Scramjets !!!! It works

From: ANTIcarrot [mailto:dante.feditech@...]

"RLV has nothing to do with space planes. The X-43 is a spaceplane. It ain't
reusable though. The DC-X would not have been a spaceplane, but it would
have been reuseable."

I never said "spaceplanes" were the only form of RLV. The DC-X and Roton
designs are a couple of alternatives; there are probably some others out
there. As far as the X-43 is concerned, it's a test bed, not a final design.

"And what will be powering your scram-jets if not highly explosive cryogenic
fuel?"

Until you asked, I admit I was under the impression that
scramjets used jet fuel. My mistake. As you noted, I'm not fond of cryo-fuel
systems, if there are alternatives. The jet-fueled White Knight and hybrid
propulsion SpaceShipOne add up to a two stage RLV design that doesn't need
cryo-fuels. SpaceDev has other hybrid designs, besides the one they built
for Scaled Composites. There was a time that the dangers and expenses of
LH/LOX were justified, because that was the only game in town. But with
cheaper, safer hybrid systems available, and WK/SS1 demonstrating that
conventional jet engines can drive a reusable `first stage', I think it
might be time to retire the cryo-fuels, especially for manned missions.

"Challanger blew up because it was deliberately flown well outside of
it's operational envelope ... The columbia broke up because of a string of
very stupid management decisions, going back to the basic design of the STS
shuttle. Please note that the shuttle is the ONLY rocket where the heat
shield, or any part of the payload, can be damaged by falling debris."

Your points are all valid. However, the "operational envelope" issue with
Challenger involved it's fuel system. The cause of the "falling debris" that
damaged the Columbia's heat shield was the fuel system. That was the point I
was trying to make. Also, the Challenger is a long way from being the only
time a launch turned into a "catastrophic disassembly" -- don't you just
love NASA-speak? Even if all the safety issues could be addressed, the cost
savings alone of hybrid systems make them worth considering.

"For instance, how you you incorporate an escape system into the design?
Or the tire explodes and you're hurtling down the runway at hundreds of
miles per hour?"

Commercial jets seem to get by without an escape systems, military jets only
have them because of the possibility of combat damage. Why would any such
system be needed in a HTO/HL TSTO, based on the WK/SS1 design? As to the
tire blowout scenario, I refer you again to common aviation practices, and
their safety record.

"What happens when you try and take off from a French airport and one of
your wheels throws a piece of jagged metal up against the TPS?"

Now, you're reaching. Do you really think there's an aircraft designer out
there who doesn't take what was learned with the Concorde crash, and
consider it in their work?

"I also agree that ELVs should be replaced. I'm just more inclined to the
TSTO VTOL RLV, instead of the SSTO HTOL RLV"

I'm no fan of the SSTO concept; TSTO seems more reasonable, at least at this
time. But HTOL offers the advantage of letting virtually any airport become
a spaceport. That might not be important for a gov't space agency, but it
widens the options for the private sector. And the safety record of HTOL in
aviation beats any VTOL system designed so far. The only thing I can think
of that might be considered a disadvantage to HTOL is that it seems to be
harder to get all those tricky, expensive, high-maintenance valves and pumps
needed for cryo-fuels to work than on VTOL systems. ;) Someone else posted
here recently that Marshall won't even look at HTOL designs that use cryo. I
suppose you and I will disagree as to that being a point against HTOL, or
against cryo-fuels... So, what do you see as the advantages of VTOL?
And cryo-fuels?

Dave