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(Space.com)   Hold everything. NASA is sending men back to the moon   (space.com) divider line 9
    More: Unlikely, NASA, SLS, John Logsdon, lunar exploration, lunar orbit, professor emeritus, space launch, Deep-Space Station Missions  
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4088 clicks; posted to Geek » on 09 Nov 2012 at 9:20 AM (1 year ago)   |  Favorite    |   share:  Share on Twitter share via Email Share on Facebook   more»



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Archived thread
2012-11-09 10:29:07 AM
2 votes:

cman: Not really. We have a lot of technology that can get us there, it is simply a matter of logistics. It takes 6 months to get from the earth to mars and really, stocking enough food, water, oxygen, fuel, and various supplies for human survival is extremely difficult that far away from earth. Plus, there is also the matter of atrophy. In a 0 gravity environment, your muscles that keep you standing upright atrophy. 6 months of that is gonna be extremely harsh on the human body.

We still have a ways to go before we can send a man to mars.


You do know that people have been on the ISS much longer than 6 months, right? They have quite expanded routines for muscle conditioning and fighting atrophy. And stocking/supplying it is routine for long periods of time. There's entire logistical processes and procedures to manage supply, and they're quite mature. Sure, they'd need to be adapted and altered for a vehicle with different purposes, but it's not like it's far-fetched.
2012-11-09 06:52:42 PM
1 votes:

dittybopper: MrBallou: Staging, not taking everything with you, etc. I'll let somebody else do the math. My point is that it's not the same as LEO and there are reasons to be there.

That makes sense if you do something useful at L2. One could make a better argument for the Moon itself, because there is the possibility of mining it for construction materials and fuel, and the gravity well you have to climb out of is much more modest than that of the Earth. You can't mine local resources at L2, though.

Just pulling numbers out of my ass, I find it hard to believe that it would be cheaper to send 5 payloads of 100,000 lbs to L2 for subsequent assembly and launch to than it would be to send 5 payloads of 170,000 lbs to LEO* for the same. In the first case, you get a total vehicle/fuel weight of 500,000 lbs, and in the second, 850,000 lbs.

I suppose you could mine and refine on the moon, and shoot it up to L2 for assembly, but then you have a large infrastructure, and that's extra cost. You've got to maintain a presence both on the moon and at L2. If you were going to do something like that, might as well just assemble in lunar orbit: You don't have the problems of drag inherent with LEO on Earth.

You don't *NEED* to worry about staging so much from orbit to wherever. You send up the payloads one at a time, assemble them in orbit, then you have a single stage to boost you out of orbit. One large stage from LEO is more efficient than a bunch of smaller ones to boost you to L2 for assembly, and then a subsequent (smaller) booster to get you to your ultimate destination. You could boost the LEO-To-Asteroid-And-Back stage to orbit pressurized but unfueled, and send up subsequent "space tankers" (essentially boosters with a big tank on on top) designed to rendezvous with the empty LTAAB and fill it up. And you could send up the crew module separately also. Obviously, you're going to want to use non-cryogenic fuels.

*Numbers based upon throw weights of Apollo CSM/LM combo ...


I am not a rocket scientist, so I could be grossly misunderstanding this, but I believe you can get to L2 with very little fuel cost by using a Lissajous orbit. So putting the assembly/refuel point at L2 would give you all the benefits of L2 over LEO (no aerodrag and reboosting required, lower fuel evaporation, and apparently it's a much more favorable environment for the hardware itself) with very little fuel cost.

Finally, there's this from actual rocket scientists:
A typical Mars departure delta-V of 4.3 km/sec (from LEO) is obtained with a perigee burn of less than
1 km/sec. Because of this we not only cash in our savings but the vehicle doing this last bit of work can be very
small. Its dry mass can be much smaller than for a traditional system or conversely our existing vehicles can do
proportionately larger tasks. For example, a Centaur class vehicle can move a 7t spacecraft from LEO to L2, refill
there, execute an Oberth exit burn, and retain enough propellant to lose over 40 lbs per day during the 8½ month
transit and finally execute a 2.7 km/sec insertion burn at Mars. In other words, a depot-augmented, long-duration
Centaur can move to Mars orbit what we can barely move to geostationary orbit on the largest rocket in the US
inventory using our existing approaches.
2012-11-09 11:02:43 AM
1 votes:

President Merkin Muffley: dittybopper: President Merkin Muffley: Bone loss as well and unlike muscle atrophy there seems to be no way to counter it.

Then we'll just have to get there faster, won't we?

Oh, man that's brilliant! Somebody call NASA, they've got untapped genius right here!


We have the technology to get there faster. It's just expensive, and we're not allowed to do it because of an international treaty that is applicable to weapons testing, but was written in such a manner to outlaw *ALL* nuclear explosions in space.

If we were to get that out of the way by amending the 1963 test ban treaty, then it would be like that line in "Mad Max": Speed's just a question of money. How fast you wanna go?
2012-11-09 10:55:40 AM
1 votes:

Feepit: FTFA: The space agency has apparently been thinking about setting up a manned outpost beyond the moon's far side, both to establish a human presence in deep space and to build momentum toward a planned visit to an asteroid in 2025.

I wasn't aware deep space was not only within our solar system but also within our planetary system!


There's not a single clear definition of deep space. It's generally taken to mean at minimum outside the solar system, but it can also refer to outside the Earth-Moon system, or even simply outside LEO. For example, the Deep Space Network is a network of antennas to communicate with interplanetary probes (mostly) inside our solar system.

dittybopper: Abe Vigoda's Ghost: Jackson Herring: Wait, I've been told by certain rugged independent farkers that Fartbama killed the space program

He definitely did not help it; him or GW. And so far, this is just a rumor.

This.

Also, why *NOT* announce it before the election? Announce it as a stimulus, and as a way to put America back on track as the leader in space exploration. It shows vision, forward thinking, and an eye to the future. Have a JFK moment, as it were. It wouldn't have hurt him with his base, and it could have only helped by making Romney either agree it's a good idea, or attack it and look like someone who doesn't want America to be at the forefront of space exploration.

It's a rumor, and actually not really a credible one at that: What can you do at L2 that you can't do in LEO? And being on the Moon confers certain advantages that come from having at least some gravity: You don't have to design the equipment intended to be used solely on the surface to work in 0g, and the cost of getting to the surface of the Moon is only very slightly higher than getting to L2.

I just can't really see a good reason for a manned presence at L2 at this point. As an outpost for travelling into the Solar System? Again, you can do that cheaper from LEO.


The Lagrangian points have the benefit of using much less fuel to remain in place than LEO. Even in high LEO, satellites must use fuel to correct their orbits due to drag from the thin atmosphere that's still present. At the Lagrangian points, the fuel required to park there is almost negligible. Additionally, the way the trajectories work out, it would be much better to have a refueling pit-stop parked at Earth-Moon L2 than in LEO for spacecraft leaving the Earth-Moon system, if you're designing your spacecraft to refuel in space before heading off. Once at L2 and refueled, the escape velocity from the Earth-Moon system is miniscule compared to LEO. In the case of the refueling depot, it's also much colder at L2, which results in less fuel evaporation while waiting for the next spacecraft to come refuel.

dittybopper: MrBallou: dittybopper: Abe Vigoda's Ghost: Jackson Herring:
You still have to get from Earth to L2. There ain't no such thing as a free lunch. Once you are there, the *REMAINING* energy required to get to the asteroid is less, but the *TOTAL* energy expended is the same.


Well if you're going for an in-space refuel architecture, you greatly simplify the probe launcher, as you now only need enough fuel to get you to L2 instead of all the way to your target. That results in a big fuel and therefore weight savings on your lift rocket. Of course, the rocket to bring fuel to the refuel depot still has to bring that fuel there (unless you're mining it from the Moon or something), so I'm not sure how the net fuel usage works out, but I imagine it would be greatly more fuel and cost efficient than a LEO refuel.
2012-11-09 10:31:57 AM
1 votes:

cman: dittybopper: Cythraul: Abe Vigoda's Ghost: Cythraul: Why?

Good practice for a manned Mars mission.

I don't even think we should be trying to do manned missions to Mars with our current level of technology. I keep reading about how extremely dangerous it is. Yes, yes, I know, nothing is discovered without risk.

We have the technology to do it relatively safely. It's just a question of money, not technology.

Not really. We have a lot of technology that can get us there, it is simply a matter of logistics. It takes 6 months to get from the earth to mars and really, stocking enough food, water, oxygen, fuel, and various supplies for human survival is extremely difficult that far away from earth. Plus, there is also the matter of atrophy. In a 0 gravity environment, your muscles that keep you standing upright atrophy. 6 months of that is gonna be extremely harsh on the human body.

We still have a ways to go before we can send a man to mars.


All those issues go away when you get there faster, and we can get there faster than six months. In fact, with a modest Project Orion vehicle, boosted to Earth orbit by the equivalent of 3 Saturn V-class rockets and assembled in orbit, you could do a round trip to Mars and back in about 125 days, or just about 4 months. We have experience with that length of time being weightless (and it would actually be half that: There would be time on Mars where they'd have some gravity).

We could build such a vehicle now. There are only two things standing in the way: Money, and the 1963 Nuclear Test Ban Treaty, which forbids nuclear explosions in space. The second object could be dealt with by amending the treaty to forbid all non-propulsion nuclear explosions in space.
2012-11-09 10:28:49 AM
1 votes:

dittybopper: Abe Vigoda's Ghost: Jackson Herring: Wait, I've been told by certain rugged independent farkers that Fartbama killed the space program

He definitely did not help it; him or GW. And so far, this is just a rumor.

This.

Also, why *NOT* announce it before the election? Announce it as a stimulus, and as a way to put America back on track as the leader in space exploration. It shows vision, forward thinking, and an eye to the future. Have a JFK moment, as it were. It wouldn't have hurt him with his base, and it could have only helped by making Romney either agree it's a good idea, or attack it and look like someone who doesn't want America to be at the forefront of space exploration.

It's a rumor, and actually not really a credible one at that: What can you do at L2 that you can't do in LEO? And being on the Moon confers certain advantages that come from having at least some gravity: You don't have to design the equipment intended to be used solely on the surface to work in 0g, and the cost of getting to the surface of the Moon is only very slightly higher than getting to L2.

I just can't really see a good reason for a manned presence at L2 at this point. As an outpost for travelling into the Solar System? Again, you can do that cheaper from LEO.


Not a physicist, but I think it has something to do with this:

mygravitywell.com
/quite hot
2012-11-09 10:09:17 AM
1 votes:

Cythraul: Abe Vigoda's Ghost: Cythraul: Why?

Good practice for a manned Mars mission.

I don't even think we should be trying to do manned missions to Mars with our current level of technology. I keep reading about how extremely dangerous it is. Yes, yes, I know, nothing is discovered without risk.


I support such a mission for one thing: pride. In our current climate we Americans are miserable. It would be nice to be able to have something that could bring us together and be proud to be American, not Democrat, Republican, Libertarian, Reptilian, but American. The moon landings in the 60s were extremely important to our nations psyche due to only bad news on the news (war in Vietnam, MLK getting shot, race riots, etc). That made us proud to be an American back then and a mission to mars would do the same for us here.
2012-11-09 09:57:02 AM
1 votes:
This article explains NASA's basic problem. Whatever project anybody might agree on every two years the politics flips over and their priorities are changed to suit the whim of Washington whether they like it or not. You can't put a 10+ year in place and any expectation of seeing it through.
2012-11-09 09:42:16 AM
1 votes:

Cythraul: Why?


Good practice for a manned Mars mission.
 
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