dave schneider wrote:
been saying: winged designs are hard, so lets put off doing another
winged design for a while, pick an easy design and see if we can get
the flight rate up.

Are the X33 style of self lifting vehicles harder or simpler than real wing
such as Shuttle ?

The shuttle is a known entity.

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) ?

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 ?

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.

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 ?

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).

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.

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.

The GNC should be
a lot simpler, especially on a LEO-version (start with a modest
computer for CEV-L, replace the Pentium with a Pentium Pro for CEV-S
(S=Selene for the moon shots), and go with an Itanium for CEV-M
(Mars);

Hardware is irrelevant. A 386 is probably more than enough. GNC is not the
only thing that needs source code. You need ECLSS, C&C, remote controllability
from ground, all the telemetry, caution alarm system, communications. You also
need al the interfaces to the actual launch vehicle.

experience with Soyuz, Apollo, and Shuttle designs; the ISS designs
are also useful input, but would be overkill on a 4-day flight.

Last I heard, going to the moon was 3 days each way. Right ? So that would be
6 days + contigency planning. How many people are you carrying to the moon ? 3
? 6 ? Shuttle's ECLSS is probably better sized than Apollo.

Also, remember that if you're going to be using the CEV as a shuttle between
earth and moon base alpha, you'll also want each CEV to bring lots of supplies
to the moon base. If you're sending 4 people to stay on the moon for a month,
you'll need to carry a couple month's worth of supplies (again, you need contigency).

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).

Modelling a capsule's aerodynamics and heat transfer should be simpler
than a winged design, thus saving CFD and wind tunnel costs.

How significant would those costs be ? Doesn'.t NASA already have plenty of
empirical experience with the shuttle's wing ? (including its behaviour during
columbia final's re-entry).