RE: The crash of NASA's culture
Matt Wronkiewicz wrote:
> What do you hope to get out of reinstating the X-33 program?
> Regardless of how much work remains to be done, the X-33 craft as
> designed was a suborbital demonstrator, not a Shuttle replacement.
> Burt Rutan beat the X-33 altitude and payload goals last year.
I'm not a fan of how the X-33 program turned out, and I think Rutan has
done something that is really cool and quite amazing -- but I couldn't
let this statement go past. Just as a note, the X-33 goals were quite
different than that of Rutan's SpaceShipOne. The X-33 was specifically
designed to provide the basis for making a decision to invest in a
reusable launch system, including both flight and ground test programs.
The SS1 was designed specifically to win the X-Prize. Quite different
goals. It was expected the X-33 would include
- Flight test in excess of Mach 10, with a goal of Mach 13 or
higher. (This was to demonstrate thermal protection systems suitable
for orbital reentry). Rutan's SS1 reached a maximum velocity of Mach
3.5. Since thermal loads run with the kinetic energy of the vehicle,
which goes as the square of the velocity, the X-33 was expected to have
more than 10X the thermal loads as SS1, requiring quite a different
design approach.
- Flight test to XXX dynamic pressure at velocity. Rutan's
vehicle was designed to essentially go straight up and straight back
down -- and it did go over 300,000' The X-33 was designed go achieve a
dynamic pressure on the vehicle structure of XXX at a certain velocity,
in order to stress the light weight structure while getting the full
reentry heating condition. While this may look like around the same
velocity, it should be noted that SS1 reached 300,000' at essentially
zero velocity (think of SS1 as a ball thrown upwards, pausing at the top
of its trajectory before falling back to the earth), whereas the X-33
was designed to power through the atmosphere at the same altitude at
more than Mach 10, giving it a much higher dynamic and thermal
requirement. If you had fired the X-33 straight up, it would have gone
quite a bit higher than SS1 -- but that was not why it was going to be
built.
- X-33 had NO payload requirement, other than carrying test
instrumentation. Rutan's SS1 had to carry a pilot and mass equivalent
to a passenger, which also meant some type of passenger module.
- X-33 had to demonstrate light weight structures and thermal
protection. Rutan's design did not have light weight, or integrated
thermal protection as a design goal. SS1 did have thermal protection,
but it was a simple spray on ablator, which was possible due to its
thermal loads 10x less than that of something like the X-33.
- X-33 had no turnaround requirements per se, although the
turnaround operations were going to be judged as what was required for
turning around a reusable orbital vehicle. SS1 had to meet the X-prize
turnaround goals. On paper, these were approximately the same.
- X-33 was going to demonstrate a highly efficient, integrated,
reusable propulsion system (the aerospike). This was needed as part of
the X-33 goals to demonstrate the propulsion system suitable for a
reusable orbital vehicle, potentially a SSTO. Rutan used a replaceable
low-efficiency hybrid rocket system on the SS1.
Burt Rutan did not beat the X-33 altitude or velocity goals. He did
beat the X-33 payload goals, but then the X-33 was not designed to carry
a payload, whereas the X-Prize requirement (to a lower altitude and
lower velocity) did have a goal of carrying a passenger.
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