Earth to Mars In Two Weeks? 45
Waves writes "Scientists at Ben-Gurion University have shown that an unusual nuclear fuel could send space vehicles from Earth to Mars in as little as two weeks. Spacecraft now take between eight and 10 months to make the same trip. Instead of using Plutonium-239 or Uranium-235 The research shows a fairly rare nuclear material, americium-242m (Am-242m), when used as an extremely thin metallic film, is capable of sustaining nuclear fission at 1% of the mass of Plutonium." Interesting. But unless I'm totally mistaken, the thermal generators on spacecraft are used only for electricity, not propulsion, at the current time.
Only 2 weeks... (Score:1)
Okay - it's based on values dependant on acquiring reasonable quantities of Am... But, what I read into this, is that an application of using another radioactive material in a different alignment/form could generate the power necessary for this short of a trip.
It's almost sounding like more and more like the early attempts at getting controlled fission to work with differing opinions on the actual arrangement of the fuel. They tired different methods, and finally arrived at what they needed.
I wonder if the explosion of distributed computing for medicine could also be applied to configuring radioactive material alignments and shielding to improve reactors?
Drat - I only get 3 weeks vacation a year so Mars is out - I guess I'll have to settle for the Dominican Republic again...
Re:Unless I'm mistaken, you didn't read it, didya? (Score:1)
Space is permeated with radiation. 90-percent of all the matter in the universe emits radiation that we cannot even perceive. Do you think a few megatons would destroy the earth and end life as we know it?
If you do, I'm truly sorry. But the fact of the matter is, the energy would dissapate. Albeit not as fast as some would want; but in a few thousand years you wouldn't be able to detect a difference.
Re:Unless I'm mistaken, you didn't read it, didya? (Score:1)
it was certainly not perceptable but they did manage to measure it, we can measure things VERY accurately with lazers and such
again, I was simply using it as an example of things we can do that could POTENTIALY have a huge effect, but really don't usualy
Re:Unless I'm mistaken, you didn't read it, didya? (Score:2)
No. You see, the amount of raditation released by our fissioning a thousand tons of this stuff in space would still be a droplet compared to the hard radiation released by our Sun in a day. It would be like "polluting" the ocean with salt by pouring the contents of a salt shaker into it.
More importantly, the implicit philosophy in your last two sentences is downright dangerous. "But what unforseen consequences could this bring? You never know until it is too late," is an insane standard -- it means you cannot ever take action, because you can never be absolutely sure there are consequences you did not forsee. The only way to adhere to that standard is to lie down and die.
Re:What about the squish factor? (Score:1)
I have been sustaining 1 g constant acceleration for nearly 24 years, and I don't seem to suffer from that. For a manned mission to Mars, the 1 g acceleration is *good* for the astronauts, because they avoid a loooong weightless situation.
Re:Unless I'm mistaken, you didn't read it, didya? (Score:2)
Actually, even merely lying down and dying would be in violation of that standard: Doing so would cause your body to decompose and release potential harmful greenhouse gasses into the atmosphere along with who knows what other consequences. Even merely ceasing to exist could potentially be harmful: How would the Earth's orbit be affected if 6 billion people simply ceased to exist. (I.E. their mass/energy was no longer a part of the universe)
It's an inherently paradoxical decision.
-JF
Re:How do you keep it from *going off*? (Score:2)
It surprises me that a foil configuration could support enough neutron capture to maintain a reaction. I am used to thinking that one needed at least a mean free path's worth of material, in three dimensions.
Re:Unless I'm mistaken, you didn't read it, didya? (Score:1)
Unless I'm mistaken, you didn't read it, didya? (Score:2)
That's the entire point of using this as nuclear fuel - the products of THIS fuel can be used as propulsion.
My question is, what ARE the byproducts of this process, and are they radioactive? Would a drive based on this process wind up spitting out a radioactive plume? If so, NO THANKS.
People To Mars (Score:1)
Does this mean that people can go to Mars too given the short duration? Come to think of it, if something lands on Mars could it blast off like on the moon, or would it need a whole big setup like when it takes off on Earth?
Re:Unless I'm mistaken, you didn't read it, didya? (Score:2)
The question is really "if the output is radioactive, does our atmosphere protect us from it." There are many many many forms of radiation in space. Our atmosphere protects us from many of them.
-JF
People could go to Mars now (Score:2)
Taking off from Mars requires a lot of gas. So does earth. Moon doesn't. But that isn't the reason for the gantry, etc. They don't help it take off, at all - (but the boosters fall away, so it'd presumably need a new system or more boosters) The gantry, etc, is there to provide for maintanence of the incredibly complex machine - and I suppose to make sure it isn't damaged in the wind.
There is almost no atmosphere on mars (until we add a bunch of plants and a few thousand years, but that's another story) and I don't think they'll be doing any maintenance. So you could certainly do it, as long as they are prepared for it, which they of course would be. Mostly by having a lot of fuel. Landing is more dangerous.
Unforeseen mistakes (Score:1)
Only thing to say about that distance in two weeks (Score:1)
"YEEEEEEEEEEEEEEEEHAW!!!!!!!!!!!!!"
"Titanic was 3hr and 17min long. They could have lost 3hr and 17min from that."
Re:This is nice. Pray tell, how do you turn it off (Score:2)
You don't - if you want to slow the spacecraft down (albeit gradually), you just spin a reaction wheel and turn the "engine" (or spacecraft) around by 180 degrees.
This sounds like one hell of a cool technology. It sounds like you get the performance of an ion drive without the need for the solar panels to "power" it, since the decay products of the Am-242 provide the ions.
Ancient tech: Rockets are insanely wasteful since you're accelerating millions of tons of propellant stuck to your engine. Oh yeah, somewhere buried under all the propellant and the tanks might be a payload, but you'd never notice it.
Current tech: Take a big heavy solar panel (or RTG) and a little bitty tank of Xenon. The big heavy electrical thing exists only to ionize the Xenon, charge a plate, and spit the Xe nuclei out the back end. It's more efficient then rockets, but you still have to accelerate the damn electrical power source needed to make the ions.
This thing: Scrap the electrical generator, just use a heavy element that not only ionizes itself, but it also automatically takes care of the spitting the particles out the back end part. The propulsion system is basically all fuel, and it all gets converted to kinetic energy in the form of fission products.
Fucking cool.
Re:People could go to Mars now (Score:2)
"Titanic was 3hr and 17min long. They could have lost 3hr and 17min from that."
Space is too big to pollute. *think* about it. (Score:4)
Um, if we took the entire mass of our *planet* and spread it around the inner solar system as a dust cloud, it wouldn't have any environmental effect on other planets in the vicinity.
How's the exhaust from a probe supposed to do anything?
I'm overlooking the fact that cosmic rays already send more hard radiation through the inner solar system than we could ever hope to put there.
The only legitimate concern is dumping radioactive waste just above the Earth's atmosphere. The simple solution: shield the ship until you're far away from Earth!
Pollution in deep space is a non-issue.
How do you keep it from *going off*? (Score:2)
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Re:Unless I'm mistaken, you didn't read it, didya? (Score:2)
Any object we send away from the earth (that is, not satelites, as they are still in orbit) will disrupt the earth's position in space. Of course, the earth is a gazillion times heavier than those object, so any displacement is so small that we can calculate it, but probably not measure it.
Still, it would be cool if we could slow down the earth rotation a bit more. If the diurnal cycle were 28 hours, I'd probably have a much easier time getting up in the morning (and sleep in the evening).
Re:Unless I'm mistaken, you didn't read it, didya? (Score:2)
What about the squish factor? (Score:1)
Although, it's still not a bad idea. If the fuel is lighter it's just more supplies you could carry. It's also less stuff you have to get into space in the first place.
spin orientation (Score:1)
Even if you could cause all the fission decays to occur along the desired axis, it would only lead to an increase in thrust by a factor of 2. At very high angular momenta (like 20 h-bar), fissions are pretty much in the plane perpendicular to the spin axis. (Thinking semiclassically.) But at low spins I don't think that's even true.
And then there's the whole question of how to align the nuclei. Even atomic spins are hard to align 100%, and aligning atomic spins isn't the same as aligning nuclear spins.
Re:Unless I'm mistaken, you didn't read it, didya? (Score:1)
it slowed down the earths rotation, albeit just barely, and it was a fairly small vehicle
everything we do in life, even burning some wood in a fireplace could have some massive unforseen consequences
should we be cautious? yes... should we be so cautious that nothing gets done? um no...
we presently use nuclear reactors to power some space vehicles, are you going to tell me that we shouldn't use another, more efficient method and just use the less efficient nuclear methods?
like it or not, solar cells simply cannot provide enough power for some applications
This was in Alpha Centauri (Score:1)
Re:This is nice. Pray tell, how do you turn it off (Score:2)
Crap, forgot this part. Probably you lob a bunch of heavy elements up there and create the Am-242 by neutron bombardment or other reaction. Separate it chemically in situ on the spacecraft, and deposit it on the "engine" plate every few days.
Since it's done in a cycle of a few days, the "missing link" would probably be "how do we rebuild our reactor after we've separated out the Am-242 from the original fuel".
> especially in space where dumping excess heat is a monumental task
Vapor-depositing Am-242 on a sheet of glass to make the new "engine" every couple of days sounds like a process that would require plenty of heat. ("Latent heat of steam is for wimps, real men worry about the latent heat of a vaporized radioactive metal!")
Of course, that probably only delays the problem. (How do you dump the heat from the glass plate into space? I dunno, maybe you just use the waste heat to drive Peltier devices and generate more electricity... but now it's sounding less like a "cheap and light self-contained ion engine" and more like a "use a big RTG to power a conventional ion engine" solution.)
This is nice. Pray tell, how do you turn it off? (Score:2)
On the other hand, this might have some very interesting applications here at home. Consider that photovoltaic cells will respond to the beta radiation from something line this as well as visible light. It is not too hard to imagine a "battery" of PV cells coated with a thin layer of am-242, sealed inside of a casing. One wonders what kind of power you could get out of this sort of thing? The stuff has a sixteen hour half life, though, so lifespan may be an issue.
Exhaust radioactivity. (Score:3)
That depends on which isomer of Am242 they're referring to ("m" denotes an isomer, a metastable energetic state of Am242 with its own decay properties). According to the handy description of Am242 at http://environmentalchemistry.com/yogi/periodic/A
They key words here are "into space". This drive will never produce enough thrust to be useful for lifting off of a planet; the exhaust throughput is far too low. Out in space, a few traces of radioactive atoms are a non-issue (we already have plenty streaming down in the form of cosmic rays).
Even if it doesn't push... (Score:1)
Of course a solar sail might be more effective. Not sure about the math.
G
Re:This is nice. Pray tell, how do you turn it off (Score:1)
Please, let's get real (Score:2)
- Launching a rocket won't slow down earth's rotation; the rocket works by reacting its exhaust mass... it's not like the "kick" of a gun.
- The "gravity whip" maneuver you originally mentioned probably did not involve "skipping a probe off the atmosphere." I'm sure it was a momentum exchange, using the earth's orbital momentum -- not the rotational momentum. Skipping a probe off the atmosphere would tend to slow the probe down, not speed it up, just in general. (It is possible to use it to change direction and potentially gain speed, but AFAIK that's not been reduced to practice yet.)
- And I don't think they measured the change it made. They may have measured the change in momentum of the probe and calculated the change in earth's momentum, but earth's momentum (whether orbital or only rotational) is so huge that this sort of momentum exchange with any spacecraft yet built would be undetectable with present technology. Work out the numbers...
Just for an example: one of the things they can measure is the effects on the earth's rotation rate of motions of the entire terrestrial atmosphere. And the changes are tiny -- very small fractions of a second in the length of a day, from motions whick take days or weeks to complete. Have you any idea how massive the entire atmosphere is, compared to a manmade object of any kind whatsoever?Not to arbitrarily bang on you, but your example was ill-chosen and then misunderstood...
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Re: Theoretically (and physically) Impossible (Score:1)
All we need now is for NASA to announce some reason to go to Mars (like huge gold mines below the surface), and we'll finally start seeing interplanetary travel.
Re:How do you keep it from *going off*? (Score:1)
Re:People could go to Mars now (Score:2)
Actually, this would be less practical than parachuting, which itself is not practical for the terminal descent onto Mars (that's why Pathfinder used an airbag, and why every other probe landed on Mars has done so with a rocket). The reason is that Mars' atmosphere is far too thin for these to be effective: Pathfinder, under a fully-open and functioning parachute, was still descending at around 185 ft/sec, which is faster than a skydiver in freefall! For comparison, on Earth the same parachute brought it down at less than 25 ft/sec.
While a lifting body would fly in Mars' atmosphere, it would be very, very fast -- and landing it would be effectively impossible. The lift-to-drag ratio of a lifting body is small (even for Shuttle, which has true wings, the L/D is only around 3:1), so the rate of descent would be impossibly high with any rational wing loading. Even on Earth, it's hard to land a highly-loaded lifting body -- this is why the X-38 Space Station "lifeboat" is landed with a large parafoil-type parachute, rather than simply landed... it's way too fast, even here.
While there are aircraft being designed for martian flight, they tend to resemble things like the Gossamer Condor and other manpowered aircraft, more than something you could use for descent from space; the vehicle would have to be all wing, and very lightweight wing at that, to work. Like mylar film over wireframe... not really great for re-entry.
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Re: Theoretically (and physically) Impossible (Score:2)
The truth of the matter is that if you have enough rocket, you can go directly to Mars from Earth at any point in their orbits, and you really won't care what the relative position is.
Just for fun, I took the one-way trip time for worst-case conjunction (100 million kilometers) with a 1/100 gravity continuous acceleration. This takes just under 12 days (accelerate half-way there, decelerate the other half); if you add a bit of time to match orbital velocity, you've still done it in under two weeks. (In fact, the coincidence of the numbers suggests to me that the value of 0.01 g is what the author was using...)
Now, I did this at conjunction (Earth and Mars on the same side of the sun, closest approach), although it was worst-case conjunction. If you want to go (or return) at opposition (meaning you'd go around the Sun en route, the trip's much longer -- on the order of 2.4 AU, or around 140 million klicks; let's use 200 million to make the argument, though, since we've got to miss the Sun by a little.
It now takes you 16.5 days, more or less. The reason it's so short is that you're continually accelerating: your velocity keeps growing, and adding just a little time at such a high velocity makes a big difference. FWIW, in the last case your velocity is over 70 km/sec at your halfway-point turnover; in the first case, traveling half the distance, it was under 50 km/sec.
Not impossible at all! Matter of fact, I'm open for a ticket right now... ;)
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This would be very difficult. (Score:2)
You also have to realize that (kinetic energy)/momentum scales like velocity. It sounds great to have your reaction mass coming out at 10% of the speed of light if all you care about is momentum per unit reaction mass. But the energy being released is 10,000 times more per unit momentum compared with normal chemical rocket fuels. If all the decay was by fission, you'd have to eat half this energy as heat. Ouch! Good way to melt your rocket ship!
And since someone said this isomer decays mostly by alpha emission, that makes it even worse. Alpha decay releases roughly as much energy, but produces very little thrust.
Re:People could go to Mars now (Score:1)
Basically, the plan goes like this:
1. Shoot an empty return spacecraft (no return fuel) to Mars using a slow, but fuel-efficient, transfer orbit. Have it land autonomously after a ~6-8 month trip, and turn on its simple mechanism to decant rocket fuel from the atmosphere. (The mechanism to do this is supposed to be just staggeringly simple...details in the book)
2. Shoot the spacecraft with the crew, and an additional dry return ship, to Mars. Use a faster orbit to get the people there, and the same slow boat for the dry craft. Land the people near the now fully fueled return craft, and land the dry return craft at a convenient place for the NEXT mission, which will be no farther than the crew can travel overland. This way, you have redundant return vehicles, one ready to go, one that will be ready in a couple months (which is the length of the planned stay on Mars).
Anyhow, it's brilliant engineering and mission planning. Zubrin says he could do the whole shooting match, with continuing trips to Mars, in ten years, for 1/10 of NASA's current budget.
I'm glad you read it; don't jump to conclusions. (Score:3)
The thing I find most interesting, and which is not addressed in the article (dammit), is whether Am-242m emits its fission/decay products in any particular direction relative to the spin axis of the nucleus. If the nucleus can be aligned with a magnetic field so that the fission products go backwards, that would be a tremendous advantage for propulsion. One more thing to look up when I get home, if it's even mentioned in my table of the isotopes...
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Re: Theoretically (and physically) Impossible (Score:2)
Whoa! I didn't mean we can do it now -- only that there's nothing theoretically or physically impossible about it, as claimed in the earlier post.
We still don't have a drive that'll manage a hundredth of a gee for weeks on end... minor point. ;) There are good reasons to believe that we'll have that tech in a while, but not yet!
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Re:What about the squish factor? (Score:1)
Re:What about the squish factor? (Score:2)
Not really. I've still got the MathCad doc open from my earlier post, so here goes... Use the same 200 million kilometers for worst-case trip (opposition, fly around the sun) at 1 g constant acceleration: time to Mars is just under 40 hours, with turnover speed of 700 km/sec.
But you're right, 1 g constant acceleration for 40 hours is some trick!
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Re:Unless I'm mistaken, you didn't read it, didya? (Score:1)
If we slow the earth's rotation down enough to make a day last 28 hours, these considerably longer days could mean higher peak temperatures. That could mean considerable climate change.
If you want a 28 hour day, I suggest you spread it over the current 24 hour per day, 7 day week, not impose blazing hot temperatures on everyone for longer.
Was that in a UFO magazine? (Score:2)
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Re:What about the squish factor? (Score:1)
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Re:This is nice. Pray tell, how do you turn it off (Score:2)
By the time you've addressed all the issues necessary for use of americium foil in a rocket, it will have been easier to just solve the problem of using antimatter as the energy source and water as the working fluid. Sure, you have to make the antimatter -- but that's not much harder than making the americium in situ... and turning it on and off is no doubt simpler (although probably breathtaking anyway).
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Re:Was that in a UFO magazine? (Score:1)
and I'm not trying to scare anybody, I'm using it as an example that we can do much more to our world and still have it continue to operate fully and comfortably