John Doe writes:

dave schneider wrote:
Have the research centers continue to work on TPS
designs, let DOD do a scram jet, and then revisit winged vessels when
we have better materials and/or design.

It is one thing to have scientists design a new TPS in a lab. You need a
shuttle to really test it. How many shuttle flights did it take before NASA
had acquired sufficient knowledge of the original TPS system to make changes
to it ?

If they develop a new TPS system, why not retrofit it on the shuttles (whether
100 or 200 series) ?

Cost. To keep costs down, the TPS on the shuttle isn't generally
stripped down to nothing and reapplied. Instead, pieces are replaced
only when necessary.

to avoid being expensive (and worse, expensive up front), so lets
concentrate on making reliable expendables that can get the flight
rate up on a pay-as-you go basis,

When you consider the "man rated" issues, would expandables really be cheaper
once you add all the redundancy and robustness that is required ?

Shuttle isn't "man rated". If NASA bends the rules (waivers) for the
shuttle, why can't they be bent for its replacement?

Expandables got popular when the russians were able to offer a seat for 20
million bucks to tourists. And they got popular whenever the shuttle was
delayed (and now grounded) while Soyuz/Progress always launch on time.

Expendables didn't "get" popular. The only entity trying to reuse
launch vehicles is NASA (and perhaps the carrier planes used by
Pegasus), and they've had a very poor record of reducing costs by
using a "reusable" vehicle.

But if you were to transpose Soyuz to NASA, wouldn't NASA make significant
modifications to "man rate" it, and then add a billion flight rules to ensure
safety which would make it just as "reliable" as Shuttle ?

See above "man rating" comments.

200-series orbiters are possible. But they would be only an
incremental improvement in design,

I think that a new and improved shuttle could be far more than "incremental".
There have not only be fairly substantial changes to the shuttle since it
first flew (TPS comes to mind), but also, experience has also shown many of
the design problems of the 100 series (for instance, access to engines,
something which original designers didn't think would be needed between flights).

Making the engines easier to pull and reinstall is fixing the symptom,
not the problem.

If the current shuttle has a series of kinks, which, when put together,
require much longer stay in OPF thus increasing costs significantly, then
fixing those kinks could significantly lower maintenance costs (for instance,
electric APUs that don't require the purging of dangerous fuel lines/tanks).
And for OMS/thrusters, perhaps they could design the plumbing such that their
purging could be greatly facilitated.

Fixing all of the "kinks" would cost billions. This isn't an
exaggeration, considering the cost of some shuttle upgrades that have
either been done, or have been canceled due to rising costs
(e.g. electric APU's).

A lot has been learned since the original shuttles, and I suspect that if you
were to put all this experience together, you could build a 200 series shuttle
that would have sighificant advantages over current ones without having to
totally re-invent the wheel.

First, it's stuck in LEO. This is true for a variety of reasons, not
the least of which is the "dead weight" of the vehicle that you
*don't* want to take out of LEO (wings, main engines, structure to
hold it all together...).

Second, it's simply not suited to exploration (ignoring the cost and
weight issues). You really don't need a payload bay 15'x60' for
manned missions to the moon and Mars. This huge bay was due to USAF
requirements that no longer apply.

Third, you don't need wings. They add complexity (moving parts),
cost, mass, and etc. Unfortunately, they don't add much value either.
For lunar and Mars missions, is there a *valid* requirement to land on
a runway?

Fourth, it's both a launch vehicle and a manned space vehicle. Why
mix the two?

Fifth...

Going to mars, the CEV is useless. ISS is useful. For building Moon base , CEV
is useless, ISS is usefull (in terms of already built systems).

This is just false. ISS is useless for either lunar or Mars missions
because it's in a very bad orbit (payload penalty paid by any vehicle
that launches from KSC to ISS). CEV can be sent up into a much more
optimal low earth orbit. CEV can return crews from the moon (let's
see ISS do that).

Jeff
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