Why LH2/LOX for lunar lander?

Why is NASA going with LOX/LH2 for the new lunar lander instead of the
seemingly more reliable hydrazine/NO4 Apollo LEM engines? It would
seem that the more easily stored hydrazine/NO4 would make for more
adaptable lengthy missions.

I understand that there were major concerns about a LEM being stranded
on the surface. Considering the hypergolic nature of the propellent,
how could this happen?
Does anybody have any info on the reliability of hydrazine based engies
vs LOX/LH2 engines?

:

Why is NASA going with LOX/LH2 for the new lunar lander instead of the
seemingly more reliable hydrazine/NO4 Apollo LEM engines? It would
seem that the more easily stored hydrazine/NO4 would make for more
adaptable lengthy missions.

Because NASA is full of hydrogen manics. Really, early in the development of
liquid fueled rockets ISP was thought to be the most important parameter to
maxiumize and the idea has stuck around since even when simple math shows it
is not the best way to go to cut costs, handling problems, toxic releases,
storage problems etc. NASA just loves hydrogen!

I understand that there were major concerns about a LEM being stranded
on the surface. Considering the hypergolic nature of the propellent,
how could this happen?
Does anybody have any info on the reliability of hydrazine based engies
vs LOX/LH2 engines?

Consider, for long term use how many sats use LOX/LH2 vs hydrazine/NO4? If
you are going to stay on the moon for more than a day what would you rather
have?

Earl Colby Pottinger

--
Cruising, building a Catamaran, Rebuilding Cabin, New Peroxide Still Design,
Writting SF, Programming FOSS - What happened to the time?

On 10 May 2006 08:59:33 -0700, wrote:

Why is NASA going with LOX/LH2 for the new lunar lander instead of the
seemingly more reliable hydrazine/NO4 Apollo LEM engines?

You sure they are? The original plan was LOX/Methane, but they've
dropped the Methane idea (for now, although some work seems to be
continuing). I haven't heard what they're replacing it with, but I'd
be surprised if its LH2.

It would
seem that the more easily stored hydrazine/NO4 would make for more
adaptable lengthy missions.

At the cost of being nasty to handle. NASA's trying to get out of the
toxic propellant business.

Brian

In article .com,
wrote:
Why is NASA going with LOX/LH2 for the new lunar lander instead of the
seemingly more reliable hydrazine/NO4 Apollo LEM engines?

They've always planned to use something somewhat more storable for lunar
*ascent* propulsion. They would prefer to avoid N2O4/hydrazine and such,
because those compounds are so toxic and so dangerous to handle that they
dramatically run up costs. They'd originally hoped for LOX/methane, but
budget trouble is pushing them back toward N2O4/hydrazine at last report.

The reason for wanting to use LOX/LH2 for lunar *descent* is their
aversion to in-orbit assembly. If you insist that everything (except
perhaps the crew) must go up in one big launch, suddenly the total fueled
mass of the lander matters a great deal. And within a given total lander
mass, you can put a lot more payload on the lunar surface with LOX/LH2
descent propulsion than with LOX/methane or N2O4/hydrazine. Storing LH2
for the few days needed to get from the Earth to the Moon is not a big
problem.

Apollo might well have used a LOX/LH2 descent stage if it had started a
little bit later. As it was, at the time the basic decisions had to be
made, LOX/LH2 propulsion was still troublesome, and it seemed too risky.
LOX/LH2 descent propulsion was penciled in for follow-on systems only.
By the time the LM actually flew, only a few years later, LOX/LH2 was
under control and the early decision looked overly conservative. (Note
that the LM descent stage *did* use cryogenics -- the helium for tank
pressurization was stored that way.)

I understand that there were major concerns about a LEM being stranded
on the surface. Considering the hypergolic nature of the propellent,
how could this happen?

Tank leaks. Helium leaks. Plumbing malfunctions. Overly-hard start
damaging the engine (a real worry -- excessive pressure transients at
startup were never entirely cured). Stage-separation problems.

Does anybody have any info on the reliability of hydrazine based engies
vs LOX/LH2 engines?

Any propellant-choice effect is swamped by differences between different
engines. The LOX/LH2 RL10 is one of the most reliable sizable rocket
engines ever built, but they aren't all like that.
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. |

wrote in news:1147276773.299680.300230
@j33g2000cwa.googlegroups.com:

Why is NASA going with LOX/LH2 for the new lunar lander instead of the
seemingly more reliable hydrazine/NO4 Apollo LEM engines?

NASA helpfully documented the reasons for all their decisions in the ESAS
Final Report.

rant
You'd think, several months after its release, that people would at least
refer to it when trying to understand NASA's reasons for doing things
rather than falling back on hoary conspiracy theories about hydrogen
mafias.
/rant

http://www.nasa.gov/mission_pages/exploration/news/ESAS_report.html

The LSAM reference design is given on pp. 23-24, and the results of the
trade studies that led to that design are given on pp. 16-22.

It would
seem that the more easily stored hydrazine/NO4 would make for more
adaptable lengthy missions.

The LSAM only uses LOX/LH2 for the LOI/descent stage. Since landing is only
a few days after launch, storability is less of a concern. The ascent stage
uses LOX/LCH4, which is more storable than LOX/LH2 but not as storable as
hypergolics.

As for reliability, the descent engines would be derived from the extremely
reliable RL-10 engine.

After the report was published, there have been rumors that the ascent
stage could wind up using hypergolics or hydrogen due to concerns over
development costs of LOX/LCH4.

LOX/LCH4 out?
http://www.nasaspaceflight.com/content/?id=4191

LOX/LCH4 in?
http://www.nasaspaceflight.com/content/?id=4286

Live by the Rumor, Die by the Rumor:
http://www.nasaspaceflight.com/content/?id=4430

--
JRF

Reply-to address spam-proofed - to reply by E-mail,
check "Organization" (I am not assimilated) and
think one step ahead of IBM.

For all the right reasons, instead of LOx/LH they should be using the
likes of h2o2/c3h4o

For their moon exit phase, a little kick start directly towards LL-1
and then the use of LRn--Rn--ion thrusters should do the trick.
After all, there's hardly any logic in folks returning from the moon if
their banked bone marrow is simply going to be too little too late in
order to save their day. In other words, the gamma and
secondary/recoil worth of hard-X-rays (especially by day) is going to
insure that no human DNA is ever going to be unscaved.

Aluminum is nearly transparent to gamma, and it's hardly worth
moderating the likes of hard-X-rays. The usage of UHMW/Polyethalene or
similar density to H2O is simply going to demand too much volume.
-
Brad Guth