Flexible Path is a Dead End

On Wed, 2 Dec 2009 11:35:47 +0100 (CET), George Orwell
wrote:

A landing would mean that the crew would have to stay on the Martian
surface for more than a year. This would mean they'd need to bring a
large amount of supplies which would mean multiple landing craft, which
would mean we'd need precision landings (CEP of no more a few hundred
meters) on a another planet with no GPS navigation. Because of the thin
atmosphere the weather on Mars has a potentially big influence on the
accuracy of such a landing, which would make it very risky indeed
(irresponsiblly so).


How long the crew stays at Mars is a function of the type of course
used to get there, not whether you land or not. You are still at the
mercy of the launch windows opened by the movement of the planets in
the solar system.

So if a crew going to Mars takes the most fuel efficient course, a
long duration or "conjunction class" mission, you have to stay at Mars
for up to 455 days until the planets align again for the return trip.
A "short duration" mission can shorten the stay to 60 or 100 days, but
you need to make a huge course correciton going out or coming back; a
gravity assist at Venus on the way home would do nicely. It doesn't
matter if you are on Mars or orbitting it, that doesn't change. Even
if you use a more advanced engine than NERVA that really shortens the
travel time, you are still at the mercy of orbital mechanics unless
you spend the whole trip accelerating and decelerating. Personally, I
don't think we'll have that tech anytime soon, so we have to think
about mission architectures with prolonged stays. We might as well
land and spend the time doing research.

There does seem a phobia about going to another planet or the Moon and
Landing; they talk about asteroids or LaGrange points like those will
grab the headlines if China lands on the Moon. But how long a crew
has to stay at Mars would be detemined by orbital mechanics, not
whether or not they land.