Space Forum / Shuttle / March 2004

One, the MER rovers weren't pushing the capabilities of the rockets that
sent them to Mars. So it was possible to use a slightly faster trajectory
than the 258 days that a classical Hohmann transfer would provide. A human
mission would be much more massive, so providing that same level of margin
would be more expensive.

Two, the robots don't have to return. The humans must wait until the
planets are aligned properly for the return trip. That won't happen in two
weeks. Generally, the first opportunity is in about 90 days, but requires
an indirect trajectory that takes longer than a Hohmann transfer. A direct
return requires a longer surface stay, up to one year.

Well, at the time the rovers went, the Earth and Mars were converging, and
on the same side of the Sun. Mars is now receding again, as the Earth takes
less time to go around the Sun.

Assuming you want a decent time on Mars, and not just a touch and go visit,
buy the time you wanted to come back, the Earth an Mars would be moving away
from each other, or, you could go when the Earth and Mars were still
converging, but still a long way apart, in which case the trip out would be
longer than the trip back.

If you want short trips both ways, you need to wait on Mars, until the right
part of both orbits again, hence the Three years.

So, Problems with a long trip out.
Long period of weightlessness
Need more consumables,
More chance of problems.

Long trip back much the same problems, made worse by having to do this after
getting to Mars in the first place.

Problems with long stay on Mars, Supplies again of course, but I'd imagine
that supplies and living systems would be robotically put there before the
mission.

Brian

--
Brian Gaff....Note, this account does not accept Bcc: email.
graphics are great, but the blind can't hear them
Email: briang1@blueyonder.co.uk
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Three years stuck inside a can feels more like a prison sentence than
a honorary mission.

We should compare this to sea ships in the 19th century regular ships
usually takes around 6 months from Hong Kong to New York, while fast
clipper ships usually took around 3 months from one destination to
another destination.

http://baegis.ag.uidaho.edu/~myron/html/clipper.htm

Of course how much time it takes depends on the destination and the
conditions.

It also should be mentioned sea voyaging ships usually had the benefit
of rest and resupply at nearby ports on its route.

I think that by current technology, an ideal time would be an around 3
months voyage.

Around 1 month travelling to Mars, around 1 month surveying Mars,
around 1 month returning home from Mars.

Much like the current ISS mission which usually last around 3 months,
before they extend it to around 6 months.

A 6 months mission seems to be pushing it (like they did today),
especially a 1 year mission (like that poor guy that once stuck aboard
Mir).

And if sending an all in one package ship is too hard.

How about sending regular shipments of supplies and parts to the
manned ship? Both before and even after the manned ship was launched.

Making the Mars mission feels more like the current ISS mission. This
will take many launches, but it will be less stressful toward the crew
(which need to do many things and travel farther than the current
space station crew).