back to article NASA-backed fusion engine could cut Mars trip down to 30 days

NASA, and plenty of private individuals, want to put mankind on Mars. Now a team at the University of Washington, with funding from the space agency, is about to start building a fusion engine that could get humans there in just 30 days and make other forms of space travel obsolete. FDR Fusion drive Rocket fuel is just so …

COMMENTS

This topic is closed for new posts.

Page:

Gold badge
Boffin

For those just knowledgable enough to be dangerous.

You're looking at pellets in the 100s of gram range accelerating a vehicle 150 000 bigger. Force = Mass x Acceleration so at 30Km/s and 0.1Kg you get a force of 3000N. By Newtons 3rd law on a body of 150 mt that's about 0.02 m/s, or about 0.002g.

So no people won't be tripping over each other. The fact it runs for 3 days might have been another clue that would not be happening.

The short impulse does make it a shock load but the same could be said of the explosions in the cylinders of a car (which this somewhat resembles).

NIAC is low budget, high risk investment into potentially game changing technology .and they've actually done phase 1 of this. All other fusion proposals have come from a fusion power background where breakeven and electricity generation are key goals. They dumped these and followed the analysis. From their PoV wrapping a fusing plasma in a series of magnetically driven foils (IE thin sheets <1mm thick) is actually a good thing as it gives them more reaction mass to push out the back.

Note they still have not generated fusion which I think is a pretty big point but if they do that will be a bargain. As for a 200KW PV array keep in mind the ISS array while big is several generations behind the SoA in PV cells, either mult junction or using solar concentrators.

14
0
Paris Hilton

Re: For those just knowledgable enough to be dangerous.

I crunched those numbers and came up with similar, but ran into some problems. Using yours (100g pellets, effective recoil of 0.02m/s) lets still consider that this jolt is happening in a microsecond apparently, or 10^-6s. So the acceleration would be 20,000m/s/s at the point of impulse. So it would certainly be an odd sensation.

Then there's the "pulsing every minute or so" part. The ship is gaining 0.02m/s each minute. So it's average acceleration would be 0.00333m/s/s. After 15 days of constant propulsion (or 1,296,000s) it'll be travelling 4320m/s which sounds pretty nippy, but this is halfway through the predicted journey and we'll only have covered 2.5M km. Somewhat short of the distance to Mars, given the closest known approach is about 22x that.

What am I missing?

0
0
Happy

Re: For those just knowledgable enough to be dangerous.

If they build it in orbit, it'd start its journey at the relevant escape velocity and accelerate from there.

0
2
Gold badge
Meh

Re: For those just knowledgable enough to be dangerous.

"If they build it in orbit, it'd start its journey at the relevant escape velocity and accelerate from there."

No. Escape velocity from Earth is roughly sqrt(2) x orbital velocity

As any standard mechanics text book would tell you.

0
0

Funding?

Kickstarter, anyone?

2
0
Black Helicopters

Re: Funding?

"...Given the tight financial strictures of the US government this is unlikely"

Just find a military application for this thing and watch the $$$ come rolling in.

0
0
K
Silver badge
Facepalm

Speed demon..

And with 200KW, thats enough to power a decent Bose sound system and a few dozen sub-woofers..

The era of the inter-planatery boy racer begins.

1
0
Silver badge

Re: Speed demon..

D'oh, I thought that was a reference to the Rastafarian space station in the novel Neuromancer, that featured a substantial sound-system.

2
0

Re: Speed demon..

I never did find out what Zion dub was.

1
0
Linux

Hand the project over to SpaceX

NASA should have made the funding conditional on the geeks at the University of Washington working with SpaceX!

This would achieve the following:

1) A much faster development and implemtation time.

2) Elon Musk has said he wants to get to Mars!

This would achieve this objective much more quickly than anticipated and, at the same time, probably please NASA, SpaceX competitors and Anti-Teslans in getting him out the way, especially if the deceleration phase failed and he found himself en route to Titan or Europa!!! (Sorry, Elon! I'm a great fan but the thought does amuse me!)

1
3

V1 in Space!

I want it, go NASA, build one now!

Also if you add a couple of extra magnetic lenses further down the exhaust you'll get a plasma cannon!

1
0

So, for those of us who are a bit thick...

...by disregarding the need to reach break even point and to keep the whole of the fusion reaction contained inside something solid, by using magnetic fields to direct the plasma, a fusion-engine spacecraft is actually properly feasible?

This is it in summary, yes? The only real issue is going to be lifting a 150t spacecraft into orbit in the first place (and presumably telling a lot of people not to look at the sky when it starts up, since that would be like staring into a teeny weeny star)?

I am literally trembling with the potential awesomeness of this project. Please someone tell me the downsides.

2
0
Gold badge

Re: So, for those of us who are a bit thick...

"This is it in summary, yes? "

Correct.

"The only real issue is going to be lifting a 150t spacecraft into orbit in the first place"

That's not exactly trivial but there are options.

" (and presumably telling a lot of people not to look at the sky when it starts up, since that would be like staring into a teeny weeny star)?"

People look at the Sun (for very short periods) fairly often and (as long as it is short) that does them no permanent harm.

"Please someone tell me the downsides."

Well the scale up is pretty substantial. The power array would be the 2nd biggest after the ISS (most PVs on sats are 1/10 the size at most). So far (IIRC) they've demonstrated single shots with Al rings without fusion and this mechanism has to deliver these rings at 1 a minute over 2 three day periods (which is a serious mechanical engineering problem in a space grade vacuum), coupled with dumping enough energy into the pellets (and actual pellet mfg on this scale is pretty substantial as well).

I guess the key question is how viable is sub-breakeven fusion. This is the critical bit that all those rings wrap round to give the thrust.

A comparison with the VASIMIR concept (to see what things it shares) might also be useful.

3
1

Re: So, for those of us who are a bit thick...

Thanks for the reply John - so there's still a fair bit of science and engineering to be solved but - but it's a probably worth about an 8 on the 'fusion thing worth getting excited about' scale.

1
0
Gold badge

Re: So, for those of us who are a bit thick...

"so there's still a fair bit of science and engineering to be solved"

Definitely. This is far from COTS technology.

"it's a probably worth about an 8 on the 'fusion thing worth getting excited about' scale"

With the caveat that this applies for its use as a propulsion technology. The electric power generation application remains as far off as ever.

0
0

Possibility for terrestrial Energy Generation

Please excuse my ignorance on the subject, but does anyone know is it possible, in theory, that this type of reactor could be used to generate energy on earth?

0
0

Re: Possibility for terrestrial Energy Generation

AFAIKS no, because in a terrestrial reactor you need to contain the whole reaction in something and get more energy out than you're putting in to make it worth doing.

But that's the question in my other post.

1
0

Re: Possibility for terrestrial Energy Generation

I thought containment might be an issue. But if the reaction is being powered by solar energy similar could be replicated on earth by use of a solar collector. I would also imagine that capturing the energy output of the reaction would also be a challenge.

This aside, this is still an amazing innovation with very exciting developments as a result.

0
0
Ru

Re: Possibility for terrestrial Energy Generation

"Possibly", is the anser to that. Extracting a decent amount of electrical energy from the reaction is likely to prove tricky (see also: thermonuclear weapons and fusion power generators), but if they get it working it should be easier than similar technologies like laser and magnetic liner inertial confinement fusion .

1
0
Boffin

Commercial power generation potential?

As I understand it at the moment, this system uses the fusion energy to convert a pellet into a 30km/s projectile.

So why is this not a possible power generation system?

Fire that projectile into the equivalent of a sand trap, and it will dump its kinetic energy as heat. There's your equivalent of the coal furnace / gas turbine / nuclear reactor. Pump water around it, get steam, add a turbine and voila - electricity. If the fusion is effective enough, you've got a system pushing out more usable power than went into it.

I'm not saying the engineering is simple, but isn't the premise sound?

0
0

Re: Commercial power generation potential?

The reason this system works well as a propulsion system IN SPACE is that you are dumping everything out the back of the drive in order to go forward, by-products and all. This means you need very little shielding on your system components as the magnetic field effectively directs the whole lot away from the squishies up front, think of it as big exhaust, that's it.

The difference when trying to use this technique as a power generation process is you have to handle not just the energy from the fusion reaction (to get your power) but the neutrons and waste as well, this means tons of shielding which needs to be replaced very frequently and is highly radioactive. Theoretically you could attempt magnetic confinement but that's the same engineering challenge as ITER etc. Confinement is a drastically different prospect that simply directing the whole lot in one direction into nothingness.

There are promising fusion power generation techniques emerging, including several aneutronic solutions, my bets would be the guys at LPPX or Polywell (EMC2), but tri-alpha looks pretty close as well. As Bussard said, the challenge is not the physics, the challenge is the politics.

2
0
Gold badge
Unhappy

Re: Commercial power generation potential?

"If the fusion is effective enough, you've got a system pushing out more usable power than went into it."

That's the point.

It is not that efficient.

The goals of space transport and Earth power generation are sufficiently different that this concept is good enough to push things around in space but not good enough for Earth power generation.

The latter (it turns out ) is much harder

0
1
Silver badge

Re: Commercial power generation potential?

If it doesn't put out more usable power than went into it, then what is the point?

Why not use the power to accelerate the propellant directly such as an ion engine? Why bother with all the extra gubbins at all?

2
3
Silver badge

Re: Commercial power generation potential?

Because even using ion drives the exhaust speeds achieved are such that you need a metric shitload of reaction mass - more than is practical to take into orbit.

Fusion exhaust is much _much_ faster, otherwise you may as well use a 200kW ion drive.

5
0
Boffin

Re: Commercial power generation potential?

Usable power for power generation is a very different thing to usable power for propulsion. I would expect this engine to actually produce more energy than was used to trigger it, but it won't be in a form that can be siphoned off to trigger the next bang.

1
0
Gold badge
Meh

Re: Commercial power generation potential?

"Why not use the power to accelerate the propellant directly such as an ion engine? Why bother with all the extra gubbins at all?"

Try and find an Ion drive with a thrust of 3000N while retaining an Isp of c3000secs.

1
0

Re: Commercial power generation potential?

Well, that's a frontier also, getting ion drives up to reasonable thrusts (right now they are mainly used on Russian satellites for station-keeping)

0
0
Gold badge
Boffin

Re: Commercial power generation potential?

"Well, that's a frontier also, getting ion drives up to reasonable thrusts (right now they are mainly used on Russian satellites for station-keeping)"

You're missing the point. An SoA big ion drive is about 100x smaller than that. They do not gang together very well (plume interference) and the power level needed for a 3000N thruster will be in the MW range at least.

The solar energy is used to run the machinery and trigger the fusion burn, which amplifies the energy you actually have to collect and store, but in a way that gives good thrust but poor options for collecting electricity out the back. This trade off is viewed as acceptable for a propulsion system (less shielding as the liners act like disposable radiation shields, renewed after every shot). Likewise the pulsed nature virtually eliminates cooling needs given the low duty cycle (completely unacceptable in common fusion power architectures) and so on.

0
0

This post has been deleted by its author

Paris Hilton

Re: I don't get it

You'd need to put the same energy in at the other end to stop. Perhaps it uses too much energy?

You would be travelling a lot faster but the window for turnaround would be far smaller. Wouldn't want to overshoot as it's a long walk home...

0
0

Re: I don't get it

"Well could you not run the engine for 6-7 days to go even faster and get there in half the time?"

I believe you could but at twice the expense in fuel.

0
0
Boffin

Re: I don't get it

It is a reaction engine: You accelerate something, and the reaction pushes the ship forward.

The thing being accelerated gets up to 30 km/s (if I got it right). So, this is your maximum speed: 30 km/s. I believe that, after 3 days, the spaceship would be at that speed - or close enough to make no difference.

That would be why You turn off the engine after 3 days - would make no difference.

0
2

Re: I don't get it

"The thing being accelerated gets up to 30 km/s (if I got it right). So, this is your maximum speed"

No, no, it doesn't work like that!

There are many ways of looking at this but it you consider the conservation of momentum, your spaceship is a system with momentum of mass times velocity. If you throw some amount of fuel mass at some exit velocity, that fuel will have negative momentum (because the velocity of fuel is negative comparing to the velocity of the ship). Therefore, the ship must compensate by increasing its momentum by the same amount. Because the mass of the ship is only going smaller (as the fuel exits) it is the velocity that must be getting higher.

Consequently, as long as you continue to throw fuel (reaction mass) out the back of the ship it will continue to accelerate, regardless of the maximum speed at which the reaction mass can fly away. If you have enough fuel, your ship will eventually approach the speed of light (when it will hit the relativistic limits).

4
0
Silver badge

Re: I don't get it

Rocket Equation

3
0
Pint

Re: I don't get it

I didn't know that! We learn something new every day... :D

0
0

This engine converts electrical energy (from a big solar array) into kinetic energy, via fusion.

It is not a generator.

3
0

I think it converts potential energy of the fuel nucleons into kinetic energy of the fusion products in the resulting plasma. The electrical energy is only used for triggering the reaction and for containment and is not added to the balance but is actually subtracted. Or so it seems to me...

P.S. Or both added and subtracted, to be precise, so its total contribution is 0

2
0
Boffin

What about shielding?

Genuine question to those who have better understanding than me.

Lets assume that, because of the length of time in space is reduced considerably and conventional radiation shielding being suitable, what about shielding against physical space debris. Indeed, is this a problem?

Making the assumption that the max speed would be approx 350,000 mph, what is the problem of physical matter, indeed if much at all? I mean we are talking about 0.05c here at max speeds. Granted odds are in favour due to smaller timeframe but then I am making assumptions just how dirty this part of the solar system is. Or am I making issues out of small odds of becoming a very pretty but brief star in the night sky?

0
1

This post has been deleted by its author

Anonymous Coward

Re: What about shielding?

I should have clarified. Im curious - if small flecks of paint and other assorted microscopic debris can mark the Space Shuttle windows in orbit, a tiny piece of matter hitting the craft at combined speed potentially in excess of 400k mph then what kind of damage would that ensue?

0
0

Re: What about shielding?

A small fleck of paint at interplanetary speeds would not just mark a window. It would likely put a hole a right through it.

However high speed collisions like that are easy to shield against with a whipple shield but you probably don't want any windows in the front.

As for breakeven. Don't forget that for breakeven in a fusion electric reactor you have to get your fusion and then convert the energy from that fusion into electricity. And thermodynamics being a pain in the butt you're going to be losing a bunch of energy to low grade heat there. The propulsion system has much lower inefficiencies and so reaches breakeven much more easily.

You put 200kW in and get more out in kinetic energy, so straight up ion will be less efficient. VASIMR will require a larger powerplant but I'm not sure if it can get a higher specific impulse out of the reaction mass.

2
0
Silver badge

Re: What about shielding?

"A small fleck of paint at interplanetary speeds would not just mark a window. It would likely put a hole a right through it."

Through the window, through the seat, through the back wall and every other wall until it exits the ship again.(*)

(*)Unless you thaw it out first.

This is one reason why designs built _heavy_ are generally favoured over the usual balsa-and-paper approach of conventional spacecraft design, especially at the kinds of speeds being considered.

1
0
Thumb Up

I frikkin love science

That is all.

0
0

This post has been deleted by its author

Anonymous Coward

isn't there enough trash in space already?

so here we are trying to figure out how to clear the debris mess from earth orbit plus we're looking at planetary debris that could destroy our home and yet we're going to throw more trash into space with this new fangled drive system? there's enough problems dealing with grains of sand traveling at 25000+mph already...

0
3

Re: isn't there enough trash in space already?

I don't think there'd be too much trash left after it's been through fusing plasma.

1
0

Re: isn't there enough trash in space already?

There is a helluva lot of difference between the space debris in earth orbit, and the exhaust products of a rocket engine, including this one.

- If they manage to get this thing going the exhaust product is the result of nuclear fusion , which tends to be rather ...hot. The pellets leave the exhaust as a plasma, so any "debris" would be near indistinguishable from the local micro-stuff naturally present.

- Simple ballistics shows that any exhaust product for a trajectory away from earth will not have the correct vector for an earth orbit. Even more so, as the vessel picks up speed eventually the net vector of the exhaust products will be *away* from earth.

3
0
Alert

Re: There is a helluva lot of difference

Actually, you're right. As soon as they start decelerating at the other end, they'll get a column of exhaust catching up, and smashing into them!

Probably best to pack some small hydrazine thrusters to step to the right and let it all fly past.

0
1
Silver badge

Re: There is a helluva lot of difference

As soon as they start decelerating at the other end, they'll get a column of exhaust catching up, and smashing into them!

No. First, you have to understand inertial frames of reference. If I'm on the roof of train and I fire a gun in the forward direction, it will have the same apparent velocity (to me, and ignoring air resistance) as a bullet fired in the "backwards" direction. Despite being in motion, the relative velocities still work out the same as if we decide that (or it's actually the case that) the train is fixed in space. This is our "inertial frame of reference". Second, you need to take into account Newton's third law: "for every action there is an equal and opposite reaction", which is the principle behind any "reaction drive", of which this is an example. Again, consider the plasma exhaust coming out of our "gun". It has a mass that is a tiny fraction of the mass of the ship, but will have a large acceleration. Since F = ma (force = mass x acceleration) and due to Newton's third law, our ship will have a balancing (reaction) force propelling it in the opposite direction to the plasma. Since the ship's mass is so many times larger than the projectile, the resulting deceleration will be much less than that experienced by the projectile.

So in summary, (1) the projectile will always accelerate away from the ship, regardless of which direction we're going, and (2) catching up with the exhaust assumes you're going forward-backward-forward for some reason, rather than forward-backward, and even then, the chance of hitting the exhaust over such vast distances is crazily small. Also, (3) detonating the pellet and turning it into plasma means that after a short time there won't be anything except a diffuse gas for anything (including other ships in the vicinity) to collide with anyway.

1
0
Silver badge
Pint

And all it requires is just a wee bit of fusion

I think it'd be faster to walk to Mars than wait for fusion to be practical.

1
4

Page:

This topic is closed for new posts.

Forums

Biting the hand that feeds IT © 1998–2017