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#200
by
QuantumG
on 30 Dec, 2014 02:26
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I'm not sure that makes any sense. Short synodic periods typically mean higher delta-V (at both ends) to get to/from the asteroid.
Maybe I wasn't clear.. why not change the synodic period
after you visit it, so you don't have to wait so long to visit it again. You're going there anyway...
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#201
by
jongoff
on 30 Dec, 2014 02:34
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You state the same Option B hardware could be used to return samples from Phobos and Deimos. These are much larger than the 100m to 500m asteroids that seem to be the target of Option B.
1. I was curious as to how much of gravity well option B hardware can handle?
It depends on the specific design. You'll definitely be stuck grabbing a smaller boulder. And there's no way you'll be able to leap off the asteroid into escape like you can from something more Itokawa sized. But the same hardware could at least grab something on the order of ~2m diameter (instead of 4m), and jump up high enough for some other form of thruster to take you the rest of the way home. That would only be like 10-15mT for a rocky boulder, but still enough to do some decent ISRU work with (and a lot bigger than you'd get back via any other realistic near-term method).
A group at Langley will be presenting a paper on the concept in about a week. Once they've presented it, I'll see if I can post a link or copy here.
You state a 3.75 m ~90mT design target.
(edit: for potential subsequent missions:)
2. By what factor do you feel this could be somewhat easily scaled up?
3. What are the main hurdles to get to say 500mT or 1k mT?
We'd have to put more structural design work into it to handle a 1000mT boulder, but there's no fundamental reason we couldn't. The surface weight of a 90mT boulder on an Itokawa type asteroid is ~2lb. So for a 1000mT boulder, you'd be talking about 25lb or so, with a diameter around 8.33m (assuming a spherical boulder of 3300kg/m^3 density). The arms would need to be about twice as long.
If I were trying to do something that big, I'd try to do a hybrid of the concept we're doing, and the TALISMAN concept from NASA LaRC. I'm pretty sure we could make a design that size close that could realistically be launched on say a Delta-IVH or maybe FH.
We were just given a much more modest design point to shoot for.
~Jon
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#202
by
jongoff
on 30 Dec, 2014 02:41
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I'm not sure that makes any sense. Short synodic periods typically mean higher delta-V (at both ends) to get to/from the asteroid.
Maybe I wasn't clear.. why not change the synodic period after you visit it, so you don't have to wait so long to visit it again. You're going there anyway...
You'd probably have to apply a much higher delta-V to move a typical asteroid into on with a synodic period that would allow a fast follow-on than you would to return a boulder or an asteroid to lunar orbit. I could be wrong, but it just seems like a backward way to solve the problem.
Really there's only a few exploration-related reasons for visiting an asteroid:
1- Demonstrating long-duration deep-space operations
2- Glory/cool stunts/firsts
3- Science
4- Testing our ISRU techniques
5- Demonstrating planetary defense technologies
Of the two asteroid approaches (free range vs ARM), free range excels at #1 and #2, while ARM excels at #3-5, and could probably help with #1. I guess it's a matter of priorities, but I just don't see a free-range NEO visit being that interesting compared to bringing something home that could be visited a lot, and used as a testbed for figuring out how to actually mine asteroids for fun and profit.
~Jon
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#203
by
the_other_Doug
on 30 Dec, 2014 03:03
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Just as a toss-in -- full asteroid redirect technology is not only a kewl idea and offers planetary defense options, it also opens up the technology for possibly the single most devastating weapon ever deployed by humanity.
If you can move asteroid around into cislunar space, then you have the technology needed to set one to drop onto the Earth. At your chosen location, if you're good enough. And if you do that with, say, a five-kilometer-long asteroid, you have the ability to set off a detonation equal to all of the nuclear weapons ever produced all going off at once.
I'm all for planetary defense. But maybe we want to be just a little careful which governments and other extremely well-funded groups can get their hands on the technology, eh? I mean, once the genie's out of the bottle, it's awfully hard to get it back inside.
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#204
by
QuantumG
on 30 Dec, 2014 03:13
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I hate to be the one to tell you this, but any grad student with a slide rule can tell you how to do that. Although the cost would be astronomical (pun intended).
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#205
by
Hop_David
on 30 Dec, 2014 18:33
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I'm not sure that makes any sense. Short synodic periods typically mean higher delta-V (at both ends) to get to/from the asteroid.
Maybe I wasn't clear.. why not change the synodic period after you visit it, so you don't have to wait so long to visit it again. You're going there anyway...
How to explain Synodic periods?
Once a year our high school P.E. class would hold an hour long marathon run. I was asthmatic and my friend Sugar Bear was overweight. So we were both dead last in the pack. The fastest guys would typically lap us 5 or 6 times during that hour.
Our synodic period with regard to the fastest guys was about 10 to 12 minutes
Sugar Bear and I ran at the same speed so we never lapped each other. Our synodic period with regard to each other was virtually infinity.
Likewise the two fastest guys were always neck and neck. Their synodic period with regard to one another was also virtually infinite.
Now here is a pic of earth plus NEOs having orbital radii of 1.1, 1.2, 1.3, 1.4 and 1.5 A.U.:
It can be seen the 1.1 AU NEO takes the least delta V. It is also going nearly the same speed as the earth. With a semi major axis of 1.1 A.U., it takes 1.1537 years to orbit the sun. It takes the earth 7.5 years to lap this closer NEO. Likewise Hohmann launch windows occur each 7.5 years.
You can have an accessible NEO. You can have an NEO with frequent launch windows. But if its orbit is heliocentric, you can't have both.
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#206
by
Vultur
on 30 Dec, 2014 19:09
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Synodic periods - good point. I wasn't really thinking in terms of ISRU, at least for the first mission, but in terms of exploring the asteroid itself. Follow up missions wouldn't necessarily be to the same asteroid.
If ISRU is the point, then yes, moving the asteroid makes sense.
If the end goal is flags and footprints or one off scientific missions, I believe ~20 billion is too high of an annual budget for NASA. As a taxpayer I would call for the elimination of NASA.
If the end goal is use of space resources and/or human settlement of space, it's worth that investment plus much more.
So (in my view) ISRU is the point.
A rock in lunar orbit would make a great test bed for entities like Planetary Resources or Deep Space Industries. Launch windows open every two weeks from a given orbit. Trip time is about a week.
For robots, light lag latency is about 3 seconds. And since signal strength falls with inverse square of distance, bandwidth is 100s to 1000s times better than something in heliocentric orbit.
A rock parked in our neighborhood would be a very helpful test bed for developing a fledgling asteroid mining technology.
Sure, but ISRU/asteroid mining/space settlement as a long term goal (which I agree with) doesn't mean it needs to be part of the
first manned mission to an asteroid.
Will the ARM necessarily pick a type of asteroid that's useful for ISRU? We might want to learn more about asteroids first and retrieve later.
However, at this point I guess I'd rather ARM go on rather than change the plan again and delay it further. But NASA should definitely be developing a deep space hab for Orion.
Just as a toss-in -- full asteroid redirect technology is not only a kewl idea and offers planetary defense options, it also opens up the technology for possibly the single most devastating weapon ever deployed by humanity.
If you can move asteroid around into cislunar space, then you have the technology needed to set one to drop onto the Earth. At your chosen location, if you're good enough. And if you do that with, say, a five-kilometer-long asteroid, you have the ability to set off a detonation equal to all of the nuclear weapons ever produced all going off at once.
Sure, but a 5 km asteroid is going to be 500 * 500 * 500 = 125 million times more massive than the 10m asteroid which is the upper end being proposed for ARM. That's vastly harder to move.
Anyway, such weapons wouldn't be used for the same reason nuclear weapons haven't been used in 70 years.
Smaller asteroids would both be easier to move and wouldn't wreck the whole earth's climate system - but we could deploy Project Thor type orbital kinetic bombardment weapons now, and haven't (or at least it isn't publicly known
).
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#207
by
Hop_David
on 30 Dec, 2014 20:22
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Sure, but ISRU/asteroid mining/space settlement as a long term goal (which I agree with) doesn't mean it needs to be part of the first manned mission to an asteroid.
At this stage of the game, manned spaceflight is putting the cart before the horse.
If we achieve resource utilization, that would be give some reason for having humans in space. ISRU would also make sustained human presence doable.
But right now Orion and SLS are consuming much of the budget that could be used for stuff like propellent depots, improved robotics, etc..
If we have to have a human spaceflight budget, I'd prefer money go SpaceX, Blgelow, Blue Origin etc.
The present path seems a good recipe to squander a lot of money to accomplish nothing except for alienating the tax paying public.
Will the ARM necessarily pick a type of asteroid that's useful for ISRU? We might want to learn more about asteroids first and retrieve later.
We agree here. I'd like to see a more thorough search and study of the smaller NEOs before we launch the asteroid retrieval vehicle. I would like to see my tax money help fund the Arkyd prospector probes.
However, at this point I guess I'd rather ARM go on rather than change the plan again and delay it further. But NASA should definitely be developing a deep space hab for Orion.
Aspects of ARM I like:
Robust SEP
Software for rendezvous and retrieval of an inanimate object not designed for rendezvous.
Both these could have many uses.
Aspects of ARM I don't like:
SLS and Orion
These are political pork. Hitching them to ARM is hanging an albatross about the neck of a worthy project.
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#208
by
Nilof
on 30 Dec, 2014 22:56
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I'm not sure that makes any sense. Short synodic periods typically mean higher delta-V (at both ends) to get to/from the asteroid.
Maybe I wasn't clear.. why not change the synodic period after you visit it, so you don't have to wait so long to visit it again. You're going there anyway...
How to explain Synodic periods?
Once a year our high school P.E. class would hold an hour long marathon run. I was asthmatic and my friend Sugar Bear was overweight. So we were both dead last in the pack. The fastest guys would typically lap us 5 or 6 times during that hour.
Our synodic period with regard to the fastest guys was about 10 to 12 minutes
Sugar Bear and I ran at the same speed so we never lapped each other. Our synodic period with regard to each other was virtually infinity.
Likewise the two fastest guys were always neck and neck. Their synodic period with regard to one another was also virtually infinite.
Now here is a pic of earth plus NEOs having orbital radii of 1.1, 1.2, 1.3, 1.4 and 1.5 A.U.:
It can be seen the 1.1 AU NEO takes the least delta V. It is also going nearly the same speed as the earth. With a semi major axis of 1.1 A.U., it takes 1.1537 years to orbit the sun. It takes the earth 7.5 years to lap this closer NEO. Likewise Hohmann launch windows occur each 7.5 years.
You can have an accessible NEO. You can have an NEO with frequent launch windows. But if its orbit is heliocentric, you can't have both.
There is the degenerate case where the two bodies have the same period, but have different eccentricities and orbital planes. In that case, the synodic period is technically infinite(you effectively have aperiodic motion), but the time between "almost identical" configurations is only one year.
Most of these orbits are unstable over long periods of time since the Earth is indeed a planet and clears it's neighborhood, so no bodies will naturally be in useful such orbits. But with active control you can keep encounters coming.
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#209
by
QuantumG
on 31 Dec, 2014 00:22
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Unfortunately I don't have the time to reproduce the math I did a few years ago (ironically, I think Hop_David helped me with it), but I remember concluding that with less than 1km/s of delta-v there's a lot of known bodies you can change to have favourable approaches to Earth, and each of them can be subsequently changed to have another favourable approach within a year. Of course, 1km/s is more than most consider feasible, as they have these silly gravity tractor ideas.
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#210
by
Hop_David
on 31 Dec, 2014 03:17
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Unfortunately I don't have the time to reproduce the math I did a few years ago (ironically, I think Hop_David helped me with it), but I remember concluding that with less than 1km/s of delta-v there's a lot of known bodies you can change to have favourable approaches to Earth, and each of them can be subsequently changed to have another favourable approach within a year. Of course, 1km/s is more than most consider feasible, as they have these silly gravity tractor ideas.
I believe the asteroids the Keck folks are looking at are ones in earth like orbits that already make close approaches to earth. For example 2008 HU4 occasionally comes near.
For such asteroids, sometimes a tiny nudge can alter a near approach so that it through the moon's sphere of influence. A lunar swing by can convert a hyperbolic orbit with a small Vinf into an earth capture orbit.
I
took a look. I believe a rock like 2008 HU4 could be nudged into earth capture orbit for as little as .04 km/s. Then some more delta V to park it in lunar orbit. If I recall correctly a total of .17 km/s according to the Keck folks.
What sort of orbital alterations did you have in mind? It seems to me they'd be more expensive than a one time expenditure of .17 km/s.
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#211
by
MP99
on 02 Jan, 2015 12:52
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You state the same Option B hardware could be used to return samples from Phobos and Deimos. These are much larger than the 100m to 500m asteroids that seem to be the target of Option B.
1. I was curious as to how much of gravity well option B hardware can handle?
It depends on the specific design. You'll definitely be stuck grabbing a smaller boulder. And there's no way you'll be able to leap off the asteroid into escape like you can from something more Itokawa sized. But the same hardware could at least grab something on the order of ~2m diameter (instead of 4m), and jump up high enough for some other form of thruster to take you the rest of the way home. That would only be like 10-15mT for a rocky boulder, but still enough to do some decent ISRU work with (and a lot bigger than you'd get back via any other realistic near-term method).
ISTM that for a realistic test of ISRU you'd want a representative sample, but that's not possible once you pluck a boulder away from any dust / rubble surrounding it?
cheers, Martin
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#212
by
Hop_David
on 02 Jan, 2015 22:14
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ISTM that for a realistic test of ISRU you'd want a representative sample, but that's not possible once you pluck a boulder away from any dust / rubble surrounding it?
cheers, Martin
With a two meter rock we could practice and hone some general asteroid ISRU skills. Attaching equipment to the surface. Digging and drilling in micro gravity. Getting regolith into solar kilns, etc.
Of course each specific ore body would require a specific set of processes and equipment. But I'm guessing we can learn some general methods with broad applications given a test bed in lunar orbit.
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#213
by
jongoff
on 02 Jan, 2015 22:22
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ISTM that for a realistic test of ISRU you'd want a representative sample, but that's not possible once you pluck a boulder away from any dust / rubble surrounding it?
Both the Altius and MDA Option B concepts involved some sort of system for removing and collecting the dust from the boulder (and its immediate environs). Altius using an electrodynamic dust collection system, MDA using Honeybee's pneumatic excavation concept. But yeah, getting the boulder "in context" with the dust that was on/around it is probably very useful from a scientific/engineering standpoint.
~Jon
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#214
by
jongoff
on 02 Jan, 2015 22:24
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ISTM that for a realistic test of ISRU you'd want a representative sample, but that's not possible once you pluck a boulder away from any dust / rubble surrounding it?
cheers, Martin
With a two meter rock we could practice and hone some general asteroid ISRU skills. Attaching equipment to the surface. Digging and drilling in micro gravity. Getting regolith into solar kilns, etc.
Of course each specific ore body would require a specific set of processes and equipment. But I'm guessing we can learn some general methods with broad applications given a test bed in lunar orbit.
And some of the better approaches I've seen for doing Option B would make follow-on collection of similar-sized boulders of differing compositions relatively affordable.
~Jon
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#215
by
Robotbeat
on 03 Jan, 2015 01:19
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...
5- I can't remember where I saw it publicly, but apparently one of the potential uses for the commercial-derived Hab module that NASA's studying under the NextSTEP BAA was to provide a hab module at the ARM asteroid sample to enable longer-duration exploration and study of the asteroid sample, and to demonstrate long-duration habitation at some place close enough you could safely make it home if something goes wrong. This would basically create a tiny man-tended NEO-lab in lunar orbit (that could also serve as a lunar gateway).
...
~Jon
Indeed! I like that idea a lot. It also solves a big supposed problem with a deep space gateway: GCR shielding. If you had a sufficiently large asteroid (300-500 tons?) you'd be able to shield the crew quarters with regolith deep enough that the radiation environment would be more benign than ISS. I think we were talking about that sort of idea years ago in one of the Gateway threads?
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#216
by
alexterrell
on 04 Jan, 2015 16:14
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. If you had a sufficiently large asteroid (300-500 tons?) you'd be able to shield the crew quarters with regolith deep enough that the radiation environment would be more benign than ISS. I think we were talking about that sort of idea years ago in one of the Gateway threads?
Let's say you have an 8m or so diameter rock, volume 250m3, in a bag, massing 500 tons. How do you turn this into your shield?
I know we've discussed ideas before for doing this with much larger asteroids.
If you're bag is 8m diameter, and 16m long, with a conducting inner coating. Apply a voltage charge to the bag and the opposite charge to the rock (with an electron gun?) could you get the rock to spread itself over the inside of the bag? 400m2 -> approx 60cm thick, leaving just enough room to squeeze a BA-330 in to it.
Or, drill out a core, put in a balloon and inflate it. Could you get the mass distribution.
This is the reason why I liked Option A (getting a whole "asteroid"). It would create an incentive to actually do something with the material.
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#217
by
savuporo
on 08 Jan, 2015 00:11
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#218
by
MATTBLAK
on 08 Jan, 2015 01:00
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I've become a fan of Solar Electric Propulsion. I want them to build the biggest propulsion module they can in the near future - be that 25 ton EELV launched, 50 ton Falcon Heavy or 70 ton Block 1 SLS launched - and test it ASAP. I think that NASA's leaning lately towards a Hab Augmentation module is actually the correct thing to do. Gaining experience with deep space long duration missions, albeit 'only' in distant retrograde lunar orbit would pay dividends later for missions to the Martian moons.
For example: adding a couple chemical propulsion stages and a larger or second Hab module to the ARM 'stack' is a manned ship you could push out to Deimos or Phobos. Block II of the SEP module could precede them with supplies and propellants for Earth return or maybe even a man-tended station for Stickney crater on Phobos!
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#219
by
savuporo
on 08 Jan, 2015 01:18
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I've become a fan of Solar Electric Propulsion. I want them to build the biggest propulsion module they can in the near future - be that 25 ton EELV launched, 50 ton Falcon Heavy..
I would care - stackable 10-ton ones have much more potential utility, and no practical loss in efficiency apart from the mass of the docking fixture.
). 