Nuclear Propulsion - The best way for space travel

Josh Cryer · 2003-02-24 17:54:05

Hmm, aren't you assuming instant acceleration and deceleration? I'm confused by your numbers.

soph · 2003-02-24 17:59:55

That's why I had a "fast route" and a "slow route"

Acceleration is a matter of minutes, so let's even divide our numbers all by 10.

Even by our most conservative estimate, you get there in 8 days.

soph · 2003-02-25 17:36:07

in addition, Mars is 48 million miles at its closest, so it could be 6 days maximum at peak season.

Preston · 2003-02-25 17:48:27

Note on magnetic fusion: Acceleration would probably take months to use up all the fuel. Also note, when Zubrin says you can get a delta v of twice the exhaust velocity, the assumption is a mass ratio (fueled mass / dry mass) of 7.5. (ln(7.5) is about 2)

Pulse fusion ships weigh 220 tonnes on paper, because of the laser banks and reactor to power it; (less if antimatter initiated concepts can work.) Magnetic fusion ships are on the same order.

edit (add on): An MICF pulse fusion ship has ~2.5 x 10^4 N of thrust using a conservive estimate of 1 pellet per second. Some authors say 100 per second may be possible, though.

soph · 2003-02-25 17:54:00

For the relatively short Mars-Earth, distances, you could probably use a pulse based ship only. However, for longer voyages, you would probably want a pulse/magnetic hybrid, for better isp. Besides, we may be able to eek a good deal of power from the reactor in the future.

But you do agree with my figures, based on a pulse fusion system (i.e. half a day<transit<7 days to Mars)?

TJohn · 2003-02-27 08:37:15

Interesting news for the Nuclear propulsion enthusiast.

http://www.spacedaily.com/2003/03022616 … u9w6g.html

RobertDyck · 2003-02-27 09:37:14

This is a curious article, with Russia providing the US with nuclear fuel, and this is for Plutonium-238. I know Uranium-238 is depleted Uranium, so the question was what is Plutonium-238. The answer is it's used for radio-isotope batteries, not a nuclear reactor. I found the original ITAR-TASS news article in English.

soph · 2003-02-28 14:21:10

So these would be heating/power devices?

Robert: I was going over Zubrin's books, and I came across the Ares. He has two versions: big, and bigger. The larger one would have a payload capacity to LEO of the Saturn V, but probably be more cost effective, because it is mostly shuttle derived boosters.
It would send an NTR phase of 70 tonnes to Mars.

The smaller one is about 75% the cargo capacity of the Saturn V to LEO, and has a launch mass of 2/3 the Saturn V. This version would have a Mars payload of 47 tonnes, roughly the same as the Saturn's lunar payload.

dicktice · 2003-02-28 18:03:48

My simple minded (ie. non-analytical) hopes for plasma solar wind sailing can be summarized as follows--
1) Principle can be tested right now in ISS orbit.
2) No propellants required...hydrogen ions from onboard ice.
3) Self-shielding in principle, from Solar flares.
4) Can be upscaled indefinitely in size, and therefore payload.
5) No thrust fall-off with distance from the Sun.
6) Straight-line astrogation, as opposed to orbital mechanics.
7) Achievable (if proven feasible) using today's engineering.
8) Equally suitable for out of the ecliptic transportation.
9) Unlimited (short of relativistic) velocity capabilities.
10) What else, I wonder, anyone?
That still leaves, for the rocket enthusiats amongst us: launching ramps, boosters, ferries, landers, orbiters, ice astroids, mining and smelting, free-vacuum electronics, ditto lasers and masers, orbiting platforms, space habitats....
None of which requires (nonexistent) fusion technology. That's because it still hasn't happened. Commercially viable fuel-cell, solar produced hydrogen-powered, not to mention hybrid cars, are hardly going to be achieved in my lifetime, for gosh sakes--if only because of no-nothing governments!
Fusion is still a pipe dream, you shouldn't keep claiming advantages for--not exactly like so-called "anti-gravity," I admit, but for all intents and purposes, very "far out." Sorry.

soph · 2003-02-28 18:07:21

Fusion is still a pipe dream, you shouldn't keep claiming advantages for--not exactly like so-called "anti-gravity," I admit, but for all intents and purposes, very "far out." Sorry.

Right, that's why ITER is set to make a 14x energy gain in 10 years.

Just because you don't like a technology, doesn't mean its a "pipe dream." We have drawn within a small margin of breakeven, thousands of times closer than we were a decade ago.

Your mentality is: I don't see it, therefore I will never see it.

And not to mention, those "goals" you listed from plasma sails are hardly achievable, at least a large number of them. Reevalutate your own pipe dreams before bashing the posts of others.

dicktice · 2003-02-28 18:58:05

Fusion: I like it, I like it...it's just that no one (including Soph) seems to know how to go about it. I wish you would go into the technique(s) for engineering a propulsion package before assuming any partiality on my part. I have always adopted do-able engineering solutions, when required, while looking foreward to something better, when available. Not being a scientist, I can't afford to pipe-dream. Back to you.

soph · 2003-02-28 19:15:15

Fusion: I like it, I like it...it's just that no one (including Soph) seems to know how to go about it. I wish you would go into the technique(s) for engineering a propulsion package before assuming any partiality on my part. I have always adopted do-able engineering solutions, when required, while looking foreward to something better, when available. Not being a scientist, I can't afford to pipe-dream. Back to you.

A fusion drive would be relatively simple in theory. You have a fusion chamber, superheated, with plasma "mirrors" bordering the chamber. Fusion takes place in the chamber, and the plasma is magnetically confined, releasing huge amounts of heating, propelling hydrogen out of the back.

In addition, at the nozzle end, the "mirror" is weakened, to allow some of the plasma out as propellant. The hydrogen is pumped through tubes bordering the chamber (there are basically three layers-chamber, hydrogen or water pipes, and magnets), where it is superheated and ejected, producing lots of isp and possibly even thrust.

dicktice · 2003-02-28 20:49:30

Gosh, Soph, that still sounds pretty hypothetical. How would one go about developing your propulsion package...any differently from the (as far as I know) only two alternatives, until now at least: the tokamak, and the laser-implosion; each of which has so far involved large--really huge--experimental facilities...merely to prove the feasibility of self-sustaining reactions...presumably with the end-objective of generating electricity via steam turbines? Would the free vacuum of space be of any advantage, maybe? (I keep looking for practical uses of the ISS.)

soph · 2003-02-28 21:00:59

Well, Tokamak is another concept for a magnetic confinement drive. But the huge Tokamak's are also designed for electricity production, which would be great for a spaceship, but not a requirement.

A spacedrive would simply need heat to propel the propellant out of the ship-the hotter, the better. It's not really all that hypothetical, the concept has been applied, it just hasn't been sustained. It works on the same basic concept as a power reactor, only we are generating thrust instead of electricity. It's similar to an NTR in method. The difference is that fusion is being used, and the magnets are used to confine the reaction.

For fusion, I can't really say what a vaccuum would do. I know isp would be higher, but that only accentuates fusion's strength compared to today's systems. It's real potential is for an interplanetary, high speed, high payload freighter, with the drive also powering the ship. They have been called the interplanetary freighters of the 21st century.

They could cycle back and forth between planets without landing, bring huge payloads at high speed, and refuel at stops.

Preston · 2003-02-28 21:35:26

Just to a address a few random points:

A burning plasma was first achieved about 12 years ago, and this very much existent fusion technology (including mirrors) has only gotten better since then.

The first fusion power plant will be DT because it's easiest and practical; this will use steam turbines. D-3He plants, where the products are all charged particles, will use direct energy conversion technology where the efficienty is greater than 90%.

Fusion research in space makes no sense, since making a vacuum is the least of their problems, and constructing a reactor in space is impossible at this point.

With regards to the plasma sail technology, I don't how you, dicktice, came up with those advantages. No propellant is required.. yes, we might as well test it on the ISS (not much a solar wind in this neighborhood, but we could fire ions at it I guess). While were at it, it's insane for NASA not to test tethers on the ISS -- it could very practically be used to raise the orbit, since the panels give plenty of electricity, and we wouldn't have to waste rocket fuel for station keeping.

There is thrust falloff from the distance from the sun, since particle flux goes down the same way light flux does. No straight line astrogation, and as far as I understand it, no travel out of the ecliptic, since the force is only directed away from the sun.

soph · 2003-02-28 21:42:11

Fusion research in space makes no sense, since making a vacuum is the least of their problems, and constructing a reactor in space is impossible at this point.

I assume here you mean doing the physical research and construction in space is pointless, not using fusion drives in space?

Can I have a link to that page-or is there a more clear copy of that image (or a similar graph to the same effect)? It's kind of blurred.

Preston · 2003-02-28 22:14:45

Yeah, I mean physical reasearch that's being done now. Fusionwill be good for propulsion in the future.

I got the image from http://web.gat.com/snowmass/mfe-final.pdf
I don't know if there is an original with better resolution somewhere.

edit: it's page 34.

dicktice · 2003-03-01 09:46:30

Preston: I won't even attempt to address fusion space propulsion, since the time to develop will undoubtedly exceed my lifetime, by generations most likely.
Regarding plasma sailing the Solar wind: My initial interest was light sailing the Solar radiation, which requires reflective sails having finite areas, capable of both accelerating/decelerating Solar orbital velocity and straight-line radial acceleration. But, since inverse-square law limits the sailing to the inner system, I was intrigued to read that the plasma sail would expand in direct proportion with the inverse-square law, maintaining constant thrust, opening up more of the system to exploration, in all directions from the Sun.
For transportation of supplies and/or colonists to extablished colonies, one-way might be acceptable, even....
I am very much in favour of tether-travel, using the ISS (now that Mir is lost to us) as anchor...to gain escape velocity without expending onboard fuel. The tether-generated electricity aspect interests me less because interplanetary travel has ongoing electrical power needs, and a variety of less-dodgy techniques are available such as thermal-electrics and solar-cells.
Incidently, while fusion experimentation per se may not benefit by being done in space, I would think that development of fusion propulsion would be. Laser/maser, electron-beam, microwave power, etc. experimentation certainly would be facilitated, of course.
I endorse space vehicles surrounded by water-ice, using steam jets for propulsion/steering for near-Earth asteroid transportation, by the way. Which reminds me, in addition to the ice for radiation shielding, I mentioned the plasma sail was said to be self-shielding.
Don't stop now...it's still not too late to come up with new stuff, while the "powers" are busy contemplating their own navels...when they're not contemplating war, that is.

soph · 2003-03-01 10:00:56

I didn't know 20 years was many generations. Proposals have been developed using today's technology for a fusion drive.

Plasma sails also have their risks. Degrading materials, subject to space debris, ultra thin, electromagnetic field (a radiation risk in itself), and others.

The tether-generated electricity aspect interests me less because interplanetary travel has ongoing electrical power needs, and a variety of less-dodgy techniques are available such as thermal-electrics and solar-cells.

A reactor is far more assured than solar cells. A rock hits the wrong spot and yourp power is gone. Heat released by fusion/fission is far more predictable than space debris!

I was intrigued to read that the plasma sail would expand in direct proportion with the inverse-square law, maintaining constant thrust, opening up more of the system to exploration, in all directions from the Sun.

What about this gives it an advantage over the superior payload/power capabilities of fusion (or to a lesser extent, fission)?

A fusion NEO buster could use ice from the object to propel it away, as well.

dicktice · 2003-03-01 10:56:20

Twenty years would take me out of the picture, Soph.
I imagine the plasma sailing spacecraft essentially as a lump of water-ice, surrounded (when sailing) by the plasma cloud of hydrogen ions (from melt-water) which would provide incidental protection from radiation (aurora-wise) in addition to the absorption protection provided by the ice thickness.

soph · 2003-03-01 11:03:18

Twenty years would take me out of the picture, Soph.
I imagine the plasma sailing spacecraft essentially as a lump of water-ice, surrounded (when sailing) by the plasma cloud of hydrogen ions (from melt-water) which would provide incidental protection from radiation (aurora-wise) in addition to the absorption protection provided by the ice thickness.

Great, and where does you payload fit into the equation?

Also, plasma sails might create Van-Allen belts, which your water can't do much to help with.

On a long mission, your plasma sails would lose some conducting power, which slows you down, and decreases the payload you can bring along.

Josh Cryer · 2003-03-01 16:37:12

I think you exaggerate the dangers involved with plasma sails, soph. The good ones will be hundreds if not thousands of kilometers across, you'd be so far from the belts that they wouldn't be an issue. They'd just be pretty lightshows for travellers.

And I don't see what you mean by degrading materials and subject to space debris, we've been over this before. A plama sail would be much more robust than a foil sail, by far more robust than any other sail out there.

And what's this, the plasma sail loses conducting power? I don't think you understand the concept of a plasma sail. I think you're confusing Zubrins Magsail. This is incorrect. I'd be willing to wager that a plasma sail engine would last much longer than a fusion engine, since it's so simple.

soph · 2003-03-01 19:45:02

Josh, if you can find an actual source that contradicts what I'm saying, fine. I'm basing what I say on published material.

It doesn't matter how robust it is-if a cometoid or meteroid hits a sail, it'll crack.

soph · 2003-03-01 19:57:23

I think you exaggerate the dangers involved with plasma sails, soph. The good ones will be hundreds if not thousands of kilometers across, you'd be so far from the belts that they wouldn't be an issue. They'd just be pretty lightshows for travellers.

Yeah, and where are you going to build and deploy sails as large as countries? Actually, you'd be right in the middle of the Van Allen belt, if a flux occurred. It's not quite safe, Josh.

And I don't see what you mean by degrading materials and subject to space debris, we've been over this before. A plama sail would be much more robust than a foil sail, by far more robust than any other sail out there.

The sturdiest titanium is subject to collisions, Josh. It's simple engineering, a collision with a hot, fast object will tear apart your sail.

As the sail is pounded with more rays, the material may lose its superconductivity. This is what I meant by degrading materials.

I'd be willing to wager that a plasma sail engine would last much longer than a fusion engine, since it's so simple.

We've had fission reactors last for 50 years. With new advances in materials and the fusion process, fusion reactors can probably last much longer.

A question: if you have these immense plasma sails, how do you slow down and stop at a planet? Land? Manuever?

Tyr · 2003-03-01 20:42:29

If you really like nuclear propulsion, you should be thrilled by this, if not, well maybe you're dead.

http://www.inspi.ufl.edu/index.html

http://www.highway2space.com/ast/presen … _knigh.pdf

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