Could we do a moon mission today?

In article ,
(Joseph Nebus) wrote:

(Mike Flugennock) writes:

While I'm no expert on the capacities of our current "heavies", I'd guess
that a Rube Goldberg multi-launch scheme like this may be a bit easier to
do today, having gotten some experience assembling components -- auto and
piloted -- in orbit, I still have to ask why when -- if we absolutely have
to -- we may be able to do it in _two_ (lander first, C&SM/TLI stage after
it).

Would you really do the lander first? As I recall from the Apollo
program, the LM was only usable for 45 days after the hypergolics were
loaded up; as a result, it was fueling them that really set the countdown
in stone...

...Given that I'd expect the lander to have a similarly constrained
mass and similarly limited pipes -- and so a similarly reduced shelf-life
one fueled -- wouldn't the first launch be better as the CSM equivalent,
maybe with the TLI stage (I'm not sure where the mass would be best put
on the boosters)? In that way if the lunar lander can't be orbited, you
can still carry on your backup mission -- lunar orbit, high earth orbit,
or earth orbit -- and you can't be left with a good lander in a viable
orbit with no crew to use it...


What was the cutoff date for the design of the LM's tanks and
plumbing, 1967? 68?

The Titan II ICBM was fueled with hypergolics and sat in silos from
1963 to 1987 being fueled and emptied numerous times. Then they were
refurbished and used as launch vehicles.

The Pioneer 10 & 11 used hypergolics. They were launched in 1972 &
1973. As of Feb 1998 Pioneer 10 still had 34kg of its original 124kg
of hydrazine left in its tanks.

Voyager 1 & 2 were launched in 1977. Both have enough hydrazine fuel
to last until 2030.

Galileo was launched in 1989. It has used hydrazine fuel until now.

I don't think the long term storage of hypergolics is a materials
problem anymore.



--
Rusty Barton - Antelope, California |"Every so often, I like to
| stick my head out the window,
| look up, and smile for the
| satellite picture."-Steven Wright

In article ,
Doug... wrote:
The one plausible reason for braking into orbit would be to make the
system fully reusable. Which is not a ridiculous idea, just really hard
to do...

Correct me if I'm wrong, here, but it seems to me that you could
construct a "lunar taxi" that would perform the functions of braking into
lunar orbit, entering a transearth trajectory and aerobraking into a
stable LEO "parking orbit" from which it can be resupplied.
You then add a return capsule to this lunar taxi, which separates from
the taxi as it approaches Earth...

That's a plausible approach, although having two separate vehicles does
complicate things somewhat, and (as you note) the taxi needs seriously
rad-hard electronics.

Another option is to do one-pass aerobraking instead of the gradual kind.
That avoids the radiation problems, but now you need a reusable
heatshield, and there are some worries about whether you have enough
aerodynamic control to cope with a somewhat-variable atmosphere.

Since the taxi module isn't manned during its repeated trips through the
Van Allen belts while aerobraking, this process becomes feasible. Yes,
you'll have to really harden all the taxi's systems so that it doesn't
incur undue radiation damage itself... but I'm under the impression that
we have that technology.

It's feasible in principle, but somewhat of a headache -- costly, limiting,
and not necessarily 100% perfect.

...And remember, you could design the
dock so that it wouldn't have to be manned unless you needed a crew up
there to perform an on-orbit resupply and mating with new lander and TLI
modules. That saves a lot of weight and system complexity.

Actually, designing it for lengthy periods unmanned may be more complex
than assuming it will have a crew continuously. The tradeoffs would
need looking at.

I have to believe that you could put together such a system using the
present launch capabilities -- especially if you add the maxed-out
configuration of the Delta IV-Heavy that certainly seems to be within a
few years' reach...

Certainly. In fact, it ought to be possible with just Atlas V 402 (the
high-end no-strapons medium configuration), given money, patience, and
good design.
--
MOST launched 1015 EDT 30 June, separated 1046, | Henry Spencer
first ground-station pass 1651, all nominal! |

In article ,
Louis Scheffer wrote:
It's true you need a heatshield, because of the radiation problem, but
it's not obvious to me that capture into orbit is more massive.
The Apollo heat shield was quite heavy.

It wasn't as heavy as the fuel you'd need for 3-4km/s of braking. (The
fuel for the equivalent maneuver, TLI, was over half of the mass of an
Apollo in parking orbit.)

Perhaps you could use a lighter
heatshield (perhaps derived from shuttle technology, so it's non-ablative)
and do some cross between aerobraking and aero-capture, where you shed
your energy in just a few orbits. I've never seen an analysis of this,
but it seems like it might be even lighter than direct entry.

Probably not much. You have somewhat less heat to deal with, but getting
adequate maneuverability is tricky (such a braking maneuver is much
fussier than a reentry which ends in a landing -- there is no such thing
as shedding too much velocity in the latter case), and the spacecraft
would have to be beefed up for longer-duration operations. (The Apollo CM
by itself was good for only a few hours.)

I think you end up being pushed to do the braking pretty much in one pass,
a la aerocapture. You have to shed most of the excess velocity on the
first pass if you don't want to wait days for the second pass.

By the way, the shuttle tiles are not particularly lightweight, especially
after you finish beefing them up to handle a sharper reentry. (Assuming
you could -- a lunar reentry is very different from LEO reentry.)
--
MOST launched 1015 EDT 30 June, separated 1046, | Henry Spencer
first ground-station pass 1651, all nominal! |