The first human mars mission?

Tom Merkle wrote:

Dick Morris wrote in message ...
John Schilling wrote:

Dick Morris writes:


The biggest question is whether it will work with Mars dust in the air
it's pulling in. That's a little more difficult to simulate, since we
don't *know* the exact composition and characteristics of the dust.

Zubrin addressed the dust issue in TCFM, as I recall. His approach was
to liquify the CO2 under pressure and then purify it by distillation, so
that any dust in the air would remain in the solution.

But there's still that pesky "liquify the CO2 under pressure" bit, which
requires refrigerators and compressors, with the moving parts and the
sliding seals, *before* you get rid of the dust. That machinery can
still get torn up if we underestimate the dust problem.

There is also the option of filtering the air before it gets to the
compressors. The engine in my car seems quite happy with that sort of
arrangement, since it's been running for almost 15 years with no obvious
signs of wear. Filtering can probably handle the vast majority of any
dust problem.
--
*John Schilling

Agree. Filtering technology is well understood. HEPA filters in most
earthbound vacuums are capable of removing dust greater than .01
microns in size. I don't think this is a serious barrier. The real
question is how much it will cost to develop a storage and fueling
method,

The propellants will be stored in the return vehicle propellant tanks as
they are made, so there will be no additional storage and fueling
requirements as such. There will just be some relatively small dia.
tubing to connect the propellant tanks with the chemical plant. The
tanks will have to be designed to store the liquid hydrogen during the
trans-Mars coast, so storing the LOX/methane propellants on Mars will
not be a great challenge. The development cost for the propellant plant
and plumbing will be a small part of the total development cost.

as well as a reliable LOX-methane engine capable of sitting
around for two years prior to launching.

This is an issue for every Mars proposal. If we can't design reliable
engines that can withstand the space (or Mars) environment for periods
measured in years then we won't go. The Russians know how to design
reliable rocket engines, and the RL-10 is also extremely reliable.
Rocket engines can be designed to be reliable if high reliabiity is a
requirement. They can also be designed for long-term storage, like the
engines on a Titan ICBM, though storage in space, or on Mars, is
admittedly a more difficult problem.

As usual with most gargantuan
engineering projects, the devil is not in the concepts but in the
details. How do you counter blow-back from a LOX-methane rocket big
enough to launch from the surface of mars to earth? It's not like you
can land a full launch pad and support facility.

The Apollo astronauts made it back from the Moon without a full launch
pad and support facility. ;-)

"Blow-back" is certainly an issue that needs to be investigated, but it
will probably turn out to be no more of a problem on Mars than it was on
the Moon. The LM Descent Engine generated about as much thrust during
the final braking maneuver as the Ascent Engine did during liftoff, and
there was very little evidence of cratering even directly under the
engine. The exhaust simply spread out horizontally in all directions.
A vehicle returning to Earth from Mars will have a much greater thrust
level, but the total exit area of the propulsion system will also be
much greater, so the pressure of the exhaust on the surface may be about
the same. Like the LM, the ERV propulsion system will be designed to
operate efficiently in a vacuum, or very low pressure (~1% Earth
sea-level) environment, so the exit pressure will be quite low.

And the reduced
gravity's gonna have even more fun with all the machinery required,
especially if you need to include a reactor to provide the required
electrical power.

All of the required machinery could be designed to operate even in 0-g
if necessary.

Typically rockets that require long-term on station time and
reliability have been hypergolic. Obviously this is not possible on an
ISRU rocket. Liquid rockets are notoriously finicky when it comes to
launch preparations. Can it all be managed from 30 light-seconds away?

The Apollo astronauts managed to fire four large liquid rocket engines
during each lunar landing flight. The J-2 engine on the SIV-B had
previously been fired during the orbital injection burn only a few hours
previously. The SPS engine was fired twice behind the Moon, approx.
half an hour after LOS, over a period of up to several days. RL-10
engines have been fired as many as seven times in a single mission.
Large liquid rocket engines can be fired without large ground support
crews fussing over them for days or weeks.

Can you get congressional support for a nuclear reactor on Mars?
That's the hard stuff, not trivial obstacles like dust in the martian
air or hydrogen storage problems.


Politics has always been the hard part. We still haven't got it right.

Tom Merkle