"SpaceShipTwo could be single stage to SUBorbit"

"J. Clarke" wrote in message
...
On 5/14/2010 11:16 AM, Jeff Findley wrote:
"J. wrote in message
...
On 5/14/2010 12:05 AM, Jorge R. Frank wrote:
On 05/13/2010 05:08 PM, J. Clarke wrote:
On 5/13/2010 4:04 PM, Jeff Findley wrote:
"Pat wrote in message
dakotatelephone...
On 5/13/2010 9:10 AM, LSMFT wrote:
What happened to the X-30?

And since when did 50,000 feet become outer space?
I like the part about it using a "liquid chemical propulsion
system",
without specifying what those chemicals are exactly.
You could certainly make a ground takeoff rocket plane that could
climb to
50,000 feet, but since numerous types of jet aircraft are capable of
flying to 50,000 feet also, what would be the point of doing this?

The promises made by X-30 were absolutely silly, in retrospect. A
vehicle
which can cruise at hypersonic speeds is going to be very different
than a
vehicle which can accelerate to orbital speeds, yet somehow X-30 was
being
sold as able to do both (makes me think of the SNL skit for Shimmer,
a
floor
polish and a dessert topping).

So let's see, a vehicle that can cruise at Mach 20 is going to be
different from one that can accelerate to Mach 25 how, exactly?

If you haven't figured it out on your own, it is not going to be worth
anyone's time to explain it to you. But the quick-and-dirty is that
cruising at Mach 20 with an airbreather is going to require remaining
at
an altitude where there is enough O2 to keep the engine going, which
radically increases the total heat load.

Which heat load goes into the fuel and out the exhaust.

Whereas a Mach 25 accelerator
will only spend a brief amount of time in the Mach region where a
scramjet will do any good, so it will need two additional propulsion
systems: one to accelerate to the minimum speed to light the scramjet,
another (necessarily rocket-based) to take over for the final boost to
orbit once the scramjet is useless. The additional weight of having
three propulsion systems more than outweighs the advantages of the
airbreather.

You seem to have missed the point.

IMO scramjets are daft for either mission. It's at times like this that
I really miss Henry Spencer. He could explain this far more eloquently
than I could.

So what do you recommend for Mach 20 cruise if scramjets are "daft" for
it?

That's a little like Peter Pan asking "What would you recommend for human
flight besides fairy dust?".

Neither fairy dust nor runway to Mach 20 hypersonic air breathing engines
exist. The difference between the two is that one is obviously pure
fantasy
even to non-engineers where the other is only an obvious fantasy to those
who know enough about engineering to crunch the numbers for themselves
and
realize that the math just doesn't work out.

In an apples to apples comparison, rocket engines for orbital launch
vehicles beat even drawing board air breathing launch vehicles for the
reasons which Jorge states.

Math always trumps faith when it comes to engineering.

I see. So your view is that Mach 20 cruise simply cannot be done, it's
eternally impossible and the laws of the universe forbid it.

That's not exctly what I'm saying. I'm saying that an air breathing Mach 20
cruise vehicle isn't the same as an orbital launch vehicle. Furthermore,
there is no air breathing Mach 20 cruise vehicle in existence today. You're
the one claiming that such an air breathing engine/vehicle would make a
useful launch vehicle. I'm claiming that such an engine/vehicle does not
exist.

People like you are pimples on the ass of progress.

If hypersonic air breathing engines were easy, we'd have them by now.
They're not easy. In fact, they're damn hard.

They haven't been proven successful due to lack of trying. As I've said
before, they are a research topic and people *have* been trying very hard to
make them work, but all we have to show for it are a few test articles that
have shown to produce positive thrust at cruise for a total duration best
measured in seconds.

Once the technology matures into something useful for hypersonic cruise, we
can re-run the numbers to see if they can do better than liquid fueled
rocket engines for orbital launch vehicles. Current numbers show that in an
apples to apples comparison that today's drawing board air breathing
hypersonic engines simply aren't useful for orbital launch vehicles. Again,
anyone who claims otherwise is selling you snake oil.

LOX is one of the cheapest fluids on the planet to manufacture because it's
made from air. Considering the state of the art in air breathing engines,
trying to get LOX off of your launch vehicles to "save money" is a fool's
errand.

Jeff
--
"Take heart amid the deepening gloom
that your dog is finally getting enough cheese" - Deteriorata - National
Lampoon