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Captured Asteroid mission - Redefining EM-2 for the bold challenge
by
Chris Bergin
on 11 Apr, 2013 15:01
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#1
by
Maverick
on 11 Apr, 2013 15:18
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Really interesting read as it covered a lot of previous and future interest. Thanks for putting that all together!
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#2
by
R7
on 11 Apr, 2013 15:24
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The more I read about this asteroid bagging thing the more I like it. Gives EM-2 crew something truly interesting to do. Develops technology and experience usable for both asteroid mitigation and utilization. For ~20 tons you get hundreds of tons of mass in high lunar orbit beckoning further ISRU experiments. One question though; with the lunar masscons how stable would the asteroid orbit be?
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#3
by
Orbiter
on 11 Apr, 2013 15:29
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I think the fact that we had that meteorite hit Russia last February might have something to do with the sudden re-purposing of EM-2. It certainly caught the public's attention to have two major asteroids involve Earth on the same day, one of them hitting Earth and hurting 1,000+ people. I think in some regards it woke us up to the dangers from space. Of course, I have no basis for this conclusion but I think it's a logical one.
I believe this is a good step in the right direction, not just for exploration, but planetary defense. The technology developed for this can be used to defend us from larger asteroids. We'll see how this goes, I'm glad they're re-purposing EM-2 instead of adding a new mission beyond 2021.
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#4
by
Proponent
on 11 Apr, 2013 16:37
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One question though; with the lunar masscons how stable would the asteroid orbit be?
Since the orbit would be quite high, I think the major threats to stability are the sun and the earth. The orbit is specifically selected to ensure that the asteroid will eventually hit the moon so there's no risk of it hitting the earth someday. That seems to be at least part of the reason that neither L1 or L2 is selected. I wonder about L4 and L5, though. They're pretty stable. How would the delta-Vs compare?
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#5
by
Chris Bergin
on 11 Apr, 2013 17:29
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Really interesting read as it covered a lot of previous and future interest. Thanks for putting that all together!
Thanks very much!
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#6
by
Lobo
on 11 Apr, 2013 21:46
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I think the fact that we had that meteorite hit Russia last February might have something to do with the sudden re-purposing of EM-2. It certainly caught the public's attention to have two major asteroids involve Earth on the same day, one of them hitting Earth and hurting 1,000+ people. I think in some regards it woke us up to the dangers from space. Of course, I have no basis for this conclusion but I think it's a logical one.
I believe this is a good step in the right direction, not just for exploration, but planetary defense. The technology developed for this can be used to defend us from larger asteroids. We'll see how this goes, I'm glad they're re-purposing EM-2 instead of adding a new mission beyond 2021.
To be honest, I think this is a -bit- of a gimmick. I'd guess that an asteroid hitting Russia, and another near miss, got the attention of some of the public, news, and some politicians. Interest means support for something that might be able to do something about such a threat hitting the US, or a large enough one hitting somewhere in the world to be very deadly. And maybe there's money to be given to NASA for pursuing the ability to do something about it?
NASA might be seeing missions that could entice additional funding from Congress, where a Gateway and lunar program doesn't seem to be getting much interest in additional funding.
It's not a gimmick that it's not a legitimate mission, but a gimmick in that it's "following the money". Boldin might help Hollywood put out a couple more "Armegedon" and "Deep Impact" type movies in the mean time to gin up a little more attention towards it. ;-)
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#7
by
Robotbeat
on 11 Apr, 2013 22:22
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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.
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#8
by
Rocket Science
on 11 Apr, 2013 22:34
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Nice piece Chris!
Interesting mission; however I still don’t buy the necessity for “humans in the loop”...
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#9
by
Orbiter
on 11 Apr, 2013 22:39
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I think the fact that we had that meteorite hit Russia last February might have something to do with the sudden re-purposing of EM-2. It certainly caught the public's attention to have two major asteroids involve Earth on the same day, one of them hitting Earth and hurting 1,000+ people. I think in some regards it woke us up to the dangers from space. Of course, I have no basis for this conclusion but I think it's a logical one.
I believe this is a good step in the right direction, not just for exploration, but planetary defense. The technology developed for this can be used to defend us from larger asteroids. We'll see how this goes, I'm glad they're re-purposing EM-2 instead of adding a new mission beyond 2021.
To be honest, I think this is a -bit- of a gimmick. I'd guess that an asteroid hitting Russia, and another near miss, got the attention of some of the public, news, and some politicians. Interest means support for something that might be able to do something about such a threat hitting the US, or a large enough one hitting somewhere in the world to be very deadly. And maybe there's money to be given to NASA for pursuing the ability to do something about it?
NASA might be seeing missions that could entice additional funding from Congress, where a Gateway and lunar program doesn't seem to be getting much interest in additional funding.
It's not a gimmick that it's not a legitimate mission, but a gimmick in that it's "following the money". Boldin might help Hollywood put out a couple more "Armegedon" and "Deep Impact" type movies in the mean time to gin up a little more attention towards it. ;-)
I wouldn't say *some*, you would have to be a hermit to not have heard about the strike - it got more hits on YouTube the first day it was uploaded than any other video.
The public is very interested, and concerned, about asteroids now that its been violently shoved in their faces. Politicians are taking advantage of that fact and that's how we're getting this mission. So in that sense, you're right, it is a gimmick.
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#10
by
PahTo
on 11 Apr, 2013 22:42
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Nice article, thanks Chris.
I think this re-purposed EM-2 is a reason for optimism and excitement if it happens. From technology demonstration and development, to a firm and fascinating destination, to the commercial appeal (or appeal to commercial interests)--it is a multi-faceted mission that can capture the interest of the world for the wonder, the technology, the potential profit and yes, even collision avoidance. And to top it off, there's even a little sense of urgency even though the first launch isn't until 2019 (SLS validation mission of 2017 not withstanding)!
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#11
by
sdsds
on 12 Apr, 2013 00:24
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The article does make this seem much more exciting (though also more boldly challenging) than the previous EM-2 definition. In terms of the bold challenges, is there much more information on the precision rendezvous? The docking? And perhaps most challenging, the EVA? Presumably for the prior EM-2 some sort of contingency EVA capability would have been present, but this mission requires much more than that. For example do all four crew members completely suit up each time anyone goes out the hatch?
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#12
by
CNYMike
on 12 Apr, 2013 03:41
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Interesting article on a concept that is an interesting twist. I hope they can pull it off.
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#13
by
Universe Daily
on 12 Apr, 2013 05:08
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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.
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#14
by
QuantumG
on 12 Apr, 2013 05:14
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Welcome to the forum. There's a difference between what is "better" and what is possible
(also, what is probable with the minimal budget)
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#15
by
deltaV
on 12 Apr, 2013 05:16
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1. The FY 2014 asteroid proposal involves a small asteroid because big asteroids, being big, are difficult to move.
2. One reason to avoid bringing an asteroid to LEO is the risk of such an asteroid reentering and damaging something.
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#16
by
sdsds
on 12 Apr, 2013 05:53
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3. Putting something in high lunar orbit provides a justification for developing the ability to go there.
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#17
by
QuantumG
on 12 Apr, 2013 06:02
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3. Putting something in high lunar orbit provides a justification for developing the ability to go there.
Honestly, I think that's disingenuous.. it's simply easier to move the smaller mass of a capsule up to high lunar orbit than it is to move 500 tons from high lunar orbit to LEO, and capture into LEO is a lot harder than high lunar orbit.
Demonstrating the capture of a 500 ton rock into lunar orbit will prove difficult enough. We don't yet know how to do it. On the other hand, actually succeeding in doing that will enable bigger rocks to be captured in the future. L5 by '95 baby!
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#18
by
Soralin
on 12 Apr, 2013 07:19
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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.
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#19
by
Proponent
on 12 Apr, 2013 11:31
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The article does make this seem much more exciting (though also more boldly challenging) than the previous EM-2 definition. In terms of the bold challenges, is there much more information on the precision rendezvous? The docking?
What would that be particularly challenging? It's a rendezvous and docking in lunar orbit with a co-operative object. That's been done before.
And perhaps most challenging, the EVA? Presumably for the prior EM-2 some sort of contingency EVA capability would have been present, but this mission requires much more than that. For example do all four crew members completely suit up each time anyone goes out the hatch?
No doubt they would, as was the case for Gemini and Apollo EVAs.
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#20
by
gladiator1332
on 12 Apr, 2013 11:56
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This is all good and exciting, but is anyone else skeptical of such an ambitious mission for the first crewed flight of Orion? Maybe I am missing something, but we have the unmanned earth orbit test flight on the Delta IV, then the unmanned EM-1 flight, and then this?
Or is NASA confident that the two unmanned flights will have enough of the issues solved that a manned LEO test flight is not needed? Pretty bold.
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#21
by
MP99
on 12 Apr, 2013 12:34
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This is all good and exciting, but is anyone else skeptical of such an ambitious mission for the first crewed flight of Orion? Maybe I am missing something, but we have the unmanned earth orbit test flight on the Delta IV, then the unmanned EM-1 flight, and then this?
Or is NASA confident that the two unmanned flights will have enough of the issues solved that a manned LEO test flight is not needed? Pretty bold.
I'm not seeing the target being there much before 2025.
That either means a long delay to EM-2, or it would be EM-3/-4/-5 that would actually go to the target.
IIRC the KISS report says 1-2 years to reach escape from LEO, 1-2 years to reach the target from there, up to 6 years to bring the object into Lunar orbit (not sure if dropping it at L2 makes that easier or harder).
I guess you can cut a little time off the mission by putting it on SLS/ICPS or FH, which will get that sort of mass to escape immediately.
Also, the feasible objects will have something like a 10 year synodic period (they're moving slowly relative to us, so when they go they take a long time before they come around again). If we catalogue something this year, it'll be back around 2023 ready for us to lasso it, then spend up to 6 more years getting it into position.
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.)
cheers, Martin
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#22
by
KelvinZero
on 12 Apr, 2013 12:54
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There is a section labelled 'safety' in the Keck report, among other things it mentions the final destination being a "high lunar orbit" which would naturally decay into the moon if abandoned. Also claims that size and mass routinely impact the earth, and that carbonaceous asteroids (the target type) break up immediately in the atmosphere and dont make it near the ground.
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#23
by
nlec
on 12 Apr, 2013 13:16
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This mission seems like overkill to chip a few fragments off of the asteroid for return to Earth. If the probe is going to capture the asteroid autonomously, I would rather see an (inflatable?) heatshield added and try to bring the whole thing back to earth without placing a crew at risk.
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#24
by
JohnFornaro
on 12 Apr, 2013 14:40
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NPR jumped on the bandwagon this morning in order to garner support from the few people who do not already vocally support this effort.
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#25
by
JohnFornaro
on 12 Apr, 2013 14:43
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3. Putting something in high lunar orbit provides a justification for developing the ability to go there.
Isn't there a celestial body already in the lowest lunar orbit possible?
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#26
by
JohnFornaro
on 12 Apr, 2013 14:45
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This is all good and exciting, but is anyone else skeptical of such an ambitious mission for the first crewed flight of Orion?
I don't think there's much opposition to the proposed effort at all.
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#27
by
ChileVerde
on 12 Apr, 2013 15:03
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That either means a long delay to EM-2, or it would be EM-3/-4/-5 that would actually go to the target.
<snip>
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?
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#28
by
Robotbeat
on 12 Apr, 2013 15:09
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This is all good and exciting, but is anyone else skeptical of such an ambitious mission for the first crewed flight of Orion? Maybe I am missing something, but we have the unmanned earth orbit test flight on the Delta IV, then the unmanned EM-1 flight, and then this?
Or is NASA confident that the two unmanned flights will have enough of the issues solved that a manned LEO test flight is not needed? Pretty bold.
Shuttle had no unmanned test flights. Honestly, I think 2 unmanned test flights is fine. The mission this time is not terribly complicated (other than the EVA, which although very interesting, I don't think is the most complicated EVA that has been done).
Grappling the capture craft can be simulated, and perhaps the arm used can be tested on ISS (if deemed necessary). I suppose it's even possible for the EVA procedures to be tested somewhat at ISS, although I'm confident (as much as anyone can be that isn't an expert in EVA) that wouldn't be worth the risk and cost of testing it in LEO space (we have the Neutral Buoyancy Lab for a reason).
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#29
by
mikegi
on 12 Apr, 2013 15:34
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This is a little off-topic ... but I really admire the veterans here who can be enthusiastic about a new proposed NASA mission that involves HSF. I've gone completely over to the Dark Side of Cynicism in the years I've been lurking here on NSF. It goes something like this:
Year One: you discover NSF.com and are fascinated by all the technical discussion of NASA's proposed missions and hardware. You believe that NASA is actually building hardware to take us to the Moon and beyond. "We're going to the freaking Moon and Mars!". You consider posters like "Jim" to be cynical old men that only rain on other people's parades and that what they recommend is just "thinking small".
Year Two: you're still optimistic but watch the grandiose plans discovered in Year One get whittled away by Congress or the Administration. You start listening more to the posters here that always include political concerns in the design of their missions/hardware. Still, you figure you can manipulate the politicians to support your missions by throwing them a bone. Hey, we're still going to land men on the freaking Moon!
Year Three: the Year One plans have been cancelled after the USGov has blown billions on it. But ... there's a new HSF grandiose plan from NASA to replace it. You're concerned about the large recurring costs of the new plan but think that, given what you've seen over the previous years on NSF, those who designed it must have received a wink-and-a-nod from those who control the purse strings. But hey, while we're not going to the Moon's surface anymore, we're still going to a freaking space station at EML-1 or EML-2!
Year Four: well, the planned Space Station at EML-1/2 has been whittled away ... and the new HSF plan to go to an asteroid has been replaced by plans to bring the asteroid here and fly a smaller HSF mission to it. Your immediate thoughts are not whether that's an exciting idea and technical challenge but, rather, whether the appropriate Administration supporters and Congressional Districts benefit from such a plan. In other words, is it viable? You begin to realize that HSF has nothing to do with space or technology or science but rather is simply disinterested politicians fighting for various quantities of cash. It's like seeing a new SciFi show that starts with plenty of pew-pew and effects but then evolves into just another "character study", this time set in space. Yawn.
Is there any reason to believe that all this new pew-pew won't devolve into just another character study?
(mods, please delete if inappropriate)
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#30
by
Robotbeat
on 12 Apr, 2013 15:38
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That's a very reasonable question to ask. Can we talk about it in a new thread?
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#31
by
Space Frog
on 12 Apr, 2013 18:49
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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?
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#32
by
MP99
on 12 Apr, 2013 19:15
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So - bag and de-spin, or de-spin first and then bag?
Bag first, then de-spin, I believe.
ISTM there will be considerable disruption to the surface - which the geologists will wring their hands ad gnash their teeth about.
Apparently, the behaviour of the dust is one of the things important to understand, and it won't be pristine, so ISTM the results will be questionable.
cheers, Martin
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#33
by
sdsds
on 12 Apr, 2013 19:58
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is there much more information on the precision rendezvous? The docking?
What would that be particularly challenging? It's a rendezvous and docking in lunar orbit with a co-operative object. That's been done before.
Yes, good point. But as for the docking, Orion will have never done that before. As for the rendezvous, is there a way to calculate the added delta-v needed to not just reach HLO, but sync up with another vehicle in HLO? It could be zero if the timing were perfect. How often would those windows occur? If the timing weren't perfect, how much propulsion would rendezvous require in e.g. the worst case?
do all four crew members completely suit up each time anyone goes out the hatch?
No doubt they would
Does this impose on the prior (unmanned EM-1) mission a requirement to depressurize the capsule while it is in cis-lunar space? Or are vacuum chambers on Earth good enough to simulate this, so it can be done the first time "for real" with crew lives at stake?
as was the case for Gemini and Apollo EVAs.
Do ya think those missions would have met modern crew safety standards?
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#34
by
Proponent
on 13 Apr, 2013 00:03
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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.
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#35
by
Proponent
on 13 Apr, 2013 00:15
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As for the rendezvous, is there a way to calculate the added delta-v needed to not just reach HLO, but sync up with another vehicle in HLO? It could be zero if the timing were perfect. How often would those windows occur? If the timing weren't perfect, how much propulsion would rendezvous require in e.g. the worst case?
It would all be calculated in advance, of course, and there would be an allowance for errors in velocity and timing. It's always possible that the allowance could prove inadequate, and the rendezvous would not be accomplished. But it's the same on every rendezvous mission that's ever flown.
do all four crew members completely suit up each time anyone goes out the hatch?
No doubt they would
Does this impose on the prior (unmanned EM-1) mission a requirement to depressurize the capsule while it is in cis-lunar space? Or are vacuum chambers on Earth good enough to simulate this, so it can be done the first time "for real" with crew lives at stake?
The first Gemini EVA was on the second manned flight. I don't believe a Gemini spacecraft had ever been depressurized in flight before. I'm sure that Orion would be extensively vacuum-chamber tested.
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#36
by
sdsds
on 13 Apr, 2013 01:02
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3. Putting something in high lunar orbit provides a justification for developing the ability to go there.
Honestly, I think that's disingenuous.
Yes there was an attempt to include some wry humor, perhaps verging on cynicism. But no, it was a genuine attempt to provide the original questioner with a semi-complete set of answers regarding the benefits of the Keck approach over the one he described. (Going a bit semiotic, the "3." was intended to signify what followed was a tertiary benefit,
not a replacement for the other two which had already been listed.)
Stated without humor or cynicism, the questioner's alternate plan would be inconsistent with the well-understood goal of using SLS and Orion for human exploration
beyond LEO, whereas the mission as outlined in the President's budget request
would be consistent with that goal.
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#37
by
Solman
on 13 Apr, 2013 01:37
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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.
Unless you use the asteroids' volatiles as propellant in a resistojet or similar propulsion system. As has been pointed out volatiles might be extracted from just having a dark colored bag. This would be true if an appropriate icy NEO could be found. Otherwise a means of extracting and heating, perhaps with mirrors, small amounts of regolith and exhausting the volatiles derived after further heating could propel the asteroid.
I realize this may be too ambitious for the first mission but some way of using the asteroid material as propellant will have to be developed if asteroid mining is to occur on a large scale.
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#38
by
Robotbeat
on 13 Apr, 2013 02:37
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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...
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#39
by
deltaV
on 13 Apr, 2013 03:04
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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?
Page 35 of the KISS study (
http://www.kiss.caltech.edu/study/asteroid/asteroid_final_report.pdf) proposes to match rotation rate with the assteroid, bag it, and then de-tumble the spacecraft/asteroid combination using RCS thrusters.
De-spin – To estimate the time and propellant required to de-tumble the asteroid, the object was assumed to have a mass of 1,100 t, be rotating at 1 RPM about its major axis, and have a cylindrical shape of 6-m diameter x 12-m long. The 200-N RCS thrusters would be used for this process and are assumed to have a moment arm of 2 m. The angular momentum of spacecraft with asteroid would be 1.7x10^6 N·m·s, and the major and minor moments of inertia (MOIs) with the spacecraft attached are estimated to be 1.65x10^7 kg·m^2 and 5.52x10^6 kg·m^2. The resulting time for despin would be ~33 minutes assuming continuous firing, and approximately 306 kg of propellant would be required.
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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?
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#60
by
sheltonjr
on 15 Apr, 2013 21:08
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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.
The Keck study includes a lot of margin for error.
The mass of the asteroid will be difficult to determine before hand but they are shooting for 500t. But they have allocated enough fuel to retrieve a asteroid that masses 1300t. Though it will take longer.
From the Keck study page 14:The return time would range from 2 to 6 years depending on the actual mass of the NEA. The concept system could return asteroids with masses in the range 250,000 kg to 1,300,000 kg, to account for uncertainties in size and density.
For de-tumble, they estimate it to take 300 Kg for the job and also added a lot of margine.
From the Keck study page 24:The propellant required to de-tumble the asteroid was estimated to be about 300 kg. A margin of 50% is added to this along with an estimated 200 kg of propellant to control the spacecraft before and after capture for a total requirement of 650 kg. Adding addition margin brings the total estimated RCS propellant load to 900 kg.
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#61
by
deltaV
on 15 Apr, 2013 21:27
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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.
Good point. The Keck study proposes spiraling out from LEO so the crappy BEO performance of Falcon Heavy would be irrelevant. If managed carefully having almost three times the payload to play with could come in handy, especially if our asteroid searches find candidates that are just a bit too big / far away. If managed poorly on the other hand I could see the bigger launch vehicle encouraging greater costs. Maybe it would be best to plan for an Atlas 551 class vehicle but keep the Falcon Heavy option in reserve?
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#62
by
Solman
on 16 Apr, 2013 00:25
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...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.
Thanks for posting that. Using water vapor from the comet in solar powered resistojets means high delta V is not as much of a problem.
It also means that you can take better advantage of the Oberth effect if using Mars capture-cool idea.
Payoff is doing ISRU from the start while developing a practical mining system.
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#63
by
A_M_Swallow
on 16 Apr, 2013 02:22
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...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.
Thanks for posting that. Using water vapor from the comet in solar powered resistojets means high delta V is not as much of a problem.
It also means that you can take better advantage of the Oberth effect if using Mars capture-cool idea.
Payoff is doing ISRU from the start while developing a practical mining system.
The tug does not have the hardware to purify the water so a mixture will be going through the resistojets. At best the thrust is not smooth and there is a risk that the jets will block.
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#64
by
Solman
on 16 Apr, 2013 02:38
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A M Swallow wrote:
The tug does not have the hardware to purify the water so a mixture will be going through the resistojets. At best the thrust is not smooth and there is a risk that the jets will block.
The tug doesn't have a resistojet either
I think that may be a valid consideration but inclusion of purifying equip. seems practical. The extra mass of the purification sys. should be easily made up for by the lower power supply and engine mass of the resistojet as compared to the SEP system.
That's assuming that maintaining the resistojet nozzle at a very high temp. wouldn't solve the problem
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#65
by
Solman
on 16 Apr, 2013 02:49
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In looking at the table Chris provided of short period comets I noticed IIRC that several pass inside the orbit of Venus. If the target comet could be nudged to a close pass by Venus then a thrust at that point coupled with a gravity assist perhaps, could really lower aphelion. This might really lower the delta V the resistojet has to provide.
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#66
by
sdsds
on 16 Apr, 2013 04:45
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If the target comet could be nudged to a close pass by Venus then a thrust at that point coupled with a gravity assist perhaps, could really lower aphelion.
What are the chances an object passing the orbit of Venus comes within the sphere of influence of that planet? Let's be generous and assume the trajectory of the object is coplanar with the orbit of Venus. The diameter of the planet's sphere of influence is 1.2x10^6 km. The orbit of Venus is 2*pi*108x10^6 km long. So I think your chances are no better than 1 in about 565 on each crossing.
It could be a long wait.
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#67
by
alexterrell
on 16 Apr, 2013 10:38
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A M Swallow wrote:
The tug does not have the hardware to purify the water so a mixture will be going through the resistojets. At best the thrust is not smooth and there is a risk that the jets will block.
The tug doesn't have a resistojet either
I think that may be a valid consideration but inclusion of purifying equip. seems practical. The extra mass of the purification sys. should be easily made up for by the lower power supply and engine mass of the resistojet as compared to the SEP system.
That's assuming that maintaining the resistojet nozzle at a very high temp. wouldn't solve the problem
Long term, using various forms of mass driver for comet retrieval will make sense. Right now, the technology for getting solid, dirty ice into a mass driver is about TRL1.
Personally I'd heat up the comet matter and capture the vapours at just above the triple point of water. Then pressurise back to a liquid for pumpng to the resito-jet.
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#68
by
alexterrell
on 16 Apr, 2013 10:44
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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.
Good point. The Keck study proposes spiraling out from LEO so the crappy BEO performance of Falcon Heavy would be irrelevant. If managed carefully having almost three times the payload to play with could come in handy, especially if our asteroid searches find candidates that are just a bit too big / far away. If managed poorly on the other hand I could see the bigger launch vehicle encouraging greater costs. Maybe it would be best to plan for an Atlas 551 class vehicle but keep the Falcon Heavy option in reserve?
At this point, it would be useful to be able to vary the specific impulse - e.g. to lower it to give more thrust for less power, and use more fuel.
That way, if the target is lighter than expected, increase the Isp to complete the mission in the alloted time, and return with fuel on board - ready for the next mission. If heavier, lower the Isp to complete the mission on time, and return empty to HEO - ideally meeting a rocket with a full container of propellant.
What's needed is a VAriable, Specific Implulse Magneto Reactor. Anyone heard of such a device?
And if such a device - call it VASIMR - isn't being used for this mission, do we pronounce it dead?
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#69
by
Solman
on 16 Apr, 2013 12:53
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If the target comet could be nudged to a close pass by Venus then a thrust at that point coupled with a gravity assist perhaps, could really lower aphelion.
What are the chances an object passing the orbit of Venus comes within the sphere of influence of that planet? Let's be generous and assume the trajectory of the object is coplanar with the orbit of Venus. The diameter of the planet's sphere of influence is 1.2x10^6 km. The orbit of Venus is 2*pi*108x10^6 km long. So I think your chances are no better than 1 in about 565 on each crossing.
It could be a long wait.
Which is why I said that the target asteroid would be "nudged" toward a Venus encounter. A retrieval system has to be able to alter the velocity of the target significantly so perhaps the wait wouldn't be that long.
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#70
by
Solman
on 16 Apr, 2013 13:02
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A M Swallow wrote:
The tug does not have the hardware to purify the water so a mixture will be going through the resistojets. At best the thrust is not smooth and there is a risk that the jets will block.
The tug doesn't have a resistojet either
I think that may be a valid consideration but inclusion of purifying equip. seems practical. The extra mass of the purification sys. should be easily made up for by the lower power supply and engine mass of the resistojet as compared to the SEP system.
That's assuming that maintaining the resistojet nozzle at a very high temp. wouldn't solve the problem
Long term, using various forms of mass driver for comet retrieval will make sense. Right now, the technology for getting solid, dirty ice into a mass driver is about TRL1.
Personally I'd heat up the comet matter and capture the vapours at just above the triple point of water. Then pressurise back to a liquid for pumpng to the resito-jet.
Couldn't see the point of cooling the vapor to condense it before heating it to exhaust it as vapor at first but it would be good to store it for use at the proper time to optimize thrust timing.
Mass drivers require mining and processing and the mass driver itself and its power supply. Seems overly complex and massive to me.
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#71
by
MP99
on 16 Apr, 2013 13:51
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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.
Good point. The Keck study proposes spiraling out from LEO so the crappy BEO performance of Falcon Heavy would be irrelevant. If managed carefully having almost three times the payload to play with could come in handy, especially if our asteroid searches find candidates that are just a bit too big / far away.
The Keck study wasn't trying to get this done in the shortest time, but I believe it is under time pressure now.
Using FH to get the mission immediately to escape would decrease mission time by a year or two, and increase capability by allowing about the same sat mass without consuming some prop spiraling out of LEO.
A 50t mission, OTOH, would increase costs.
cheers, Martin
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#72
by
yg1968
on 17 Apr, 2013 00:17
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#73
by
Hop_David
on 17 Apr, 2013 16:51
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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.
In an ideal circular 3 body system, L4 and L5 are very stable. However the earth moon neighborhood has the sun as an influence. The sun can destabilize rocks parked at EML4 and 5.
An ordinary 2 body orbit at EML2's altitude would travel about .9 km/s. But since EML is moving at the same angular velocity as the moon, it's moving 1.2 km/s. If nudged loose from the moon's Hill Sphere, an object from EML2 would sail to a 1.8 million kilometer apogee, beyond earth's Hill Sphere.
An
orbit's specific energy is 1/2 v^2 - Gm/r.
Specific energy for EML4 and 5 is about -.52 megajoules per kilogram.
Specific energy for EML2 is about -.18 megajoules per kilogram.
Specific energy for a parabolic orbit is zero. An incoming rock would be hyperbolic wrt earth and so have a positive specific energy.
Once at EML2, a small deceleration wrt moon would drop the rock deeper into the moon's hill sphere where it'd stay put for awhile without station keeping.
So EML2 is my favorite at the moment. My BOTEs for parking a rock at EML2:
Catching an Asteroid.
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#74
by
Hop_David
on 17 Apr, 2013 18:41
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In looking at the table Chris provided of short period comets I noticed IIRC that several pass inside the orbit of Venus. If the target comet could be nudged to a close pass by Venus then a thrust at that point coupled with a gravity assist perhaps, could really lower aphelion. This might really lower the delta V the resistojet has to provide.
Best case for this scheme is perihelion at Venus and aphelion at earth. The rock would have a Vinfinity of 2.5 km/s.
I believe they're hoping to shed hyperbolic excess V by doing a lunar swing by. But 2.5 km/s is too much to shed in this manner.
Using a comet's water for reaction mass assumes a mining and transportation infrastructure to get water to the rocket engines. A far more ambitious project than what the Keck study calls for.
If the comet has a perihelion as close to the sun as Venus, I would guess out gassing would make for a chaotic, violent environment on the comet's surface -- not good for the mining and transportation infrastructure nor the rocket engines.
It's possible for short period comets to have their aphelions lowered by planet fly bys. There may already be some accessible dead comets whose insulating mantle protects an icey core. Who knows? Personally I'd give even odds there are one or two dead comets within easy reach.
But it's a pretty sure bet that there are water rich carbonaceous rocks within reach of Keck style missions.
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#75
by
HappyMartian
on 21 Apr, 2013 03:56
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....
Once at EML2, a small deceleration wrt moon would drop the rock deeper into the moon's hill sphere where it'd stay put for awhile without station keeping.
So EML2 is my favorite at the moment. My BOTEs for parking a rock at EML2: Catching an Asteroid.
....
But it's a pretty sure bet that there are water rich carbonaceous rocks within reach of Keck style missions.
Yep, there are lots of meteoroids and asteroids that companies could eventually capture and move to a stable high Lunar orbit, not an unstable EML2 orbit.
As the mass continuously increases of those captured meteoroids, asteroids, and their eventual Deep Space Habitat space station needed for ISRU, so would the annual amount of propellant required to maintain them in an unstable EML2 orbit.
However, a stable high Lunar orbits means that for at least a century no propellant is needed to maintain the orbit of the Deep Space Habitat space station and the increasing mass of captured meteoroids and asteroids.
The Keck
Asteroid Retrieval Feasibility Study At:
http://kiss.caltech.edu/study/asteroid/asteroid_final_report.pdfhas the following:
Page 6 "Placing a 500-t asteroid in high lunar orbit would provide a unique, meaningful, and affordable destination for astronaut crews in the next decade."
"These three factors combined suggest the immediate vicinity of the Moon as a reasonable choice. Whatever the final destination the mission must clearly define the end-of-mission conditions and asteroid maintenance and disposal effort (e.g., lunar surface). For the purposes of the trajectory design described later, we assumed a high lunar orbit as the destination for the returned asteroid."
An "affordable destination" is a stable high Lunar orbit in the "immediate vicinity of the Moon as a reasonable choice" which means, not an unstable and distant EML2 orbit.
An asteroid in an unstable EML2 orbit is part of the President's politically unsupported and vague anti-Moon policy with "increasingly demanding targets" that would add significant flight time and risk for Orion missions to captured and hauled asteroids.
Note:
"So I believe it’s more important to ramp up our capabilities to reach -- and operate at -- a series of increasingly demanding targets, while advancing our technological capabilities with each step forward."
From:
REMARKS BY THE PRESIDENT ON SPACE EXPLORATION IN THE 21ST CENTURY April 15, 2010 John F. Kennedy Space Center Merritt Island, Florida
At:
http://www.nasa.gov/news/media/trans/obama_ksc_trans.html Do we want Orion to fly politically devised higher risk and more "demanding" captured asteroid missions to an unstable and distant EML2 orbit or do we want lower risk and quicker missions to a captured asteroid in a stable high Lunar orbit?
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#76
by
KelvinZero
on 21 Apr, 2013 04:09
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Im confused.
Both the recent Keck report and the recent nasaspaceflight article seem to be discussing using a High Lunar Orbit.
(which btw is very cool, if just for the view)
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#77
by
sdsds
on 21 Apr, 2013 06:08
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The advantage of the high lunar orbit is that the asteroid stays firmly bound within the Moon's sphere of influence. No small perturbation would lead to the asteroid leaving the vicinity of the Moon, thus it can't come crashing into the Earth.
(The Obama speech in 2010 was not about bringing asteroids into the Earth's vicinity.)
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#78
by
Robert Thompson
on 21 Apr, 2013 08:13
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The advantage of the high lunar orbit is that the asteroid stays firmly bound within the Moon's sphere of influence. No small perturbation would lead to the asteroid leaving the vicinity of the Moon, thus it can't come crashing into the Earth.
How stable is HLO wrt mascons?
How much station keeping compared to EML2?
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#79
by
Proponent
on 21 Apr, 2013 08:35
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In the Keck study, the asteroid did not leave HLO over a twenty-year period with no station keeping at all. Of course, some station keeping might be still desirable if rendezvous with an Orion is planned.
I'm pretty sure, by the way, that in HLO the dominant perturbations come from the sun and the earth, not from mascons. The further you are from a body, the less important are its deviations from spherical symmetry.
Staying at lunar L2 requires on the order of 10 m/s per year (see the attached presentation), depending on the strategy chosen and the precision needed
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#80
by
Robert Thompson
on 21 Apr, 2013 12:35
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#81
by
Chris Bergin
on 25 Apr, 2013 18:12
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#82
by
Hop_David
on 25 Apr, 2013 19:05
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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!
Allowing an object at EML1 or 2 to fall to the moon will generally result in an orbit with a 60,000 km apolune and 4,000 km perilune. This lunar orbit with a 32,000 km semi-major axis is only a nudge away from either EML1 or EML2 (the apolune can pass near both since it's in a rotating frame)
In orbital sims the closest orbit I can get that lasts 20 years is a 38,000 km apololune and 4000 km perilune. I guess that's about a 21,000 km semi major axis.
Get the apolune much higher and the orbits seem short lived. If rock sails through EML1 at apolune, it will tend to fall into a 100,000 km x 300,000 earth orbit that is periodically perturbed by the moon.
If the rock sails through EML2 at apolune, it generally sails to a 1.8 million km apogee. SEL1 and 2 are 1.5 million kilometers from earth, so if the apogee is near either of these two, it can sail out of earth's sphere of influence altogether.
Not conclusive, but that's my experience.
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#83
by
Chris Bergin
on 31 Jul, 2013 15:14
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RELEASE 13-240
NASA Completes First Internal Review of Concepts for Asteroid Redirect Mission
NASA has completed the first step toward a mission to find and capture a near-Earth asteroid, redirect it to a stable lunar orbit and send humans to study it.
In preparation for fiscal year 2014, a mission formulation review on Tuesday brought together NASA leaders from across the country to examine internal studies proposing multiple concepts and alternatives for each phase of the asteroid mission. The review assessed technical and programmatic aspects of the mission.
"At this meeting, we engaged in the critically important work of examining initial concepts to meet the goal of asteroid retrieval and exploration," said NASA Associate Administrator Robert Lightfoot, who chaired the review at the agency's headquarters in Washington. "The agency's science, technology and human exploration teams are working together to better understand near Earth asteroids, including ones potentially hazardous to our planet; demonstrate new technologies; and to send humans farther from home than ever before. I was extremely proud of the teams and the progress they have made so far. I look forward to integrating the inputs as we develop the mission concept further."
In addition to the internal reviews of concepts for the mission, managers also discussed the recently received more than 400 responses to a request for information in which industry, universities, and the public offered ideas for NASA’s asteroid initiative. The agency is evaluating those responses.
With the mission formulation review complete, agency officials now will begin integrating the most highly-rated concepts into an asteroid mission baseline concept to further develop in 2014.
The asteroid redirect mission is included in President Obama's fiscal year 2014 budget request for NASA, and leverages the agency's progress on its Space Launch System rocket, Orion spacecraft and cutting-edge technology development. The mission is one step in NASA's strategy to send humans to Mars in the 2030s.
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#84
by
Khadgars
on 14 Aug, 2013 17:34
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#85
by
JohnFornaro
on 14 Aug, 2013 18:51
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Good catch. Threw an eyeball over it.
There are more than twelve qualifications governing the feasibility of the twelve candidates "already" identified.
But hey: It's a start. I suppose they'll need more money?
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#86
by
rayleighscatter
on 23 Apr, 2014 23:11
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I was thinking about EM-2 today and that the mission commander would almost certainly have to be from among the current active astronauts. I noticed though that there's only 1 former shuttle commander still active (Scott Kelly) and I'd have to think he'd be at his permissible radiation limit after the year long ISS mission.
This would be the first manned flight of a new vehicle without an experienced commander since Mercury. That is unless they consider ISS commanders or future commercial crew flight commanders. I wonder if ISS command and launch vehicle command are considered that similar?
