Possible Space Propulsion Systems

[Brian Rogers]

I need some inspiration or ideas on a WIP I have going which requires some serious acceleration.

To make my story work I need travel times in space that won't absolutely bore the reader. Unfortunately the reality is that even at 10 gees of acceleration, it would still take days to just decelerate and begin orbiting a planet from any significant speed (.05-3% light speed).

My story is set very far into the future so using exotic matter is not out of the question but I want to be accelerating at 100 gees. I already have ways to counteract such force for the people on board the ship, I just need an actual propulsion engine that has such a high impulse and thrust to achieve acceleration like this over extended time periods.

As you can imagine, I want to keep the math fairly accurate (hard sci-fi) and the distances I'm covering are just from planet to planet (50 million km) or so, no need for warp drives. Any ideas or devices you've written of yourself or read in other books are welcome!

 

[Dennis E. Taylor]

To decelerate from 3% of light speed to zero at 10g will take 1.06 days. To get to Saturn from Earth at 2g will take 6 days (accelerating constantly. Longer if you want to stop there).

 

[Brian Rogers]

o decelerate from 3% of light speed to zero at 10g will take 1.06 days.

Yes! That's why I want to figure out some propulsion system that could theoretically get me going 100g so then it would only take an hour or thereabouts.

 

[Vladd67]

How about an advanced version of this
http://www.telegraph.co.uk/news/sci...orks-and-could-get-to-Moon-in-four-hours.html

 

[Vertigo]

There's still a lot of debate about that one. It disobeys the law of conservation of momentum. And a major clue to the doubtfulness of the experimental results was that it apparently continued producing thrust even after it was shut down! And even if it does work in some strange way I'm not sure you're going to be getting 100g out of it.

Personally I'd go with an anti-matter drive. I believe out of all the energy sources we can so far believably imagine, it produces more bang per gram that anything else.

 

[Serendipity]

Re EM Drive - the latest experiments in Germany do not claim definitively to have produced the thrust. However, they say the results are promising, but further work needs to be done for confirmation, or otherwise. If it does work, then there are going to be a lot of questions about why it really works and I suspect we will be getting a significant update to the laws of physics.

Those are the facts... my gut feel says this works... there's been too many independent experiments (NASA, China and now Germany) reporting there is something going on.

 

[Brian Rogers]

Interesting - so although today EM Drive seems to defy physics, it also seems to produce some sort of result, although that is very minimal and in doubt due in part to the limited testing facilities we have. Can't really test it in space now can we

But my story is set far into the future so perhaps there is a way to make it seem feasible...although I'd have to invent some new law of physics at least for my own understanding haha.

Appreciate the ideas so far -

Personally I'd go with an anti-matter drive.

Any sort of drive you are referring or have seen used in other similar settings?

 

[Ray McCarthy]

Unfortunately the reality is that even at 10 gees of acceleration, it would still take days to just decelerate and begin orbiting a planet from any significant speed

Days!
In my SF, the Starships have to spend 3 to 6 months decelerating and THEN can only do a "fly by", orbit would take nearly a year to achieve.

Gives folk time to learn languages etc.

All non-exotic* drives chuck stuff out the back. This can be powered by:
1) Chemical reaction: The reaction products are chucked out the back
2) Electricity from Solar panels, thermoelectric fission pile, fission power station, fusion power station, or Anti-matter power station
You can use the electricity to accelerate plasma: Ion Drive or Ion Drive + linear Accelerator or Photon drive. Simple low power Ion drives use a single electrode system and Xenon. Advanced ones might use separate linear accelerators several km long for oxygen and hydrogen from water. The "plasma" torch of that would extend a very long distance and be dangerous.
3) Direct Blast Drive: AKA Project Orion: Chucking bombs out the back (Fission, Fusion or Anti-matter)

Anti-matter has to be expensively manufactured. Thus it's an extremely dangerous battery system.

Above about 2G you need tanks with breathable liquid the same density as your flesh. Breathable liquid DOES exist, but it's the wrong density (currently) for acceleration tanks.


[* Exotic drives are Warp Bubbles, unspecified hyperspace / jump gates / star gates / worm hole generators and such that "bypass" light speed limits, likely can only be safely deployed in deep space (if possible at all!).]

 

[Ray McCarthy]

although today EM Drive seems to defy physics, it also seems to produce some sort of result,

There is no evidence that a non-photonic EM drive works. It only has advantage (as does photonic drive) of using no reaction mass. It's less efficient use of electricity than Ion Drive. The bigger your Linear Accelerator, the less reaction mass an Ion drive uses.

There are two kinds of laser drive:
1) A true photonic drive. Efficiency is low, but max V is high as the photons are speed of light. Any EM drive, if it is real at all can only be similar or worse.
2) Ablative drive. A laser on ground (or not on the craft) focuses on a shield which is "burnt away". That creates thrust. There is also some photonic thrust. Note a solar sail is using particles of the solar wind more than photon propulsion.

 

[Brian Rogers]

Days!
In my SF, the Starships have to spend 3 to 6 months decelerating and THEN can only do a "fly by", orbit would take nearly a year to achieve.

Hey Ray, I see that in your work and I love the realism, but my story takes place on planets and colonies and not within ships. Unless I simply change how a crew operates on a ship (i.e. cryo sleep) then a large portion of the plot would be forced to be constrained to ships traveling here and there. I will put some thought into cryo-sleep though as it might be a good device to use to keep the plot outside of ships and ages of characters consistent throughout the story since they wouldn't age...hmmm

A major stumbling block of lower speed and acceleration though is how to make industry and infrastructure traveling from deep space into near orbit useful. They would have to contain DECADES worth of supplies for a colony or planet they visit since their trips would take so long (setting is 12 light years and multiple systems). Each delivery would be like a massive holiday and any missed delivery or mishap could kill off the entire colony! At least with high speed and accel. those situations are solved for me. So much to consider...

 

[Ray McCarthy]

You can see why Space Opera doesn't worry about it!

My Talent series is actually mostly planet based. Even "Starship Chief" and "The Master's Talent". Spaceships are as exciting as a normal Nuke Sub patrol in peace time.

 

[Vertigo]

One of the best sources for bringing much of this stuff together is Atomic Rockets: http://www.projectrho.com/public_html/rocket/ But you are likely to find that disappointing as it is rooted in hard science which is generally pretty disappointing from an SF perspective when it comes to interstellar engines.

The idea of an antimatter drive is really just that; an idea. It pops up in loads of SF books. It appeals to SF authors because of the extremely high ratio of energy from fuel. However the biggest problem with almost any of these drives is not the fuel but the reaction mass. That is the stuff you sling out the back and which actually gives you your thrust (action - reaction). And unless you go down the ramjet approach (which has its own little suite of cans of worms) then you have problems carrying sufficient reaction mass to be able to travel under thrust for your whole journey.

And if you are going down the hard SF route that is always going to be one of your biggest limitations. Now I would have to say that if you have come up with a way to handle 100g acceleration then you have already had to do a lot of handwavium; there is nothing in existing physics that will permit this. Therefore I'd stick with handwavium for your drive and just don't go into too much detail.

The bottom line is that with our current knowledge of science there is simply no way you are going to make interstellar journeys in short timescales.

Edit: oh and bear in mind that if you are travelling those sort of distances with those sort of accelerations then you need to consider the effects of time dilation.

 

[Brian Rogers]

true - my handwavium as you put it has to do with utilizing superconductive magnets powered by an advanced Tokomak reactor to achieve magnetic fields diametrically opposite to the forces such acceleration creates. The same thing we did with levitating a mouse on Earth (1g) just extrapolated by using greater energy, more powerful magnets and the idea that "technology will be more advanced in the far future and therefore more believable".

I appreciate the ideas - most of this the reader will never have to know and I may not even generally state but its best to have such ideas in the background so as character refer to different things the setting seems more real.

 

[Vertigo]

Hmmmm those two things are not quite the same. What was done was to apply a force equal and opposite to the force of gravity as result of which there is no acceleration and your mouse floats. You must remember that the force of gravity only produces acceleration when an object is allowed to fall. In your space ship if you counteract the force giving you your 100g then you have... no acceleration and you go nowhere. Your problem for surviving that acceleration is not to do with the acceleration but the inertia.

As I say I wouldn't try to go hard SF on your drives if you want this sort of acceleration. Our current physics simply doesn't permit it.

 

[Ray McCarthy]

utilizing superconductive magnets powered by an advanced Tokomak reactor to achieve magnetic fields diametrically opposite to the forces such acceleration creates

That doesn't work. A fluid tank with density of flesh that also carries oxygen will work to 10G for a prolonged period as part of a life support machine. Even then the lungs, stomach etc all has to be filled. The only current available breathable liquid has the wrong density. However it sounds possible.

Due to INHERENT power / mass / fuel / energy constraints, acceleration of a distance somewhere between Kuiper Belt and Oort Cloud is possible. You must have enough fuel to decelerate at other end after coasting.

Hence most Interstellar SF with large amounts of regular travel has speculative / fantasy / SF / hypothetical "exotic" drives not involving reaction mass as mentioned before.

 

[Brian Rogers]

Perfect - honestly I'm glad my "hard sci-fi" ideas have been thrashed! Takes a lot of research work out of the equation (other than proper times and speeds) to keep my quasi-physics in order.

In fact in my WIP the real "hard science" only pertains to certain basic topics. My exotic matter drive, handling acceleration, cryo-sleep, etc. can certainly all be simply "assumed" to be invented over the passage of time. I also throw in a variance of M-Theory to make other technology possible in this future time so that's certainly speculative and fantastical.

This conversation makes me realize its better to remain consistent and fantastical if other areas of my technology are already that way rather than trying to make something hard-science in one aspect of a story and fake-science in another. Even if I personally like hard-science to be more prevalent, its the reader's understanding and reaction to my quasi-physics that will make or break the setting as something they could believe. Any thoughts on that particular topic? I know I'm thread jacking my own thread...

 

[Serendipity]

In fact in my WIP the real "hard science" only pertains to certain basic topics. My exotic matter drive, handling acceleration, cryo-sleep, etc. can certainly all be simply "assumed" to be invented over the passage of time. I also throw in a variance of M-Theory to make other technology possible in this future time so that's certainly speculative and fantastical.

Ahem... you could go for Alcubierre's Drive and assume further work has been done on it to make its dimensions more realistic... this is where I tiptoe away....

 

[Ray McCarthy]

you could go for Alcubierre's Drive

I assumed that's what his warp bubble drive was.

It's fine. But if you use it "in system" the Galactic Council may seize your ship and try you for genocide (Jo insists that only applies to Tellurians and anyone else it's Xenocide)

 

[Brian Rogers]

hmm...from all the "research" I've done I've noticed that subluminal warp using an Alubierre toroid actually is far more reasonable. The black hole (contraction of space in front) and white hole (expansion of space behind) horizons which would generate the Hawking radiation and destabilize nearby masses only occur at superluminal velocities. Where have you seen subluminal speeds using a warp drive causing havoc to the surrounding space?

 

[Ray McCarthy]

It's only superluminal Alubierre Warp drive that has the shockwave.
It's not viable for sub light drive. Ion drive for sub light fine. The whole point of Alubierre Warp drive is to bypass limitation of regular space limit of C. Even at 1G (never mind 1.5G which is possible without a tank, though lying down most of the time!) getting to a significant velocity doesn't take that long. 10G is masochists in a coma in a breathable liquid tank, if it's more than a few seconds!
https://www.sffchronicles.com/threads/560590/

Current Ion drives are very low power, no linear Accelerator and only solar power usually. Hence low G. A hypothetical Ion Drive using fusion power (or even fission PSU) and several km of linear Accelerator can easily do more than 1G and not use a lot of reaction mass. The longer the linear Accelerator the higher the exit speed of particles, so you can get more velocity or use less reaction mass (at expense of needing more power, likely very much less power consumption than Alubierre Warp, which is the main flaw of Alubierre* )


(* Go on use it for the Starship Drive, but don't talk about the power consumption. I decided on vaguer never explained method of starship drive._