Do we have any data to justify the assumption that the asteroid might be rotating as slowly as 1 RPM? That's not a very high rate of rotation afterall, and 2 times the rotation rate would take 4 times the fuel to de-spin, wouldn't it? Or longer moment arms.
3. Putting something in high lunar orbit provides a justification for developing the ability to go there.
Second thread for this mission, given this is covering elements in and outside of the new mission - such as realigning EM-2 and such.http://www.nasaspaceflight.com/2013/04/captured-asteroid-mission-redefining-em-2-challenge/
An elliptical lunar orbit with a 50,000 km semi-major axis has about -0.1 km2/s2 C3
Capturing a small, icy asteroid would be a pretty convenient way to get hundreds of tons of water... Put it in a bag pressurized to above triple point of water, heat it slowly with the Sun, spin slowly so all the solid parts went to the bottom of bag (may need a tether so center of mass isn't inside the asteroid), and place a "dehumidifier" cooled by radiators inside the bag, collecting the water as it condenses on the cooling coils. No chipping away at anything required. You could extract most of the volatiles that way.The only thing is that there probably aren't any icy asteroids until you get out in the asteroid belt, closer to Mars...
If it's gimmicky at all, it's that this mission is being responsive to something the public might actually care about (asteroids, oh my!).But to be honest, NASA /needs/ to connect to any kind of public awareness that is out there (in connection with space). Otherwise, people will just start asking, "Why are we worrying about stuff up there when there's plenty of stuff to worry about down here?" Now, you and I may think pursuing HSF and supporting the expansion of humanity into the cosmos is worthwhile for its own merits, but everyone else thinks we have our heads in the clouds.It is pretty valuable (in regards to building public support for space exploration, public or private) to be able to point to the asteroid threat (which is real, not just a gimmick) and say, "See what happened in Russia? THAT'S why we care about what goes on up there." It's much harder to justify an outer planets science mission (something also worth doing because learning about stuff is awesome) to the average Joe than it is to show how NASA is addressing something (in even a small way) that could actually affect his life.
Quote from: Robotbeat on 04/11/2013 10:22 pmIf it's gimmicky at all, it's that this mission is being responsive to something the public might actually care about (asteroids, oh my!).But to be honest, NASA /needs/ to connect to any kind of public awareness that is out there (in connection with space). Otherwise, people will just start asking, "Why are we worrying about stuff up there when there's plenty of stuff to worry about down here?" Now, you and I may think pursuing HSF and supporting the expansion of humanity into the cosmos is worthwhile for its own merits, but everyone else thinks we have our heads in the clouds.It is pretty valuable (in regards to building public support for space exploration, public or private) to be able to point to the asteroid threat (which is real, not just a gimmick) and say, "See what happened in Russia? THAT'S why we care about what goes on up there." It's much harder to justify an outer planets science mission (something also worth doing because learning about stuff is awesome) to the average Joe than it is to show how NASA is addressing something (in even a small way) that could actually affect his life.Conan O'Brien mentioned this proposed mission in his monologue the other night (April 11). Aside from the fact that he wasn't on his A-game that night, it was interesting to listen to the audiences' response (starts at 1:40):http://teamcoco.com/video/category/monologue#video=50843I think that the average Joe hears about NASA's plan to lasso an asteroid and says 'meh'.
Additionally we get a tech demo of a SEP tug suitable for HSF-scale activity.
I'm trying to gain a better understanding of the "stable lunar orbit" the Keck authors envision. They wrote that in this orbit the asteroid has a "C3 with respect to the moon below -0.1 km2/s2."If I'm doing the math correctly, a lunar orbit with that C3 would have a semi-major axis of 24514 km and thus an orbital period of 95.59 hours. If the orbit were circular its altitude above the lunar surface would be 22776.6 km, and it would take 185.4 m/s of added delta-v to reach lunar escape velocity.Are those values plausible? Correct?
I apologize if this is covered (I haven't seen anything about it), and maybe this is a stupid question, but how do they intend to stop the captured asteroid's tumbling or rotating? It's pretty safe to assume that it's going to be tumbling, so the only thing I can imagine they're planning on doing is bagging the thing and then dissipating the rotational energy through friction with the inside of the bag. Which would, of course, transfer those forces to the spacecraft, which would then use it's RCS system to gradually correct for them? The only other thing I could imagine working is some kind of harpoon-probe with an aimable hall effect thruster on it, to de-spin the object before it's bagged. So - bag and de-spin, or de-spin first and then bag? Or am I missing something?
The S/C would then match the surface velocity and primary spin state of the target while maintaining station at the final station-keeping location...Final closure motion would be initiated while remaining in the synchronized motion state. Control would be disabled just before capture and re-established following a successful capture and securing of the target body.
I would worry about a significant tear that might occur during spindown once they've captured the asteroid.
Quote from: Robotbeat on 04/13/2013 02:37 amCapturing a small, icy asteroid would be a pretty convenient way to get hundreds of tons of water... Put it in a bag pressurized to above triple point of water, heat it slowly with the Sun, spin slowly so all the solid parts went to the bottom of bag (may need a tether so center of mass isn't inside the asteroid), and place a "dehumidifier" cooled by radiators inside the bag, collecting the water as it condenses on the cooling coils. No chipping away at anything required. You could extract most of the volatiles that way.The only thing is that there probably aren't any icy asteroids until you get out in the asteroid belt, closer to Mars...Wiki says there are 93 known near Earth comets.http://en.wikipedia.org/wiki/Near-Earth_object
I'm trying to gain a better understanding of the "stable lunar orbit" the Keck authors envision. [...] a semi-major axis of 24514 km
Quote from: Universe Daily on 04/12/2013 05:08 amWouldn't make better sense to tow a BIG asteroid to Earth and leave it in orbit there? Astronauts will need to travel to lunar orbit to reach the little thing NASA is preparing to fetch. We could hollow out a big one and use it as a space station. Thick dirt walls make excellent shielding against solar and cosmic radiation. Surely that would benefit us more. Big asteroids are big, they have much more mass. Which means you need a lot more fuel to move them. Basically, if you're using the same type of propulsion for each, and moving them the same amount (same delta-v), you need the same % of it's mass in propellent for each to move them. ( http://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation )So, if you want to do the same thing with an asteroid 1000 times the mass, it takes 1000 times as much fuel.And mass scales with radius^3, so if you wanted something that has 10x the radius, it would be (10^3) = 1000 times as massive.
Wouldn't make better sense to tow a BIG asteroid to Earth and leave it in orbit there? Astronauts will need to travel to lunar orbit to reach the little thing NASA is preparing to fetch. We could hollow out a big one and use it as a space station. Thick dirt walls make excellent shielding against solar and cosmic radiation. Surely that would benefit us more.
Quote from: ChileVerde on 04/12/2013 03:03 pmQuote from: MP99 on 04/12/2013 12:34 pmI also wonder whether L2 is the right place for this. It needs to have an orbit that will passively dispose of itself into the Moon if Congress stops paying the bills to go back to it, ISTM L2's potential energy means it could eventually wander into an Earth orbit. (Someone correct me on that if it's wrong.)I don't know about the long-term orbitology associated with L2, but have also wondered about EML4/5. As points of stable equilibrium, wouldn't they be worry-free places to park asteroids?Orbitalogically speaking, all of L1-3 are all unstable. The Keck paper envisions parking the asteroid in lunar orbit rather than at L2 explicitly because an eventual collision with the moon rather than with the earth can be guaranteed.I'd wondered about L4 and L5 too. I'll bet it's more difficult to arrange a low-delta-V capture there than in high lunar orbit.
Quote from: MP99 on 04/12/2013 12:34 pmI also wonder whether L2 is the right place for this. It needs to have an orbit that will passively dispose of itself into the Moon if Congress stops paying the bills to go back to it, ISTM L2's potential energy means it could eventually wander into an Earth orbit. (Someone correct me on that if it's wrong.)I don't know about the long-term orbitology associated with L2, but have also wondered about EML4/5. As points of stable equilibrium, wouldn't they be worry-free places to park asteroids?
I also wonder whether L2 is the right place for this. It needs to have an orbit that will passively dispose of itself into the Moon if Congress stops paying the bills to go back to it, ISTM L2's potential energy means it could eventually wander into an Earth orbit. (Someone correct me on that if it's wrong.)