There is more than one way to get to the moon and planets,
which way is the best is now beginning to be debated.
as the space shuttle is set to return tomorrow, NASA
understands that it needs a replacement for the aging shuttle
fleet. The questions is: replace it with what? What is the
mission? What criteria should be used to determine what the
next manned spacecraft should be able to do?
This Popular Mechanics article says it may look something
like the illustration on the left. According to the article,
the “primary requirement is to ‘ensure crew safety through
all mission phases.'” One would think that is a given, but
perhaps I am mistaken. The other stated goal is to have a
vehicle able to go beyond Earth orbit.
The article is kind of fuzzy on the details but it appears
the Lockheed Martin shuttle would be made up of three parts
(crew module, mission module, and propulsion stage),
each launching separately. The modules would
then dock in low earth orbit (LEO) and continue on to its
destination, whether the space station or the moon and
beyond. While this certainly makes for mission flexibility, I
think it increases the complexity and the number of things
that could cause mission failure.
For example, it could take six to nine or more launches,
depending on the mission, to assemble the required modules in
LEO. As we should have learned from our experience in
building the International Space Station, a lot of things can
and will go wrong while trying to assemble a multi-module
space craft in LEO.
I could be wrong, but I seem to remember a debate, during
the early part of the race to moon, whether to go directly
there or use multiple launches and assemble in LEO and then
go on to the moon. The decision was to go directly to the
moon because, it was determined, it was simpler (and simpler
is more reliable and usually safer).
Nonetheless, I guess the closest analogy is one of a train
and its modular design. When bigger payloads are needed, you
add more engines and then more cars to carry more cargo.
Don’t need to carry more but want to go farther? Add more
propulsion and fuel. In other words, you configure the craft
to meet the mission.
Another big change, but perhaps a retrograde one when
returning, is the shuttle would not glide back to Earth but
rather, would use parachutes. Much like the spam-in-a-can
capsules of the 1960’s and 70’s. Thus, the dream of a shuttle
that could fly into space and fly back, much like the
commercial aircraft of today, would end.
Whether this is the winning design is too early to
determine, but I wonder if the design criteria shouldn’t be
made clearer, first.