How Far Are We Really From Plasma Rockets?

[Tony]

http://www.chron.com/disp/story.mpl/hotstories/6964775.html

Like many red-blooded American teens coming of age during the 1960s space race, Franklin Chang-Diaz dreamed of chasing cosmonaut Yuri Gagarin to the stars.

There was a hitch, of course. Chang-Diaz wasn't American. He lived outside the United States. And the Costa Rican didn't even speak English.

No matter. Chang-Diaz would overcome these obstacles and more to fly a record-tying seven missions aboard the space shuttle. Along the way the physicist would also develop a plasma rocket that promises a revolutionary approach to spaceflight.

The rocket, potentially, could blast the next generation of astronauts to Mars in just 39 days, about one fifth of the time required by existing rocketry.

The article pains an optimistic picture, which I'm totally down with, but how realistic is it? Will we really see this technology in our lifetimes?

[icerat]

According to Wikipedia (http://en.wikipedia.org/wiki/Variable_Specific_Impulse_Magnetoplasma_Rocket) -

In this lab, a 50kW prototype was constructed, and underwent testing in a vacuum chamber. Later, a 100kW version was developed, and this was followed by a 200kW prototype. After a long period of rigorous testing in a 150 m3 vacuum chamber, the latest configuration was deemed space-worthy, and it was announced that the company had entered into an agreement to test the engine on the International Space Station, on or before 2013.

Sounds like it is well on the way

[Monketey Ghost]

Our space programs are so limited and rickety. Chemical rockets, sheesh!

Here's to the future!

[BenBurch]

Problem is that nuclear and nuclear-electric rockets have a LOT of political resistance.

[icerat]

Problem is that nuclear and nuclear-electric rockets have a LOT of political resistance.

I suspect that resistance may have dropped in the past decade. Many on the political left, who typically lead that kind of resistance in the past, seem to have become more accepting of nuclear power as an option against AGW.

I think the various nuclear Navies around the world is some pretty solid evidence it's doable.

[jasonpatterson]

I suspect that resistance may have dropped in the past decade. Many on the political left, who typically lead that kind of resistance in the past, seem to have become more accepting of nuclear power as an option against AGW.

I think the various nuclear Navies around the world is some pretty solid evidence it's doable.

The big fear, I think, is that if a nuclear spacecraft explodes during launch, it's instant fallout. If a nuclear sub explodes, it all goes into the ocean, and we don't care about that so much... Not my view, but what I've heard from folks who oppose nuclear powered spacecraft.

[DogB]

The big fear, I think, is that if a nuclear spacecraft explodes during launch, it's instant fallout. If a nuclear sub explodes, it all goes into the ocean, and we don't care about that so much... Not my view, but what I've heard from folks who oppose nuclear powered spacecraft.

That's about right. It's completely wrong thinking of course but that never stopped anybody before.

[shadron]

The big fear, I think, is that if a nuclear spacecraft explodes during launch, it's instant fallout. If a nuclear sub explodes, it all goes into the ocean, and we don't care about that so much... Not my view, but what I've heard from folks who oppose nuclear powered spacecraft.

While I don't think that nuclear RTGs are protected quite this heavily, they have been similarly rated to withstand a maximal rocket explosion:

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[shadron]

An ion engine was used to power the 2007 Dawn mission to Ceres and Vesta, and Deep Space 1. A mission to Saturn is being readied using an ion thruster. One such thruster recently finished a 12,000 hour test, processing 245 pounds of Xenon.

[dasmiller]

An ion engine was used to power the 2007 Dawn mission to Ceres and Vesta, and Deep Space 1. A mission to Saturn is being readied using an ion thruster. One such thruster recently finished a 12,000 hour test, processing 245 pounds of Xenon.

Ion thrusters had been in use on commercial spacecraft for at least 10 years before that.

[HansMustermann]

The thing is, 200 kW is peanuts. It won't get a rocket off the ground. To put it into perspective a Spitfire (Mk VB, to be precise) had a 1,096 kW engine (1,470 hp.) A WW1 Sopwith Camel in the last iterations had slightly over 100 kW.

Ion engines are great for applications where you need very little thrust for long times, but don't want to haul a lot of fuel for it either. They win "bang per buck", so to speak, where the "buck" is actually kilo of fuel carried, but the absolute "bang" is still abysmal compared to chemical rockets.

Don't get me wrong, I'm not saying they suck. They have their niche where they beat anything else. But they still have a very long way to go before they'll beat chemical rockets outside that niche.

[Mark6]

The big fear, I think, is that if a nuclear spacecraft explodes during launch, it's instant fallout. If a nuclear sub explodes, it all goes into the ocean, and we don't care about that so much... Not my view, but what I've heard from folks who oppose nuclear powered spacecraft.
This is "the big fear", but resistance HAS dropped, significantly. When Galileo probe was launched in 1989, there were big protests and IIRC some serious court challenges -- serious in the sense they actually had a shot a stopping the launch. Cassini launch in 1997 had one court challenge which was dismissed very quickly, and couple dozen protesters. New Horizons launch (also RTG powered) was neither protested nor challenged.

I agree that launching an actual nuclear reactor would evoke more resistance than an RTG, but overall resistance to nuclear energy in US has decreased.

[Mark6]

As someone pointed out on JREF a week or so ago, generations X and Y are much more accepting of nuclear power than baby boomers are. First because they did not grow up in the shadow of nuclear annihilation and thus do not equate "nuclear power" with "bombs", second because they DID grow up with threat of global warming, and third because they have somewhat better grasp of risk-benefit analysis -- or at least of "lesser of two evils". (The last part is just my own observation, and might be wrong.)

So to answer OP: We may see nuclear-electric rockets when last of 60's protesters are dead or in nursing homes.

[mhaze]

The big fear, I think, is that if a nuclear spacecraft explodes during launch, it's instant fallout. If a nuclear sub explodes, it all goes into the ocean, and we don't care about that so much... Not my view, but what I've heard from folks who oppose nuclear powered spacecraft.

Subs can in fact explode, when they are hit with a torpedo. Nuclear spacecraft cannot explode. During a launch, the first stages - chemical, either solid, liquid or hybrid - may be said to "explode".

These are stacked systems - long cylindrical multi stage rockets. All that is needed to protect the integrity of the nuclear rocket in the final stage is to insure positive separation and recovery in the case of spontaneous dis assembly of the first and or second stages.

Sense the issue, blow explosive bolts, ignite small separation rockets, move the thing away, begin the recovery sequence, etc.

"Fallout" in the case of multiple failures causing the plutonium to hit the planet would be dirty bomb style not nuclear explosions and in fact even that could be practically eliminated by building the casings to control downward velocity and insure some tunneling into the ground on impact.

[Simon39759]

Subs can in fact explode, when they are hit with a torpedo. Nuclear spacecraft cannot explode. During a launch, the first stages - chemical, either solid, liquid or hybrid - may be said to "explode".
These are stacked systems - long cylindrical multi stage rockets. All that is needed to protect the integrity of the nuclear rocket in the final stage is to insure positive separation and recovery in the case of spontaneous dis assembly of the first and or second stages.
Sense the issue, blow explosive bolts, ignite small separation rockets, move the thing away, begin the recovery sequence, etc.
"Fallout" in the case of multiple failures causing the plutonium to hit the planet would be dirty bomb style not nuclear explosions and in fact even that could be practically eliminated by building the casings to control downward velocity and insure some tunneling into the ground on impact.

Would it be feasible to get the nuclear material in tiny amounts (to reduce the consequence of a fallout) over several flight and assemble the reactor directly in orbit?

There would presumably need a bunch of flights anyway to assemble such a rocket...




The thing is, 200 kW is peanuts. It won't get a rocket off the ground. To put it into perspective a Spitfire (Mk VB, to be precise) had a 1,096 kW engine (1,470 hp.) A WW1 Sopwith Camel in the last iterations had slightly over 100 kW.
Ion engines are great for applications where you need very little thrust for long times, but don't want to haul a lot of fuel for it either. They win "bang per buck", so to speak, where the "buck" is actually kilo of fuel carried, but the absolute "bang" is still abysmal compared to chemical rockets.
Don't get me wrong, I'm not saying they suck. They have their niche where they beat anything else. But they still have a very long way to go before they'll beat chemical rockets outside that niche.


How much does the rocket weight for its 200 kW? I guess it must be considerably more than a WWI plane...

And how long can the engine run? What amount of fuel does it need to carry with it? I know that it is quite a bit less than a chemical rocket, but to what extent?

I know of the concept, mostly from SF books, but, I have to say, I have no real understanding of how it really work in real life.

[phunk]

The thing is, 200 kW is peanuts. It won't get a rocket off the ground. To put it into perspective a Spitfire (Mk VB, to be precise) had a 1,096 kW engine (1,470 hp.) A WW1 Sopwith Camel in the last iterations had slightly over 100 kW.

Ion engines are great for applications where you need very little thrust for long times, but don't want to haul a lot of fuel for it either. They win "bang per buck", so to speak, where the "buck" is actually kilo of fuel carried, but the absolute "bang" is still abysmal compared to chemical rockets.

Don't get me wrong, I'm not saying they suck. They have their niche where they beat anything else. But they still have a very long way to go before they'll beat chemical rockets outside that niche.

They wouldn't be used for launch of course, the rocket would be staged and the ion engines used for everything after achieving low earth orbit.

[dasmiller]

How much does the rocket weight for its 200 kW? I guess it must be considerably more than a WWI plane...

The motor itself isn't terribly big or heavy. The problem is the 200 kW power system that you need to drive it. Chemical rockets store energy in the reaction mass itself (kind of a clever trick, when you think about it), but ion motors need a separate power source.

And how long can the engine run?
Until it runs out of fuel or power, or simply wears out. Different motor variants have different wearout mechanisms, of course, but pretty much any motor that has metal in contact with plasma is going to have a limited operating life. That applies to conventional rocket motors, too.

What amount of fuel does it need to carry with it? I know that it is quite a bit less than a chemical rocket, but to what extent?

That's mostly determined by "specific impulse," or "Isp" which is basically the total amount of thrust that you can get from a pound (kilogram, whatever) of fuel.
A really good conventional rocket burning H2 and O2 can get a vacuum Isp of something over 400 sec. Electrically-augmented conventional thrusters can get nearly 600 sec. I've seen Hall-Effect thrusters at around 1500 sec, and XIPS at 2500-3000 sec. Beyond that, I'd have to actually look things up.

A quick look shows NERVA at about 850 sec; the nice thing about NERVA was that it was producing real thrust (Hall-effect and XIPS put out about as much thrust as a high-powered flashlight). IIRC, though, NERVA put out a mind-boggling amount of radiation. I know, you're thinking "but we're in space. Who cares about radiation." Seriously, it was putting out a LOT of radiation. OTOH, I know a lot more about space radiation effects now than I did back when I was reading about NERVA. I might not find the problem as daunting now as I thought it was then.

[Simon39759]

But NERVA was a nuclear rocket, a different beast from the ion rockets, no? Although, an fascinating concept in its own right...

[BenBurch]

NM. I had that wrong.

[dasmiller]

But NERVA was a nuclear rocket, a different beast from the ion rockets, no? Although, an fascinating concept in its own right...

Oh, yes, NERVA was a very different kind of thing. But since we were talking about interesting space propulsion systems . . .

[Simon39759]

And it definitively qualifies there.

[Roboramma]

Oh, yes, NERVA was a very different kind of thing. But since we were talking about interesting space propulsion systems . . .

NERVA sounds cool: looking it up on wikipedia I bumped into something called Prometheus, which was a recent look by NASA at nuclear propulsion. It seems like a pretty good idea, but the program was started in 2003 and cancelled again in 2005. :(

Apparently it was meant to look into NERVA like systems as well as develop better RTGs.

[Robo Sapien]

NASA just announced 5 minutes ago that it has plans to build a revolutionary new rocket powered by a thousand hamsters inside a wheel. The only fuel required is a few pounds of carrots and lettuce.

Also, NIF (https://lasers.llnl.gov/) is close to achieving star-like fusion technology, that if made portable could some day power spacecraft.

http://www.youtube.com/watch?v=dmIHD6P3rdo


What ever happened to that laser sail idea?