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#240 by JohnFornaro on 12 Apr, 2013 14:21
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This is why beneficent Providence has created lawyers and diplomats.
Win The Future? I thought they just evolved from the primordial ooze. -
#241 by JohnFornaro on 12 Apr, 2013 14:23
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I'm curious if the capture mechanism could also be used to remove spent upper stages from earth orbit to help mitigate orbital debris. Any comments on if that would be a good dual use of the technology developed if this goes forward?
Good idea and commercial companies are probable already working on that. Also on how to reuse that material in space ( repurpose )
The capture part might come in in different concepts for different items.
The SEP could be refueled.
NASA doesn't have a mandate to do this, and the USG has no need for repurposing those stages. -
#242 by JohnFornaro on 12 Apr, 2013 14:35
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What's the TRL on that Anthropomorphic Kinetic Impactor Tool?
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#243 by Robotbeat on 12 Apr, 2013 15:10
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What's the TRL on that Anthropomorphic Kinetic Impactor Tool?
Apollo heritage.
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#244 by JohnFornaro on 12 Apr, 2013 15:27
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#245 by Eric Hedman on 14 Apr, 2013 04:35
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I talked with my congressman Jim Sensenbrenner today, who is on the house science committee, about this idea. I asked what he thought of it. If his opinion is any indication of the rest of the committee and Congress as a whole, NASA and the White House need to do some serious convincing that this is a good idea. Has anyone else heard from their member of Congress on this?
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#246 by Robotbeat on 14 Apr, 2013 04:43
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Eric: Except for a few cases (Like Rep. Rohrabacher who actually supports leveraging the private sector more in spaceflight, which you'd think ALL the pro-space Republicans would support, but don't) the Republican Senators support the Moon (if they support ANY space-related stuff), and the Democrats support whatever the administration says (or, if they're in NASA HSF areas, like Florida or Texas, then they are pro-SLS and pro-Orion). Or, again, they don't care.
...But I think this hits on one of the drawbacks of ANYTHING new that sounds cool and interesting coming from NASA these days: Even if it means no new money, it will /look/ expensive. That looks bad if you're in a budget-cutting environment where seniors (etc) are being asked to make cuts. -
#247 by Eric Hedman on 14 Apr, 2013 04:52
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Eric: Except for a few cases (Like Rep. Rohrabacher who actually supports leveraging the private sector more in spaceflight, which you'd think ALL the pro-space Republicans would support, but don't) the Republican Senators support the Moon (if they support ANY space-related stuff), and the Democrats support whatever the administration says (or, if they're in NASA HSF areas, like Florida or Texas, then they are pro-SLS and pro-Orion). Or, again, they don't care.
Chris:
...But I think this hits on one of the drawbacks of ANYTHING new that sounds cool and interesting coming from NASA these days: Even if it means no new money, it will /look/ expensive. That looks bad if you're in a budget-cutting environment where seniors (etc) are being asked to make cuts.
I think you're right. I was at my representative's town hall meeting today. He go lots of questions on Social Security, Medicare, Obamacare, Sequester, Gun rights/control, etc. Which begs the question, how hard will the administration fight for this plan if at all? Will it get funded? I don't know. -
#248 by Robotbeat on 14 Apr, 2013 04:58
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Right, all those things are 100 times more important for everyone not in a space district, even with the "oh no, asteroids!" angle.Eric: Except for a few cases (Like Rep. Rohrabacher who actually supports leveraging the private sector more in spaceflight, which you'd think ALL the pro-space Republicans would support, but don't) the Republican Senators support the Moon (if they support ANY space-related stuff), and the Democrats support whatever the administration says (or, if they're in NASA HSF areas, like Florida or Texas, then they are pro-SLS and pro-Orion). Or, again, they don't care.
Chris:
...But I think this hits on one of the drawbacks of ANYTHING new that sounds cool and interesting coming from NASA these days: Even if it means no new money, it will /look/ expensive. That looks bad if you're in a budget-cutting environment where seniors (etc) are being asked to make cuts.
I think you're right. I was at my representative's town hall meeting today. He go lots of questions on Social Security, Medicare, Obamacare, Sequester, Gun rights/control, etc. Which begs the question, how hard will the administration fight for this plan if at all? Will it get funded? I don't know.
I doubt the Administration will fight hard to support it, it's not worth the political capital; and the plan is to keep funding levels basically flat (with this plan partially being chosen because it's something theoretically possible with flat budgets). Since it keeps Orion and SLS alive and even with a purpose, it is possible it could have the support of some space district folks, at least the Democrats (like Nelson), unlike FY11 which the space district folks hated. I'd be surprised if it totally passed, though. -
#249 by a_langwich on 14 Apr, 2013 06:37
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Quote from: Langwich
The TRL levels of the hardware mentioned in the paper are said to be at TRL 6 or better. Which specific parts are you concerned about?
Uhhhh.... These?It will probably come as a surprise to some that the asteroid capture mechanism itself is "assumed" to be at TRL6. As is DSH, ECLSS, 40 kW class SEP, and more.
More? "reliable robotic anchoring capability"; "Structural characterization, especially of the surface layers"; "dust levitation and settling behavior [mitigation thereof]"; "gravity tractor (GT) concept"; "Proximity operations"; "extraction and purification of water"; "autoreduction of the major mineral magnetite"; "using the released CO as a reagent for the extraction, separation, purification, and fabrication of iron and nickel products". All of these assumed to be at TRL6. No exceptions given.
After re-reading the paper, I misunderstood what it was saying about TRL 6. As you said, it's not a claim, it's an assumption they used for the cost estimates. SEP and the capture mechanism are included in this assumption. I don't see the SEP being a problem, it seems a modest enhancement of current production hardware, clustered together. There's no doubt the actual capture operation is risky, but I don't see any problems building the hardware. You are talking about billions of dollars to design this? The design presented can be executed in a straightforward manner. If you want to test it, capturing can be tested in LEO or GEO using a dead satellite, for much less than a billion.
DSH, ECLSS, anchoring capability, gravity tractor, autoreduction, extraction/purification of water, are outside the scope of this project. Even at that, whatever project does include the ones besides DSH and ECLSS will not assume TRL-6: the point of such a project at this asteroid would be to DEVELOP those technologies, not to depend on their maturity.
The only mentions of manned missions in the Keck report are described as strictly notional possible applications once the asteroid is available: it's like a car salesman saying once you possess one, a minivan could be used to get groceries, go on vacations, take kids to school, etc. You don't then fault the salesman for not including the price of groceries, vacations, and schooling in the price of the vehicle. Criticizing a report detailing an unmanned asteroid capture program for not including the entire budget of the manned program is just not getting it.
The most critical piece of the timeline is starting to characterize and identify NEAs, and that's the piece in next year's budget. Virtually everybody agrees it needs to be done, although various groups strongly believe NASA should give them the money to get the job done.Quote from: JohnFornaroNice handwave about how a "capture" isn't a "capture".
I suppose I didn't word it clearly: the question is who is doing the capturing, the ~15 tonne object, or the ~500 tonne object? Where does the 500 tonne asteroid go? Wherever the hell it wants to, with very minor and persistent respectful suggestions from our little spacecraft and thrusters. The desired end result is a capture, but at the start the asteroid is dictating the speed, direction, and rotation. Point is, one of the connotations of "capture" is that the captor is dictating the terms, whereas in this case the captive has a lot of weight to throw around.Quote from: JohnFornaroQuote from: LangwichWe are talking the 2021-2025 time frame...how many events in 2021 have you planned out in detail?
Nice ad hominem. Somehow my personal schedule pertains to the accomplishment of this mission?
It's not an ad hominem. And it's not about the accomplishment of the mission, but about the impracticality of making precise plans about something so far in the future. Change is certain. There is nothing wrong with not having detailed plans for 2021...and that's the point.Quote from: JohnFornaroThis mission, properly costed, is probably closer to $46B than to $2.6B. Above, I've included some of the line items that have not yet been discussed, but which have been deliberately handwaved away, while deceiving policymakers about the accurate costing and feasibility of the asteroid retrieval mission.
Re: $46 billion...You're a loonie! Now THAT'S an ad hominem.
I don't know if lawmakers have been deceived: right now they are funding some astronomy to characterize NEAs. And that's what they'll be getting. In the future, they may choose to fund an unmanned asteroid capture and retrieval mission. Separately, they have chosen to fund the development of the SLS launcher, and Orion capsule, and they are getting said development. That development is planned to include several test flights, demonstrating expanding capability, one of which has repeatedly been mentioned to include flying toward/around the moon. If the asteroid is at the moon then, that mission might well visit the asteroid. If NASA wants to use a DSH to visit the asteroid, then NASA may choose to ask for funding, but that hasn't happened and is just one of several possibilities. If NASA wants to develop ISRU gear to be tested by a manned or unmanned mission, and it is costly enough not to stick in their normal tech development programs, then they may ask for that too.
If the asteroid were in place by EM-2, that mission almost certainly would not include a DSH, in the same way Apollo 8 did not include a LEM. In that case, trips to the asteroid might be used to inform the design of the DSH, or material from the asteroid might be used to augment shielding of a later-produced DSH. Even without a DSH, or even without SLS, or even without a manned space program, the asteroid would provide valuable opportunities, though obviously its value and the ability to take advantage of it increase with each of those.QuoteDid they mention that the asteroid is "unique"? Yeah. Here: "There are roughly a hundred million NEAs approximately 7-m diameter".
The paper characterized the situation with asteroids pretty well, I thought: lots of them, few well known, and the search is for one with extremely specific characteristics. The initial part of the project is to start identifying and characterizing NEAs, looking for the desired properties. (Recognizing that those without the desired properties for this mission are still interesting for other reasons.)
Because our ability to move heavy objects far from earth is limited, we are looking for one in a precise orbit. It needs to share a very similar orbit to earth's, periodically slowly approaching the earth, and whose synodic period needs to be such that we can observe it when it's close on one approach and have a second approach a few years later around the time the spacecraft reaches it. The spacecraft will nudge that close approach just enough closer for lunar capture.
In addition to its orbit, the authors specify a particular composition, a carbonaceous C-type asteroid. Finding such an asteroid (right orbit, right size, right composition) should not be hard given plenty of time, but as you try to compress the timeline, it becomes very hard to impossible. I say impossible now, because the example they chose, NEA 2008 HU4, cannot be brought to the moon much before 2026, as I understand it. (And we have no idea whether it is C-type.) To make 2021, the spacecraft would need more thrust/coast time, such that it should have already started by now. So we'd need another candidate that has a close approach in 2021, and AFAIK there isn't one known right now. We can find one, but that takes time, and as time goes on the available synodic periods is dropping (eight years or less now, seven years or less next year, for a 2021 capture), and the possible thrust/coast time is getting less.
That's the problem to tackle now, and it seems to me 2025 is ambitious.
They mention another approach, picking one of the larger 100m better characterized asteroids and grabbing a 7m rock from it, or scooping up ~500 tonnes of material from it. I'm not sure that approach has as much synergy with the manned program. The need to accomplish most of the science at the 100m asteroid grows, and the usefulness of the return product for ISRU/extraction/attachment/deflection is a bit diminished. That mission starts to look like an unmanned visit to an asteroid, with a very large sample return by virtue of the use of the high lunar orbit. -
#250 by JohnFornaro on 14 Apr, 2013 15:37
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After re-reading the paper, I misunderstood what it was saying about TRL 6. As you said, it's not a claim, it's an assumption they used for the cost estimates.
Exactly.
The technique that they are using is to get the mission camel toe into the funding tent with the seduction of lowballing the cost estimate as a necessary first step. They have already achieved this in part, with $105M being included in Mr. O's budget proposal. There is a full court press to get this mission approved, as is being demonstrated in the press. The recent puyblic outreach video is part of the effort. Interestingly enough, it demonstrates that NASA can perform public outreach when it desires.
Should this mission end up in the next NASA authorization act, it would be less likely to be canceled from that point onward. As has been demonstrated over and over again regarding huge NASA programs, actual mission accomplishment would not necessarily be required, particularly since the promised delivery date is so far into the future.Quote from: LangwichSEP and the capture mechanism are included in this assumption. I don't see the SEP being a problem, it seems a modest enhancement of current production hardware, clustered together. There's no doubt the actual capture operation is risky, but I don't see any problems building the hardware. You are talking about billions of dollars to design this? The design presented can be executed in a straightforward manner. If you want to test it, capturing can be tested in LEO or GEO using a dead satellite, for much less than a billion.
It is certainly a fair debate point to argue about how readily a 40kW SEP tug can go thru DDT&E. Yes, I'm suggesting a "few" billion dollars to achieve this. It would be interesting to hear your suggestions as to the cost of this crucial subsystem. While I am sure, in my inccocence, that the SEP system could be "executed in a straightforward manner", in my ongoing criticism of this mission prioritization, I am certain that this is an "optimistic" view of how the SEP tug would be developed and implemented.
Clearly, the reality of a "bag" on the non-tumbling asteroid depicted in the PR video exists only in the imagination of the video producers. The video clearly depicts that the "Basic principles [have been] observed and reported". Five more to go.
As an aside, as of today, per the video, they have already ruled out these technologies: "dust levitation and settling behavior [mitigation thereof]"; "Structural characterization, especially of the surface layers"; "gravity tractor (GT) concept"; "extraction and purification of water"; "autoreduction of the major mineral magnetite"; "using the released CO as a reagent for the extraction, separation, purification, and fabrication of iron and nickel products". Presumably these costs would be borne elsewhere.
Here's one example of how they are already moving goalposts around. The "structural characterization of the surface layers" would take place on the bag modified asteroid after delivery to lunar orbit. The Keck report implies that this is important science, but would not study these characteristics in situ. The astros would find out about the asteroid by applying their anthropomorphic kinetic impactors to the bag's contents.
If it is true that "the point of such a project at this asteroid would be to DEVELOP those technologies, not to depend on their maturity", then, in an honest estimate, these development costs would be included. They are not. Their intent is to pull a JWST, and the Keck Kids are well on the way to pulling it off. This mission will be the next unmanned mission to drain financial resouces from the other unmanned missions, including, for example, MSR.
These following capabilities, "reliable robotic anchoring capability" and "Proximity operations" would be achieved by the bag and the necessary orbital mechanics requiring the spacecraft to sneak up behind the asteroid in order to nudge it back to the lunar orbit.Quote from: LangwichThe only mentions of manned missions in the Keck report are described as strictly notional possible applications once the asteroid is available: it's like a car salesman saying once you possess one, a minivan could be used to get groceries, go on vacations, take kids to school, etc. You don't then fault the salesman for not including the price of groceries, vacations, and schooling in the price of the vehicle. Criticizing a report detailing an unmanned asteroid capture program for not including the entire budget of the manned program is just not getting it.
The analogy fails. But here's how the failure is corrected.
It's like the car salesman saying that he will design and build you a minivan of unknown cost for one use only, picking up a rock from across the country and bringing it back to the outskirts of your town, where you can get on an as yet non existant bus and go see it. He assures you that the rock will be very interesting, and well worth the cost of the minivan, and the bus ticket, even if you must wait for a decade to get the rock.Quote from: JFNice handwave about how a "capture" isn't a "capture".
Quote from: LangwichI suppose I didn't word it clearly: the question is who is doing the capturing, the ~15 tonne object, or the ~500 tonne object?
Surely it is clear which is doing what. The fifteen ton bag and SEP thingy are to be capturing a 500 ton non-tumbling asteroid. -
#251 by Warren Platts on 14 Apr, 2013 18:51
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Their intent is to pull a JWST, and the Keck Kids are well on the way to pulling it off. This mission will be the next unmanned mission to drain financial resouces from the other unmanned missions, including, for example, MSR.
Not going to happen: the Science Directorate isn't going to touch this thing with a 10 foot pole. It would have to come out of the HSF exploration budget. -
#252 by Robotbeat on 14 Apr, 2013 20:03
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SMD may be okay with some coordination vis a vis the survey portion and a few other parts with genuine scientific payback and "synergy" (gag at that word), but you're right. SMD would be really, really ticked off if they're made to bear a large part of the financial cost of this.Their intent is to pull a JWST, and the Keck Kids are well on the way to pulling it off. This mission will be the next unmanned mission to drain financial resouces from the other unmanned missions, including, for example, MSR.
Not going to happen: the Science Directorate isn't going to touch this thing with a 10 foot pole. It would have to come out of the HSF exploration budget.
The budget seems to spread the cost pretty widely, though, across the HSF areas. -
#253 by yg1968 on 14 Apr, 2013 23:24
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Here is Jon's viewpoint on this new mission:
http://moonandback.com/2013/04/11/a-change-of-heart-in-neo-size-of-interest/ -
#254 by a_langwich on 15 Apr, 2013 11:07
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The technique that they are using is to get the mission camel toe into the funding tent with the seduction of lowballing the cost estimate as a necessary first step.
The mission camel toe, eh? Hahaha.QuoteThey have already achieved this in part, with $105M being included in Mr. O's budget proposal. There is a full court press to get this mission approved, as is being demonstrated in the press.
The $105M included for the next year, insofar as it is used for the astronomy, can really stand on its own. It informs planetary situational awareness, planetary/solar system science, commercial mining organizations, and any missions interested in small NEAs. If the ACR mission never happens, that research will still be very valuable.QuoteIt is certainly a fair debate point to argue about how readily a 40kW SEP tug can go thru DDT&E. Yes, I'm suggesting a "few" billion dollars to achieve this.
The Boeing 702 satellite, available now, uses 4.5kW Xenon thrusters that have an ISP of 3800s. I have no doubt this is not the largest possible thruster Boeing could have built, it is probably matched to the size of the solar arrays of the satellite. The AEHF also has thrusters in that power range. This asteroid project proposes to use five 10kW thrusters at 3000s ISP. There have been lab demonstrations of more powerful systems. If imagination utterly failed, they could simply use 12 4.5kW Boeing thrusters in a cluster. Off the shelf, with multiple failure redundancy. The power subsystem to drive the thrusters was of more concern to Keck Institute team. But it, too, can be subdivided. There are good reasons to prefer a design with fewer components, but again if for some reason you can't scale up, you can cluster.QuoteClearly, the reality of a "bag" on the non-tumbling asteroid depicted in the PR video exists only in the imagination of the video producers. The video clearly depicts that the "Basic principles [have been] observed and reported". Five more to go.
As I said, if NASA managers are uncomfortable with the risk of the capture operation after running simulations (that was good enough for MSL), they could launch and test on a tumbling inoperative satellite. Or you might be able to work up some sort of model analog to test in the NBF.QuoteIf it is true that "the point of such a project at this asteroid would be to DEVELOP those technologies, not to depend on their maturity", then, in an honest estimate, these development costs would be included.
No. The Keck report makes very clear what its scope is, and that scope is asteroid capture and retrieval. If / when we decide to do one or more of those notional applications, they can be funded, and the asteroid will be very helpful. But those projects wouldn't get under way for another decade, and we might choose to do some and not others. It's conceivable some of those might be done using X-Prize like funding of commercial groups, if the Lunar X-Prize pans out.Quote
They are not. Their intent is to pull a JWST, and the Keck Kids are well on the way to pulling it off. This mission will be the next unmanned mission to drain financial resouces from the other unmanned missions, including, for example, MSR.
Really? You really think people are out there wanting and scheming to go way over budget?
Regardless, the "other unmanned missions" largely fall under science, and if NASA decides to fund ACR from the science budget, I think they'll run into fierce opposition. The science part of this, IMO, is less competitive than the opportunities for technology development.
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#255 by JohnFornaro on 15 Apr, 2013 13:10
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This asteroid project proposes to use five 10kW thrusters at 3000s ISP.
As I said, it is certainly a fair debate point to argue about how readily a 40kW SEP tug can go thru DDT&E. I also mentioned that the reality of a "bag" on the non-tumbling asteroid depicted in the PR video exists only in the imagination of the video producers. Maybe the engineers could work up a model, and eventually attempt to grab a tumbling sat in LEO, if they should get funding. Right now, asteroid bag capture exists only in a video. I assume that's TRL1.Quote from: LangwichThe Keck report makes very clear what its scope is, and that scope is asteroid capture and retrieval.
That's technically true. As Jon Goff mentioned:Quote from: Jon GoffBut somewhere along the process, that idea seemed to go off the rails. Instead of NEOs being a quick "target of opportunity" that could be visited cheaply along the way to the Moon and eventually Phobos, Deimos, and Mars, you started seeing concept architectures coming out of NASA for these massive NEO mission stacks complete with four or five new pieces of expensive in-space hardware that needed to be developed (a Hab module, an MMSEV, a CPS, a big solar electric tug or two, etc, etc) just to visit a NEO.
I would agree that the Keck Kids have limited their "estimate" to asteroid capture and retrieval, assuming the pre-existence of a great number of other expensive items.
Do you have a cost estimate for the "four or five new pieces of expensive in-space hardware that need[ed] to be developed?"
Why is it not necessary to consider these costs when discussing the immediate prioritization of this mission, without necessary support funding, as evidenced in its inclusion in the President's budget proposal for NASA?Quote from: LangwichReally? You really think people are out there wanting and scheming to go way over budget?
Really? You believe that the costs of this mission, whose main component is a solid TRL1, will be $2.6B, and that the money for the other things will just "appear"?
What flavor kool aid do you recommend? -
#256 by R7 on 15 Apr, 2013 18:01
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I also mentioned that the reality of a "bag" on the non-tumbling asteroid depicted in the PR video exists only in the imagination of the video producers. Maybe the engineers could work up a model, and eventually attempt to grab a tumbling sat in LEO, if they should get funding.
also in the budget thread:the NASA video, which is the only "source" out there today, shows the bag approaching a non-tumbling asteroid. No other devices are shown in the video; the de-tumbling maneuver is merely "assumed" by the producers of the video. The Keck Kids assert that they will capture and detumble the asteroid, in that order, on page 28. The video clearly shows that they will detumble and then capture the asteroid. Somebody's going to have to decide how they want to proceed.
Look at the star field for cues on the video from 1:25 onwards. The video does not depict bagging non-tumbling asteroid, but situation where the bagger-craft has positioned itself on asteroid's spin axis (sensed using laser ranging, the preceding green beams) and then spins itself up to match asteroid's spin (logically using RCS). The bagger sees stationary asteroid, and rest of the universe rotating around it. When asteroid is secured in the bag RCS is used to spin down the combo (from 2:00 onwards in the video). -
#257 by JohnFornaro on 15 Apr, 2013 18:54
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Look at the star field for cues on the video from 1:25 onwards. The video does not depict bagging non-tumbling asteroid, but situation where the bagger-craft has positioned itself on asteroid's spin axis (sensed using laser ranging, the preceding green beams) and then spins itself up to match asteroid's spin (logically using RCS). The bagger sees stationary asteroid, and rest of the universe rotating around it. When asteroid is secured in the bag RCS is used to spin down the combo (from 2:00 onwards in the video).
I did look at that before I posted. It's a matter of judgement, but the Keck paper "assumes" one rpm; in the video I do not see one rpm. Furthermore, the video asteroid would have only a primary spin axis; the solar panels are not retracted as mentioned in the Keck paper; other tumbling axes are not at all considered.
The mission profile per the Keck paper is a one shot deal. There's plenty of time to characterize the spin of one asteroid, but no means to find another if the "cooperative" aspects of the chosen asteroid do not, well, cooperate.
Of the hundred million candidates, they must find the "lazy" asteroid first; yet another cost, hand waved away by the political insiders who push this mission.
Also note that they plan to shut down comm with the bagger droid until its rate of rotation settles down to allow resumption of a comm channel with Earth. -
#258 by R7 on 16 Apr, 2013 06:26
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only a primary spin axis; the solar panels are not retracted as mentioned in the Keck paper; other tumbling axes are not at all considered.
Could the NEO candidates still tumble wildly enough to foil the mission? AIUI tumbling is not stable over longer periods.QuoteThe mission profile per the Keck paper is a one shot deal. There's plenty of time to characterize the spin of one asteroid, but no means to find another if the "cooperative" aspects of the chosen asteroid do not, well, cooperate.
If an asteroid says no it means ... well just ram the bagger at it and hope for the best Seriously, before the video came out I thought the plan is to do just that, ingest a tumbling asteroid into the bag, start tightening it and let friction forces sort out which way the (well padded! 
) spacecraft starts rotating.QuoteOf the hundred million candidates, they must find the "lazy" asteroid first; yet another cost, hand waved away by the political insiders who push this mission.
Is there even a way to measure spin rates of objects that small millions miles/kms away?QuoteAlso note that they plan to shut down comm with the bagger droid until its rate of rotation settles down to allow resumption of a comm channel with Earth.
No some sort of low-bandwidth omnidirectional backup? -
#259 by alexterrell on 16 Apr, 2013 10:50
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Is there even a way to measure spin rates of objects that small millions miles/kms away?
Yes, in most cases, if you can see it and measure the magnitude, you should be able to measure the spin from the magnitude oscillation, unless it is very, very uniform, or very very slow.
You never read Rendez-vous with Rama?
) spacecraft starts rotating.