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/sci/ - Science & Math

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6093224 No.6093224[DELETED]  [Reply] [Original]

10,000 newtons of thrust for 120 hours using less than 1 metric ton of fuel - is it plausible, and if so, how?

>> No.6093226

>>6093224

What type of fuel?

>> No.6093228

>>6093226
Any type that science can imagine, other than obviously futuristic antimatter-type stuff.

>> No.6093236

>>6093228
Without antimatter-type stuff, the answer is no.

>> No.6093239

>>6093236
Is it absolutely, positively no? Is there any way to get the power of 20,000 ion drives while retaining the same efficiency? What about warp drives? How would one build an interplanetary car?

>> No.6093272

>>6093239
Basically, ion drives and magnetoplasmadynamic drives need ASSLOADS of power - they have inherent low thrust limits, so if you scale up an ion drive to 10 kN, the engine masses 400 metric tons and sucks up a full gigawatt of power.

Basically, ANY ion-drive concept has a critical thrust-limiting problem: since you are accelerating ions, the acceleration region is chock full of ions. Which means that it has a net space charge which repels any additional ions trying to get in until the ones already under acceleration manage to get out, thus choking the propellant flow through the thruster.

The upper limit on thrust is proportional to the cross-sectional area of the acceleration region and the square of the voltage gradient across the acceleration region, and even the most optimistic plausible values (i.e. voltage gradients just shy of causing vacuum arcs across the grids) do not allow for anything remotely resembling high thrust. And if you try to pump the power up any more, then arcs jump between the grids and neutralize everything and the drive stops working.

>> No.6093281

>>6093239
use a mass effect drive

>> No.6093280

>>6093272
OK, so forget ion drives. Solar sails are also too slow. Antimatter takes too long to harvest. Chemical propellants are to inefficient. What about quantum vacuum plasma thrusters?

>> No.6093283

Calculate specific impulse, check the wiki page for theoretical specific impulse limits and viola.

>> No.6093286

>>6093281
That's not a thing.

>> No.6093288

>>6093280
There actually does exist a proposed, seriously-considered propulsion system which actually exceeds your specifications. Unfortunately, it exceeds them by too much, and cannot be scaled down.

I am referring, of course, to the Orion drive. The calculated exhaust velocity is actually a bit over your required specific fuel consumption, and the maximum thrust exceeds your requirements by over an order of magnitude!

Unfortunately, the drive is powered by fucking nuclear bombs exploding behind your ship (which would tend to disrupt nearby traffic and annoy environmentalists.)

>> No.6093290

>>6093288
The calculated exhaust velocity is about 43,000 m/s , which slightly exceeds your fuel efficiency requirement, and the thrust is a full 263,000 N. Unfortunately, that thrust is delivered in the form of a large number of short, sharp, shocks, which shock absorbers mitigate but it's still going to play merry hell with the spines of anyone on the ship.

>> No.6093291

>>6093288
I have read about that. Is there a way to create a nuclear reactive fluid that makes smaller nuclear explosions with the same efficiency?

>> No.6093293

>>6093288
Gotta figure out a clever way to reach critical mass with a smaller amount of fissile material so you can scale it down. Has any serious work been done on this?

>> No.6093294

>>6093291
If such a thing exists, all details on it are no doubt heavily classified. Even some of the specifications of the original Orion are classified, because knowing the exact dimensions of the pusher plate would allow you to reverse-engineer the shaped nuclear charges involved. Which would let you build a CASABA-HOWITZER device, which is what happens when you tune a shaped nuclear charge for a hot, fast, tight explosion for weaponry instead of a slower, more spread-out one for propulsion, and Point This End Towards Enemy instead of towards your spaceship.

>> No.6093297

>>6093293
LOADS of work has been done on making small nuclear explosives. Huge bodies of it, with vast advances - all the way down to the Davy Crockett, which was about the size of a football.

However, it is all classified, for reasons which should be obvious.

>> No.6093301

>>6093297
A football-sized atomic bomb would still create too large of an explosion to be used continuously for propulsion.

>> No.6093306

>>6093301
Not to mention you'd need a shitload of them to make course corrections.

>> No.6093331

You might be able to increase the yield of ion propulsion if you could get your ions to spin / eject at the same time as a magnetic moment....

>> No.6093334

>>6093331
I don't think conventional elctromagnets would be able to cause the desired effect.

>> No.6093355

Ion drives in combination with a fusion reactor. Sure it is not possible with current technology, but who cares!

>> No.6093374

>>6093294
So it'd be like a Kamehameha wave?

>> No.6093375

That would be a specific impulse of 440000s.

No.

>> No.6093399

A good list of various drive systems is avaliable here:

http://www.projectrho.com/public_html/rocket/enginelist.php#table

Although it's a website primarily meant as a resource for writing science fiction, so the numbers are somewhat optimistic and presented with annoyingly little in the way of a citation, it's designed to be a resource for writing damned realistic hard science fiction, and so they're usually pretty on track.

>> No.6093410

nuclear explosions should do it, 1 metric ton of plutonium would exert enough power I guess, but I haven't calculated it.

>> No.6093411

>>6093375
Whoops, yeah, I did my calculations wrong. Accidentally divided by 10 somewhere; this is the actual number. Orion drive doesn't even have that much specific impulse, nor ion drives; the only even theoretical propulsion systems with that much are "antimatter sci-fi stuff" : Fusion rockets, Antimatter rockets, and antimatter-powered fusion rockets.

Oh, and fission-fragment systems, but those have shit thrust. Worse than ion engines.

>> No.6093713

>>6093224
Take chemical rocket.

Increase efficiency to 90%

Do basic calculations and see what happens.