Scramjets !!!! It works

> From: Dave Logsdon [mailto:templar@...]

> The jet-fueled White Knight and hybrid
> propulsion SpaceShipOne add up to a two stage
> RLV design that doesn't need cryo-fuels.

But not an orbital RLV though. I've also yet to see a design for a launch
vehicle with a hybrid engine. Not that I'm saying that it's impossible, but
because of its low impulse, such systems will always face substantial
performance penelties in comparison to liquid or solid fuels.

> I think it might be time to retire the
> cryo-fuels, especially for manned missions.

For sub-orbital flights, maybe. Then again an engine like the RL10 has a
excillent reliability record - which at present is unmatched by any hybrid.

> Your points are all valid. However, the
> "operational envelope" issue with
> Challenger involved it's fuel system.

Er - no. The operational envelope had to do with the O-Ring seal on the
multi-section strap on booster. The cold weather meant it couldn't expand
properly, and the solid rocket exhaust began to leak out. It had nothing to
do with cryogenics until the the SRB ripped loose and smashed the tank's
super-structure. I put it to you that if your biggest engine rips loose and
damages the super-structure at high speed, you're screwed no matter what
design you use. ;)

> The cause of the "falling debris" that
> damaged the Columbia's heat shield was
> the fuel system.

Again that is I'm afraid very much incorrect. The only reason the tank has
insulation in the first place is because if it didn't, ice might form and
fall off during launch, damaging the shuttle's heatshield. Spot the irony.
Watch a saturn-v l;aunch sometime. You can see it's covered with ice that
falls off during launch. This was never a serious issue before the shuttle.

> Even if all the safety issues could be
> addressed, the cost savings alone of
> hybrid systems make them worth considering.

That's like saying, 'Cars crash and are unreliable. We should all start
using bicycles.' lanes fall out of the sky. Ships sink. Cars crash. And yes,
rockets do blow up sometimes. It's more often the case that they're blown up
by ground control after they go off course rather than an accident. And
that's basically a philosophy of 'make everything as light weight as
possible and hope for the best'. An RLV probably wouldn't be built like
that.

> 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?

In case of systems failure. Would you really like to tell your astronauts,
"We're pretty sure it's safe, but on the off chance we're wrong you're
completely screwed?" Combat jets sometimes fail for no apparent reason
because they're flying at the endge of material science. You're going to be
flapping your wings on the other side of that edge in any kind an RLV. And
escape route is a really good idea.

> 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 thik you'll find the solution was, don't make your aircraft go faster than
M0.9. ;)

> But HTOL offers the advantage of
> letting virtually any airport
> become a spaceport.

Where as VTOL has the advantage of making any patch of concrete anywhere
into a space-port. Consider the Harrier and the A-10. Which needs more
concrete? Which has greater flexibility?

No HTOl designfor space has ever been tested. None of the engines even exist
on paper, let alone in real life with a reliable record.

> So, what do you see as the
> advantages of VTOL?
> And cryo-fuels?

Vertical take off is the way every rocket has ever worked.
It's a proven method.
The design shapes are very simple. Hence easy to build and maintain.
Though it would be a higher G reentry, this would translate to less heat
absorbed by the spacecraft.
Heatshields can be kept small (with only the base being armored) which
allows heavier but more reliable technology.
Small VTOLs can operate from almost anywhere.
They can be sold commercially, because the design doesn't lend itself to
weapons deployment.
No useless weight in orbit.
With very slight modifacations and refueling in orbit, the VTO can go to
Luna, Mars or GEO.
Multiple landing options, including parasail or powered landing.
Greater flexibility in positioning the base of operations.
Able to land and take off in bad weather.
Fewer enviromental (sound) problems.

Example design for a small TSTO VTOL:
http://www.hobbyspace.com/AAdmin/archive/SpecialTopics/RocketCom/titlePage.h
tml

ANTIcarrot.