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#40
by
aero
on 13 Apr, 2013 04:29
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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.
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#41
by
bubbagret
on 13 Apr, 2013 04:32
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#42
by
HappyMartian
on 13 Apr, 2013 06:31
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3. Putting something in high lunar orbit provides a justification for developing the ability to go there.
Doing this initial NEO capture mission is going to cost a lot of money.
However, developing and using the new NEO capturing and mining technology, carefully using the ISRU propellant, gaining experience with the sustained use of a stable high Lunar orbit, and making full use of the meteoroid or asteroid material that would eventually be 'mined' to make effective GCR shielding for a Skylab II DSH could all be quite useful.
How many meteoroids and asteroids could companies eventually capture and move to a stable high Lunar orbit? Maybe lots. Will there be some problems? Sure.
ISRU propellant being produced in both a stable high Lunar orbit and on the surface of the Moon would make reusable single stage Landers quite doable, useful, and affordable.
Such Lunar surface and high orbit asteroid ISRU propellant might also be used to land some Skylab II DSHs at the Lunar polar ISRU base and then preposition some more at the Stickney crater ISRU base on Phobos. Attach some very large inflatable habs to the Skylab II DSHs and...
Skylab II Making a Deep Space Habitat from a Space Launch System Propellant Tank 2012 By Brand N. Griffin, David Smitherman, Kriss J. Kennedy, Larry Toups, Tracy Gill, and A. Scott Howe
At:
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20120016760_2012017550.pdf
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#43
by
HappyMartian
on 13 Apr, 2013 06:45
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#44
by
sdsds
on 13 Apr, 2013 07:58
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EDIT: Perhaps my calculation is off by a factor of 2. See:
An elliptical lunar orbit with a 50,000 km semi-major axis has about -0.1 km2/s2 C3
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 "C
3 with respect to the moon below -0.1 km
2/s
2."
If I'm doing the math correctly, a lunar orbit with that C
3 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?
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#45
by
KelvinZero
on 13 Apr, 2013 10:22
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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...
I didn't think it would be that easy, but was implied in that Keck paper that volatiles could be extracted. How difficult would it be to extract water from something like this for example? (or from whatever it looks like before it becomes a meteorite)
http://en.wikipedia.org/wiki/CI_chondrite#Chemical_composition(I decided to ask this on its own thread:
http://forum.nasaspaceflight.com/index.php?topic=31640.0 )
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#46
by
grakenverb
on 13 Apr, 2013 11:28
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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.
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'.
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#47
by
Rocket Science
on 13 Apr, 2013 12:30
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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.
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=50843
I think that the average Joe hears about NASA's plan to lasso an asteroid and says 'meh'.
Pretty much says it all.... Thanks for the link.
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#48
by
Danderman
on 13 Apr, 2013 15:24
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This is a very interesting proposal.
I have no clue how NASA plans to move a 500 ton asteroid to lunar orbit.
Having said that, it will be very difficult for the agency to keep its attention on this mission for the next 10 years. There will be many changes in the political environment, many crises, and plenty of opportunities to amend the plan to fit whatever the politicians want at the moment. So, the odds of this actually happening are very small.
It will be interesting to see the impact of this announcement on the proposed commercial asteroid mining ventures.
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#49
by
KelvinZero
on 13 Apr, 2013 15:39
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The average joe isn't hollering to give NASA more money either.
This is what you get.
Given the tiny budget we can expect for a mission on top of SLS/Orion development it is better than I conceived possible. We may actually get to work on the core goal of VSE, to 'bring the solarsystem into earth's economic sphere'.
Yeah it is pretty cheap. That is so awesomely better than over priced and never completed.
Additionally we get a tech demo of a SEP tug suitable for HSF-scale activity. This is an awesome paradigm shift if it is politically acceptable to develop something so useful without being forced to risk human lives pointlessly just to pork-up the mission.
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#50
by
aero
on 13 Apr, 2013 15:44
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Additionally we get a tech demo of a SEP tug suitable for HSF-scale activity.
Now that is a really good point!
Once the first one is built and works, there are a number of uses for "knock-off" designs. Unfortunately discussing them would be OT for this thread.
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#51
by
HappyMartian
on 13 Apr, 2013 16:10
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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?
Various stable Lunar orbits do exist.
"How stable are they? Ely and his colleagues calculate that certain elliptical, high-inclination, high-altitude lunar orbits may remain stable for periods of at least a century. Indeed, Ely hypothesizes the orbits could last indefinitely."
From:
A New Paradigm for Lunar Orbits At:
http://science1.nasa.gov/science-news/science-at-nasa/2006/30nov_highorbit/
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#52
by
a_langwich
on 13 Apr, 2013 16:43
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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?
Bag and de-spin, but you are missing a step...spin up to match, bag, and de-spin.
From section VI, Mission Design -> Capture and Post-Capture Operations, p.33
http://www.kiss.caltech.edu/study/asteroid/asteroid_final_report.pdf :
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.
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#53
by
Orbiter
on 13 Apr, 2013 17:17
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I would worry about a significant tear that might occur during spindown once they've captured the asteroid.
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#54
by
bubbagret
on 13 Apr, 2013 17:45
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I would worry about a significant tear that might occur during spindown once they've captured the asteroid.
If they used all 4 200 newton thrusters at once to de-spin the asteroid, with a grand total of 180# of thrust, I doubt that there would be much to worry about.
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#55
by
Solman
on 14 Apr, 2013 02:27
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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...
Wiki says there are 93 known near Earth comets.
http://en.wikipedia.org/wiki/Near-Earth_object
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#56
by
Robotbeat
on 14 Apr, 2013 03:23
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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...
Wiki says there are 93 known near Earth comets.
http://en.wikipedia.org/wiki/Near-Earth_object
...and the one with the /smallest/ aphelion has an aphelion of 4AU, i.e. well past the orbit of Mars:
http://neo.jpl.nasa.gov/cgi-bin/neo_elem?max_rows=0;fmt=full;action=Display%20Table;type=NEC;show=1&sort=ad&sdir=ASC(sort by "Q")
Of course comets come into the inner solar system, it's just that they don't stay here long and the delta-v to them is very large.
But there are icy asteroids in the asteroid belt.
Even so, a very-short-period comet might be a better candidate for capture since it'd spend some of its orbit down near 1 AU (or 1.5 AU, if we wanted to capture it around Mars...), where you'd get a little Oberth effect (from being deeper in gravity well of the Sun) and more solar energy for the electric propulsion.
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#57
by
sdsds
on 15 Apr, 2013 04:03
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I'm trying to gain a better understanding of the "stable lunar orbit" the Keck authors envision. [...] a semi-major axis of 24514 km
Further to this, I calculate the Hill Sphere of the Moon to have a radius of 61,464 km.
[1] Wikipedia asserts it has a source for the claim that, "it appears that stable satellite orbits exist only inside 1/2 to 1/3 of the Hill radius." The more strict of those would put the limit at 20,488 km, and the Keck orbit would not quite qualify. But it comfortably meets the less strict (1/2) requirement, and they have clearly chosen cleverly an orbit that numerical simulation shows is stable for 20 years or more, which is certainly plenty of time for EM-2 to get there, even with "standard" NASA delays!
In the context of sending EM-2 to visit a captured asteroid in such an orbit, I'm betting NASA will want the spacecraft on a "free return" trajectory for the out-bound leg. If so it should be possible to estimate delta-v values for a Hohmann-style transfer to the rendezvous orbit.
[2] I get 370 m/s at perilune followed by 233 m/s at apolune.
----
[1] I understand NASA once declared the radius of the Moon's sphere of influence to be 64,374 km. That's only because that distance is exactly 40,000 miles. It's close, though!
[2] I used the free return trajectory data provide at:
http://www.braeunig.us/apollo/free-return.htm
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#58
by
alexterrell
on 15 Apr, 2013 18:46
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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.
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.
Though there's the question of economies of scale. I would guess a 1,000 ton asteroid would cost about 20% more than a 500 ton asteroid - subject to a suitable launcher.
So - it might make sense to use a Falcon Heavy and scale up the mission. The launch savings might exceed the marginal cost of an a larger retreival spacecraft.
As for Low Earth Orbit - it requires 160m/s to brijng the asteroid to High Earth Orbit. A further 7,000m/s to bring it to a low orbit. Besides, humanity will expend a lot of energy hauling stuff up to high orbit. There's no sense in hauling stuff down.
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#59
by
alexterrell
on 15 Apr, 2013 18:49
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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.)
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.
How about an orbit that will cause Earth impact if not visited every two years by an Orion space craft?
