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Mission To Mars
February 1, 2001 9:35 AM   Subscribe

Mission To Mars What if we could get there in about two weeks?
posted by Skot (21 comments total)

 
Then we should do it. We should be doing it anyway.
posted by owillis at 10:21 AM on February 1, 2001


The engine described in that article is all well and good, but how do you turn it off? (And I don't believe their 2 week figure anyway.)
posted by Steven Den Beste at 11:31 AM on February 1, 2001


Article saith, "Unlike other radioactive materials, such as plutonium and uranium, very small amounts of americium produce chain reactions. These reactions pump out large amounts of energetic ions or fission products.

"Ronen calculates that if the americium is shaped into a thin film, the energetic ions produced by the nuclear chain reactions will be ejected out of the film."

This all sounds fine and dandy. But I think I'd like them to mine the americium and manufacture the thin films on the moon.

posted by jfuller at 11:47 AM on February 1, 2001


You can't mine americium. It doesn't occur naturally. You refine it out of spent reactor fuel. (By the way, it's pronounced amm-err-EE-see-umm.)
posted by Steven Den Beste at 1:19 PM on February 1, 2001


Is that cheap to do? Cheaper than strapping a bunch of chemical rockets onto a shuttle? Because that's really what the bureaucracy at NASA is worried about. Cost.
posted by rlef98 at 1:30 PM on February 1, 2001


Sounds interesting. Of course, since they used that nuclear word again, they will probably run into some opposition.
posted by quirked at 1:57 PM on February 1, 2001


Build your own americium powered rocket engine using left over smoke detector parts.
posted by kaefer at 2:03 PM on February 1, 2001


Sounds like a bad idea, at least until we get more reliable chemical rockets. To explain; you'd have to launch the nuke rockets out of the atmosphere with a chemical rocket, then engage the Americium strip rockets, since it doesn't have the oomph to get out of earth orbit (thanks for the pronunciation, Stephen -- a byproduct of learning all of one's science by reading is a pathological inability to pronounce any of the words).

Unfortunately, even the workhorse Titan IVs have failure (read: explosion) rates of up to 10%.

So yeah, you can expect the usual anti-nukes in space response from us Luddites.
posted by norm at 2:11 PM on February 1, 2001


rlef98, blame not the bureaucracy at NASA. They'd love to do this cheap OR expensive. Blame our elected representatives, who generally only vote in favor of NASA programs that collectively create jobs in their districts. Really, it's much less stressful to just always remember that NASA is at one level sheer pork.

This is ultimately a method that has applicability not for exploration but for colonization. It would also make the outer planets accessible, and could lead to reasonable interstellar mission durations (i.e. <100y).
posted by dhartung at 3:00 PM on February 1, 2001


Of course, if we'd made our "Moonbase Alpha" the spent reactor fuel would be up there already.

posted by D.C. at 3:04 PM on February 1, 2001


Is that cheap to do? Cheaper than strapping a bunch of chemical rockets onto a shuttle? Because that's really what the bureaucracy at NASA is worried about. Cost.

A mission to Mars powered by chemical rockets would be a technological feat akin to reaching orbit atop a steam engine - it's such a difficult, expensive proposition that it's kind of silly to even think about it.

Every reduction in weight sets off a chain reaction to further reduce the weight; you have to burn multiple kilos of fuel to fling one kilo of payload into orbit, but you have to burn more fuel to lift that fuel, and so on. Reducing the payload by any amount reduces the fuel required by a much larger amount. Correspondingly, increasing the efficiency of your fuel/engine setup reduces the fuel required by a large amount. Reducing the amount of fuel reduces the size of the booster, which reduces the weight, which reduces the weight of the fuel needed to lift the booster, and so on as everything shrinks recursively and you continue to save money. Thus a small improvement in engine efficiency can represent a large savings.

Plain old solid-core nuclear rockets like the ones tested in the NERVA project are twice as efficient as hydrogen/oxygen engines like the ones used on the Space Shuttle. Gas core engines would be some four times more efficient than that. The article does not specify the efficiency of this americium engine, either because it is only a superficial look or because the designers haven't gotten that far yet. I notice they're talking about a 14 day transit time, though, which means they're thinking of accelerating the entire way. In order for that to be practical, the specific impulse (efficiency) of this sort of engine has to be spectacularly high (otherwise you'd have to carry an impractical quantity of fuel).

In other words, no matter how expensive this thing is, it'd save money. It could be most of the cost of the space vehicle and it'd still be cheaper than chemical rockets.

-Mars
posted by Mars Saxman at 3:19 PM on February 1, 2001


A manned trip to Mars doesn't make sense. People seem to be in favor of it because it would be sensational, not because it would actually serve any purpose. (Matt says this is OK to do) Here's my opinion on that subject.)

There's also a different technical issue which no-one knows how to solve: How do you shut 3 or 4 people up into a small space where they cannot avoid each other for two years without a murder taking place? Evidence is that this may not be possible even with picked people.
posted by Steven Den Beste at 3:55 PM on February 1, 2001


It's relatively easy to separate Americium out of spent fuel, though it leaves a mess behind. Since it's a different element, it has different chemical characteristics. So it isn't necessary to use a mass separator (such as is used to extract U-235 from U-238); it can be separated with normal chemical reagents. But first, all the metal in the fuel rod has to be turned into water-soluble salts (probably with HCl or H2S04 but possibly with HFl) so it will dissolve.

That's also how they purify plutonium. But it's far from as easy as I just made it sound, because it all has to be done by remote control through leaded glass, and once the americium is removed you've got a lot of highly radioactive water-soluble salts which have to be stored somewhere.

Also, you need to make sure you don't accidentally assemble a critical mass, because if you do your lab will be vaporized, along with much of the surrounding countryside.
posted by Steven Den Beste at 5:09 PM on February 1, 2001


So is this "thin-film nuclear" material the same stuff that's in my laptop monitor?

;)
posted by daveadams at 5:27 PM on February 1, 2001


There's also a different technical issue which no-one knows how to solve: How do you shut 3 or 4 people up into a small space where they cannot avoid each other for two years without a murder taking place?

Sure, there's a technical solution - use a continuous acceleration trajectory, get there in 14 days, do whatever you need to do, and get home in another 14...

It ain't nothin plain old brute force can't solve. <g>

-Mars
posted by Mars Saxman at 6:33 PM on February 1, 2001


Ironically (sorry for no link, but it shouldn't be hard to find), the number of murders in public schools fell 60% from 1990 to 2000.

Seems like a big problem, doesn't it?

(Then again, most of the 1990 murders were black kids in the inner city, and middle America only cares when white people shoot each other, right?)

Peace,
Kevs
posted by Kevs at 9:19 PM on February 1, 2001


I wonder whether the scientists are estimating 14 days of continual acceleration, or do they mean seven days accelerating and seven more decelerating. Because if their craft accelerates for 14 days straight, it's going to be travelling pretty damn fast by the time it reaches Martian orbit. It's going to take an equal amount of time and force to reverse the momentum it will have built up during the first half of the trip.

Of course, it's still more attractive than simply blasting a craft to Mars. But the mechanism for getting such frightfully explosive fuel into orbit is problematic.
posted by Loudmax at 4:48 AM on February 2, 2001


I think Kevs meant that comment to go in the chicken-finger-gun thread. Just a hunch.
posted by dhartung at 10:35 AM on February 2, 2001


This explains his "You fools, the martians will eat you alive" post in the chicken thread.
posted by sonofsamiam at 10:38 AM on February 2, 2001


I wonder whether the scientists are estimating 14 days of continual acceleration, or do they mean seven days accelerating and seven more decelerating.

The latter. The idea is that the occupants of the capsule feel 1 g the entire way, with a brief period of weightlessness in the middle when the craft is turned around to begin decelerating.

Getting to Mars in less than 14 days would demand acceleration greater than 1 g, which might be technically possible, but would be rough on the crew.

-Mars
posted by Mars Saxman at 11:49 AM on February 2, 2001


They're not going to get any 1G out of the engine technology being described here. Not even close. The theory here is similar to the theory behind an ion drive.

The fundamental idea is to try to get the most impulse possible per unit of propellant which is onboard. If a gram of propellent is expelled at twice the speed, it results in twice as much acceleration to the spacecraft. In many cases where you're trying to accelerate a craft the only important number is the total change in velocity; the amount of time it takes to do it isn't important. So an ion drive (or the one proposed here) work by producing a very small impulse but one which can be maintained for days without running out of fuel. Each kilo of propellant does more work.

NASA launched a science satellite a couple of years ago which had an ion drive on it. The propellant was Xenon gas. The drive works by ionizing the gas and then accelerating it with an electric field. It also has more conventional thrusters on it for cases when rapid changes are needed. So far it's been quite successful.
posted by Steven Den Beste at 1:45 PM on February 2, 2001


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