multiple launch moon mission vs. Single Launch moon missions

In this message I consider the failure probability for a moon mission
based on multiple EELV vs. a mission based upon a single launch. I
argue that it would be nothing short of engineering / management folly
to design our return to the moon with anything but a multiple
launcher, multi-supplier, failure-tolerant mission architecture.

If the mission is assembled from major, independent and
self-sustaining elements in LEO (say 8 of them for purposes of
argument) and one of the launches fails, then you have 7 of the pieces
successfully in a parking orbit. One additional launch, with a spare,
and the mission could continue. This an example of an anomaly that can
be handled and the mission still completed, rather than a failure.

A single launch mission that has a launch failure incurs a very high
cost in destroyed hardware, and more important to the mission, a long,
long downtime while the single-supplier booster is re-rated for
launch. This is the scenario we are in today with respect to ISS
modules designed to be flown on the shuttle.

While it is more likely that a multi-launch mission scenario will have
a launch failure (given the same base launch failure rate) over the
course of the entire mission, I believe that the ability to absorb a
launch failure can be designed into the program. Given the inherent
failure rate of launchers in general, I think this in the only prudent
way to go.

What is needed, program-wise, to gracefully absorb a launch failure?

* Launch abort capability for the crew
* multiple, flight-ready spares for all elements
* Launch Capacity available greater than average need.
* Multiple launch suppliers
* A design philosophy that any single element may not work.
* The political spin control ready to explain the a launch failure
isn't a mission failure

An example? The GPS satellite constellation. Each satellite can be
launched separately. A launch could fail but the overall system can
function (sometimes at a degraded level) despite a failure. Delta's
are down? Launch on Atlas. You could launch two satellites (or
three...etc) at once if that made sense from a launcher point of view.

Another example, this one a bit more controversial – is the ISS. While
not the perfect example, consider this; while the shuttle has been
grounded, progress and soyuz has been able to keep the overall system
functioning.

In conclusion it would be nothing short of engineering / management
folly to design our return to the moon with anything but a multiple
launcher, multi-supplier, failure-tolerant system.

"Fred K." wrote in message
om...
If the mission is assembled from major, independent and
self-sustaining elements in LEO (say 8 of them for purposes of
argument) and one of the launches fails, then you have 7 of the pieces
successfully in a parking orbit. One additional launch, with a spare,
and the mission could continue. This an example of an anomaly that can
be handled and the mission still completed, rather than a failure.

A single launch mission that has a launch failure incurs a very high
cost in destroyed hardware, and more important to the mission, a long,
long downtime while the single-supplier booster is re-rated for
launch. This is the scenario we are in today with respect to ISS
modules designed to be flown on the shuttle.

If the lunar vehicle consists of 8 pieces, it's entirely possible that only
one of those pieces is capable of supporting human life. You still have a
single point of failure that can result in death. You could launch a spare
capsule capable of re-entry, but that is different from assembly in space.

Having multiple suppliers would be nice, but the launch rate may be too low
to support that. At the time humans launch, there will only be two pieces,
because all other components will be assembled before they launch. As I see
things, humans will launch, dock, and go straight to the moon without
wasting a lot of time in orbit. If there is a base waiting for them on the
moon, then a fast trip reduces the amount of life support supplies they need
in space.

If the mission is assembled from major, independent and
self-sustaining elements in LEO (say 8 of them for purposes of
argument) and one of the launches fails, then you have 7 of the pieces
successfully in a parking orbit. One additional launch, with a spare,
and the mission could continue. This an example of an anomaly that can
be handled and the mission still completed, rather than a failure.


Why LEO? Your throwing away one of the major advantages of a multiple launch
Lunar Mission. Popular Science has an article about a possible Lunar Mission.
the mission is launched with a Shuttle-C like configuration. Each Shuttle-C can
lift half as much as the old Saturn V, so it counts as a multiple launch Lunar
Mission. The shuttle-C has a rocket engine at it's base, in this case an RS-68,
that feeds from the External Tank. Once the external tank is emptied, the RS-68
and the External tank is ejected, and underneath is an RL-10 engine that boosts
the rest of the ship plus 6 astronauts to Lunar Orbit. Another Shuttle-C boosts
a fuel tank for the lander, which the 6 astronauts are in, into Lunar Orbit.
The lunar lander portion docks with the fuel tank and ignites its engines
using residual fuel. the acceleration causes fuel from the docked tank to pour
into the Lunar Lander, and when the tank is emptied. the lunar lander cuts its
engines, ejects the tank, and restarts its engines so it can land on the Moon.
Each portion of the Lunar mission flies to the Moon separately and no attempt
is made to construct a larger engine in Low Earth orbit. The unmanned parts of
the mission might even be propelled by a nuclear-electric ion engine instead of
an RL-10, where it could take a month to reach the Moon rather than 3 days.
Astronauts need to get to the Moon quickly however lest they needlessly use up
their consumables. So the bulk freight can used high efficiency rockets while
the Astronaut module uses chemical rockets to get to the Moon.

Tom