The Stars are not Far, Mars Mission 2071. Options

[Big D]

The catch with space travel is that it always involves chucking something out the back.

If you have a fusion-powered plasma rocket, you're still doing the same thing. If you want max Isp, you tap off some of the raw plasma from the reactor and chuck it out the back while it is still hot. Unfortunately, you're not talking about much mass here. It may be thrown out the back at high-C, but without significant mass, your acceleration will suffer.

Or, you can add reaction mass (eg H2) to the plasma stream as it is chucked out the back. The plasma heats the reaction mass, averaging out the temp somewhat and allowing you to chuck a larger amount of mass out the back at still decent speeds. You massively lower the Isp, but pick up a lot more thrust. How you balance this depends on how fast you wanna get there and how much reaction mass you wanna lug there.

Or, you can convert the heat from the fusion reaction to electricity, run that through an ion drive (or VASIMR, which is basically the same thing), and... chuck reaction mass out the back. Again, VASIMR lets you choose between chucking a little mass out the back at high speed, or a lot at lower speeds. There's still a trade off between speed and gas mileage.

There's also the Nuclear Salt Water Rocket, which I believe was another one of Zubrin's ideas. I haven't seen if anybody has vouched for his numbers, and they might not be as good as a fusion plasma rocket, but it might or might not be simpler/cheaper.

Finally, for bulk cargo, where speed isn't as critical, I really, really like the magsail (specifically, the M2P2) concept, which doesn't chuck anything out the back at all--at least not as reaction mass. It just uses a small amount of fuel to expand a EM bubble that serves as a sail against the solar wind. Sounds very promising.

Oh, and don't forget that if you're not thrusting the whole way, you can do an external centrifuge using tethers, a la Mars Direct.

Finally... this is SR. Expect any crew who aren't there to do magical research to be low on essence. That takes care of a lot of the meat issues, since you strategically replace the parts most vulnerable to failure. Most crew should also be accomplished riggers, since that's the cheapest way to get work done outside wherever you are. Don't put on a suit unless you need to.

Random thought... can you use spirits (summoned from the ground) to aid re-entry?

[edit] Oh, and I forgot... the most efficient rocket would actually be a plasma rocket that used antimatter to heat H2, which would then be chucked out the back.

[kzt]

[Demerzel]

Well Frank, the primary flaw in your logic is you believe that this energy can be converted wholesale into motion.

I’m willing to grant you infinite source of energy, whatever you want in this discussion I’ve not once restricted the power output of the energy source.

However your ability to convert that unlimited energy source into momentum is what is in question. You are waving your hands and claiming the hardest part of the problem is solved and using the easiest part to justify it.

[FrankTrollman]

[Demerzel]

[FrankTrollman]

[Butterblume]

I find it to hard to discuss in this thread, I just can't follow who said what earlier :|.

Still, I am not giving up on the fusion-bomb driven spaceship. It would work with todays technology, it can achieve accelerations of 1g and more, and it can achieve up to a tenth of the speed of light.

So if it is possible to do it one way, there most likely are other ways.

Oh, I believe, like others here, that accelerating all the way with about 1g isn't that efficient. And, you not only need fuel to get fast, you also need fuel to decelerate...

@ demerzel: heat isn't that big a factor, because the plasma isn't in contact with the ship, and like someone said, vacuum is a good thermic insulator ;).

[Moon-Hawk]

[Cthulhu449]

You can't FTW YA RLY the solid physics that Dem is giving you. Well you can if you want your SR games to be soft sci-fi like Star Wars or Star Trek, but if fusion reactors and heat and space travel work in a way that makes sense based on our current knowledge of physics (and fusion reactors do, we can contain the energy in magnetic fields and not have it "blow up," the reaction just isn't self-sustaining and requires more input than it outputs) then your idea doesn't work out, Frank. It's really interesting, and all power to you and anyone who wants to have it in their game, but reasonable based on demonstrated SR tech and physics: no.

Really, though, arguing physics in a game that has elves and spells is kinda pointless. If you came on the boards and said that everything falls at 21 m/s^2 in your game because you did some calculations that show we are being lied to and that is the true acceleration of a body in a vacuum towards the planet, I wouldn't really care; but you'd be just as "wrong" as you are now unless something drastic changed about the earth or how the universe works.

@Magnetic containment: What you are trying to do is put the reactor in a perfect closed system to try and ignore the heat, but such a thing doesn't exist in reality. The magnetic field is created by something on board the ship, which is more mass, more energy, and more heat. It brings up the same problems and adds some as well.

[kzt]

[Demerzel]

Frank,

You don’t even come close to understanding the problems associated with what you’re proposing.

There are two issues with what you propose.

The first is energy generation, and I’m not saying that there’s any problem with you having a virtually unlimited supply of energy. Somehow you believe if you overcome this problem you can just waive away the rest of the issue. However the second part is where you’re stuck.

The second part, and the only part that matters, is converting energy into motion. You go though all this effort to argue that infinite energy means you can have whatever acceleration you want, but it’s not true.

You can only convert energy into work with limited efficiencies. We talked about the possibilities of a fusion rocket with a core equaling the temperature of the sun, but you aren’t willing to accept that the limitations due to reaction mass so you want something better.

If you want some sort of electronic propulsion that accelerates the reaction mass to large fractions of C then you have to deal with the fact that your electric generator is quite simply a heat engine. An AMAZINGLY well understood concept in physics based on centuries of thermodynamics. A heat engine has one input and two outputs.

1 input: Heat

2 outputs: Useful work + Waste Heat

The only way this device works is to transfer heat from a hot mass (your fusion core) to a cold mass (something you’re ignoring and pretending does not matter). Now on Earth the cold source can be huge heat absorbers (Evaporative cooling towers, rivers, oceans, etc.) however in space it has to be on your ship. Maybe some sort of heatsink, but at the energy levels you’re talking about they have to be huge, and if they are huge you start having to make your ship bigger and then you need a more powerful engine. Remember that vacuum is a great insulator and only radiative heat loss from the light emitted from your hot heat sinks will be dissipating. There’s no ocean to conduct the heat away as in an ocean going vessel.

And even then you STILL need reaction mass!

Lets just say you’ve got two points in space no planets or other gravitational sources around. You want to move a 100,000 ship from point A to point B 75 billion meters away. If you accelerate at 1g for 1 day then –1g for 1 day, and can eject reaction mass at a velocity of .01c (A HUGE speed for the amount mass you’re proposing), you will need more than 200,000 kg of reaction mass (216,451 kg).

Now if you take the same amazing engine scaled down to only produce 0.01g acceleration and go 10 days of +0.01g and 10 days of –0.01g you’ll get exactly as far on only 12,210 kg of reaction mass.

And that’s assuming you sent your reaction mass needed for the return trip ahead of you on a slower trip way ahead of you leaving. Otherwise a 100,000 kg ship is way too small for anything interesting apart from a god photo shoot from orbit.

To sum up, even a super powerful ion drive accelerating your ejecta to 0.01c using tremendous amounts of electricity that would never be possible to generate without so much waste heat you’re broiled bacon when you arrive.

Your two day trip is absurd. Your standing by it is absurd. Your steadfastly arguing the source of energy is sufficient with absolutely ignoring how you turn that energy into motion is absurd.

Want to make it close to feasible? Take two months, not two days.

[Demerzel]

[knasser]

I think most of us can see the problem with the weekend trip to Mars idea. It isn't feasible given what we know of physics and the cannon setting doesn't support it because there are major differences between a fusion station on Earth, with abundant cooling methods, and rapidly baking spaceship in a vaccuum. And the problem with modern day fusion is not stopping it from going critical as Frank says (that's a risk with fission, not fusion), but of stopping it fizzling out when you take the plug out of the wall.

However, if a GM wants to make it possible, then all we need are vaguely plausible solutions to the problem of heat dissipation that will keep the tone of the game believable.

I'd offer the following two bits of game fluff.

Modern day (i.e. 2070) nanotechnology provides staggeringly efficient heat to electricity conversion. Picture a heat driven engine, like you'd find in a powerplant. It works but there's always a lot of energy given off as heat because of the scale of the thing. But skrink it down, shrink it really far down. Make it less than a millimetre long. Now give it a few billion brothers and sisters, mass-produced in the zero gravity workshops at Lagrange point. What you have is a cube of carbon-like material, surprisingly light, measuring 2 metres on a side. Look at it closely and you'll see that it's endless layers of these engines, but on anything other than a microscopic scale, it's a magic block that eats heat at a staggering rate and gives off electricity with high efficiency. Taking less than 14 months to manufacture 2 metres^3 and costing a mere 1.7 billion :nuyen: it's Ares bargain of the year.

Nature abhors a vaccuum, and so does heat. But now you can smuggle more heat into a vaccuum than ever before with the Mitsuhama Heat Train™. With almost a mile of ultra-fine nano-webbing stretching out for behind your spaceship with our unique patented capillary heat disipation technology, you add an effective surface area to your ship of over four-hundred square miles, all of high-grade heat-radiating material. As an added bonus, the beautfiul effect of the glowing lace train behind your ship will make excellent publicity material for your mission. Simply detach before entering orbit and unfurl a new one for the return journey (size when folded approx 2m square, toe super-heat-conducting toe-rope not included).

Now the above two ideas satisfy my need to for realism as an amateur physicist. Demerzel might have more of a problem in the same way that I can't watch any Hollywood film involving computers, a doctor friend of mine can't immerse herself in anything set in a hospital and someone close to me who has a degree in history freaks out about five minutes into any period film. But then you always run into those problems with People Who Know Things. :) Frank was after a SR bit of future tech that would keep him from cooking his astronauts. Hopefully these are pretty cool examples. Who knows, maybe they'll exist one day. :)

-K.

EDIT: I've just read Dermezel's comment about this stuff making it into cannon. I don't want my comment about running into experts to sound like I'm saying the sub-week trip to Mars is only going to bother physics post-grads. I think a high-proportion of SR players would have a problem with it and it would detract from the realism of the game. The presence of elves doesn't mean you can dispense with realism. It means clinging to it is even more important than it was before!

[FrankTrollman]

[Cthulhu449]

Oh, I understand why you press on Dem, no problem there. I agree with both your and knasser's sentiment in regards to realism in SR. Sometimes though you just have to know you're right and let the other guy "win." Anyone paying attention knows the real score, chummer.

But Frank, that last thing you posted is the worst physics yet. You can't reflect heat from something attached to your ship to push your ship forward like a sail. It doesn't make sense for many reasons. If you don't understand why, you are in way over your head.

I am starting to wonder though if you are serious, Frank, or if you are simply seeing how long you can keep this going. :)

[knasser]

[FrankTrollman]

[ChicagosFinest]

Gamers have the best since of humor

[Butterblume]

SR has superconductors, so creating the containment field for a fusion reaction doesn't generate much heat. The fusion itself occurs in a vacuum, so the same argument that disallows heat dissipation into space prevents the ship from heating up rapidly. Thermodynamically speaking, the heat transfer from one very hot object (fusion-generated plasma) to a cool object (ship) is faster than from the cool object (still ship) to a cold one (space), but the ship has a far greater surface area, so it might just be enough to shed excess heat.

I don't want to be an ass, but I just have to repeat myself. If it's possible today to build a spacecraft with relative effective nuclear pulse propulsion, why should it be impossible to build one more advanced with future tech?

[Cthulhu449]

@ Butter: Not to keep it going, this is the last post I promise, but Butter, the discussion is in regards to the scope and speed of such a ship, not whether the technology has any merit or not.

Also, in regards to heat dissipation, because of the vacuum space is not conducive to dissipating heat contrary to what you have said, even with the large surface area of the theoretical ship.

[knasser]

[knasser]

[Butterblume]

[FrankTrollman]

There are several considerations.

1 Can we get the really large amount of energy required to move a ship from Earth to Mars in a rapid acceleration?

Yes Shadowrun has access to tremendously large amounts of energy. 9 Years ago in game time they sent a trip which went 5 times the distance in 90 times the time.

2. Can we pack enough fuel to get there and back?

Yes The fuel for a fusion drive is measured in kilograms, not tonnes.

3. Can we get into and out of the Earth's atmosphere?

Yes THere's a spirit-protected mass driver in Tanzania that will launch vessels into space using magic and technology cheaply and safely. It doesn't even use any power from the ship.

4. Can we handle the reaction at all?

Yes Shadowrun keeps stable energy yielding fusion reactions going for years at a time.

5. Can we get forward motion out of the energy we are getting from the fusion reaction?

Yes The explosive power of the reaction can be translated to forward motion by any of a number of means. Superconductors can transmit heat into substances hat release energy at specific waelengths that can be focused into directional lasers, the reaction itself can be "contained" off ship with hard vacuum cleaving it from the ship itself causing the resultant explosion to "push" on the ship rom the outside, or the plasma can be released as a jet from the ship. All of these provide forward motion without running a turbine that would inevitably heat up and melt the ship.

6. Can we dissipate the heat that will inevitably generate anyway?

Yes Not only are e forced to ask ourselves how this would even be a prblem if we were considering doing what is essentially the same thing with a chemical explosive for 6 months, but seriously, we got superconductors and dozens of tonnes to throw around. Some of it could be concentrated, heated, and hurled into space, or some of it could be released into he void in the form of electromagnetic radiation. Essentially, if you can figure out a way to dissipate the heat generated by 8 people living in a confined space for 6 months (like Project Discovery already did), you can use the same techniques to keep your ship running at operating temps for two fucking days.

---

The objections primarily fall into two categories:

1. "But none of the current Mars plans call for anything like that kind of speed!"

True. That's because they are based on current technology and don't have fusion power, super conductors, or virtually free lift into orbit. Keep in mind that the very pages that claim such a speed is impractical put in such caveats as "unless you could put a municipal power station on board" or "unless you had access to something much hotter than the sun" - we have those things.

2. "This will destroy the Shadowrun universe!"

Posh! The Shadowrun universe already has a manned base on Mars. It's in the basic book on page 42. It also has orbital resorts, asteroid miners, and competing lunar installations. Space is a part of the Shadowrun universe and the assumed high travel times make most gaming tables avoid it. Bringing a fast journey option to the table brings space to the table. The background which has always been there is no open to be the foreground. That's good.

The number of fast ships capable of afterburnering it to Mars is doubtless going tp be exceedingly small. We aren't looking at Traveller style space Winebegos just yet. What we are looking at is the possibility of characters interacting with the Mars stuff that has been being tossed around since the 90s.

-Frank

[knasser]