Re: LSAM
- From: John Schilling <schillin@xxxxxxxxxxxxx>
- Date: 7 Apr 2006 13:20:53 -0700
In article <1144373040.583282.36820@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>, Jake McGuire
says...
John Schilling wrote:
That was my question. *What* added functionality? Assuming a vertical
rocket landing CEV, what added functionality is required for it to also
serve as an LSAM?
At a minimum, the CEV needs lunar surface thermal control, lunar night
power storage (?), lunar surface dust mitigation, and internal
operations in a gravity field. The CEV may also need lower-thrust
rocket engines for the final descent to the lunar surface.
I don't think there's any expectation that a bare CEV is going to sit
out a lunar night. If it's on the moon past sunset, it will be at some
sort of a lunar base, which can provide support services. I think.
Plausible. I don't even know when the first scheduled nighttime
mission under the current "plan" is.
And the thrust differential is partially mitigated by the fact that
the CEV will touch down on the Moon with half a tank of gas, whereas
it will be dry landing on the Earth. You may be able to do without
a second set of engines.
So now you have engines inside the heat shield,
Or engines on the lee side of the vehicle (e.g. DC-X/Delta Clipper).
Or a CEV propulsion module seperate from the CEV crew entry module
(e.g. Apollo CSM).
And you need one of those options *anyhow*. Even without lunar
landing on the menu, the CEV needs a few km/s of delta-V for its
other mission requirements, and it needs a way to get its crew
down to Earth. So, one way or another, with or without the lunar
landing, you'll need serious engines and a serious heat shield
on the same vehicle.
and engines that are going to be used for three thousand meters per
second of delta-V (assuming a lunar crasher descent stage) in vacuum.
Right. I'd actually like to get that up to 4,500 m/s. That alllows
you to do everything from lunar deorbit through Earth return with no
further staging, seperation, or refuelling events, and I think it can
reasonably be done. But, 3000 m/s as a minimum.
The CEV is going to need that anyhow, either integral or from a closely
coupled service module, space tug, whatever. Might as well give it
the integral capability and just add external tankage as needed.
Or, if we're going the space tug/service module approach, make that the
propulsive unit for the CEV/LSAM as well. Again, overlapping requirements
and external tankage.
That traditionally drives you to large nozzles, which are hard-ish to >package.
External tanks will also make RCS system design trickier,
but it's possible that something that can handle wind loads while empty
will be able to handle control loads when full.
And the split-vehicle approach means the CEV has to handle a docked LSAM.
If it can do that, it can probably handle a drop tank.
Thermal control, dust mitigation, and internal layout w/re gravity,
sure. I don't think those are going to seriously compromise CEV
design.
There's some discussion of this in section 4 of the ESAS final report
[1]. The result came out as "going to be a pain to accomodate, not
worth it", but I find a lot of their arguments to be pretty thin. Like
how no docking mechanism on a lunar CEV/LSAM reduces commonality with
the ISS CEV. There also seems to be a fair bit of "We consider Design
1. X is a problem with Design 1, so we reject it. We now consider
Design 2. X is a problem with Design 2. It turns out that X is
actually not important, so we will go with Design 2."
Thanks for the reference, and yes, some of the logic is rather strained.
NASA, clearly wants to do Apollo all over again, as closely as possible
only bigger. I don't think that's the way to go.
Bottom line: You need a propulsion module that can carry four canned
astronauts from LLO to the lunar surface and back again. Whether that
propulsion module is integrated with the tin can or a seperate unit,
the following things seem almost trivially true:
A - it can carry four canned astronauts from LLO to lunar surface and
back whether we call the can an "LSAM" or a "CEV"
B - the same propulsion module can carry an LSAM/CEV from LEO to LLO,
and then from LLO back to LEO, with only extra fuel required.
C - the astronaut can suitable for a week or two on the lunar surface,
is mostly suitable for a week or two in space.
So, do the detail work to make the capsule multifunctional, decide whether
the high-deltaV propulsion module is integral or seperate, add external
tanks, and build one vehicle that gets the job done.
Yes, it means you have to do things like carry the weight of the heat
shield down to the lunar surface and back. That's not a huge deal, not
nearly so big a deal as designing an entire second spacecraft, unless
your margins are already stretched to the limit.
Which they were in 1969. If they still are, it's time to admit we haven't
learned anything in almost forty years, pack our bags and go home.
Well, NASA at least.
--
*John Schilling * "Anything worth doing, *
*Member:AIAA,NRA,ACLU,SAS,LP * is worth doing for money" *
*Chief Scientist & General Partner * -13th Rule of Acquisition *
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