On Jan 6, 3:02*am, Pat Flannery wrote:
....
I can't for the life of me figure out why Robert Clark is constantly
coming up with ideas for so radically modifying something that already
exists that it effectively becomes a entirely different spacecraft, but
without the advantages that a whole new design would offer.

Pat

The $42 million costs for the basic spacecraft is significantly less
than the $150 million development cost of the Whiteknight2 and
SpaceShipTwo:

Sales are rocketing at Virgin Galactic.
http://www.virgingalactic.org/2008/0...are-rocke.html

and the result would be a vehicle that could do significantly more
than the Virgin Galactic system. It could act as a suborbital space
tourism vehicle, but it also could act as a very high speed point-to-
point transport system. Imagine a cross-Atlantic trip instead of
taking 6 hours only took 1/2 hour. Or a cross country trip instead of
taking 5 hours only took 20 minutes.
Moreover, it could also serve as the reusable first stage of a TSTO.
I'm arguing it could be used to reduce the costs to space if used as a
reusable first stage booster for a TSTO system. The Air Force for
instance believes such a TSTO could cut launch costs by 50%.
The Russian engines that would need to be added would be relatively
low cost. According to this page, in the mid 90's Aerojet purchased 36
of them from the Russians for only $1.1 million each(!):

NK-33.
http://en.wikipedia.org/wiki/NK-33#History

Installation of the lox/kerosene tanks and modifications to
strengthen the body frame to carry the extra loads would also be
relatively low cost.
The 68,600 kg empty weight of the orbiter sans engines could probably
be reduced also. The main system that could probably be removed would
be the Orbital Maneuvering System (OMS). This is used for final
orbital insertion of the shuttle and changes of its orbit. This
wouldn't be needed for a first stage vehicle or a suborbital vehicle.
I don't trust the value given for the OMS weight however on the
Atlantis Astronautix page. It says this:

Main Engine: OME. Main Engine: 14,912 kg (32,875 lb). Main Engine
Thrust: 53.367 kN (11,997 lbf). Main Engine Propellants: N2O4/MMH.
Main Engine Propellants: 12,412 kg (27,363 lb). Main Engine Isp: 316
sec. Spacecraft delta v: 700 m/s (2,290 ft/sec).

The OME refers to the OMS engine. The engine does not weigh 14,912
kg. Perhaps they are referring to the entire OMS system, both pods.
That seems unlikely as well, unless they are including the propellant
weight.
In any case it's this OMS system weight that I'm trying to find out
to subtract off.


Bob Clark