Mode decision?

"Doug..." wrote in message
...

Like I say, I know we have at least *some* of the info we need to start
wrangling this decision. And we're talking about a 10-year program,
right? That's not that much longer than Apollo had.

The shuttle flew 100 times in 20 years and we could do the same with lunar
rockets. I don't know if that's Bush's vision or not.

I would like to reach a point where building new habitats is easy. That
would eliminate one constraint on space activity. The other constraint is
the cost of flying. Once you have a destination, that gives you more
incentive to solve the cost of flying problem.

In article ,
Derek Lyons wrote:
Assembly has some up-front overhead costs, but at present, so does
all-in-one launch, since we have no suitable heavy launchers.

The overhead of orbital assembly is more than up front, but continues
throughout the assembly operations phase is the mission is of any
size. You take a performance hit either per launch in the form of the
rendezvous and docking hardware, or across the whole pipeline by using
an OTV.

True, and there are overheads in the final hardware as well, because
modularization usually costs you at least a little bit.

On the other hand, there are overheads for all-in-one launch too, and
those should not be forgotten. For example:

+ Everything has to fit, or else be able to unfurl automatically and very
reliably, even when a larger fixed structure would work better.

+ The return capsule you haul to the Moon or beyond needs to be
aerodynamic for launch as well as reentry, and needs structure that can
handle a worst-case launch abort with a crew aboard (a capability needed
only during the first three minutes of the flight).

+ Spacecraft configuration is constrained by launch packaging limits, e.g.
the requirement that (essentially) the return capsule be on top.

+ Opportunities for checkout after launch but before departure are very
limited (e.g. you may not be able to get into the lander then).

+ Growth potential is very limited, and even initial missions may be in
jeopardy if the launcher designer doesn't take as skeptical a view of
spacecraft mass estimates as von Braun did. (Preferably a more skeptical
one, in fact -- as it was, the LM had mass trouble.)
--
MOST launched 30 June; science observations running | Henry Spencer
since Oct; first surprises seen; papers pending. |

(Henry Spencer) wrote in message ...
True, and there are overheads in the final hardware as well, because
modularization usually costs you at least a little bit.

On the other hand, there are overheads for all-in-one launch too, and
those should not be forgotten. For example:

[snip]

All excellent points, all true. And though generally I'm
a fan of orbital assembly there are other alternatives
beyond monolithic launch. There is, to borrow a page out
of Zubrin's book, surface rendezvous, which ought to work
incredibly well on the Moon, due to the short travel times.
Indeed, if the goal is a lunar base then surface rendezvous
would already be a part of the program, so you might as
well take advantage of it. The first thing you can do is
shrink the size of the lunar lander, since it doesn't have
to serve as a long term habitat for the crew and really
only needs to have emergency capabilities (i.e. getting
back to lunar orbit).