In sci.space.history message , Thu, 29
Dec 2011 11:27:28, Sylvia Else posted:

On 29/12/2011 7:05 AM, Dr J R Stockton wrote:
In sci.space.history , Tue, 27
Dec 2011 12:15:52, Sylvia posted:

The US demonstrated the release of the space shuttle orbiter from the
carrier aircraft during the early flight tests. The carrier aircraft, a
747, wasn't also acting as a tanker, but I can't see that makes any
difference.

In such a configuration, there isn't much point in moving fuel from the
tanker to the orbiter anyway. The carrier aircraft just puts the
orbiter at a suitable place and velocity and releases it, at which time
the orbiter starts its engines and continues the climb.


An orbiter burns its fuel in ten minutes. But a carrier aircraft, even
if fuelled on the runway, will take an hour or more to get it from there
to the separation point. For cryogenic fuels, one could use heavier
insulation in the aircraft (with a little cryogen in the orbiter,
perhaps, to have it pre-chilled).

With the orbiter fuelled at take-off, that fuel mass must be supported
along a longer load path leading to a hard and imperfectly smooth
runway. But with the orbiter fuelled at altitude, the fuel load path
then leads to a pair of somewhat elastic wings supported on soft air.

Even with an orbiter fully-fuelled in the runway, it could be useful to
provide top-up fuel from the tanker aircraft before separation.

One might even consider an air-to-air transfer of orbiter fuel from
another tanker aircraft.


In the situation where the orbiter is attached to the carrier aircraft
at take off, there seems little point in running the orbiter's engines.
Doing so just requires them to operate over a wider range of ambient
pressures, and also to operate for longer.

You, I think, are the first to suggest running the orbiter's main
engines while it is attached to the carrier. That might be useful if
taking off from an aircraft carrier or other very short runway, but it
would require extra strengthening of and near the attach points.

If they are not operating, then no fuel is being consumed, so there's
nothing to top up except perhaps some boil-off, but I find it hard to
believe that the it would be worth carrying the mass of the extra
machinery in the orbiter to allow that.

As I observed, there would be an hour or more's boil-off. IIRC, STS was
topped up until near launch time. All that would be needed in the
orbiter would be a pair of moderately small pipes from the tanker, each
with in principle a single valve to close it off for release. The pumps
would be in the carrier.

In the case where the orbiter takes off independently, it needs landing
gear, or other arrangements, capable of handling its takeoff weight.

I was not considering that case.

In addition, it would need inflight refuelling equipment that
presumably gets carried to orbit. To me it seems improbable that that
would mass less than the extra structure required to allow the fully
fuelled orbiter to sit on its carrier aircraft.

As above.

In any case, whether the orbiter takes off seperately, or attached to
its carrier aircraft, the system appears to be 'SSTO' from 1000km/h and
a few tens of thousands of feet. Where are the numbers showing that
that's feasible without using a new type of engine?

The proposed Stratolaunch Systems "Falcon 5" system is two-stage, not
counting the aircraft.

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