Pros and cons of lunar plan....article

[holmec]

The link to the article follows:<br />http://www.space.com/adastra/adastra_zubrin_051208.html<br /><br />I have to confess, I do not totally understand or agree with the cons the writer brings up.<br /><br /> />On the more problematic side is the decision to develop such a large Crew Exploration Vehicle (CEV). While a large CEV certainly enables larger crews and greater comfort, it will cost more to develop, produce and launch than a smaller capsule. Furthermore, because of its excessive mass, the large CEV makes direct return lunar missions impossible, thus mandating a lunar orbit rendezvous mission architecture. This, in turn, will require the costly development and production of lunar excursion modules, and impose return rendezvous phasing complications that could hamstring the operations of a lunar base, especially if surface stays greater than two weeks are desired.<<br /><br />What seems to escape the writer is that lunar orbit rendevous works, and trying anything else just might be more costly. Plus I do not see how earth orbit rendezvous will hamstring a lunar base. The writer gives no explination.<br /><br /> />Another cause for concern is the decision to launch the CEV after the HLV delivers the rest of the mission components to orbit. The HLV’s cargo will include stages employing cryogenic liquid hydrogen/oxygen propellant, and this propellant will start to boil away immediately after launch. Thus for the mission to succeed, the CEV must be launched on time, within a few weeks at most of the prior flight, without fail.<<br /><br />What??? Boil away?? to where??? And don't we have fridges and airconditioners on Earth that we cannot keep the fuel form "boiling away"? This makes no sense to me.<br /><br /> />Operating the shuttle program for the next five or six years to deliver a few space station payloads early will cost us $30 billion. All that money could be saved simply <div class="Discussion_UserSignature"> <p> </p><p><font color="#0000ff"><em>"SCE to AUX" - John Aaron, curiosity pays off</em></font></p> </div>

 

[formulaterp]

<font color="yellow">What seems to escape the writer is that lunar orbit rendevous works, and trying anything else just might be more costly. Plus I do not see how earth orbit rendezvous will hamstring a lunar base. The writer gives no explination. </font><br /><br />Actually Zubrin is saying that lunar orbit rendezvous (not earth orbit) will hamstring the lunar base. I imagine his concern is that the lack of a direct return capability means that a long term crew on the lunar base also requires a CEV in lunar orbit at all times. This may not be practical.

 

[darkenfast]

"What??? Boil away?? to where??? And don't we have fridges and airconditioners on Earth that we cannot keep the fuel from "boiling away"? This makes no sense to me. "<br /><br />Keeping crygenic liquids from "boiling off" in space is done by passive means, such as insulation. Active means, such as a refrigeration unit, are not feasible. The vacuum of space is itself the best insulation, which is why it can be done at all. Liquid Hydrogen is quite a bit colder than the other commonly used liquids, hence is the hardest to accomodate. This makes Liquid Oxygen and Liquid Methane good choices, as they last a lot longer. The improved capability over the previously used hypergolic fuels, and the possibility of producing Methane elsewhere in space make it worth the change.

 

[radarredux]

> <i><font color="yellow">What??? Boil away?? to where??? And don't we have fridges and airconditioners on Earth that we cannot keep the fuel form "boiling away"? This makes no sense to me.</font>/i><br /><br />Hydrogen, being the smallest atom, has a habit of leaking through containers. Also, being the smallest and lightest, in gas form, it takes up the greatest amount of volume for a given pressure..<br /><br />The fuel cell industry here on Earth face similar challenges. How do you store the Hydrogen?</i>

 

[tomnackid]

Actually, H is the lightest atom, but the Helium molecule is smaller since H always exists in nature as molecules of H2 but Helium, being a noble gas, exists as individual atoms.

 

[holmec]

>keeping the cryogenic prop from "boiling away" is a big issue however modern insulation systems can keep the prop for much longer than a few weeks.<<br /><br />So I assume your saying that within a period of a few weeks the plan will still work, Shuttle_guy. <div class="Discussion_UserSignature"> <p> </p><p><font color="#0000ff"><em>"SCE to AUX" - John Aaron, curiosity pays off</em></font></p> </div>

 

[holmec]

I see your point, but the plan doesn't call for a permanently manned base, more of a outpost to be frequented by humans. Anyway the CEV is supposed to be remotely controled. What difference does it make if its "parked" in lunar orbit, just as long as the hydrogen fuel doesn't deplete? <div class="Discussion_UserSignature"> <p> </p><p><font color="#0000ff"><em>"SCE to AUX" - John Aaron, curiosity pays off</em></font></p> </div>

 

[holmec]

>This makes Liquid Oxygen and Liquid Methane good choices, as they last a lot longer.<<br /><br />Whick poses a question. For the booster to launch the CEV and LM to the moon, would liquid methane leak less and would it be a better choice?<br /><br />Also will methane be a better choice for the CEV's service module so the astronauts can get back to earth? <div class="Discussion_UserSignature"> <p> </p><p><font color="#0000ff"><em>"SCE to AUX" - John Aaron, curiosity pays off</em></font></p> </div>

 

[holmec]

>"Also will methane be a better choice for the CEV's service module so the astronauts can get back to earth?"<br /><br />I do not understand your question. <<br /><br />Thanks, you answered the question. <div class="Discussion_UserSignature"> <p> </p><p><font color="#0000ff"><em>"SCE to AUX" - John Aaron, curiosity pays off</em></font></p> </div>

 

[josh_simonson]

Now if we launched the crew to a useful space station, then launched the HLV second while the crew were comfortably housed, there wouldn't be a problem here.

 

[holmec]

>Now if we launched the crew to a useful space station, then launched the HLV second while the crew were comfortably housed, there wouldn't be a problem here.<<br /><br />I really don't think this is an unmanagable problem anyway. I think the writer of the article is bringing up weird questions. <br /><br />like shuttle_guy said:<br /> />I am saying a few weeks delay in launching the CEV to the on orbit stack is not a problem. <<br /><br />---its hard to get a plain "Yes" from an engineer.----<br /> <div class="Discussion_UserSignature"> <p> </p><p><font color="#0000ff"><em>"SCE to AUX" - John Aaron, curiosity pays off</em></font></p> </div>

 

[radarredux]

> <i><font color="yellow">lunar orbit rendezvous (not earth orbit) will hamstring the lunar base.</font>/i><br /><br />This has bothered me for a while: if the LSAM ascent vehicle cannot dock with the CEV, is the crew hosed? Or if they dock to the CEV and find something wrong with the CEV, is the crew hosed?<br /><br />One of the criticisms of the t/Space CXV-CEV architecture is that there was no direct abort to Earth option for the CEV. But it seems that the current ESAS does not have a direct abort to Earth capability from the Lunar surface either.</i>

 

[holmec]

>But it seems that the current ESAS does not have a direct abort to Earth capability from the Lunar surface either.<<br /><br />Abort from the surface of the moon???? What is this science fiction??? When has any explorer aborted from an island to his homeland? If we had that exploration would be simple and risk free.<br /><br />Aborting is for flying projectiles, when your on the moon there is no abort. Your stable, your alive. You just need ways to keep alive for long periods of time if something goes wrong.<br /><br />I think someone needs to have a hiking/campling experience away from civilisation then you'll understand. <div class="Discussion_UserSignature"> <p> </p><p><font color="#0000ff"><em>"SCE to AUX" - John Aaron, curiosity pays off</em></font></p> </div>

 

[subzero788]

On the subject of possible failures, one of the risks with the Apollo LM was that the everything depended on the single accent engine--if it was to fail then 2 men would have been stuck on the moon, with no hope of rescue. I am aware that the design of the new LSAM is not very clear at this stage but I would think a certain level of redundancy would be appropriate, such as a backup engine or ensuring enough supplies to last an extra week or more so I resuce could be attempted. Has anyone heard anything about to this or is it still to early?

 

[dobbins]

"If we die, we want people to accept it. We are in a risky business and we hope that if anything happens to us it will not delay the program. The conquest of space is worth the risk of life."<br />-- Gus Grissom<br /><br />Have we become so risk adverse that we lost sight of the fact that some risks are worth taking?<br /><br />

 

[nyarlathotep]

>>"Have we become so risk adverse that we lost sight of the fact that some risks are worth taking?"<br /><br />Scrimping on engine out capability on a $150B vehicle to save a dozen extra pounds for moonrocks is not a risk worth taking.

 

[dobbins]

Well, let us know when you find that magic spare engine that only weighs a dozen pounds.<br /><br />

 

[krrr]

The Soviet LK had a backup engine. Its mass was 126 pounds. Scale that up to an LSAM ascent stage and you get... well yes a little more than a dozen pounds but not that much.<br /><br />Lunar ascent is the most dangerous part in a lunar expedition. Some extra redundancy isn't unreasonable there.<br />

 

[radarredux]

> <i><font color="yellow">Well, let us know when you find that magic spare engine that only weighs a dozen pounds.</font>/i><br /><br />Got one, and its a Methane/LOX! <img src="/images/icons/smile.gif" /><br /><br />http://www.xcor.com/methane_rocket_engine-content.html</i>

 

[dobbins]

"Lunar ascent is the most dangerous part in a lunar expedition."<br /><br />No, transEarth injection is the most dangerous. If you fail to achieve the correct orbit on ascent the CEV can come down to where you are. If that burn leaving Lunar orbit fails you are dead meat.<br /><br />

 

[bwhite]

RL-10s weigh 300 pounds each. And have run on methane.

 

[krrr]

If the engine fails within the first 95% of the ascent, the result is a crash.<br /><br />TEI failure results in some orbit from which a rescue by another CEV would be at least theoretically possible.

 

[holmec]

>Spider: Excellent telling of how Grumman built the LEM, how LOR was decided etc... <<br /><br />LOL<br /><br />I guess its that managers accept risk and engineers don't but explain everything. <div class="Discussion_UserSignature"> <p> </p><p><font color="#0000ff"><em>"SCE to AUX" - John Aaron, curiosity pays off</em></font></p> </div>

 

[radarredux]

> <i><font color="yellow">There is a hugh jump from that thruster to a say, 15,000 pound thrust engine.</font>/i><br /><br />Yeah, but this one looks so cute <img src="/images/icons/laugh.gif" /></i>