Earth to Mars in 6 to 8 weeks!

[Correa Neto]

OMFG!
I hope it works!
http://www.universetoday.com/95991/n...ks-not-months/

[sphenisc]

Those MARS-500 simulation guys are going to be pissed.

[Agammamon]

Sooo - its a fusion version of Orion.

[Agammamon]

'Course, instead of spending a huge amount of money to develop thus engine we could spend a much smaller amount refurbishung Orion.

And Orion has the advantage of having a huge specific impulse and can push a 5,000 TON spaceship to Mars in the same timeframe without needing a freaking huge reactor to provide power and having to support even larger radiators to handle the heat load.

[Travis]

Yes but that means nukes and nukes are evil. Greenpeace said so.

[Correa Neto]

I would love to see any one of these projects becoming reality and zooming across space.
I foresee, however, lots of noise coming from ignorant environmentalists, especially when it comes down to Orion.
And nope, not saying all environmentalists are ignorant. I'm saying some are.

[Acleron]

Originally Posted by Travis

Yes but that means nukes and nukes are evil. Greenpeace said so.

Those nasty scientists are going to ruin the vacuum for everybody.

[rjh01]

Sounds a bit suspect to me. They are trying to fuse lithium and hydrogen together. So far this has not been done in a controlled way.

[jasonpatterson]

Originally Posted by rjh01

Sounds a bit suspect to me. They are trying to fuse lithium and hydrogen together. So far this has not been done in a controlled way.

They aren't interested in doing it in a controlled way. The plan is to blow up a fusion bomb with a spaceship sitting on top, just like Project Orion (which had fission bombs instead.) The only control would be in the timing and orientation of the explosion. I sincerely hope they don't throw any more money down this pit.

[rjh01]

Originally Posted by jasonpatterson

They aren't interested in doing it in a controlled way. The plan is to blow up a fusion bomb with a spaceship sitting on top, just like Project Orion (which had fission bombs instead.) The only control would be in the timing and orientation of the explosion. I sincerely hope they don't throw any more money down this pit.

Currently the only way to do this is use a fusion bomb. If it could be done without one then it could be used for electricity generation on earth.

[Correa Neto]

The way I see it, mankind has lots of useless nukes stored. Cold war times are long gone, a smaller ammount of nuclear warheads is enough to keep the ballance of terror.

So, sending these nukes to space is not a bad idea IMHO. If the thing works, we have a fast spacecraft. If it does not, well, at least you've seen some fireworks.

[WhatRoughBeast]

Originally Posted by jasonpatterson

The plan is to blow up a fusion bomb with a spaceship sitting on top, just like Project Orion (which had fission bombs instead.) The only control would be in the timing and orientation of the explosion.

Sorry, but you need to follow the links and do some math. The Huntsville page gives a target number for thrust of 10 kN, using 10 explosions / second. This is 1 kN-sec per explosion. Note, though, that the link has a math error. 10 kN thust is .5% of a Space Shuttle main engine thrust, not 2%. If all of the thrust were provided by radiation, this would require a .1 kiloton event, and you would have a point. But it doesn't.

They refer to a "hockey puck" sized fuel element. This is vaporised and ejected to produce thrust. For lack of a better set of numbers, let's assume 0.1 kg mass and 10,000 m/sec exhaust velocity. That's actually a fairly modest Isp of 1000. (The Space Shuttle does about 400, and ion drives can get to about 10,000.)This gives the required thrust. Energy required (at 100% efficiency) is 5 million joules, or just about 1.2 milliton or 2.5 pounds of TNT. Is it enough?

To do 100 million km in 50 days requires an average velocity of about 23 km/sec. A boost/deceleration time of 2 days (200,000 sec) at each end of the mission implies an acceleration of about .115 m/sec^2, or .01 g's. A thrust of 10,000 N implies an average vehicle weight of 1 million kg. Total fuel load is 400,000 kg, so there are no major problems with mass fraction. To a first approximation, the numbers work.

In short, a first cut at the math says that the "fusion bomb" you're worried about is somewhat larger than a hand grenade (the US M67 has 6 oz of HE), but not all that much. It is certainly smaller than an artillery shell (for example, the US 155mm howitzer shell carries about 15 pounds of HE).

[Spindrift]

Wasn't this used in the Jerry Pournelle/Larry Niven book Footfall?

[WhatRoughBeast]

Originally Posted by Spindrift

Wasn't this used in the Jerry Pournelle/Larry Niven book Footfall?

Footfall used a more conventional Orion design. It's the sort of vehicle that jasonpatterson was objecting to. See http://en.wikipedia.org/wiki/Project...ar_propulsion) for basic info.

This version uses many more, and much smaller, "bombs" to do the work.

[Brian-M]

For the sake of comparison, can anyone tell me what the time to get to mars (and slow down to orbit) would be if you used a rocket with replaceable fuel tanks that could be replaced for full tanks in orbit prior to departure?

I assume that the 214 day figure is for spacecraft that have to carry all the fuel for the journey up from the surface of the earth with them. I'm wondering how fast the journey could be done with conventional rockets if we had an orbital refueling station.

[WhatRoughBeast]

Originally Posted by Brian-M

For the sake of comparison, can anyone tell me what the time to get to mars (and slow down to orbit) would be if you used a rocket with replaceable fuel tanks that could be replaced for full tanks in orbit prior to departure?

I assume that the 214 day figure is for spacecraft that have to carry all the fuel for the journey up from the surface of the earth with them. I'm wondering how fast the journey could be done with conventional rockets if we had an orbital refueling station.

In this case, it makes no difference. 214 days to Mars indicates a free-return transfer orbit. For this technique, you do a brief burn in Earth orbit, then coast the rest of the way to Mars orbit, where you do another brief burn to slow down and synchronize with Mars. This is not the same as a Hohman transfer orbit, which takes less fuel but needs 258 days. The difference is that a free-return orbit allows you to return to Earth if you decide not to enter Mars orbit. You just don't fire your rockets, and after a two-year flight you're back in the hood. Either way, earth-orbit refueling is a must, at least for current technology.

See http://web.mit.edu/12.000/www/finalp...j/index9t.html

Trying to figure out an absolute mimimum transit time is hopeless unless you're willing to do a lot of specifying of details about vehicle and living quarters mass. You've got to be able to jettison the empty fuel tanks in flight, and doing that reliably is not an easy task. Or do you do like Apollo did with the LEM, but on a llarger scale? The devil is in the details.

[Brian-M]

Originally Posted by WhatRoughBeast

Trying to figure out an absolute mimimum transit time is hopeless unless you're willing to do a lot of specifying of details about vehicle and living quarters mass. You've got to be able to jettison the empty fuel tanks in flight, and doing that reliably is not an easy task. Or do you do like Apollo did with the LEM, but on a llarger scale? The devil is in the details.

How about this, let's say the rocket has enough fuel to accelerate at a constant rate of 1G for 100 hours (burning fuel at a diminishing rate as the mass of the ship decreases to maintain a constant acceleration).

What kind of minimum timeframe would we be looking at for a ship parked at the earth-moon L₁ point to crash into Mars? (We'll assume that the habitable section of the rocket will detach and use it's own independent propulsion system to get it safely to the surface).

And the same again for only 24 hours worth of 1G acceleration. (Just vaguely approximate figures, so we can contrast it to the new propulsion system.)

ETA:

Or for some reason wouldn't it be possible to significantly reduce the duration of the flight by increasing the velocity at which the rocket leaves earth-orbit?

[WhatRoughBeast]

Originally Posted by Brian-M

How about this, let's say the rocket has enough fuel to accelerate at a constant rate of 1G for 100 hours (burning fuel at a diminishing rate as the mass of the ship decreases to maintain a constant acceleration).

What kind of minimum timeframe would we be looking at for a ship parked at the earth-moon L₁ point to crash into Mars? (We'll assume that the habitable section of the rocket will detach and use it's own independent propulsion system to get it safely to the surface).

OK, that one is doable. Since we're going for best-case, lets assume that the two are at closest approach, with earth at aphelion and Mars is at perihelion. Distance is just about 53 million km.

Now consider your acceleration. As it happens, continuous 1g acceleration gives you more than you realize. For constant acceleration, time and distance are related by t = sqrt(2s/a), or equivalently s = 1/2 at^2, where t is time, s is distance, and a is acceleration. Plugging the numbers into this says you make it to Mars in 28 hours. Of course, you might want to keep in mind that velocity at impact will be more than 1,000 kilometers / second. It's not relativistic, but it's getting there. All of this ignores the effect of the sun's gravity, but with these numbers that's not a problem.

It also ignores deceleration. To a first, very rough, approximation, your independent lander will have to decelerate at intolerable levels. Like, 10 g's for 3 hours. Or 28 g's for one hour.

Quote:

And the same again for only 24 hours worth of 1G acceleration. (Just vaguely approximate figures, so we can contrast it to the new propulsion system.)

Heh. Let's go instead for 24 hours of .1 g's.

Plug in the new numbers. Distance at burnout is about 3.7 million kilometers, so you need to coast 50 million km. Velocity is a mere 86 km/sec. Of course, that's about 300,000 km / hour, so coast time is about 150 hours, or 6 days. Once again, these numbers indicate that the effects of the sun's gravity can pretty well be ignored.

Quote:

ETA:

Or for some reason wouldn't it be possible to significantly reduce the duration of the flight by increasing the velocity at which the rocket leaves earth-orbit?

Absolutely. For very simple orbital transfers, like the one we're discussing, the faster you go the quicker you get there. But keep in mind that the harder you boost to get going, the harder you have to boost to stop. This means you have to boost more fuel, and that takes more fuel. It's not exactly a lose-lose proposition, but it ain't pretty. See http://en.wikipedia.org/wiki/Tsiolko...ocket_equation for a start. Ignoring the math, think about

Quote:

Delta-v is of fundamental importance in orbital mechanics. It quantifies how difficult it is to perform a given orbital maneuver. To achieve a large delta-v, m0 either must be huge (growing exponentially as delta-v rises), or m1 must be tiny, or ve must be very high, or some combination of all of these.

[WhatRoughBeast]

If you're going for top-of-the-food-chain propulsion, antimatter is the way to go.

However. In matter-antimatter reactions, a whole lot of the resulting energy is accounted for by neutrinos and gamma rays. Neither of these, particularly the neutrinos, is obviously useful for producing thrust. The numbers I've seen indicate an estimated Isp of 1,000,000. This indicates an effective exhaust velocity of 10^7, while simple intuition says that it ought to be c, or 3 x 10^8.

Using ve of 10^7, let's take a look at your benchmark performance.

Pulling 1 g for 100 hours gives a final velocity of 3.6 x 10^6 m/s. Note that your constant acceleration is not how the Rocket Equation does things, but let's pretend that it does.

Plug your numbers into the Rocket Equation. You will find that your requirements can be fulfilled with a ship which carries 30% of its weight in antimatter. Not only that, the fuel mass is sufficiently small that something close to constant thrust is reasonable.

So, as long as you're willing to go for the gold and specify a wildly unfeasible propulsion technology, you can always get what you want, as well as what you need.

[Cainkane1]

Originally Posted by Correa Neto

OMFG!
I hope it works!
http://www.universetoday.com/95991/n...ks-not-months/

Its a crying shame Percival Lowell wasn't right about a civilization on Mars. Humans will have to put one up there.

[Mikemcc]

The technique that I'm looking forwards to and is still looking rather promising is Bussards polywell fusion. p-B fusion looks a lot easier using this technique and could deliver a constant thrust design that would give comparable results. EMC2 (funded by the US Navy) are presently scaling up the experiment with the WB-8 reactor and are funding more work.

http://newenergyandfuel.com/http:/ne...acts-extended/

http://www.talk-polywell.org/bb/index.php

[Brian-M]

Okay, so this new engine is clearly far from an essential breakthrough for the sake of getting to Mars in a reasonable amount of time. More a case of being a convenient alternative to hauling ludicrous amounts of fuel into space.

Now I'm wondering what's wrong with using a simple nuclear pile and a large quantity of water for reaction-mass? Your standard steam-powered rocket ship scenario.

Originally Posted by WhatRoughBeast

So, as long as you're willing to go for the gold and specify a wildly unfeasible propulsion technology, you can always get what you want, as well as what you need.

In that case, how about a baking-soda and vinegar powered ship?

[Correa Neto]

Depends on what do we mean by reasonable. OK, it sounded like pure semantics, but that's not what I mean.

Such engine (as well as Orion), IF it works, could be very handy to send large robotic probes to Mars and beyond. Such spacecraft would be faster than today's too.
As for manned flights, well... Again, IF it works as advertised, its faster. 8 weeks to reach Mars is not a long trip. Especially if you are going to stay there say, for 6 months. Even if its not as good as they say and the trip would actually take four months.
Now, if this is a reasonable time for a manned flight, depends on the circunstances. Motivations, ship and crew size, etc.

[WhatRoughBeast]

Originally Posted by Brian-M

Now I'm wondering what's wrong with using a simple nuclear pile and a large quantity of water for reaction-mass? Your standard steam-powered rocket ship scenario.

Nothing at all. Of course, to get the Isp you need, you have to superheat the water, not just boil it. Chemical and fusion reactions have the advantage that they heat the working fluid as they produce it. For steam, you have to heat something which will heat the steam, and this is very difficult for the temperatures you need.

[BenBurch]

Originally Posted by rjh01

Currently the only way to do this is use a fusion bomb. If it could be done without one then it could be used for electricity generation on earth.

It has occurred to me to wonder if we could generate electricity with nuclear weapons?

Like detonating them in a deep salt formation which becomes molten, and then pumping up the heat for use in a geothermal plant.

[Acleron]

Originally Posted by Brian-M

Okay, so this new engine is clearly far from an essential breakthrough for the sake of getting to Mars in a reasonable amount of time. More a case of being a convenient alternative to hauling ludicrous amounts of fuel into space.

Now I'm wondering what's wrong with using a simple nuclear pile and a large quantity of water for reaction-mass? Your standard steam-powered rocket ship scenario.



In that case, how about a baking-soda and vinegar powered ship?

Yuk

Malt and yeast and then you can enjoy the residue.
(There was definitely an SF story along these lines)

[Andrew Wiggin]

Originally Posted by WhatRoughBeast

Footfall used a more conventional Orion design. It's the sort of vehicle that jasonpatterson was objecting to. See http://en.wikipedia.org/wiki/Project...ar_propulsion) for basic info.

This version uses many more, and much smaller, "bombs" to do the work.

The craft the humans made was a conventional Orion with full sized fission bombs going off on a once-every-few-seconds basis, but the ships the invaders used were powered by tiny fusion bombs going off at the rate of many per second.

[elgarak]

Originally Posted by Travis

Yes but that means nukes and nukes are evil. Greenpeace said so.

Well, as far as I am concerned, Greenpeace can go and **** themselves.

(I'm inclined to believe you think the same way, but I just feel it needed to be said.)

[NutCracker]

Originally Posted by elgarak

Well, as far as I am concerned, Greenpeace can go and **** themselves.

(I'm inclined to believe you think the same way, but I just feel it needed to be said.)

Hm. since nukes do have the capacity to whipe, say, NYC from the face of the earth in an instant, I would be inclined to say that the assertion "nukes are evil" is not inherently rediculous.

[rjh01]

Originally Posted by BenBurch

It has occurred to me to wonder if we could generate electricity with nuclear weapons?

Like detonating them in a deep salt formation which becomes molten, and then pumping up the heat for use in a geothermal plant.

I suggest there would be huge problems with this.
1. How would you get the heat out while leaving the radioactivity behind?
2. A lot of the heat would be wasted.
3. Against a certain treaty against exploding weapons.
4. It would be able to be used for only a few weeks (at best) and then another bomb would be needed.

[Brian-M]

Originally Posted by rjh01

I suggest there would be huge problems with this.
1. How would you get the heat out while leaving the radioactivity behind?
2. A lot of the heat would be wasted.
3. Against a certain treaty against exploding weapons.
4. It would be able to be used for only a few weeks (at best) and then another bomb would be needed.

I'll have a go at this:

1. You reuse your medium of thermal transfer. Eg, recirculating water.
2. So?
3. Checking Wikipedia, the Treaty on the Non-Proliferation of Nuclear weapons encourages nations to dispose of nuclear weapons in a peaceful manner, which would include power generation. Nothing against detonating weapons that I could see. Plus, any nation can withdraw from the treaty with three month's notice.
4. That still amounts to many decades of power generation before existing weapons run out.

[Roboramma]

Originally Posted by Brian-M

3. Checking Wikipedia, the Treaty on the Non-Proliferation of Nuclear weapons encourages nations to dispose of nuclear weapons in a peaceful manner, which would include power generation. Nothing against detonating weapons that I could see. Plus, any nation can withdraw from the treaty with three month's notice.

Not the relevant treaty. See here:

http://en.wikipedia.org/wiki/Partial_Test_Ban_Treaty
Though it seems it doesn't prohibit underground explosions.

The Comprehensive Nuclear Test Ban Treaty does prohibit such explosions, but it has not been ratified.

Quote:

The Comprehensive Nuclear-Test-Ban Treaty (CTBT) bans all nuclear explosions in all environments, for military or civilian purposes. It was adopted by the United Nations General Assembly on 10 September 1996[1] but it has not entered into force as of May 2012.

[rjh01]

Originally Posted by Roboramma

Not the relevant treaty. See here:

http://en.wikipedia.org/wiki/Partial_Test_Ban_Treaty
Though it seems it doesn't prohibit underground explosions.

The Comprehensive Nuclear Test Ban Treaty does prohibit such explosions, but it has not been ratified.

However I think it has been several years since any nuclear detonation.

Originally Posted by Brian-M

I'll have a go at this:

1. You reuse your medium of thermal transfer. Eg, recirculating water.
2. So?
3. Checking Wikipedia, the Treaty on the Non-Proliferation of Nuclear weapons encourages nations to dispose of nuclear weapons in a peaceful manner, which would include power generation. Nothing against detonating weapons that I could see. Plus, any nation can withdraw from the treaty with three month's notice.
4. That still amounts to many decades of power generation before existing weapons run out.

One more problem is that you would need to keep the water isolated from the radioactive salt. This can be done via pipes. If you build them before the detonation then you would risk damaging them during the explosion. Not sure how you could do it quickly after the detonation. You would also need to protect the pipes against corrosion.

You would also have to protect against radiation leaks. The salt would get very radioactive especially if you had several detonations in the same place.

[soylent]

There's also http://en.wikipedia.org/wiki/Nuclear_salt-water_rocket

[WhatRoughBeast]

Originally Posted by soylent

There's also http://en.wikipedia.org/wiki/Nuclear_salt-water_rocket

That's a really fun idea. The part of it that I don't see addressed is one of materials. The nozzle must handle both high temperature and an extremely high neutron flux. I'm not at all certain about feasability.

ETA: And, while I think of it, there is a really nasty single-point failure mode. If you get a pump failure during boost, the flow rate drops and the reaction zone moves forward into the plumbing. Probably not good.