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Forum » SpaceEngine » Science and Astronomy Discussions » Space Drives (Sci Fi Engines, and possible non fiction engines.)
Space Drives
SpaceEngineerDate: Wednesday, 07.11.2012, 20:58 | Message # 16
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I think that the only realistic technology that we could use in near future to reach the stars, are small automatic probes with a laser sail propulsion system. In short, the probes have a huge thin sail, which is accelerated by the pressure of a laser beam fired from the Solar system. Lasers can based in Earth's orbit, or a more splendid idea - on Mercury's orbit, where they can be powered directly by sun light.

http://www.aleph.se/Trans/Tech/Space/laser.txt

Why is a laser sail the only reasonable idea? Because traditional rocket ships (even anti-matter) must carry fuel to accelerate the ship and carry extra fuel to accelerate the fuel too. This extra fuel may take 90% of a ship's mass, and this is very bad. Instead of it, lasers and an energy source to power them are left in the Solar system, and the ship must carry only a sail (which may still take 90% of its mass, but the spacecraft may be a thousand times smaller that an anti-matter spacecraft).

The only thing that I dislike is that most proposed designs are flyby probes. Imagine a small probe that flies at 0.1c and reaches the Barnard star after a 60 year trip, and... passes it during one day! It won't even be able to catch detailed images of some planets. Scientific results of such a mission will be more than zero, and this is after 60 years of waiting! This makes no sense to me. Interstellar probes should definitely stop at the target system and start its complex exploration.

To stop a probe in the system, Zubrin (I guess it was Zubrin) purposed a two-stage sail: the first stage separetes from the spacecraft near the target system and works as a mirror that reflects the laser beam from the Solar system back to the spacecraft, that it uses a second (smaller) laser sail to decelerate. Another scheme is to use anti-matter engines to decelerate. This is still much more effective to have laser sail acceleration system and carry fuel for the deceleration stage only. This idea was used in the "Avatar".

Another idea on how to decelerate a spacecraft from relativistic speed to a relatively small speed (100-1000 km/s) is a magnetic parachute (proposed by Zubrin again). The final deceleration can be done by antimatter or even fusion engines.

--------------

Another idea that we really may implement is the near future is based on nanotechnology. We may build a very small, few milligrams "spacecraft" that contain nano-robots, and shoot it from a huge linear accelerator buildt in space. When it reaches the target system, it decelerates using a solar sail, a magnetic parachute or even something else, then find a planet or a moon to land on and start to build various systems - antennae to connect with Earth, interplanetary probes to explore the planets, etc.

*





 
Antza2Date: Wednesday, 07.11.2012, 23:11 | Message # 17
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Lasers can based in Earth's orbit, or a more splendid idea - on Mercury's orbit, where they can be powered directly by sun light.

I think that we can improve this concept. Why not have a large amount of light-gathering satellites orbiting the Sun. Those satellites would then beam the light they gather to linking satellites on a higher orbit, which in turn would beam all the gathered light into a single satellite on even higher orbit. That Satellite would fire an extremely powerful laser to the sail of the ship. This type of setup would increase the thrust immensely.

The setup would look much like this

Attachments: 3699022.jpg(97Kb)





Go to antza2.deviantart.com for cool photos!

Edited by Antza2 - Wednesday, 07.11.2012, 23:15
 
HarbingerDawnDate: Thursday, 08.11.2012, 02:19 | Message # 18
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Quote (Antza2)
Those satellites would then beam the light they gather to linking satellites on a higher orbit, which in turn would beam all the gathered light into a single satellite on even higher orbit.

The process of transmitting energy like that is very inefficient. You could simply take all the satellites and make them into one massive satellite and then get much more power because you don't lose any through wireless transfer.

In any case, I support more "conventional" propulsion systems, where the craft creates its own thrust. For a long interstellar voyage, perhaps some sort of nuclear electric propulsion system could be devised. All that would be required is a nuclear reactor of some kind that can generate power for the very long times required to fly to another star (might require a fusion reactor), and advanced electric engines, preferably very high Isp engines like today's ion engines, but with more thrust. Something similar to VASIMR, but a bit more efficient. This would allow for the craft to reach high speeds (though not quickly) and be able to maintain control over itself for the entire journey, including being able to slow down and go into orbit around its target star.

My biggest problem with trying to execute any interstellar mission with current technology is that by the time the probe arrives, all its technology might by hopelessly outdated. We may even design a new type of spacecraft that can get to the same destination before the probe even arrives, thus making the entire mission pointless. Imagine that in the year 2060 we launch an interstellar probe that will take 80 years to reach its destination. Then in the year 2135 we build a new ship with warp drive that can reach the same destination in 8 months. That ship would reach the system when the other one still had not arrived, and it would have modern technologies and could orbit any planet in the system if it wanted to. The first ship would then become completely redundant, essentially useless.

That is the problem with trying to launch missions that have such a long duration. You risk making a wasted effort due to the progression of technological development.





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SpaceEngineerDate: Thursday, 08.11.2012, 09:17 | Message # 19
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Quote (HarbingerDawn)
The process of transmitting energy like that is very inefficient. You could simply take all the satellites and make them into one massive satellite and then get much more power because you don't lose any through wireless transfer.

Solar collector satellites should be "anchored" in orbit of some massive body (Mercury is perfect) - otherwise solar light pessure and impulse from a laser beam will push them away (a mirror that focuses solar light on the laser is like a solar sails, and the laser itself is like a photon engine). This idea was proposed by R. Forward in his "Rocheworld" novel.

Quote (HarbingerDawn)
My biggest problem with trying to execute any interstellar mission with current technology is that by the time the probe arrives, all its technology might by hopelessly outdated. We may even design a new type of spacecraft that can get to the same destination before the probe even arrives, thus making the entire mission pointless.

This assertion makes no sense to me. If a warp drive is impossible, interstellar flight will take dozens of years anyway, and will be extremely expensive. So there's no sense to sending a new probe to the same system, it's better to send it to another one. If our civilization was able to launch one probe every 10 years, there'd be 8 other probes on a trip to 8 different stars when the first probe reached Barnard's star. The scientific result of 9 missions to different stars would be bigger anyway than 9 missions sent to the same star.

*





 
BlueplanetDate: Friday, 09.11.2012, 08:36 | Message # 20
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Antza2, That picture is sick, and it reminds me of the ship Destiny in SGU, where this ship used the sun to recharge its engines. Dr.Kaku, a theoretical physicist, said that a type 2 civilization will use the sun for energy. We are a type 0 as he claimed, and it will be some time before we get to the point of actually using our mother star.




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Edited by Blueplanet - Friday, 09.11.2012, 08:37
 
HarbingerDawnDate: Friday, 09.11.2012, 10:09 | Message # 21
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Dr.Kaku, a theoretical physicist, said that a type 2 civilization will use the sun for energy. We are a type 0 as he claimed

He did not invent that scale, that is the Kardashev scale and was invented by Russian astrophysicist Nikolai Kardashev in 1964.





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BlueplanetDate: Friday, 09.11.2012, 10:18 | Message # 22
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He did not invent that scale, that is the Kardashev scale and was invented by Russian astrophysicist Nikolai Kardashev in 1964.


Right Nikolai invented this scale, but my statement never said Dr.Kaku did, I was just quoting what he said off of a video I watched.





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Edited by Blueplanet - Friday, 09.11.2012, 10:22
 
HarbingerDawnDate: Friday, 09.11.2012, 11:49 | Message # 23
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Right Nikolai invented this scale, but my statement never said Dr.Kaku did, I was just quoting what he said off of a video I watched.

From the way you wrote it you made it sound like the original idea was his. I was just clarifying.





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SlyReaperDate: Monday, 19.11.2012, 22:07 | Message # 24
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I've always been quite keen on the idea of nuclear salt-water rockets for interplanetary travel. Even the environmentalists can't get upset about them because the exhaust velocity exceeds solar escape velocity. The idea is you have enriched uranium or plutonium salts dissolved in water and suspended in a neutron moderating mesh. To "burn" the fuel, you pump it to the arse end of the ship, whereupon it reaches critical mass. Keep pumping the fuel and you get a continuous nuclear flame. Even better, with some clever geometry and fluid dynamics, you can make it so that peak neutron flux occurs outside the ship, thus vastly reducing the requirement for making your materials ridiculously heat resistant.

So it's basically Project Orion, but moderately less insane. Since it doesn't strictly involve detonating nuclear devices, it's not covered by the treaties that killed Orion, and since it's a continuous flame rather than pulses, you don't have to muck around with pusher plates; mechanically, it could be a fairly simple machine.

As for interstellar travel, I don't see that being possible any time soon. The trouble is you need an awful lot of fuel to move the colossal amount of fuel needed to move the humongous amount of fuel needed to move a tiny mass anywhere close to the speeds necessary to make the trip in a single human lifetime. Any engine capable of interstellar travel in a reasonable amount of time would, I think, be something totally exotic and not yet imagined.
 
SalvoDate: Tuesday, 20.11.2012, 16:25 | Message # 25
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What about deuterium?
I think it might be userful for space drives, but maybe i'm wrong, I have to do a search...





The universe is not required to be in perfect harmony with human ambition.

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architeuthisDate: Wednesday, 21.11.2012, 00:41 | Message # 26
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This assertion makes no sense to me. If a warp drive is impossible, interstellar flight will take dozens of years anyway, and will be extremely expensive. So there's no sense to sending a new probe to the same system, it's better to send it to another one. If our civilization was able to launch one probe every 10 years, there'd be 8 other probes on a trip to 8 different stars when the first probe reached Barnard's star. The scientific result of 9 missions to different stars would be bigger anyway than 9 missions sent to the same star.


True, especially for close by stars but, I think Harbingers general argument still holds up. Take a hypothetical situation, lets say at some point we launch a seedship towards Tau Ceti which accelerates up to .1 c in a brachistochrone trajectory. It will take roughly 240 years (in Earth reference frame) to get there. Then say 25 years after the seedship launches a technological breakthrough allows us build ships capable of accelerating up to .5 c. A seedship launched with the new technology now takes only 50 years or so to get to Tau Ceti so it will pass the older ship enroute and by the time the original seedship arrives it will find a 165 year old colony instead of the virgin territory they were expecting. This example has many simplifying assumptions but you get the idea, this is the basic problem with generation ships, and it only gets more and more absurd the farther away we want to go. Now if we are using a sufficiently powerful drive system, even if warp drive is miraculously invented, the people who leave early might only be a few decades rather than a few centuries late to the party.

Zubrin's NSWR, if its even possible (this may be a case of the devil dwelling in the details), would be crazy powerful for travelling within a solar system. But to get even to Alpha Centauri this drive still would take centuries. This is no way to start a galactic empire. The tyranny of rocket equation implies that the only way we are going to ever expand beyond sol (with realistic mass ratios) is by using photon (or laser mirror) or more likely antimatter drives.

I made a table of some approximate travel times to Alpha Centauri for drives of interest. Please take these numbers with a grain of salt as I calculated using theoretical maximums for specific impulse for most of the drives, which in some cases may be 1 or 2 orders of magnitude beyond what is realistic. Time is to log scale.

Attachments: 7909997.png(24Kb)


Edited by architeuthis - Wednesday, 21.11.2012, 01:03
 
SpaceEngineerDate: Wednesday, 21.11.2012, 01:15 | Message # 27
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Quote (architeuthis)
A seedship launched with the new technology now takes only 50 years or so to get to Tau Ceti so it will pass the older ship enroute and by the time the original seedship arrives it will find a 165 year old colony instead of the virgin territory they were expecting.

First, I was talking about an unmanned probe. Even with your digits, it's still better to send new probes to other stars. Only if a new starship would cost as the carrier rocket cost now, it will be economical sense to overtake the old missions.

*





 
SlyReaperDate: Wednesday, 21.11.2012, 22:25 | Message # 28
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Quote (architeuthis)
Zubrin's NSWR, if its even possible (this may be a case of the devil dwelling in the details), would be crazy powerful for travelling within a solar system. But to get even to Alpha Centauri this drive still would take centuries. This is no way to start a galactic empire. The tyranny of rocket equation implies that the only way we are going to ever expand beyond sol (with realistic mass ratios) is by using photon (or laser mirror) or more likely antimatter drives.


I never said it would be a candidate for interstellar travel, but it would be awesome for interplanetary. At the moment, even sending people to the moon is beyond our grasp, let alone Mars or beyond.

Maybe if we invent a cure for ageing, then slowboating it between stars might be feasible; what does a journey of 1000 years matter when you're already a million years old?

Antimatter - I struggle to see that ever being doable. It's hard to imagine an antimatter containment system that isn't several orders of magnitude heavier than the antimatter it's containing. And we don't even know how to make the stuff except via the hugely expensive and inefficient process of atom smashing. Perhaps if we were somehow able to flip normal matter into antimatter at minimal energy cost, it might be doable.

But if we're delving into extremes like that, another idea I've heard, which is still within the known laws of physics (but is completely bonkers) is a black hole drive. The Hawking radiation given off by a black hole increases asymptotically as the mass approaches zero. So if we had a black hole the mass of, say, a small mountain range, it would give off a great deal of energy until it was depleted. It would in fact violently explode in very short order, releasing its rest mass as pure energy, so you would need to keep feeding it matter to keep it stable. But if you did, it would function as a perfect matter-to-energy converter, at least efficient as a matter-antimatter reaction. Use it to power a massive gamma ray beam out the arse-end of your ship.

There are a number of problems with this of course. Firstly, the radiation pressure would greatly hinder any attempt to feed more matter into it. Secondly, it's hard to imagine how you would mount the micro black hole into the structure of the ship. Thirdly, we have no idea how to manufacture black holes of this size in the first place. Fourthly, and perhaps the biggest problem, would be that if the system feeding matter into the black hole ever malfunctioned (or you simply ran out of matter), it would explode with planet-shattering force. Getting it to shut down gracefully would be a hell of a job.
 
R136a1Date: Monday, 21.01.2013, 06:15 | Message # 29
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The next big way for fuel is probably a plasma-type material rocket fired from a "space elevator". which would make fuel much more efficient and cheaper. almost cutting it off by 90% of its costs and mass.




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Tank7Date: Saturday, 26.01.2013, 18:51 | Message # 30
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I like the possibilities of interstellar travel, but I do spend a fair amount of time thinking about shoter term future goals, within the solar system. I feel that science fiction has a severe tendency to overlook "the in-system stage" of our potential development as a civilization. I think a really good set of articles is in the following:
Wikipedia: Non-Rocket Spacelaunch From that link I especially recommend Launch Loop as my favorite, but there are several good ones, from the well known Space Elevator to the somewhat crazy Skyhooks/Rotovators.

This reminds me of a board game called High Frontier I have read about:
High Frontier focuses on the solar system and it's exploitation for the theme. You play one of several factions (UN, USA, EU, Russian Federation, People's Republic of China) and the goal of the game is to achieve a state of affairs known as "exoglobalization". Basically, it is the next logical step of economic mastery where you can use the many billions of tons of precious metals such as gold and platinum believed to be within some of the near earth asteroids, and also your manufacturing process is free from all the environmental, legal, tax, etc. constraints of industry on the surface of earth. The first player to get to this point wins the game. There is basically only one resource in this game, it is water, under the assumption that crews need it to survive and you electrolyse it to make more LOX rocket fuel for your ships. At first, water must be expensively exported from earth against the pull of gravity, then it can be mined from craters in the moon and such places (ice), and eventually you colonize the asteroid belt and achieve exoglobalization by being able to mine both water and precious metals right out of the asteroid.

Wikipedia: Asteroid Mining

Board Game Geek: High Frontier

EDIT: I feel like this reply needs elaboration here for a more solid feel of being relevant to the thread topic. Basically, the board game's concept of exoglobalization feels very correct to me in a way, though it is obviously simplistic with the "water is money" thing for Crew survival and LOX fuel. The various forms of non-rocket spacelaunch mentioned in wikipedia, such as a space elevator or launch loop, would deal with the first stage for us. As soon as it becomes economical to extract stuff from near earth asteroids, life should be a blast. Ofcourse to have something like a space elevator you more or less require world peace (no dumb comments on world pleace please, i know how unrealistic it is), with nobody trying to force you to believe their religion by pointing a Kalashnikov at you and so on. Otherwise the space elevator or any other such single piece of super expensive infrastructure is very vulnerable to sabotage, terrorism, or even "legitemately" declared warfare. Once non-rocket space launch is achieved, then even LOX rockets would be perfectly sufficient to go between Earth LEO and Near Earth Asteroids, though I still expect to see plenty of low thrust alternatives especially for robotic missions.

Conclusion
I guess in the end I am trying to say we don't necessarily need insane space drives yet. A Launch Loop, which is my personal favorite, would require a very serious amount of electricity. It is possible with current technology, but a breakthrough in Fusion reactors would be very welcome indeed. Generally, the level of civilization you can have is strongly linked to the energy available. Rome had water/gravity, imperial europe had coal, and now we have some nuclear and oil, but still plenty of coal. People really need to stop hating nuclear -.- /rant


Edited by Tank7 - Saturday, 26.01.2013, 19:10
 
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