"Jon S. Berndt" wrote in
:

Don't know if this has been discussed before, but I noticed some time
ago that the LSAM will be discarded after it performs its duties. What
are some thoughts on a less wasteful approach:

1) An LSAM that travels between lunar orbit and lunar surface in one
piece (reusable),

Depends on the lunar orbit. Low lunar orbit is not stable enough for
long-term storage due to lunar mascons. It could probably be made to work
if in-space propellant resupply were economical enough. Otherwise, Earth-
Moon L1 is probably better, and can double as a jumping-off point for
planetary missions as well.

2) A CEV that goes from ground-to-earth-orbit-and-back ONLY (crew
taxi),

Could be quite economical, since it could be commercially developed, and
therefore optimized for higher flight rates due to the existence of other
customers.

3) An Earth/Moon transfer vehicle that ONLY goes between earth
orbit and lunar orbit (reusable; stationed at ISS),

There are some tough tradeoffs here. Propulsive braking into LEO is not
practical unless in-space resupply becomes economical. Aerobraking into
LEO requires either high radiation tolerance (multipass aerobraking
involves multiple lengthy passes through the Van Allen belts) and
probably an infeasible amount of shielding if the spacecraft is manned,
or it requires a substantial heatshield for single-pass aerobraking.
Single-pass aerobraking is also tricky because the small scale height of
the Earth's atmosphere (compared to, say, Mars or Titan) tends to magnify
the effects of nav errors. A manned vehicle would probably want an abort-
to-surface option, which involves a full lunar-return heatshield. For the
same reason, single-pass aerobraking into an ISS rendezvous orbit would
also be tricky. It will probably be a non-trivial R&D exercise all on its
own.

4) A fuel/cargo/resupply transfer vehicle that takes stuff anywhere.

Maybe this is too complicated, but it seems wasteful to me to throw
away one LSAM for each access to the lunar surface.

Oh, agreed, but that's likely going to be the answer for any architecture
designed with low flight rates in mind. The trade studies don't favor the
options that require extensive infrastructure (in-space propellant
resupply, L1 stations, etc) until the flight rate gets high enough to
amortize the infrastructure development costs more quickly.


--
JRF

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