Thursday, November 29, 2012

To Space and Beyond With Nuclear Energy

One of the things that you can do with nuclear energy is produce a lot of energy for a long length of time with an exceptionally small amount of uranium – or dilithium crystals, whichever is available. So if you need energy for an extended period of time – say, the time it takes to get from Earth to Mars, then nuclear energy has considerable utility – and you don’t have to worry about dust blocking the sun, as on some of the solar driven rovers.

Now, a group of scientists are thinking bigger – sending astronauts to Mars and beyond and doing it in a way that could get them there and back successfully. This is a barrier that hasn’t been breached, so while this project is in early days, it’s very intriguing.

A team of researchers, including engineers from the Los Alamos National Laboratory, this week reported their successful demonstration of a new concept that could provide reliable nuclear power for space exploration. The technology is still years away from the warp drive of Star Trek, but it could provide a means of propulsion for space travel beyond the moon.

I’m not sure warp speed is even a goal, but fine – it’s hard to avoid Star Trek in this context. And as long as this is what you’re up to, why not dream big? Pluto, anyone?

"We could have a nuclear-powered rocket that could get to Pluto in two years; whereas a chemical rocket would take seven years," said Paul Czysz, Ph.D., professor of aeronautical engineering at Parks College.

"We think it is the enabling technology," he told TechNewsWorld. "If you are really going to do something on this scale, you need to have something other than chemical rockets."

This article doesn’t say so, but even with this as a fanciful extension of the project, you probably couldn’t get astronauts out to Pluto and back with this technology – at least, not alive. And keeping the space travellers alive is a goal of this project.

Anyway, here’s what this gaggle of rocket scientists are up to:

"This is really a new old system, as it is a new platform build on an old technology," said Michael Podowski, Ph.D., professor of nuclear engineering at Rensselaer Polytechnic Institute.

"The Stirling engine is an old one," he pointed out, but "the concept is very healthy. The nuclear factor is not an issue at this point. However, [achieving] efficiency will require a lot more work.

"While the concept is interesting and it makes good use of the elements involved," Podowski told TechNewsWorld, "it will require more work. It is as simple as that."

How old is the Stirling engine? – think 19th century old. The article doesn’t really describe its characteristics very well, so I went over to How Stuff Works for a fuller explanation.

The Stirling engine is a heat engine that is vastly different from the internal-combustion engine in your car. Invented by Robert Stirling in 1816, the Stirling engine has the potential to be much more efficient than a gasoline or diesel engine. But today, Stirling engines are used only in some very specialized applications, like in submarines or auxiliary power generators for yachts, where quiet operation is important. Although there hasn't been a successful mass-market application for the Stirling engine, some very high-power inventors are working on it.

I guess the writer means the deep space scientists as well as others. But what is it about the Stirling engine that might work in a nuclear application? I’d point to these:

The gasses used inside a Stirling engine never leave the engine. There are no exhaust valves that vent high-pressure gasses, as in a gasoline or diesel engine, and there are no explosions taking place. Because of this, Stirling engines are very quiet.

So it appears to have a variation on a containment chamber. But it looks like the nuclear reaction would happen outside the engine:

The Stirling cycle uses an external heat source, which could be anything from gasoline to solar energy to the heat produced by decaying plants. No combustion takes place inside the cylinders of the engine.

A possible scenario would be to use reactors like those on nuclear submarines to drive the engine.

I’m still curious that no one has found a sizeable niche for these engines – I tend to be suspicious of “miracle” technologies that can’t gain traction – especially in nearly 200 years. That can mean scalability problems – I’ve read that it’s a big mechanism for the power it can generate. On the other hand, the engine’s ability to output a constant level of energy without much variation likely hurts it in an automotive context, but might be beneficial for a rocket.

In any event, this is an interesting development that might allow humanity to break through the artificial barrier between the moon and the rest of space. Maybe we won’t have to wait for dilithium crystals to send astronauts to Pluto.

6 comments:

jim said...

One fun speculation is where we could've been by now hadn't highly successful atomic space drive research such as Project Rover hadn't been nipped in the bud in the late sixties. I recall them boasting about six month round trips to Mars in the late 1980s! That suggests that we could've been wading around on Titan by now!
Nuclearphobia sure took its toll!

James Greenidge
Queens NY

Anonymous said...

Project Rover was cancelled in 1972, as the US space program was winding down generally after the Apollo moon landings. I don't see any evidence that its abandonment was due to "nuclearphobia." Richard Nixon wasn't exactly anti-nuclear; in fact, the next year he announced his energy plan which foresaw 1,000 power reactors operating in the US by 2000.

jim said...

Folksy and gentlemanly Dr. Robert Jastrow at NASA's Columbia U office here then mentioned at a NY Historical Society forum I attended with the Campaign For Space and L-5 Society circa 1984-5 (poor brilliant Judith Resnik was a guest there too. Unreal) about how the budding Earth Ecology and antiwar movement was impacting non-naval nuclear development and how horrified "eco" papers were of open-air nuclear rocket engine tests as well as stroking apprehensions of Russian nuclear satellites, shelving enthuse for US nuclear reactors in space. They very badly wanted nuclear engines for Mars. The Jackass Flats engineers ought have books pining that. (Jastrow also displayed a cool post-Apollo space station chart of two Skylab-type hulls connected by long cables rotating about a nuclear reactor "hub" for artificial gravity which NASA ought dig out for public viewing). He mentioned how difficult it was in the Cold War nuclear anything fear climate to lobby for RTG missions beyond Viking and how Galileo almost started off as a underpowered solar-paneled concept like Juno is. Unfortunately Nixon's grand nuclear plan ended up just that; just another gov't proposal since he had a hotel to worry about.

James Greenidge
Queens NY

Anonymous said...

I am left wondering how they plan to use this plentiful electrical power to propel a spacecraft. Ion engines? Can those actually reduce a Mars trip to 2 years? I always thought ion engines were only good if you weren't in a hurry?

jim said...

The basis for early atomic rocket engines was to literally pump any working fluid right through a hot reactor to create a high impulse exhaust. It would even work with water were you so desperate, as nicely described in the movie "Destination Moon" in the early 1950's!

James Greenidge
Queens NY


Engineer-Poet said...

"This article doesn’t say so, but even with this as a fanciful extension of the project, you probably couldn’t get astronauts out to Pluto and back with this technology – at least, not alive."

Why not?  If you can hold temperature and regenerate water and atmosphere, food isn't that big of an issue.  A recent development which showed that certain archaebacteria can convert CO2 and electrons to methane with 80% coulombic efficiency (oxygen evolved at the anode) suggests that life support can be done with little more than a reliable source of electricity for an energy source.  (I'm not sure what you'd do with the methane, but there have to be any number of chemotrophic bacteria which could eat it and become a food source for something like zooplankton.  Zooplankton feed fish.  You might be able to go from CO2 to tilapia in 3 steps.)

"I’m still curious that no one has found a sizeable niche for these engines – I tend to be suspicious of “miracle” technologies that can’t gain traction – especially in nearly 200 years."

They're external-combustion, meaning that heat has to be pushed through a wall into a working fluid which has to be at very high pressure to get good power density.  This requires high-strength, high-temperature alloys and precise fabrication (contrast automotive engines made of aluminum).  This makes them expensive.

What the Stirling brings to space missions is much greater thermal efficiency than thermoelectric converters.  This means a smaller heat source and much smaller radiators.