Re: Griffin Calls STS, ISS "Mistakes"

"Monte Davis" <monte.davis@xxxxxxxxxxx> wrote in message
news:01fvj1tmev5qh3o722s34k4l7umq5deovh@xxxxxxxxxx
> "Pete Lynn" <pete@xxxxxxxxxxxxxxxxxx> wrote:
>
> > A 747 sized carrier aircraft should be good for
> > around a five ton payload to LEO. If one is willing
> > to accept a smaller payload and/or rocket
> > propulsion on the carrier aircraft, then a much
> > smaller carrier aircraft is possible.
> >
> > A good carrier aircraft might enable the kind of fast
> > prototyping of a wide variety of much smaller and
> > simpler vehicles that is desired for the development
> > of CATS.
>
> Calling it "747 sized" glides right over the much
> thornier question of its performance -- how high is it,
> and more importantly, how fast is it going when the
> orbiter detaches?

A reasonable limitation that I tend to favour is such that the carrier
vehicle can still return to the original runway. This sets a practical
limit to the how high and how fast question - not very. Probably high
enough that upper stage rocket engines can be designed for vacuum,
probably less than 100 km and no more than mach four. The carrier
vehicle tends to be similar in GLOW to the upper stage/s.

> Back off for a minute and get some perspective. The
> crucial difference between space and aviation, deeper
> than any consideration of physics or technology, is the
> scale of *demand*. Last year, the whole world's
> demand for payload to orbit was the equivalent of the
> cargo of one small freighter or a few tens of jet
> airliners.

Which is why I tend to favour payloads in the 500-1000 kg range, but
this requires something of a new paradigm in payloads. Many here would
argue that optimal payload size is somewhat larger than this, around
five ton seems more accepted. Either way, the existing market selects
for existing launch vehicles, higher flight rates requires new markets.

A large scale X-Prize type rocket powered HTHL vehicle with a payload of
say 20 ton might get 500kg to LEO. The drymass of such a lower stage
might only be a couple of ton, it can mostly just be fuel tanks with a
rocket engine perhaps half the size of a comparable vertical takeoff
lower stage. Technically this is not that hard.

> So far, neither passenger nor cargo nor FedEx
> demand has been enough to produce a working fleet
> of large supersonic -- let alone hypersonic -- aircraft.
> Even the world's air forces have, by and large,
> backed away from the costs associated with Hustlers,
> B-1s, and B-70s.

Note that such aircraft are designed for very high flight rates and
ranges where efficiency matters. A crude rocket powered low aspect
aircraft with large margins can actually be relatively inexpensive.
Probably in the hundred million or less range. It is built for climb,
efficiency matters little.

> If the large and extensively proven demand for point-
> to-point travel and cargo on Earth won't pay for
> development of a hyperplane, how the hell do you
> expect the much smaller demand for LEO to do
> so?

Though this is a somewhat separate question, point to point rocket
travel will require yet lower costs again. I expect the LEO market to
kick in first. Hyperplanes obviously do not add up, rockets make more
sense than hypersonic air breathers.

Perhaps think instead of a convention lower stage rocket with wings and
takeoff gear added. This is not necessarily that much more expensive
than a standard lower stage, (smaller engines), and is reusable. The
trick is to not be too ambitious with the lower stage, keep it in the
realm of conventional aircraft materials and practices.

Personally I would be inclined just to weld up a stainless steel
equivalent of a large low aspect ratio motorised hanglider, (~100m^2),
and add a rocket stage, so to speak.

Pete.


.

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