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#520
by
Steam Chaser
on 11 Apr, 2015 03:18
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Let's suppose the asteroid redirect mission is redirected to Mars orbit and then back to a distant retrograde lunar orbit using SEP per the NAC finding as described in Marcia Smith's article that Graham linked above. (The finding doesn't mention Phobos although it was discussed).
Accounting for various potential benefits of the mission (tech demo, planetary science information, information useful in a "HSF robotic precursor" sense, giving something for astronauts to do in cislunar space during the early decade of SLS/Orion operations, paving a path on NASA's "Journey To Mars", etc), and also accounting for cost and risk, which would make more sense?
- pure SEP technology demonstration without other appendages
- ARM "Option B" moved to Mars, i.e. retrieve a boulder from Phobos or Deimos and bring it back to be investigated during an SLS/Orion mission
- something closer to OSIRIS-REx, returning much smaller samples of Phobos and/or Deimos, but with more science instruments to investigate the moon(s) while there, also possibly with Orion gathering the samples instead of an Earth return capsule
- something closer to the Boldly Go Institute's SCIM mission, which would skim through the upper Martian atmosphere gathering air/dust samples similar to the Stardust mission and return the samples, also possibly with Orion gathering the samples
- a mission that demontrates the SEP Mars-and-back trip, but that doesn't return any samples (but unlike the pure SEP tech demo above it could do work while at Mars, or maybe drop off a companion spacecraft like a Mars telecom orbiter or a remote sensing science spacecraft)
- some combination of the above
... or, supposing a big chunk of money like $1.25B for this sort of robotic precursor/exploration tech demo work were actually available, would it make more sense to spend it on something else entirely like an ice-prospecting lunar rover and/or lunar sample return sort of mission as proposed to be run from Orion, or an EAM/habitat demonstration with Orion?
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#521
by
Robotbeat
on 11 Apr, 2015 23:44
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The sample could be used for testing ISRU technology eg oxygen extraction.
No.
They're still only talking about a rock.
Next time you're near a body of water pick up a rock and take it home and try to extract water from it.
Actually,
Yes.
Crush it up, reduce with hydrogen which gives you water vapor. Electrolyze the water to get back the hydrogen and you're left with oxygen. We've tested before (in Hawaii).
We already do both electrolysis and water vapor recovery on ISS, so half of the cycle is already fairly routine.
Oxygen is 6/7ths of the mass used in a hydrolox rocket engine and can even be used straight by some electric thrusters (such as the ELF thruster work that MSNW is getting paid to demonstrate in the >100kW class range by the NextSTEP NASA deep space initiative). That means that once you can demonstrate ISRU, you can refuel your SEP craft with asteroid material and at least 85% of your lander or high-thrust stage propellant as well.
That would certainly be enabling for extensive Mars exploration. (Or any kind of extensive space exploration.) Propellant is the vast majority of IMLEO. If you get 90%-95% of your propellant from space, you've just drastically reduced the per-mission launch requirements.
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#522
by
jongoff
on 12 Apr, 2015 01:12
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The sample could be used for testing ISRU technology eg oxygen extraction.
No.
They're still only talking about a rock.
Next time you're near a body of water pick up a rock and take it home and try to extract water from it.
Actually, Yes.
Crush it up, reduce with hydrogen which gives you water vapor. Electrolyze the water to get back the hydrogen and you're left with oxygen. We've tested before (in Hawaii).
We already do both electrolysis and water vapor recovery on ISS, so half of the cycle is already fairly routine.
Oxygen is 6/7ths of the mass used in a hydrolox rocket engine and can even be used straight by some electric thrusters (such as the ELF thruster work that MSNW is getting paid to demonstrate in the >100kW class range by the NextSTEP NASA deep space initiative). That means that once you can demonstrate ISRU, you can refuel your SEP craft with asteroid material and at least 85% of your lander or high-thrust stage propellant as well.
That would certainly be enabling for extensive Mars exploration. (Or any kind of extensive space exploration.) Propellant is the vast majority of IMLEO. If you get 90%-95% of your propellant from space, you've just drastically reduced the per-mission launch requirements.
And if either Phobos or Deimos really is a captured carbonaceous chondrite asteroid, there can be a non-trivial (IIRC >10%) amount of water bound up chemically in the rock. The potential for buried ice on Phobos or Deimos is also very interesting, but would require different tools to access. If Phobos or Deimos is ARM's act 2, adding those extra capabilities (either sensors or drilling tools) might be feasible at a modest delta-cost.
~Jon
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#523
by
Robotbeat
on 12 Apr, 2015 01:46
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Even if we're just talking oxygen, though, this allows you to fill up on both ends, near Earth escape /and/ in Mars orbit. That's a big deal. In combination with Mars surface ISRU, that means all you really need for each mission is to get the astronauts to and from near-Earth-escape along with some food and a little hydrogen (which can be used to produce water for the crew), the rest can be reused or recycled. That's one rocket launch per Mars mission once it's set up (although it'd only be good for 10-15 missions before end of life).
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#524
by
TrevorMonty
on 12 Apr, 2015 05:19
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SEP tug not only delivers ISRU equipment it also provides the high powers required for resource extraction and processing.
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#525
by
notsorandom
on 13 Apr, 2015 19:59
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So realistically what will ARM cost? Squyres makes a pretty good point that the $1.25 billion dollar figure is not believable. This thing will have a suite of scientific instruments, a new larger than any previously built ion propulsion system, and some sort of rock grabber all for only $450 million more than OSIRIS-REx.
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#526
by
Robotbeat
on 13 Apr, 2015 20:27
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So realistically what will ARM cost? Squyres makes a pretty good point that the $1.25 billion dollar figure is not believable. This thing will have a suite of scientific instruments, a new larger than any previously built ion propulsion system, and some sort of rock grabber all for only $450 million more than OSIRIS-REx.
Osiris-Rex needs a return capsule.
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#527
by
jongoff
on 14 Apr, 2015 00:17
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So realistically what will ARM cost? Squyres makes a pretty good point that the $1.25 billion dollar figure is not believable. This thing will have a suite of scientific instruments, a new larger than any previously built ion propulsion system, and some sort of rock grabber all for only $450 million more than OSIRIS-REx.
Osiris-Rex needs a return capsule.
My guess is the cost will depend strongly on the procurement strategy. If they go NASA in-house, and insist on everything being built to Class A levels of reliability, I'm sure they could make it cost as much as they want to. If they leverage the fact that commercial companies are interested in this class of SEP stage (part of the point of four of the ARM BAA Phase I contracts), keep the instruments minimalist (reflying ones preferably that have flown before), and allow the capture mechanism to be a higher-risk (say Class C) element, $1.25B doesn't seem that crazy.
~Jon
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#528
by
Danderman
on 05 May, 2015 18:07
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This one won't survive the end of the Obama administration.
After the next president is installed, there will be period of a year or so in which the new administration will figure out the strategic issue of whether to replace ARM with a new mission or announce a technology development program so that One Day We Can Go to Mars.
A third alternative is for the new president to announce we are going to Mars but not really plan for it.
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#529
by
Robotbeat
on 05 May, 2015 18:24
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This one won't survive the end of the Obama administration.
After the next president is installed, there will be period of a year or so in which the new administration will figure out the strategic issue of whether to replace ARM with a new mission or announce a technology development program so that One Day We Can Go to Mars.
A third alternative is for the new president to announce we are going to Mars but not really plan for it.
Depends on who is elected. A lot of people seem to already think they know who it will be.
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#530
by
savuporo
on 19 Aug, 2015 17:54
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#531
by
redliox
on 19 Aug, 2015 18:28
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Btw, maybe i missed it or didnt see it posted, but there were a bunch of pretty ARM presentations at the recent SBAG meeting
http://www.lpi.usra.edu/sbag/meetings/jun2015/agenda.shtml
Although not directly related to ARM, but I also saw in their schedule a meeting and discussion of the small body Discovery missions. That would have been of interest.
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#532
by
NovaSilisko
on 19 Aug, 2015 18:33
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I really like the sound of the planetary defense demo, actually. I hope to see that happen.
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#533
by
DougSpace
on 06 Sep, 2015 07:13
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Concerning your cartoon, what about storing water ice in space and doing the electrolysis on demand in orbit/lagrange? No need to store leaking LH2. I think Doug Plata mentioned that idea.
I'm not sure that I've ever advocated storing water in space to electrolyze on demand. At any rate, there are alternatives to consider. Electrolyzed propellant could be produced and stored in permanently-shadowed craters on the Moon to be delivered anywhere in cis-lunar space on demand thereby potentially negating the need for most orbital depots. Likewise, periodic launches to LEO (such as by FH) followed by spiraling of cargo to an EML staging point using ion propulsion negates much of the need for in-space chemical propellant except for crew as well as cargo from LLO to Luna.
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#534
by
TrevorMonty
on 06 Sep, 2015 08:15
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Concerning your cartoon, what about storing water ice in space and doing the electrolysis on demand in orbit/lagrange? No need to store leaking LH2. I think Doug Plata mentioned that idea.
I'm not sure that I've ever advocated storing water in space to electrolyze on demand. At any rate, there are alternatives to consider. Electrolyzed propellant could be produced and stored in permanently-shadowed craters on the Moon to be delivered anywhere in cis-lunar space on demand thereby potentially negating the need for most orbital depots. Likewise, periodic launches to LEO (such as by FH) followed by spiraling of cargo to an EML staging point using ion propulsion negates much of the need for in-space chemical propellant except for crew as well as cargo from LLO to Luna.
Converting water to LOX and LH takes large amounts of energy, 1 ton of cryogenic fuel requires 6.7MW/Hr or 0.76KW 24/7 for a year (see attached paper). It is better to do as much of this conversion in space at a fuel depot where you have access to sun 24/7. Any space based (eg EML1) power plant is going to be cheaper per kW to put in place and maintain than a lunar power plant. The other plus is that because the fuel depot has a cryogenic plant, it can store cryogenic fuel indefinitely.
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20010039031.pdf
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#535
by
daveklingler
on 23 Sep, 2015 04:43
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Concerning your cartoon, what about storing water ice in space and doing the electrolysis on demand in orbit/lagrange? No need to store leaking LH2. I think Doug Plata mentioned that idea.
I'm not sure that I've ever advocated storing water in space to electrolyze on demand. At any rate, there are alternatives to consider. Electrolyzed propellant could be produced and stored in permanently-shadowed craters on the Moon to be delivered anywhere in cis-lunar space on demand thereby potentially negating the need for most orbital depots. Likewise, periodic launches to LEO (such as by FH) followed by spiraling of cargo to an EML staging point using ion propulsion negates much of the need for in-space chemical propellant except for crew as well as cargo from LLO to Luna.
Converting water to LOX and LH takes large amounts of energy, 1 ton of cryogenic fuel requires 6.7MW/Hr or 0.76KW 24/7 for a year (see attached paper). It is better to do as much of this conversion in space at a fuel depot where you have access to sun 24/7. Any space based (eg EML1) power plant is going to be cheaper per kW to put in place and maintain than a lunar power plant. The other plus is that because the fuel depot has a cryogenic plant, it can store cryogenic fuel indefinitely.
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20010039031.pdf
I see the part that says that making 500 tonnes of lox and lh2 would require 707 kWe (482 kw for electrolysis, 55 kw for hydrogen refrigeratiion, 78 kw for oxygen refrigeration, plus 15% margin) while the depot is in sunlight, but I'm not finding your 0.76KW number. What am I missing?
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#536
by
TrevorMonty
on 23 Sep, 2015 05:13
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0.76kw x8800hrs (1year) =6.7mw/hr
So product 1t of propellant a year you need 760W of continuous power.
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#537
by
daveklingler
on 25 Sep, 2015 05:36
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0.76kw x8800hrs (1year) =6.7mw/hr
So product 1t of propellant a year you need 760W of continuous power.
Ah. You mean 6.7 MW-Hrs, not 6.7 MW/Hr. I get it.
But the actual number in the paper is 707 kw, not 760, unless I'm still missing something? And I see 707 kw for 500 metric tons, which is only 12.5 kw-hrs per metric ton.
Of course, both times I've looked at this paper I've been a bit bleary-eyed, which is my lame excuse for missing something obvious, if in fact I have.
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#538
by
TrevorMonty
on 25 Sep, 2015 12:24
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At beginning of paper they say 380kw continuously over a year for 500t. 380kw/500 = 0.76kw per ton.
Because depot is in earth orbit it only gets sun for 61.5% of time so straight away you need to almost double size solar arrays. Hence 700kw.
NB a depot at EML1 would have sun 24/7.
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#539
by
daveklingler
on 26 Sep, 2015 04:22
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0.76kw x8800hrs (1year) =6.7mw/hr
So product 1t of propellant a year you need 760W of continuous power.
Okey doke. It all makes sense now. Sorry. I got tripped up over the 6.7MW/hr thing. But I think 7.6kw isn't that big an array for 500 mT of propellant, and I guess that's the authors' point. I'm now sold on taking water to orbit for propellant depots.
Thanks for posting that paper!
