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#260
by
ehb
on 30 Jan, 2015 21:29
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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.
~Jon
Jon,
Did the Langley group present the paper ? If so, will they allow a link or copy here ?
Thanks,
-ehb
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#261
by
Solman
on 31 Jan, 2015 00:39
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Since we are not likely to get lots of missions flying to an asteroid and bringing it back to earth, I am for bring the biggest one that I can. I do understand that so far we have very brought back very little rocks from space. Now think what you could do with hundreds of tons.
To that end I think it is worth noting that schemes such as those using lasers or concentrated sunlight to directly use the asteroid itself as reaction mass can move much more mass per unit time than SEP.
Matloff measured 1 km/s jets coming off a meteorite exposed to concentrated sunlight in a vacuum chamber. If a laser system were to equal this, then per unit of energy applied to the reaction mass, a laser producing a 1 km/s jet would produce 1000 times as much thrust as a SEP with a 33 km/s exhaust velocity.
The laser might be heavier and have a lower overall efficiency vs. a SEP system but it would only carry enough propellant to get and keep itself within range of the target asteroid since the asteroid itself would provide the reaction mass. IIRC some laser rockets concepts exceed 5000 sec. Isp.
Lasers are scalable by simply adding more units.
Direct solar could perhaps use many units capable of attaching themselves to each other and the asteroid, deploying mirrors and using fiber optic cables to bring their combined energy to bear on a spot to produce thrust.
Applied to future Mars development lasers can provide variable Isp and beamed in-space propulsion and surface base support.
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#262
by
Nilof
on 04 Feb, 2015 23:34
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TWO YEARS....JUST TO LEAVE EARTH ORBIT?! That's beyond crazy talk! If we wish to apply SEP practically to even the unmanned portion of human space flight the escape from Earth shouldn't need more than 6 months! Humans and Van Allen belts anyone? Wasting time is just as bad as wasting money!
This is for a vehicle that can launch on an Atlas V. With a Falcon Heavy you can skip the spiraling phase entirely. The Keck report spacecraft is also somewhat underpowered at 40 kW and uses the most conservative solar array options. The only bottleneck in terms of time is the size(in power, not mass) of the propulsion unit. Plainly put, bigger is better, and bigger requires space-rating high power electronics, which requires ARM or something similar.
For comparison, Ad Astra's baselined
VASIMR tug working at 200 kW can do the spiral out maneuver in ~3-4 months, for a spacecraft of a similar size.
Keep in mind that this is a vehicle optimized to bring back well over 50 times it's IMLEO mass. A vehicle massing less than 20 tonnes at launch that can bring back a 1300 ton rock. For a stony asteroid, even if it is bone dry, at least one fourth of the mass will be oxygen. With oxygen ISRU, this effectively nets you >300 tonnes of LOX in lunar orbit using a launcher that can barely put 20 tonnes into LEO. With that kind of payoff at such a low cost, waiting for a few years is more than worth it.
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#263
by
redliox
on 05 Feb, 2015 04:48
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TWO YEARS....JUST TO LEAVE EARTH ORBIT?! That's beyond crazy talk! If we wish to apply SEP practically to even the unmanned portion of human space flight the escape from Earth shouldn't need more than 6 months! Humans and Van Allen belts anyone? Wasting time is just as bad as wasting money!
This is for a vehicle that can launch on an Atlas V. With a Falcon Heavy you can skip the spiraling phase entirely. The Keck report spacecraft is also somewhat underpowered at 40 kW and uses the most conservative solar array options. The only bottleneck in terms of time is the size(in power, not mass) of the propulsion unit. Plainly put, bigger is better, and bigger requires space-rating high power electronics, which requires ARM or something similar.
For comparison, Ad Astra's baselined VASIMR tug working at 200 kW can do the spiral out maneuver in ~3-4 months, for a spacecraft of a similar size.
3-4 months is a decided improvement - that I'd work with but strictly uncrewed.
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#264
by
john smith 19
on 05 Feb, 2015 15:17
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TWO YEARS....JUST TO LEAVE EARTH ORBIT?! That's beyond crazy talk! If we wish to apply SEP practically to even the unmanned portion of human space flight the escape from Earth shouldn't need more than 6 months! Humans and Van Allen belts anyone? Wasting time is just as bad as wasting money!
This is for a vehicle that can launch on an Atlas V. With a Falcon Heavy you can skip the spiraling phase entirely. The Keck report spacecraft is also somewhat underpowered at 40 kW and uses the most conservative solar array options. The only bottleneck in terms of time is the size(in power, not mass) of the propulsion unit. Plainly put, bigger is better, and bigger requires space-rating high power electronics, which requires ARM or something similar.
For comparison, Ad Astra's baselined VASIMR tug working at 200 kW can do the spiral out maneuver in ~3-4 months, for a spacecraft of a similar size.
3-4 months is a decided improvement - that I'd work with but strictly uncrewed.
True but there are 3 problems with that approach.
FH has
no flight history, although that should change.
VASIMR has
no flight history, although that will hopefully change but there seems to be no date for it.
VASIMR needs a 200Kw power source. That's either a) A solar array the size of the one on the ISS (hopefully somewhat lighter) or b) A small nuclear reactor, the successor to the DUFF experiment perhaps. 200Kw is a 268Hp engine.
From NASA's PoV that is a
huge set of mission risks and new developments.
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#265
by
Nilof
on 05 Feb, 2015 17:25
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TWO YEARS....JUST TO LEAVE EARTH ORBIT?! That's beyond crazy talk! If we wish to apply SEP practically to even the unmanned portion of human space flight the escape from Earth shouldn't need more than 6 months! Humans and Van Allen belts anyone? Wasting time is just as bad as wasting money!
This is for a vehicle that can launch on an Atlas V. With a Falcon Heavy you can skip the spiraling phase entirely. The Keck report spacecraft is also somewhat underpowered at 40 kW and uses the most conservative solar array options. The only bottleneck in terms of time is the size(in power, not mass) of the propulsion unit. Plainly put, bigger is better, and bigger requires space-rating high power electronics, which requires ARM or something similar.
For comparison, Ad Astra's baselined VASIMR tug working at 200 kW can do the spiral out maneuver in ~3-4 months, for a spacecraft of a similar size.
3-4 months is a decided improvement - that I'd work with but strictly uncrewed.
True but there are 3 problems with that approach.
FH has no flight history, although that should change.
VASIMR has no flight history, although that will hopefully change but there seems to be no date for it.
VASIMR needs a 200Kw power source. That's either a) A solar array the size of the one on the ISS (hopefully somewhat lighter) or b) A small nuclear reactor, the successor to the DUFF experiment perhaps. 200Kw is a 268Hp engine.
From NASA's PoV that is a huge set of mission risks and new developments.
Indeed, the trade was made for a reason. In my previous post I mostly wanted to highlight that the spacecraft in the Keck report was very conservative(though still perfectly adequate for the mission), and that there is nothing inherently slow about SEP. It is a growth technology that can still improve its performance by several orders of magnitude as it matures, unlike chemical which essentially reached its theoretical peak for the in-space role in the sixties.
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#266
by
jongoff
on 06 Feb, 2015 01:08
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VASIMR isn't the only option for higher power SEP. Most of the NASA ARV designs I've seen so far baseline power levels above 100kW using multiple Hall Effect Thrusters. I wish MSNW's RF plasma thrusters were more ready, because once they're ready they should be able to get good thruster efficiency even using storable propellants like hydrazine or water, but they're still in development.
But long-story short, none of the current ARV designs I've seen involve a 2yr spiral out, most of them are closer to 6-9 months, if launched to LEO, and many concepts involve starting from a higher orbit.
~Jon
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#267
by
Hop_David
on 06 Feb, 2015 16:59
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3-4 months is a decided improvement - that I'd work with but strictly uncrewed.
Once again, the Keck vehicle is robotic. Not for sending humans to Mars but for fetching rocks. With a medium sized launcher, you can park many tonnes of asteroid in lunar orbit.
Yes, it will take years. Does this mean the SEP vehicle would be useless for getting people to Mars fast? Quite the contrary.
One of the first goals of Planetary Resources is to park water rich asteroids. What could we do with 100s of tonnes of hydrogen and oxygen in lunar orbit? Lots. And quick trips to Mars is one of them.
A
reusable Earth Departure Stage (EDS) based at EML2 could plausibly do a 3 km/s burn at perigee. This could send a ship on a 5.7 month transfer orbit (The usual Hohmann path averages 8.5 months).
How about if we're using disposable Earth Departure Stages? Mars Semi-Direct uses disposable EDS. If we don't have to worry about getting the EDS back to EML2, more propellent could be devoted to the perigee burn. A 7 km/s perigee burn would be plausible.
Gobs of propellent in lunar orbit can make for faster Mars trips and considerably larger Mars launch windows.
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#268
by
AlanSE
on 09 Feb, 2015 20:25
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One of the first goals of Planetary Resources is to park water rich asteroids. What could we do with 100s of tonnes of hydrogen and oxygen in lunar orbit? Lots. And quick trips to Mars is one of them.
A reusable Earth Departure Stage (EDS) based at EML2 could plausibly do a 3 km/s burn at perigee. This could send a ship on a 5.7 month transfer orbit (The usual Hohmann path averages 8.5 months).
It seems to me... that we need to know how you get there in the first place. Any human payload would almost certainly be delivered by chemical rockets. By that I mean they had to burn from LEO to a transfer trajectory to EML2 with a chemical rocket. It'll also need to do some burns once it gets close.
Given that, it just seems so strange to talk about a reusable EDS. Why would you concern yourself so much with reuse of this stage when you're already throwing away the stage you used to get there? If you consider a holistic interplanetary reusable rocket network, the optimization gets much more complicated. It may still be possible to reuse your upper stage by refueling at a LEO propellant depot (fueled from Earth surface), then travel to EML2 where you reload from asteroid propellant. All 3 of the burns involved would be kind of close to 3 km/s. Maybe 4 km/s.
I know this isn't a new subject, but this has always bugged me. Optimizing reusability is going to be quite complex involving transport networks between LEO, spots around the moon, Mars, and so on. As such, the most attractive scenario will probably be to just take your rocket wherever you're going, and the station that you're docking with will add it to its inventory and decide how best to put it to use.
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#269
by
Nilof
on 09 Feb, 2015 23:47
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One of the first goals of Planetary Resources is to park water rich asteroids. What could we do with 100s of tonnes of hydrogen and oxygen in lunar orbit? Lots. And quick trips to Mars is one of them.
A reusable Earth Departure Stage (EDS) based at EML2 could plausibly do a 3 km/s burn at perigee. This could send a ship on a 5.7 month transfer orbit (The usual Hohmann path averages 8.5 months).
It seems to me... that we need to know how you get there in the first place. Any human payload would almost certainly be delivered by chemical rockets. By that I mean they had to burn from LEO to a transfer trajectory to EML2 with a chemical rocket. It'll also need to do some burns once it gets close.
Given that, it just seems so strange to talk about a reusable EDS. Why would you concern yourself so much with reuse of this stage when you're already throwing away the stage you used to get there? If you consider a holistic interplanetary reusable rocket network, the optimization gets much more complicated. It may still be possible to reuse your upper stage by refueling at a LEO propellant depot (fueled from Earth surface), then travel to EML2 where you reload from asteroid propellant. All 3 of the burns involved would be kind of close to 3 km/s. Maybe 4 km/s.
I know this isn't a new subject, but this has always bugged me. Optimizing reusability is going to be quite complex involving transport networks between LEO, spots around the moon, Mars, and so on. As such, the most attractive scenario will probably be to just take your rocket wherever you're going, and the station that you're docking with will add it to its inventory and decide how best to put it to use.
The transfer stage needed to go from LEO to L2 can be much smaller since you only need to send a capsule there with the crew right before departure. The bulk of the spacecraft can be moved to EML2 by other means, such as SEP tugs which would be easier to reuse.
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#270
by
kkattula
on 10 Feb, 2015 01:25
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It seems to me... that we need to know how you get there in the first place. Any human payload would almost certainly be delivered by chemical rockets. By that I mean they had to burn from LEO to a transfer trajectory to EML2 with a chemical rocket. It'll also need to do some burns once it gets close.
Given that, it just seems so strange to talk about a reusable EDS. Why would you concern yourself so much with reuse of this stage when you're already throwing away the stage you used to get there?
...
The transfer stage needed to go from LEO to L2 can be much smaller since you only need to send a capsule there with the crew right before departure. The bulk of the spacecraft can be moved to EML2 by other means, such as SEP tugs which would be easier to reuse.
And the L2 to Mars propulsion stage would need to store propellants for months with near zero loss. Plus long duration power systems, radiation hardening, mm protection, etc. If discarded after TLI, the LEO to L2 stage may only need an endurance measured in hours.
Although it could also be more efficient to move ISRU propellant from L2 to an LEO depot, then have a re-usable EDS move the crew from LEO to L2. Reduces the launch requirement to an LEO crew taxi and consumable cargo. An ACES style tanker stage could go from L2 to LEO, unload a reasonable amount of propellant, and still have enough to return empty to L2.
Edit: BOTE says approx. 25% of the propellant loaded at L2 could be unloaded at an LEO depot.
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#271
by
Hop_David
on 10 Feb, 2015 13:43
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by refueling at a LEO propellant depot (fueled from Earth surface)
Assuming lots of propellent at EML2 why would LEO depots be supplied by earth surface?
EML2 is 3.5 km/s from LEO. And 3.1 of that 3.5 is circularizing at LEO -- much or all of that 3.1 could be done by aerobraking. So delta V from EML2 to LEO can be
as little as .4 km/s.
When the trip from earth's surface to LEO is cut out of the equation, trips between orbits in the earth-moon neighborhood would be around 3 to 4 km/s. This makes for much less difficult mass fractions and sturdier ships. Most inter-orbital vehicles could remain in space and thus never have to suffer the extreme conditions of an 8 km/s re-entry into earth's atmosphere. Re-use becomes far less difficult.
Routine access to our orbital assets in cislunar space is the goal. It's no coincidence that sounds like Spudis, Spudis has been talking about the same thing: water. Water which can be made into rocket fuel. Only an asteroidal propellent source in high lunar orbit doesn't have the moon's 2.4 km/s gravity well.
I'm not talking just reusable EDS but reusables vecicles for travel between LEO, GEO, EML1&2 and beyond.
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#272
by
Hop_David
on 10 Feb, 2015 13:54
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And the L2 to Mars propulsion stage would need to store propellants for months with near zero loss.
If trips to Mars were the only market for extra-terrestrial propellent, I'd say forgot about it.
But see my post above. Routine access to destinations throughout cislunar space. Also EDS to other Near Earth Asteroids. Not to mention propellent in lunar orbit would make the moon much more accessible.
The asteroidal propellent wouldn't just be sitting there between Mars launch windows.
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#273
by
the_other_Doug
on 10 Feb, 2015 18:22
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I m bemused at how the proponents of fuel depots keep popping depots up as the cure-all for all future interplanetary flight development, when the technology to create liquid hydrogen and liquid oxygen from lunar and asteroidal sources is still in the realm of energetic arm-waving, as is the technology for maintaining such fuels in liquid states for months or years.
Yes, fuel depots may one day be developed and used. But the technology just isn't developed, and won't be practical for decades to come. It makes no sense to posit activities in the 2020s or even 2030s being dependent on such depots when I can't see them being available for another 50 to 100 years...
Just sayin'...
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#274
by
redliox
on 10 Feb, 2015 18:27
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I m bemused at how the proponents of fuel depots keep popping depots up as the cure-all for all future interplanetary flight development, when the technology to create liquid hydrogen and liquid oxygen from lunar and asteroidal sources is still in the realm of energetic arm-waving, as is the technology for maintaining such fuels in liquid states for months or years.
Yes, fuel depots may one day be developed and used. But the technology just isn't developed, and won't be practical for decades to come. It makes no sense to posit activities in the 2020s or even 2030s being dependent on such depots when I can't see them being available for another 50 to 100 years...
Just sayin'...
In other words, ISRU is needed more than a fuel depot or else you're left with empty tanks in orbit.
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#275
by
A_M_Swallow
on 10 Feb, 2015 18:42
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I m bemused at how the proponents of fuel depots keep popping depots up as the cure-all for all future interplanetary flight development, when the technology to create liquid hydrogen and liquid oxygen from lunar and asteroidal sources is still in the realm of energetic arm-waving, as is the technology for maintaining such fuels in liquid states for months or years.
Yes, fuel depots may one day be developed and used. But the technology just isn't developed, and won't be practical for decades to come. It makes no sense to posit activities in the 2020s or even 2030s being dependent on such depots when I can't see them being available for another 50 to 100 years...
Just sayin'...
Methane is a good fuel for propellant depots to sell. Methane is space storable and can be kept at similar temperatures to LOX using sun shields.
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#276
by
Hop_David
on 10 Feb, 2015 19:43
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I m bemused at how the proponents of fuel depots keep popping depots up as the cure-all for all future interplanetary flight development, when the technology to create liquid hydrogen and liquid oxygen from lunar and asteroidal sources is still in the realm of energetic arm-waving,
For sustained human presence we will eventually need to develop ISRU. Or are you arguing against human spaceflight?
as is the technology for maintaining such fuels in liquid states for months or years.
As I mentioned, the Mars windows each 2.14 years aren't the only times a depot might be used.
Mars isn't the be-all and end-all space destination. In fact it is a distraction if the goal is near term revenue streams.
Yes, fuel depots may one day be developed and used. But the technology just isn't developed, and won't be practical for decades to come. It makes no sense to posit activities in the 2020s or even 2030s being dependent on such depots when I can't see them being available for another 50 to 100 years...
To put this in context I was replying to a would-be Mars colonizer.
I think near term asteroid use is a lot more plausible than colonizing Mars. But should asteroid use become profitable then there's something greater than a snowball's chance for Martian colonies.
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#277
by
the_other_Doug
on 10 Feb, 2015 19:46
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I m bemused at how the proponents of fuel depots keep popping depots up as the cure-all for all future interplanetary flight development, when the technology to create liquid hydrogen and liquid oxygen from lunar and asteroidal sources is still in the realm of energetic arm-waving, as is the technology for maintaining such fuels in liquid states for months or years.
Yes, fuel depots may one day be developed and used. But the technology just isn't developed, and won't be practical for decades to come. It makes no sense to posit activities in the 2020s or even 2030s being dependent on such depots when I can't see them being available for another 50 to 100 years...
Just sayin'...
Methane is a good fuel for propellant depots to sell. Methane is space storable and can be kept at similar temperatures to LOX using sun shields.
Again, this seems like energetic arm-waving to me. "Just toss on some sun shields" isn't exactly rigorous engineering.
You know what my nightmare is in re this subject? The following announcement, after spending $100 billion in setting up a fuel depot system:
"Due to unanticipated heat transfer along the sun shield structure into the tankage itself, temperatures have reached a level where either the stored fuel must be vented to space, or else run the risk of an explosion in the tankage."
It's not cheap or trivial to set up ISRU bases and microgravity storage depots, and in engineering terms, the devil is in the details. Until and unless adequate lossless cryo storage on-orbit -- for months and years -- is demonstrated, we're all just waving our arms extremely energetically to posit fuel depots sitting at LaGrange points just waiting to support Mars missions in the 2030s.
Again, all in my own humble opinion.
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#278
by
Nilof
on 10 Feb, 2015 20:01
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LH2 depots at 1 AU will likely never be viable, but LOX depots in cis-lunar orbits are certainly viable, and that part of the ISRU work is fairly easy. You can extract LOX even from bone-dry rock with relative ease, much like LUNOX was supposed to do for lunar soil. Even if that is as far as you go with depots, it is still a very worthwhile thing to do as it significantly reduces the mass needed for lunar landings.
Carbonaceous chondrites offer an opportunity to sweeten the deal by also providing fuel. Since (surprise surprise!) carbonaceous chondrites contain a lot of carbon by mass, making LH2 fuel makes little sense. If you have lots of carbon available, there is no reason not to use the extra reaction mass by using methane instead, which also gives synergy with Mars surface ISRU, especially considering that both moons of mars are chondrites.
Alternatively, if extracting hydrogen from chondrites is impractical, there is always the option of making Carbon monoxide... which is also a fuel with great Mars ISRU synergy.
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#279
by
redliox
on 10 Feb, 2015 20:42
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LH2 depots at 1 AU will likely never be viable, but LOX depots in cis-lunar orbits are certainly viable, and that part of the ISRU work is fairly easy. You can extract LOX even from bone-dry rock with relative ease, much like LUNOX was supposed to do for lunar soil. Even if that is as far as you go with depots, it is still a very worthwhile thing to do as it significantly reduces the mass needed for lunar landings.
Oxygen and methane seem to be the best bets because of oxygen's copiousness and their similar liquid temperatures. Hydrogen can't match the latter so well.
Carbonaceous chondrites offer an opportunity to sweeten the deal by also providing fuel. Since (surprise surprise!) carbonaceous chondrites contain a lot of carbon by mass, making LH2 fuel makes little sense. If you have lots of carbon available, there is no reason not to use the extra reaction mass by using methane instead, which also gives synergy with Mars surface ISRU, especially considering that both moons of mars are chondrites.
We know what Mars and the Moon are made off, not so much carbonaceous asteroids. I say that in reference to soil analysis; with Mars at least we've had Viking and Phoenix for soil chemistry. Prospect them first, but don't setup mining claims just yet. With luck, that will change after Osiris-Rex and Hayabusa 2.
