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#260 by JohnFornaro on 16 Apr, 2013 13:41
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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.
1) 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 ...
2) 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.
3) 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.
4) No some sort of low-bandwidth omnidirectional backup?
1) IDK. Spin is not the only issue; there are also orbital characteristics. Ideally, the candidate will be the right size, right type, and already be on a trajectory headed to Earth at the time of the capture. The spacecraft will go "behind" it, spin itself to relative stability with the rock's major spin axis, then bag it.Quote from: KeckTo 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.
2) Of course, if the object has any spin around its long axis, most bets are off. They hope to find a perfectly thrown "football". A key factor for their success will be the hunt.
3) This is the opportunity for the Arkyd fleet to strut its stuff. Note that the characteristics of the video asteroid are not quite the same as mentioned in the paper. Subsequent marketing videos are expected to correct this issue.
4) IDK.
Juist revisiting my issues about the cost estimate:Quote from: KeckThe large mass of the captured asteroid and relatively low thrust available from the Hall system, require that the spacecraft + asteroid must have the delta-V necessary to target the lunar gravity assist well before the lunar encounter. This requirement, which appears feasible, is not unlike the requirement of the Dawn mission...
Except that they assume the reader won't notice that the Dawn mission didn't deal with a 500 ton (or 1100 ton, depending on their "margin") object. Which kinda makes ya wonder what they mean when they say "not unlike".
But what happens when they get the bag to, well, Bag-End?Quote from: KeckAdditional work still remains for the preliminary design of final insertion operations and the final asteroid parking orbit. ... For a long duration solution, a propellant resupply or an additional propulsion stage after Earth arrival may be required depending on the outcome of the detailed stability analysis.
Did you say that you wanted the asteroid in a stable orbit? Oh. That's going to cost a bit more. The twenty year "retirement" plan to keep it in a stable orbit.Quote from: KeckIs a parametric estimate based on mostly mass-based Cost Estimating Relationships (CERs) using historical cost data.
IOW, they've already got a spreadsheet on asteroid bags; plug in the mass and boom -- "historical" cost data comes out. Trust them. They've got costs covered.
Their mention of the Stewart Platform is an interesting suggestion of a "solution" which again depends completely on the tumbling rate and geometry of the asteroid. I imagine it would have to be about 6m in diameter to have enough moment arm to accomodate tumbling. It would be between the thrusters and the spacecraft body. It basically mimics an exotic dancer's hip movements:
There's a poster here who complains bitterly about the TRL argument. It's not seen by him as having any validity whatsoever on the feasibility of this mission.
What's TRL-6 like, the casual observer might ask. How about solar sails?
Solar sail technology within NASA is currently at 80% of TRL-6, suitable for an in-flight technology demonstration.
That was in 2010. Next year, they expect a TRL of 9:
http://www.parabolicarc.com/2013/02/26/nasa-sunjammer-solar-sail-set-for-launch-next-year/
As I keep saying, there's no question but that the technology can be improved. With enough money (the UBS), I'm sure they can bring the bag from TRL1-3, up to 9. Note that TRL doesn't tell the whole story either. The solar sail might very well fly as a secondary payload on an F9, but it is not equipped to do the work that its proponents hope for. It will be a demonstration mission only. TRL levels only get ya but so far.
There's no principled problem with doing a demo "bag" mission, but they always precede the "real" missions by a number of years. The Keck paper makes no realistic projection of how they would proceed. The paper is designed to get only the first $2.6B, falsely promising that is the entire cost of the final object. It is not, by any stretch.
Don't get me started on the TRL6 "snowblower". -
#261 by R7 on 16 Apr, 2013 18:22
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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?
Alas, so long ago I seem to have forgotten the technical details...
Apparently radar is also good to a certain extent. -
#262 by alexterrell on 17 Apr, 2013 13:46
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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?
Alas, so long ago I seem to have forgotten the technical details...
Apparently radar is also good to a certain extent.
Radar might be good for a near object, but the reflection strength decreaes with the fourth power of distance.
A laser would work but would need to be set up - where as determining rotation rates is something astronomers do all the time with regular telescopes.
In Rama, they discovered a large object on a hyperbolic trajectory. They could detect no spin. Then, using more powerful telescopes they found a very slight magnitude fluctuation, which showed a spin rate giving approx -1g at the equator. -
#263 by Hop_David on 17 Apr, 2013 15:12
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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?
Alas, so long ago I seem to have forgotten the technical details...
Apparently radar is also good to a certain extent.
Planetary Resources hopes to build several generations of Arkyd telescopes. The first generation will be LEO. The third generation Arkyd 300 will leave earth orbit and take a closer look at the most promising candidates.
The Arkyd 300, is also called the Rendezvous Prospector. "Orbiting the asteroid, the Rendezvous Prospector will collect data on the asteroid’s shape, rotation, density, and surface and sub-surface composition."
If NASA's going to work with PR and DSI on this project, Arkyd reconnaissance is one of the first things they should help fund. Voters and taxpayers are already calling for a more complete inventory of Chelyabinsk sized rocks. The Arkyds seem a good way to achieve this goal.
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#264 by JohnFornaro on 18 Apr, 2013 18:26
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If NASA's going to work with PR and DSI on this project, Arkyd reconnaissance is one of the first things they should help fund. Voters and taxpayers are already calling for a more complete inventory of Chelyabinsk sized rocks. The Arkyds seem a good way to achieve this goal.
Pretty much agree with that aspect. -
#265 by JohnFornaro on 19 Apr, 2013 13:35
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This post was Off-Topic where the conversation started, so I post it here instead.
Until we have an extra terrestrial propellant source, there's not much incentive for propellant depots or orbital ferries. And without depots and ferries, there's little reason to invest in mining lunar ice.
Well, you certainly could go for the ice that's ten years away, and not go for the ice that's three or four days away.
Once the rock is at EML2, it will be 8 days and 3.5 km/s from LEO. ... don't hold your breath waiting for landers that'll get humans to the moon's surface....
And the TRL for mining ice at 40 degrees kelvin is better?
That is correct. Once you handwave away the ten year delivery time, you eventually do have water nearby. I'll have a hard enough time holding my breath for those ten years. EML-1, as you know, and as is my preference, is three or four days away. Everytime there could be a proximate destination, you prefer to suggest the distant one.
Even so, the current "plan" is for LLO, also three or four days away.
There's no question about the low TRL of mining lunar ice. The question, that is, the trade, which you continue to overlook, is a full comparison of the two options.
You and I have talked about the limitations of a delta-vee analysis alone, especially regarding the time needed. At this early stage in the "design" of a propellant manufacturing capability, I think it would be fair to grant either approach the same time and money. YMMV.
In the UBS then, it would take, say, ten years to develop either an asteroid based infrastructure or a lunar based infrastructure to deliver water to EML2. And exactly "x" dollars for each system. So now we wait for the water to be delivered. Ten years for "y" tons of water in the one system, and eight days for "y" tons of water in the other.
If the asteroid based system is so good, that it should be preferred over the lunar system, then it had better cost very little. We have already demonstrated sample retrieval from the lunar surface, to the tune of about a hundred pounds with forty year old technology. And we have demonstrated unmanned sample retrieval from an asteroid to the tune of a few grams.
The only reason one of these systems is favored today is because it has presidential favor. The favor was not granted on the basis of practicality, pragmatism, utility, nor cost.
Both Happy Martian and Jim keep pointing out how NASA should obey the "law of the land". The asteroid mission is nearly the law of the land.Quote from: JFOver the ten to twenty years while this first hundred ton demonstration is instantiated, we will learn a lot more about the characterization of the one hundred million some odd candidate asteroids.
Quote from: H_DSuch characterization wouldn't commence with the retrieval of an asteroid. It would start much sooner with the launch of the Arkyd probes. And it would continue during and after retrieval.
Glad we agree here.Quote from: H_DA large part of the first vehicle's price will be design costs. The second, third, and fourth retrieval vehicles would be cheaper. NASA has said it hopes to work with PR as well as DSI. Why would PR sit on its hands all that time? ...
Planetary Resources has said they would reduce cost via mass production. ...
Your imaginary NASA prohibition of reuse is easily debunked. See the reuse of the Themis hardware to study the moon in the
I can't speak as to PRI's business plan, so it would be better for you to ask them where their hands are. Of course, their upcoming Arkyds are expected to cost less. They are a private company, and not beholden to political interests. Furthermore, they have not revealed anything larger than the reconnaisance sat fleets. If you care to speculate about the size and cost of their future retrieval vehicles, it would be interesting to read about.
While we would want to think that NASA's second, third, and fourth vehicles would be cheaper, that remains to be seen. After all, the shuttle's costs never really declined.
There's some talk of NASA using the MSL chassis for a future Mars mission, but that still remains to be seen. There is no stated need for NASA to re-use any hardware for any mission, so not only can I not provide a cite supporting that, I cannot find any data showing declining price curves either.
Themis has indeed demonstrated the small scale value of re-usablility in a mission which had well known fiscal restraint. Themis is a straw, compared to Ares, the DIVH Orion launch, the SLS system, and so forth. You are free to grasp it.
I did inadvertently mis-speak however. There is the un-stated need for NASA to only build one-off missions. Apology issued.Quote from: H_DAnd if there were such a policy, then it would prohibit reusable lunar lander/ascent vehicles. As well as reusable ACES tankers.
The stated policy, since 04-15-10, is no re-usable lunar landers. BTDT. You know this to be true. Just the other day, Mr. Bolden stated, "NASA won't land another man on the Moon in my lifetime". Therefore no ACES landers either. You also know this. It is stated policy of the OP of the other thread!
I guess there's always women. In heels, per Lori Garver's tweet.Quote from: H_DX tonnes of water could have plenty of uses.
While the asteroid retrieval vehicles would use ion engines, they could use chemical to avoid the long slow spiral from LEO to C3=0. The water from the first retrieval would make subsequent retrievals easier.
The water could also be used for tugs that would ferry sats from LEO to GEO, you know the stuff they want to use lunar ice for.
As for leading to human exploration? PR's goal is profitably mine extra-terrestrial resources, not send humans to Mars or elsewhere.
However profitable space exploitation is a prerequisite for human activity beyond flags and footprints publicity stunts. If you like, you can wait for far-sighted governments to build space infrastructure needed for human settlement. Wake me up when you get a bite.
Everybody knows that water is useful. Thanks for the reminder. Of course they could use chemical, as long as mass isn't an issue. How long is the wait for converting the 100 tons of water to propellant? Not the wait from when the plant is operative at scale. The wait from today to the point where the plant opens shop. Where is the funding for this concurrent project development? Plus, how far does one hundred tons of water go to get this imaginary second mission to an icy rock? Or is "X" necessary tons handwaved into existance?
Wake me up when the rock gets here. I'm not holding my breath. -
#266 by HappyMartian on 19 Apr, 2013 16:12
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If NASA's going to work with PR and DSI on this project, Arkyd reconnaissance is one of the first things they should help fund. Voters and taxpayers are already calling for a more complete inventory of Chelyabinsk sized rocks. The Arkyds seem a good way to achieve this goal.
Pretty much agree with that aspect.
Yep.
And if the captured NEO derived propellant and GCR shielding become available in a stable high Lunar orbit along with Lunar polar ice derived propellant and regolith GCR shielded surface habitats, we could have a useful combination to significantly reduce BLEO and Lunar surface mission costs and risks.
Are any of our international space exploration partners seriously interested in human missions to a captured NEO in a high Lunar orbit?
In the short term, is Congress going to be interested in spending the money for developing the eventual high Lunar orbit infrastructure that would be needed, including a DSH and equipment to produce the ISRU propellant and GCR shielding?
Or is Congress going to prefer Lunar polar ISRU missions with our international partners providing the Lander and habitats?
Or are we going to try to do high quality NEO surveys and capture and place a NEO in a high Lunar orbit while also doing international Lunar surface missions at the same time?
What is both doable and affordable? Could three 'nearby' destinations, the International Space Station, DSH/NEO in a stable high Lunar orbit, and a Lunar polar ISRU propellant facility create a much more stable space exploration program than would be the case of having only one or two such destinations?
Could we maintain an international focus on doing propellant ISRU at both BLEO destinations? Would it also be possible to do needed PROFAC research at the ISS?
What could be the options for various private spacecraft to eventually be involved with or lead missions to the high Lunar orbit DSH/NEO?
Could such a 'three destination' space exploration program give private spacecraft other doable and useful destinations instead of just the ISS in LEO?
Could a private company manage the high Lunar orbit DSH/NEO ISRU propellant production facility?
Edited. -
#267 by Hop_David on 19 Apr, 2013 17:33
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You and I have talked about the limitations of a delta-vee analysis alone, especially regarding the time needed. At this early stage in the "design" of a propellant manufacturing capability, I think it would be fair to grant either approach the same time and money. YMMV.
Actually I agree that lunar ice is what we should go for first. I wish we were developing reusable lander/ascent vehicles, landing Bigelow habs at the poles, etc.
I also wish that far sighted governments were funding human settlement of space.
If wishes were horses...
In the mean time I can see a chance of asteroid retrieval leading to use of extra terrestrial propellant. Once we got started on the extra terrestrial propellant habit, it'll be a hard jones to kick. When we have that addiction, the fix stashed in the lunar cold traps will be more interesting.
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#268 by Hop_David on 19 Apr, 2013 18:09
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And if the captured NEO derived propellant and GCR shielding become available in a stable high Lunar orbit along with Lunar polar ice derived propellant and regolith GCR shielded surface habitats, we could have a useful combination to significantly reduce BLEO and Lunar surface mission costs and risks.
NEO propellant in high lunar orbit alone could significantly reduce BLEO and lunar surface mission costs and risks. Instead of 6 km/s from LEO to land a power source or Bigelow hab, it's only 2.5 km/s to the lunar surface.
This could enable putting more massive power sources on the lunar surface, larger volume habs, etc. -
#269 by Hop_David on 19 Apr, 2013 18:39
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The stated policy, since 04-15-10, is no re-usable lunar landers. BTDT. You know this to be true. Just the other day, Mr. Bolden stated, "NASA won't land another man on the Moon in my lifetime". Therefore no ACES landers either. You also know this. It is stated policy of the OP of the other thread!
Focus. You're assertion was:And since there is the stated need for NASA to only build one-off missions, there will not be any re-usable components to this extra terrestrial propellant source infrastructure.
Somehow you have morphed present administration not interested in the moon to No re-usable lunar landers, tankers, no reusable NASA components of any kind EVER.
Sure I'd agree with the former. If the latter were true then there's no point arguing for NEO water or lunar water, as I said. At least not from NASA.
Happily this No Re-Use policy is a figment of your imagination. -
#270 by Hop_David on 19 Apr, 2013 18:51
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In the short term, is Congress going to be interested in spending the money for developing the eventual high Lunar orbit infrastructure that would be needed, including a DSH and equipment to produce the ISRU propellant and GCR shielding?
...
Could a private company manage the high Lunar orbit DSH/NEO ISRU propellant production facility?
Don't know what DSH is. As for maintaining a high lunar orbit NEO ISRU propellant production facility, Planetary Resources has expressed an interest in doing exactly that. They are well funded, founders include Google's Brin as well other deep pocket investors with impressive track records. Bechtel is now working with PR.
I would give PR alone better than even odds of realizing their goals. If they get some help from the government, their chances are even better. -
#271 by aero on 19 Apr, 2013 19:14
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Quote
I would give PR alone better than even odds of realizing their goals. If they get some help from the government, their chances are even better.
Such help could come in several forms. Design of a successful capture/return vehicle is only one. Others are contracting to locate suitable asteroids using their telescope fleet. Contracting for the launch of such fleet. Contracting for close evaluation of candidates. and so forth. -
#272 by JohnFornaro on 19 Apr, 2013 19:34
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The stated policy, since 04-15-10, is no re-usable lunar landers. BTDT. You know this to be true. Just the other day, Mr. Bolden stated, "NASA won't land another man on the Moon in my lifetime". Therefore no ACES landers either. You also know this. It is stated policy of the OP of the other thread!
Focus. You're assertion was:And since there is the stated need for NASA to only build one-off missions, there will not be any re-usable components to this extra terrestrial propellant source infrastructure.
Somehow you have morphed present administration not interested in the moon to No re-usable lunar landers, tankers, no reusable NASA components of any kind EVER.
Plenty of focus, young Paduan. The "Stated Policy" is "No re-usable lunar landers, tankers, no reusable NASA components of any kind". I did not extrapolate from "this administration" to "EVER". "Stated Policies" can change from administration to administration; in principle, the *cough* Ron Paul *cough* administration could go for serious HSF.
True, the stater of that policy added the gratuitous, "not in my lifetime" clause, but this is easily "enforced" by wasting most every dollar NASA gets for HSF for the next three years. The agency promises to be a shadow of its former self in that time.
There may not be a "stated policy" for NASA to only build "one-off" missions, but the instantiation of past missions is probably a reliable indicator of the re-usability for future missions. There is nothing in NASA's charter about this, nor has the government specified a need for re-uability. You know this too.Quote from: H_DHappily this No Re-Use policy is a figment of your imagination.
They are not planning to use the asteroid bagger again. They will build a new, completely different one, if they ever build and use the first one. I've mentioned the possibility that a second Mars mission might use the MSL chassis. MSR will be all new. You cannot provide any cite for the expected re-use of any NASA spaceflight equipment, except possibly the Orion capsule. They are not even going to build the first copy of any of the interesting hardware.
What policy? Me no see Policy. Me make up what Policy must be. You mileage vary. Me wish for pony. -
#273 by Hop_David on 19 Apr, 2013 19:38
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Such help could come in several forms. Design of a successful capture/return vehicle is only one. Others are contracting to locate suitable asteroids using their telescope fleet. Contracting for the launch of such fleet. Contracting for close evaluation of candidates. and so forth.
Quite so.
Since Chelyabinsk, a lot of voters have been urging their congress critters to fund an asteroid search that gives us knowledge of the Tunguska and Chelyabinsk sized rocks as well as dino killers.
Helping finance the Arkyds is the best and most cost effective way to do this, IMO. -
#274 by Hop_David on 19 Apr, 2013 19:45
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Me make up what Policy must be.
Exactly. But you didn't need a wall of text to admit this. -
#275 by KelvinZero on 19 Apr, 2013 21:46
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I dont know why we are debating asteroid collection vs lunar reusable landers.
It isn't this asteroid collection idea that is an obstacle to a lunar architecture. Take this away, you don't get a reusable manned lunar lander.
The moon thread is way too quiet. You want to talk about the moon, do it there to keep it active.
(edit: After going to look at the moon forum, I want to amend that to quiet on any constructive topic.. plenty of wailing and knashing of teeth) -
#276 by a_langwich on 20 Apr, 2013 06:04
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Quote from: Keck
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.
2) Of course, if the object has any spin around its long axis, most bets are off. They hope to find a perfectly thrown "football". A key factor for their success will be the hunt.
No, it doesn't have to be the "perfectly thrown football." It means the capture mechanism design team for this study chose to limit the amount of effort they expended on this detail. An actual detailed design, which is in the budget, would tackle the various what-ifs. They chose this as a test case to design against, not as the only possible solution, nor as the most convoluted problem to work against.
I agree, though, the hunt for a candidate is a key prerequisite. The Keck budget did not include hand-outs for all the companies with clever ideas on how to identify NEAs, but since this is broadly useful, I suspect NASA or NSF may fund more than is strictly needed for the ACR mission. Indeed, the paper mentioned several (all terrestrial IIRC) projects, already funded, coming online by the 2017 time frame which would vastly improve our capabilities.QuoteJuist revisiting my issues about the cost estimate:
Quote from: KeckThe large mass of the captured asteroid and relatively low thrust available from the Hall system, require that the spacecraft + asteroid must have the delta-V necessary to target the lunar gravity assist well before the lunar encounter. This requirement, which appears feasible, is not unlike the requirement of the Dawn mission...
Except that they assume the reader won't notice that the Dawn mission didn't deal with a 500 ton (or 1100 ton, depending on their "margin") object. Which kinda makes ya wonder what they mean when they say "not unlike".
They are clearly referring to trajectory and timing of burns. They aren't assuming the reader won't notice mass differences, they are assuming the reader will be intelligent enough to catch their point about how that mass will make a difference. The thrust/weight ratio will be similarly tiny, in comparison to trajectories calculated using chemical rockets on typical spacecraft (eg planetary probes).QuoteBut what happens when they get the bag to, well, Bag-End?
Quote from: KeckAdditional work still remains for the preliminary design of final insertion operations and the final asteroid parking orbit. ... For a long duration solution, a propellant resupply or an additional propulsion stage after Earth arrival may be required depending on the outcome of the detailed stability analysis.
Did you say that you wanted the asteroid in a stable orbit? Oh. That's going to cost a bit more. The twenty year "retirement" plan to keep it in a stable orbit.
Again, they are saying the detailed analysis included in their budget would refine the numbers. There's no point in getting super-detailed with hypotheticals. The indications are the orbit would be stable for at least 20 years. If NASA screwed up, never did any further analyses to define a more stable orbit, and this orbit decayed quickly for some reason, and they "Skylabbed" it by not boosting, it would crash into the moon. Not great, wasteful, just like Skylab, but no harm done.QuoteThere's a poster here who complains bitterly about the TRL argument. It's not seen by him as having any validity whatsoever on the feasibility of this mission.
I explained why I thought the SEP was very feasible; it is not much larger in size than several commercial options, and smaller than tested experimental designs. For the capture mechanism, I believe the concept is straightforward enough to rapidly advance to the point where it could be responsibly flown. It is a Newtonian mechanics problem. We're not talking space-based nuclear or fusion drives here, just forces and moments on a particular structural design.
Since Bigelow has extensive experience in inflatable structures, perhaps they could also have a hand in building these inflatable rings.QuoteThere's no principled problem with doing a demo "bag" mission, but they always precede the "real" missions by a number of years. The Keck paper makes no realistic projection of how they would proceed. The paper is designed to get only the first $2.6B, falsely promising that is the entire cost of the final object. It is not, by any stretch.
Well, NASA could certainly drag it out and blow billions on ever more detailed tests, but I think a detailed finite element model of the spacecraft and simulation would answer many questions, and then devising an "electric bull" mount to dynamically test the control electronics and subsequently the full spacecraft would take care of most of the rest. Okay, maybe it would be more like a 3D lapidary tumbler than electric bull, but the electric bull seemed more evocative.
The de-spinning task is just attitude control starting with high initial angular velocities. There is some question about how much power your solar panels would produce while spinning, but lower power (above a tiny threshold) just means it takes longer to de-spin. -
#277 by aero on 20 Apr, 2013 07:32
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Quote
The de-spinning task is just attitude control starting with high initial angular velocities. There is some question about how much power your solar panels would produce while spinning, but lower power (above a tiny threshold) just means it takes longer to de-spin.
Attitude control is by chemical thrusters so lack of solar power won't have any effect until the back up batteries run down. Such an event would mean LOM. I don't expect that to happen because of a central mission step, unless there are failures. -
#278 by JohnFornaro on 20 Apr, 2013 12:49
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Me make up what Policy must be.
Exactly. But you didn't need a wall of text to admit this.
Exactly. But you asked for a cite as if it were a statement of documented fact.
Intead of having a policy and even a "flexible path", what NASA provides is an ever changing empty cup of tea leaves, which we must read.
Technically, and legally, it is true that the President stated that the policy of NASA is to go visit a rock, and he has just trumpeted his "mission accomplished" meme for having not deviated from that "policy" for the last three years.
Gone is any rational rationale for an asteroid mission. In fact, there was not much of a discussion as to the justification of this personally chosen policy preference, based on faulty logic. It was presented to the nation and NASA as a non-transparently arrived at done deal, not subject to negotiation or revision.
If you think there's a conspiracy involved, move along, move along.
This is business as usual. Top down direction of policy and goals; made for corporate insider advantage; based on faulty reasoning, false costing, and admittedly incomplete scoping. It is another example of kicking the can down the road.
Pretty much the reason you disregard the body of the text is because there's not a falsehood, nor an illogical construct in it.
Primitive man say: Me see politix as usual. -
#279 by JohnFornaro on 20 Apr, 2013 14:30
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No, it doesn't have to be the "perfectly thrown football." It means the capture mechanism design team for this study chose to limit the amount of effort they expended on this detail. An actual detailed design, which is in the budget, would tackle the various what-ifs. They chose this as a test case to design against, not as the only possible solution, nor as the most convoluted problem to work against.
Exactly.
They simplify their analysis because they're taking a first stab at solving a very difficult problem. They are not working under the UBS at the moment, so they're probably funding this study themselves. Ultimately, the taxpayer will bear the costs. Other than the problem that simplfied analysis leads to low cost estimates, it's a perfectly understandable simplification.
The criterial of "perfectly thrown football" is pretty broad. A wildly tumbling football is hard to catch, but there's a pretty wide range of perfect and wobbly spirals which are relatively easy to catch. The footbal analogy can only go but so far, since the catching mechanism weighs about 200 pounds, and the "asteroid" only about 5 pounds.
Glad you agree with my characterization that they must find the "lazy" asteroid first.
Note that their moment arm is only two thirds of the moment arm of the "study" asteroid. Their analysis suggests to me that they only considered de-spinning in one axis. With this assumption for the sake of a "simple" discussion, then they are saying that with 800 N of thrust, they can stop an 1100 ton asteroid from spinning, starting at 1 rpm, in 33 minutes, using 300 kg of their hypergolic prop.
The asteroid will have some tumble; the RCS system will have to be gimbled or Stewart platformed, and controlled by sensors and software. There's four clusters of four thrusters. No doubt that the problem of despinning the asteroid could be solved. You can see the necessary complexity involved. When you see complexity, you also see cost.
From their budget numbers, they've allocated $223.5M for propulsion systems, of which the RCS system is a part, I'm guessing. Who knows what proportion of that line item pertains to RCS. Again, remember that somebody else is bearing the costs of bringing this novel RCS system to TRL-6.
You can't dig any deeper into the Keck paper than this, however.
From their Figure 6; interesting to note that their science cams, lidar, spectrometer, and all will be inoperative once the bag is deployed. Seems pretty unavoidable in this "pre-decisional" design. Not sayin' that I have a better suggestion. But: Not much science will be done on that rock for the next ten years.Quote from: LangwichThey are clearly referring to trajectory and timing of burns. They aren't assuming the reader won't notice mass differences, they are assuming the reader will be intelligent enough to catch their point about how that mass will make a difference. The thrust/weight ratio will be similarly tiny, in comparison to trajectories calculated using chemical rockets on typical spacecraft (eg planetary probes).
Exactly. They are referring to trajectory and burn timing as you reaffirm. The resemblance to Dawn is only superficial concerning these two requirements. What's not superficial is the mass of an 1100 ton tumbling object, and the resulting necessary cost of retrieving that honker. This, they continue to estimate, holding up instead superficial similarities, which are easy for congress critters to gloss over.Quote from: LangwichAgain, they are saying the detailed analysis included in their budget would refine the numbers. There's no point in getting super-detailed with hypotheticals. The indications are the orbit would be stable for at least 20 years. If NASA screwed up, never did any further analyses to define a more stable orbit, and this orbit decayed quickly for some reason, and they "Skylabbed" it by not boosting, it would crash into the moon. Not great, wasteful, just like Skylab, but no harm done.
Again, you're exactly right about the endgame, "wasteful, just like Skylab", and the resulting harm depends on these two terms, not upon the un-liklihood of another spectactular fireball over Chelyabinsk.
I'm suggesting that the "refinement of the numbers" to only get the rock to Bag-End are underestimated by a factor of ten to twenty.Quote from: LangwichI explained why I thought the SEP was very feasible; it is not much larger in size than several commercial options, and smaller than tested experimental designs. For the capture mechanism, I believe the concept is straightforward enough to rapidly advance to the point where it could be responsibly flown. It is a Newtonian mechanics problem. We're not talking space-based nuclear or fusion drives here, just forces and moments on a particular structural design.
Since Bigelow has extensive experience in inflatable structures, perhaps they could also have a hand in building these inflatable rings.
Again, I do not complain about the theoretical technical feasibility. I complain about the false costing, the sketchy prioritization; the timliness; the actual benefit of a hoped for 100 tons of water; yada yada.
You are free to characterize the bag as a "straightforward" concept, but you are compelled to admit that a lunar mission is also a "Newtonian mechanics problem". They all are. Your not too discerning filter admits every mission.
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.