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#300
by
Hop_David
on 17 Feb, 2015 01:59
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http://spacenews.com/op-ed-10-reasons-why-an-asteroid-redirect-mission-is-worth-doing/
By Jonathan Goff of Altius Space Machines
It's mostly just a toned down and professionalized version of the blog post I did a few weeks back on Selenian Boondocks. The SpaceNews guys liked it and thought it would make a good op-ed, so we decided to give it a bigger audience.
It'll be fun to see the comments and/or hatemail I get from this one. :-)
~Jon
Wow, Lori Garver commented on
Goff's article.
Her comment is consistent with
what she's been saying all along:
Yesterday, NASA Deputy Administrator Lori Garver opened the conference, describing NASA’s proposed asteroid retrieval mission, and the potential for private companies, like Planetary Resources, to contribute to the mission.
But there are those who will say Garver was only looking for something SLS and Orion could do. Garver is one of SLS and Orion's strongest critics. The notion that she was trying to find a mission to justify SLS is horribly clueless.
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#301
by
TrevorMonty
on 17 Feb, 2015 02:45
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Great article. ARM needs all the good PR it can get.
It may even become a tourist attraction one day.
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#302
by
john smith 19
on 17 Feb, 2015 07:43
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It's mostly just a toned down and professionalized version of the blog post I did a few weeks back on Selenian Boondocks. The SpaceNews guys liked it and thought it would make a good op-ed, so we decided to give it a bigger audience.
Re-reading this I wonder how many people could name
all of the reasons you gave for doing this. My guess is, not many.
When this was first proposed I thought it a brilliant first step to do ISRU by not having to haul 100s of tonnes up well just to get decent radiation shielding.
But I'd not realized there are so many
other reasons to do it.
BTW by "man tended habitats" are you (possibly) talking tests to close the life support systems loop?
With decent rad shielding and long term propellant storage that's starting to sound like the foundations for a
real exploration programme, almost by accident.
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#303
by
A_M_Swallow
on 17 Feb, 2015 17:59
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{snip}
BTW by "man tended habitats" are you (possibly) talking tests to close the life support systems loop?
With decent rad shielding and long term propellant storage that's starting to sound like the foundations for a real exploration programme, almost by accident.
The long term testing of life support systems is probably a useful spin off.
Any "man tended habitat" at an asteroid is likely to contain a laboratory.
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#304
by
jongoff
on 17 Feb, 2015 23:56
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It's mostly just a toned down and professionalized version of the blog post I did a few weeks back on Selenian Boondocks. The SpaceNews guys liked it and thought it would make a good op-ed, so we decided to give it a bigger audience.
Re-reading this I wonder how many people could name all of the reasons you gave for doing this. My guess is, not many.
When this was first proposed I thought it a brilliant first step to do ISRU by not having to haul 100s of tonnes up well just to get decent radiation shielding.
But I'd not realized there are so many other reasons to do it.
BTW by "man tended habitats" are you (possibly) talking tests to close the life support systems loop?
With decent rad shielding and long term propellant storage that's starting to sound like the foundations for a real exploration programme, almost by accident.
By man-tended habitats, I meant space facilities that don't continuously have astronauts at them. Ie they have people there for a few weeks at a time, then just robots for several months, etc.
~Jon
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#305
by
Robotbeat
on 18 Feb, 2015 23:27
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Good article! I think you've won me over to Option B, by the way (although Option A is still neat).
Also, I think Lunar DRO is essentially interchangeable with EML1/2, since getting between them takes delta-vs measured in tens or hundreds of m/s, not multiple km/s. At least in my mind. If you put a habitat in EML2, you can move it to EML1 or lunar DRO or even Earth-Sun Lagrange point just with on-board station-keeping propellant (if you're very careful with it).
It's my understanding a DRO can endure for quite a few decades without the need for station keeping.
EML1 and EML2 needs minor station keeping but when the object you're keeping in place is hundreds of tonnes, even a small delta V station keeping budget can be hard.
This is true, but the station-keeping requirements are only as large as your uncertainties. If you're clever, you can get them very small.
But that's kind of missing the point of what I really meant: If, for whatever reason (i.e. long-term stationkeeping requirements, etc), you change your mind of whether you want a spacecraft sitting at EML1, EML2, LDRO, or even ESL1/2, you can move the spacecraft to one of the other places with a relatively modest delta-v.
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#306
by
TrevorMonty
on 19 Feb, 2015 00:08
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Could a SEP do the station keeping? Hopefully in low thrust high ISP (high fuel economy) mode.
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#307
by
A_M_Swallow
on 19 Feb, 2015 05:07
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Could a SEP do the station keeping? Hopefully in low thrust high ISP (high fuel economy) mode.
Yes. Depending on which orbit you are in the burn time changes. Low lunar orbit may require burns to last 10 months per year, although you can have more than one gap.
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#308
by
Hop_David
on 19 Feb, 2015 16:18
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Good article! I think you've won me over to Option B, by the way (although Option A is still neat).
Also, I think Lunar DRO is essentially interchangeable with EML1/2, since getting between them takes delta-vs measured in tens or hundreds of m/s, not multiple km/s. At least in my mind. If you put a habitat in EML2, you can move it to EML1 or lunar DRO or even Earth-Sun Lagrange point just with on-board station-keeping propellant (if you're very careful with it).
It's my understanding a DRO can endure for quite a few decades without the need for station keeping.
EML1 and EML2 needs minor station keeping but when the object you're keeping in place is hundreds of tonnes, even a small delta V station keeping budget can be hard.
This is true, but the station-keeping requirements are only as large as your uncertainties. If you're clever, you can get them very small.
But that's kind of missing the point of what I really meant: If, for whatever reason (i.e. long-term stationkeeping requirements, etc), you change your mind of whether you want a spacecraft sitting at EML1, EML2, LDRO, or even ESL1/2, you can move the spacecraft to one of the other places with a relatively modest delta-v.
I suspect you're correct that it'd be easy to move between LDRO, EML1 and EML2.
But I have to admit I don't know squat about DROs.
I've heard them mentioned in the Keck paper and elsewhere. Orbital mechanics folks I have a lot of respect for say they're long term stable. But I hate taking anything on faith. Wish I knew some numbers so I could try to construct some models.
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#309
by
Proponent
on 19 Feb, 2015 22:26
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What do you need to know? Isn't it enough just to model an object in a retrograde lunar orbit at 60,000-ish kilometers?
I think it's going to be a little harder to cruise over to L1 or L2 than it would be from a prograde lunar orbit. My thinking is that in the DRO, the orbital angular momentum is reinforced by the moon's orbital angular momentum about Earth (the flip side of the DROs greater stability).
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#310
by
Hop_David
on 20 Feb, 2015 14:22
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What do you need to know? Isn't it enough just to model an object in a retrograde lunar orbit at 60,000-ish kilometers?
I think it's going to be a little harder to cruise over to L1 or L2 than it would be from a prograde lunar orbit. My thinking is that in the DRO, the orbital angular momentum is reinforced by the moon's orbital angular momentum about Earth (the flip side of the DROs greater stability).
Perilune, semi-major axis, inclination to the moon's orbital plane, barycentric longitude of perilune.
And all of the above assume an elliptical orbit. I'm not even sure the path's an ellipse. At around 60000 km from the moon I would guess the earth bends the ellipse about the moon. I've sometimes tried to use Kepler 2 body models to ball park velocity, position. But for paths near a body's sphere of influence this model can be way off.
I have a Java 3 body sim of the earth, moon & neglible mass 3rd body. To model a DRO I need a position vector as well as a velocity vector.
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#311
by
jongoff
on 20 Feb, 2015 16:24
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What do you need to know? Isn't it enough just to model an object in a retrograde lunar orbit at 60,000-ish kilometers?
I think it's going to be a little harder to cruise over to L1 or L2 than it would be from a prograde lunar orbit. My thinking is that in the DRO, the orbital angular momentum is reinforced by the moon's orbital angular momentum about Earth (the flip side of the DROs greater stability).
Perilune, semi-major axis, inclination to the moon's orbital plane, barycentric longitude of perilune.
And all of the above assume an elliptical orbit. I'm not even sure the path's an ellipse. At around 60000 km from the moon I would guess the earth bends the ellipse about the moon. I've sometimes tried to use Kepler 2 body models to ball park velocity, position. But for paths near a body's sphere of influence this model can be way off.
I have a Java 3 body sim of the earth, moon & neglible mass 3rd body. To model a DRO I need a position vector as well as a velocity vector.
Hop, you should ping Mike Loucks--he's a big fan of yours, and he can probably show you the tools you'd need to run an analysis like this. He's done a lot of work with lunar swingbys, WSB orbits, and recently DROs.
~Jon
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#312
by
Proponent
on 20 Feb, 2015 20:36
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What do you need to know? Isn't it enough just to model an object in a retrograde lunar orbit at 60,000-ish kilometers?
I think it's going to be a little harder to cruise over to L1 or L2 than it would be from a prograde lunar orbit. My thinking is that in the DRO, the orbital angular momentum is reinforced by the moon's orbital angular momentum about Earth (the flip side of the DROs greater stability).
Perilune, semi-major axis, inclination to the moon's orbital plane, barycentric longitude of perilune.
And all of the above assume an elliptical orbit. I'm not even sure the path's an ellipse. At around 60000 km from the moon I would guess the earth bends the ellipse about the moon. I've sometimes tried to use Kepler 2 body models to ball park velocity, position. But for paths near a body's sphere of influence this model can be way off.
I have a Java 3 body sim of the earth, moon & neglible mass 3rd body. To model a DRO I need a position vector as well as a velocity vector.
I've played around with DROs in my own simulation, and I can confirm your intuition that no DRO will be an ellipse with stationary Keplerian parameters. Therefore, I don't think it matters greatly that you have a particular set of initial parameters, since they're going to change relatively quickly anyway. What you can do is demonstrate that DROs are quite stable for a broad range of parameters (just let your sim run for a few decades) and that prograde lunar orbits of similar radii are not stable. Then you can look at what it takes to get from a DRO to an L-point. I don't think it will make a great deal of difference exactly which DRO you start from.
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#313
by
MP99
on 21 Feb, 2015 19:43
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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.
Serious question: You've constructed a round trip from EML2 to LEO that requires at least 6 distinct burns over several days. Because of that, you would probably need to avoid cryo LH2. Or would you not? So I'm validly curious what your solution is.
Option 1: Have a spacecraft that can avoid boil off. If you can do it for a propellant depot, then I guess you can do it for this as well. But how much would that weigh? Would it very negatively affect other aspects of the design?
Option 2: Use some other propellant. Like what? Would that be some methane / LOX engine? How much worse would the specific impulse be? Would water even be a step in the processes to make these?
Boiloff is a relative term. Depending on your heating and your level of insulation (and your amount of active cooling) you will have either zer boiloff or some finite rate of propellant loss. The heating rates once you get from from earth (which happens pretty quickly once you leave LEO) drop by almost an order of magnitude, so boiloff should also decrease substantially.
The question is how much propellant boils off, and can you live with it. With reasonably good insulation and/or sunshielding, it's probably not a big deal for missions shorter than a month, even with LOX/LH2. I know that's longer than has been demonstrated so far, but there's data on these things. The reason they haven't pushed this very hard so far is that for most Centaur missions you run out of either RCS propellants, battery juice, or pressurant long before then anyway. My guess is once IVF is working, you'll start seeing them doing longer missions.
~Jon
If you're running a relatively short mission with a low fundamental boiloff rate, I wonder if there's any point in compressing the boiloff into a COPV?
Obviously, pumping will create some heat, so you'd need to keep it away from the cryos, but it should stabilise down (to lox-ish temps?) if attached to a radiator. I'm assuming that heat input to the COPV (compressing the gas) will be low given the low boiloff rate.
Gas could be used for pressurization, running the IVF internal combustion engine, cold gas thrusters, etc.
Cheers, Martin
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#314
by
Hop_David
on 21 Feb, 2015 22:41
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I've played around with DROs in my own simulation, and I can confirm your intuition that no DRO will be an ellipse with stationary Keplerian parameters. Therefore, I don't think it matters greatly that you have a particular set of initial parameters, since they're going to change relatively quickly anyway. What you can do is demonstrate that DROs are quite stable for a broad range of parameters (just let your sim run for a few decades) and that prograde lunar orbits of similar radii are not stable. Then you can look at what it takes to get from a DRO to an L-point. I don't think it will make a great deal of difference exactly which DRO you start from.
I followed your advice. Launching from EML1 at about .4 km/s I got orbits that lasted 167 days which is longer than I expected.
The bright red pellet differs from the indigo pellet by only 2 or 3 meters per second. This seems to be a fragile orbit.
(The dark maroon and olive green paths are objects I placed at EML1 and 2 -- they tend to drift from their positions after a short time)
Then I tried launching from 10,000 kilometers above EML1 (wrt earth) or about 10,000 km deeper within the moon's gravity well. This seems to give pretty stable orbits. Here's after 20 years:
The slowest pellets differed from the fast by 6 meters/sec so these are less vulnerable than the orbits starting from EML1.
EML1 and 2 move prograde wrt to the moon at .15 or .16 km/s. So after doing a perilune burn to raise apolune, the above orbit would need to kill all it's apolune velocity and then spend another .15 km/s to match velocities with EML1 or 2.
It seems to me the LDROs are about .4 km/s from EML1 and EML2.
Edit: Let the sim run over night. About 100 years. There's still 3 DRO pellets!
Looking closely at the lower right a dark trail can be seen. This is a pellet I had placed at the leading trojan point. The pellet I had placed at the trailing trojan is gone. (When I have n-body sims that include the sun, EML4 and 5 are no longer permanent). These 3 DRO pellets have outlasted a trojan pellet.
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#315
by
Solman
on 23 Feb, 2015 03:04
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#316
by
Nilof
on 23 Feb, 2015 10:00
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[....]
Looking closely at the lower right a dark trail can be seen. This is a pellet I had placed at the leading trojan point. The pellet I had placed at the trailing trojan is gone. (When I have n-body sims that include the sun, EML4 and 5 are no longer permanent). These 3 DRO pellets have outlasted a trojan pellet.
Wow. Now THAT is really impressive.
What would the delta-v cost of moving into a highly elliptical Earth orbit or landing on the Moon be? Similar to EML1/EML2? If so, these two Lagrange points may not see a lot of traffic.
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#317
by
Hop_David
on 23 Feb, 2015 17:07
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[....]
Looking closely at the lower right a dark trail can be seen. This is a pellet I had placed at the leading trojan point. The pellet I had placed at the trailing trojan is gone. (When I have n-body sims that include the sun, EML4 and 5 are no longer permanent). These 3 DRO pellets have outlasted a trojan pellet.
Wow. Now THAT is really impressive.
What would the delta-v cost of moving into a highly elliptical Earth orbit or landing on the Moon be? Similar to EML1/EML2? If so, these two Lagrange points may not see a lot of traffic.
I've just been letting
my sim run. I attached a screen capture should anyone want to try my numbers.
When I came in this morning the sim's been running 240 years. One of the green DRO pellets was rather forcefully evicted sometime during the night. And you can see some of pellets that were evicted earlier occasionally revisit their old neighborhood. The EML4 and 5 pellets have been expats for some time.
Are these DROs easy to reach?
The DRO pellets seem to be moving about .3 km/s wrt moon. The moon moves about 1 km/s wrt earth. So at the DRO's furthest point from the earth it's moving .7 km/s wrt earth. A 6678 x 430000 km ellipse has an apogee speed of about .17 km/s. So I am guessing a little more than .5 km/s for DRO rendezvous at apogee.
For all the really big ellipses, the LEO burn is about 3.1 km/s. So I'd say LEO to DRO is around 3.6 km/s. This about the same as a quick route to EML1.
The DRO's I'm looking at are near equatorial orbits. I'm guessing DRO to landing on lunar equator is about 2.7 km/s and DRO to landing on a lunar pole is about 2.8 km/s.
I've always assumed there were weak instability boundaries leading from EML1/2 to any point on the lunar surface, but I don't know this for a fact. So I've called delta V from EML1/2 to the moon 2.5 km/s (a little over lunar escape velocity).
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#318
by
CJ
on 24 Feb, 2015 00:16
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Regarding the "Option B" under consideration (grabbing a small boulder off a larger asteroid), I can't seem to find any mention of how, exactly, the existence of a suitable-size boulder on a target asteroid would be known? It seems to me that one would have to know this in advance of sending the ARM retrieval probe, yet I can't see any mention of this factor?
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#319
by
Proponent
on 24 Feb, 2015 01:26
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Have a look
here. The three current candidates have all been imaged -- one (Itokawa) by a Japan's Habayusa spacecraft, the other two (Bennu and 2008 EV
5) by radar.