Re: LSAM
- From: "Jake McGuire" <jamcguir@xxxxxxxxx>
- Date: 6 Apr 2006 18:24:00 -0700
John Schilling wrote:
In article <1144362324.895432.303570@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, 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. 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.
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."
The 4 km/sec descent/ascent delta V also has to come from somewhere.
If we assume the CEV *won't* do a vertical rocket landing on Earth, then
we need *one* major extra subsystem for the combined vehicle. Unless your
margins are absurdly thin, it's almost certainly cheaper to put one more
subsystem on your first vehicle, than to design a second from scratch.
But if instead of designing the second from scratch, you reuse the
avionics hardware, most of the avionics software, and most of the ECLSS
system, changing only the hull this all sits in?
Reusing subsystems still leaves you with all the integration cost, which
is a significant fraction of the total. And some of the subsystems, you
may not be able to reuse.
True. But I suspect that at this point we are getting into the part of
aerospace engineering where you need to run the numbers, and also
inconveniently, the part where IMLEO-based cost modeling breaks down.
[1] http://images.spaceref.com/news/2005/ESAS.REPORT.04.PDF page
124-129
-jake
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