travel

[Lafayette]

A question or an idea popped in my nonscientific/non mathematical brain reading Hail Mary. It mentioned the problem of not having enough fuel for the extreme distances of space travel. And was wondering if there was a way to create fuel and/or energy on a spaceship while it's traveling in space. Has this idea been address before? If so, what were or are the answers? Is NASA working on it? Or is this considered a dumb question/idea?

 

[Venusian Broon]

Hi Lafayette,

It is not a dumb idea. There are a number of ideas that have been proposed. The one that popped into my head when I read your comment was the Bussard ramjet scoop. Essentially as the craft moves through space it scoops up (hence the name) the hydrogen that is just lying about in interstellar space*. This hydrogen is funnelled in by a magnetic field till it is squeezed into the back of the ship to produce nuclear fusion, which is used to propel the ship further on - hence collecting more hydrogen.

A recent study showed that it was a little bit easier than we thought....but still not practical for, likely a long time yet. The problem is that they estimated that we would need to generate a magnetic funnel about 150 million km wide for it to work.

We are nowhere trying to make such a magnetic structure!

See here, Anton talks about it:

Edit:

Another article discussing this: New Calculations Show That an Interstellar Bussard Ramjet Drive Would Need a Magnetic Field Stretching 150 Million Kilometres

includes a little at the end: "At present, it seems as though sending tiny sailcraft to the nearest stars using directed energy propulsion (DEP) is the only practical option."

Essentially you propel a very light spacecraft by beaming a high energy laser beam, at its 'sail' to give the craft momentum....although how one makes such a craft slow down when it reaches a star...I don't know. I'd guess your only going to be able to do a 'fly-by' using this method!


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* There is about, as a rule of thumb, about 1 hydrogen atom per cubic centimetre in the universe.

 

[Robert Zwilling]

Bringing fuel into space is a real problem right now. For any kind of serious traveling which will require the use of fuel, the current plan is to launch a ship from Earth that is a engine with a huge fuel tank that sits on top of a ship with a huge fuel tank to get the whole thing off the ground. This design has gone through many changes and might still be changed some more. There is no set up for making fuel in sufficient quantities using raw materials found in space or on other planets or moons, though there plenty of plans of how it might be done.

So far as I know there has been no standardization of what kind of engine everyone would use in space which means there is little chance that everyone could use the same fuel once they get off of earth which would limit refueling by different groups. The current craze is looking for the cheapest kind o fuel that can get the job done. Kerosene is a popular product. Methane is also being considered.

Engines that are powered by electric thrust could be one solution. There is only one kind of electricity so once it was generated or collected and stored, it could be used by everyone.

Originally, real space travel by people was supposed to be limited by how much water could be taken on a ship which were very small back then. It couldn't be compacted, so it had a weight and size problem that would be very expensive to overcome. Now that water has been found on the Moon and Mars, that is a good source of hydrogen, and oxygen, which could also be used as a universal space fuel. Liquid hydrogen is used to get the big space craft off the Earth. Its a common enough product and there is plenty of ground based infrastructure to support its use. It might take a lot of engineering to build a hydrogen fuel facility on the Moon or mars that could produce and store large volumes of liquid hydrogen and oxygen. If the hydrogen didn't have to be liquified, perhaps hydrogen airships could become practical for space ships that never leave the Moon or Mars.

 

[Swank]

Engines that are powered by electric thrust could be one solution. There is only one kind of electricity so once it was generated or collected and stored, it could be used by everyone.

What does this mean? "Electric thrust" usually refers to some sort of plasma drive that uses reaction mass. That reaction mass usually needs to be a specific kind of "fuel".

If the hydrogen didn't have to be liquified, perhaps hydrogen airships could become practical for space ships that never leave the Moon or Mars.

What's an "airship" in the context of an airless moon?

 

[Swank]

At present, all forms of spacecraft acceleration involve action/reaction - something needs to be going in the opposite direction of the spacecraft. The difference between different systems comes down to what the mass going out the back is, and how it came to have a velocity away from the ship. So you can take sawdust and oxygen and burn them to make thrust, or you can take that same mass and split their atoms and produce much, much more thrust. But you need to throw some stuff out the back.

The quasi exception is that you could power a spaceship by converting energy to light, and then lasering that light out the back end. Light doesn't have mass, but it has momentum, and the momentum can be harvested by the light losing frequency. This is also how a light sail works. But a laser drive has to be incredibly strong to move a ship, and how light weight could the energy source and laser be?

 

[Vertigo]

What does this mean? "Electric thrust" usually refers to some sort of plasma drive that uses reaction mass. That reaction mass usually needs to be a specific kind of "fuel".

I've always thought this is the ultimate problem. To shift any significant amount of spacecraft mass over a long period of time you're going to need significant amounts of reaction mass and, of course, the more reaction mass you are carrying the more reaction mass you need to accelerate it. And so on.

And was wondering if there was a way to create fuel and/or energy on a spaceship

The problem is you can't just create 'fuel' or energy out of nothing. So you have to either be carrying all that fuel in some form already or collect it on the way.

The best solution has always seemed to me to be the Bussard ramjet as mentioned by @Venusian Broon but that has all sorts of issues bearing in mind that collecting all that mass with the scoop will create significant drag, so your engine needs to overcome that drag as well as accelerate the mass of the space craft. I'm not fully up to date on research in that area but I seem to recall you also have to get the spacecraft up to fairly significant velocity before it becomes effective.

As for energy (without considering reaction mass) there is always solar energy but that drops off rapidly the further you move from the sun and is pretty negligible once you get into interstellar space. Lasers are an option but again as @Venusian Broon already mentioned you will have issues with deceleration. Otherwise energy will have to come from nuclear fusion or fission which also requires fuel although I'd imagine a lot less than the reaction mass you'll need to propel with that energy.

 

[Robert Zwilling]

Air ship in space would have hydrogen and oxygen gas instead of liquids as a fuel. The tanks would be very large, giving the appearance of Earth air ships.

If there was a practical ion engine for short hauls in low gravity, it could use a small traditional combustion engine for braking, requiring a smaller amount of fuel.

It is possible to produce methane from carbon, hydrogen, and water. These elements are found on Mars near the surface and could be used to make simple hydrocarbon fuels for traditional combustion engines. If combustion engine air ships proliferate on Mars early on, its possible that among the first structures built on Mars could be hydrocarbon fuel production centers, better known as gas stations.

 

[Christine Wheelwright]

This is a sobering thread because it accurately demonstrates the difficulty. The technological challenges are huge and we will probably never get beyond our own system. I think even a manned mission to Mars may be beyond our grasp in the coming half century or so. It really bugs me when idiots like Musk fool people into thinking we are close (although it is possible he actually believes this himself on some delusional level).

 

[AllanR]

For extreme distances, I assume you mean interstellar... The energy requirements are immense.
Even for a gram centimetre scaled spaceship —"Sending the lightweight spacecraft involves a multi-kilometer phased array of beam-steerable lasers with a combined coherent power output of up to 100GW." The tiny vessel would only be able to do fly bys and perhaps achieve fifteen percent of the speed of light. Woe be to whatever it collides with.... we could be sending off a relativistic kill vehicle!

Breakthrough Starshot - Wikipedia

en.wikipedia.org

 

[benmf]

A question or an idea popped in my nonscientific/non mathematical brain reading Hail Mary. It mentioned the problem of not having enough fuel for the extreme distances of space travel. And was wondering if there was a way to create fuel and/or energy on a spaceship while it's traveling in space. Has this idea been address before? If so, what were or are the answers? Is NASA working on it? Or is this considered a dumb question/idea?

In The Sparrow by Mary Doria Russell, astronauts hitch a ride to another planet on the back of an interstellar traveler.

 

[Swank]

This is a sobering thread because it accurately demonstrates the difficulty. The technological challenges are huge and we will probably never get beyond our own system. I think even a manned mission to Mars may be beyond our grasp in the coming half century or so. It really bugs me when idiots like Musk fool people into thinking we are close (although it is possible he actually believes this himself on some delusional level).

I don't think Mars is that far if you use a nuclear motor or Orion.

 

[paranoid marvin]

This is a sobering thread because it accurately demonstrates the difficulty. The technological challenges are huge and we will probably never get beyond our own system. I think even a manned mission to Mars may be beyond our grasp in the coming half century or so. It really bugs me when idiots like Musk fool people into thinking we are close (although it is possible he actually believes this himself on some delusional level).

I guess it depends on what you mean by 'we'. Probes have already travelled incredible distances, and relayed valuable information about what they've found.

Humans are fragile creatures, and all the expense and difficulties are mainly about keeping us alive inside the craft. I agree that it's far less likely that humans will travel to Mars than that they will. It will be insanely expensive, incredibly dangerous and with very little reward at the end other than to say 'we did it'.


By far the best way forward is human-computer integration, with astronauts having bodies capable of withstanding the hazards of space travel. This could be having mechanical bodies with human brains (very much like Robocop) or mechanical avatars (very much like... er.... Avatar). At the moment astronauts are enclosed with a mechanical suit - all that would happen is that the human became integrated with the suit. This type of technology is much closer to being within our grasp, much cheaper and with better chance of success.

 

[Swank]

I guess it depends on what you mean by 'we'. Probes have already travelled incredible distances, and relayed valuable information about what they've found.

Humans are fragile creatures, and all the expense and difficulties are mainly about keeping us alive inside the craft. I agree that it's far less likely that humans will travel to Mars than that they will. It will be insanely expensive, incredibly dangerous and with very little reward at the end other than to say 'we did it'.


By far the best way forward is human-computer integration, with astronauts having bodies capable of withstanding the hazards of space travel. This could be having mechanical bodies with human brains (very much like Robocop) or mechanical avatars (very much like... er.... Avatar). At the moment astronauts are enclosed with a mechanical suit - all that would happen is that the human became integrated with the suit. This type of technology is much closer to being within our grasp, much cheaper and with better chance of success.

If radiation is a problem, having a mechanical body surrounding a radiation vulnerable brain isn't going to solve it.

And that's assuming having a mechanical body isn't going to kill you all the other ways.


It would likely be easier to use gene therapy to make people better able to withstand radiation, or treat the damage.

 

[Robert Zwilling]

I don't think efforts to get to Mars, and especially the Moon, are that far away. Space flight is a big part of science fiction that seems like it must true. It could be similar to crossing the Atlantic 700 years ago, and you can pretty much see what's there before you get there now. Workers health has never been a big priority and if the work has a high status value, everyone is willing to let people do what they want to do.

100 years ago airplanes were a very big deal, carried a lot of risk, and every other day a plane fell out of the sky. A lot of people didn't know what aviation could be good for or how it would change the world, but that didn't stop anyone. People like Musk have no sense of reality as they simply buy solutions to any problems they may come across. If he wants to go to Mars, then he will do whatever he has to to get people there. The other day he said his company (shades of Alien!) could be on Mars in 3 or 4 years. I think part of the drive is fueled by the idea that there might be something on the Moon or Mars that will prove to have great technological value back on Earth that will be incredibly useful and of course extremely valuable. In layman's terms it's called gold fever, but if his space ships work, I think it's a done deal.

In 7 years, the space station is supposed to be demolished by a space tug boat that will push it into a planned descent where it burns up over a vast expanse of ocean. The tub boat is an engine attached to a big fuel tank. If it can be built and successfully launched, that design could go a long way towards powering space flight. The "big" ships wouldn't have to return to Earth every time, they could get refueled in space. That takes a lot of wear and tear out of the equation. The ships stay in space, and the crews and supplies go back and forth between Earth and the ship.

For a while everything would be neutral, happy days, but eventually there might be some temptation to arm the ships with weapons that are far in excess of what is needed, like in case of space pirates, which could provide an even bigger reason for having a presence in space.

 

[paranoid marvin]

I've mentioned this in a different thread, but as a race we are far more risk-averse than we were 50 or 100 years ago.

One of the reasons why I think people question the Moon landings today is because it was such a risky business. But we have to remember that those first astronauts were test pilots and decorated war veterans; they were already risking their lives daily, so one more risk was part of the job.

Today we have a much more cautious approach, and a failure - especially one that caused a fatality - would set the programme back quite some way. I would say that in today's world there is no way that astronauts would have been sent to the Moon in 60s technology.

The surprising thing is the US didn't press for a mission to Mars in the 1970s. But the Moon was as much a political statement as anything else. The first manned mission to Mars will only set off when the safety of its crew and the likelihood of success of its mission are as close to 100% as it is possible to be.

And that isn't likely to happen this Century, unless some rich, adventurous individual decides on a private venture, as did those who attempted to scale unconquered mountains.

 

[paranoid marvin]

If radiation is a problem, having a mechanical body surrounding a radiation vulnerable brain isn't going to solve it.

And that's assuming having a mechanical body isn't going to kill you all the other ways.


It would likely be easier to use gene therapy to make people better able to withstand radiation, or treat the damage.

I was thinking as much of the lack of requirement for living/sleeping quarters, food, water, oxygen etc. Of course the brains inhabiting the machines would likely go crazy unless they were only turned as and when they were needed.

The more likely preferred method would be an Avatar, with the controller safe at home on Earth. Or alternatively human conciousness transferred into an inanimate object; but that has as many ethical issues as anything else.

 

[Swank]

I've mentioned this in a different thread, but as a race we are far more risk-averse than we were 50 or 100 years ago.

One of the reasons why I think people question the Moon landings today is because it was such a risky business. But we have to remember that those first astronauts were test pilots and decorated war veterans; they were already risking their lives daily, so one more risk was part of the job.

Today we have a much more cautious approach, and a failure - especially one that caused a fatality - would set the programme back quite some way. I would say that in today's world there is no way that astronauts would have been sent to the Moon in 60s technology.

The surprising thing is the US didn't press for a mission to Mars in the 1970s. But the Moon was as much a political statement as anything else. The first manned mission to Mars will only set off when the safety of its crew and the likelihood of success of its mission are as close to 100% as it is possible to be.

And that isn't likely to happen this Century, unless some rich, adventurous individual decides on a private venture, as did those who attempted to scale unconquered mountains.

There is no lack of people today willing to take the chances the first astronauts did.

As far as everyone else goes - we have no idea if we would have made it to the moon if any of our crewed rockets had Challengered prior to Apollo. But we got lucky, and the only deaths were a pad fire.

I think the main thing was that people of the '50s and '60s were living in the future. We are mired in our pasts, and don't believe in the future - unless it is a dystopia.

 

[Swank]

I was thinking as much of the lack of requirement for living/sleeping quarters, food, water, oxygen etc. Of course the brains inhabiting the machines would likely go crazy unless they were only turned as and when they were needed.

The more likely preferred method would be an Avatar, with the controller safe at home on Earth. Or alternatively human conciousness transferred into an inanimate object; but that has as many ethical issues as anything else.

We already have robot craft with controllers on earth.

If we could transfer consciousness into machines, we'd likely have a lot of other more basic engineering issues solved.


As far as astronauts and conditions go - a motivated and stimulated intelligent, sane adult can live in little more than a coffin, eating the same thing every day, for a year without losing their minds. That isn't a real issue compared to environmental damage.


I imagine the actual spacecraft will use a combination of water, magnetic, polyethylene, drugs, moveable environments and flare prediction to keep them healthy.

 

[Vertigo]

The more likely preferred method would be an Avatar, with the controller safe at home on Earth. Or alternatively human conciousness transferred into an inanimate object; but that has as many ethical issues as anything else.

I think the communication delay would always make this approach impractical.

 

[Robert Zwilling]

Intelligent space robots need to be aware of their surroundings in real time.

Satellites using AI to control their operations are coming. How smart will they be.

Currently the satellites are given preprogramed steps to carry out their operations. 7 months ago China allowed ground based AI to control one of their observational satellites for 24 hours and supposedly they have no idea why it picked the targets to picture that it did. Apparently the Chinese have launched at least one satellite with onboard AI, possibly already doing things on its own.

The idea being that the satellites spend a lot of time doing nothing or collecting meaningless data and by using AI, the satellites could be actively looking for things to look at based on human activity, natural or unusual events. Sounds like they would be scanning the Earth 24/7. It is also hoped that the satellite could avoid collisions, monitor space junk, and look after its own operational health. The European Space Agency is developing on board AI systems. The observational satellites need to be able to figure out what kind of human activity is worth monitoring.

To operate in space, the AI satellite would probably need to be aware of its immediate surroundings. There would probably be a remotely operated kill switch installed in AI satellites. Would it just be a simple on off switch or be a destructive device, or both. If it could analyze its own operational health and was capable of figuring out what people were up to down on Earth, perhaps it might get to wondering why it was carrying a bomb or why there was a device to turn off the power without its control.