In late 1960, RAE decided that the proposed HTP/kerosene third stage for Black Prince would not be able to put a communications satellite weighing 600lbs into a 5 000 nautical mile orbit. [NB this is not a geosynchronous orbit], and so Saunders Roe were asked to produce a study for a liquid hydrogen upper stage. This they then did, with their usual thoroughness. The basic design data were:
|All up weight||7 000 lb approx.|
|Propellants||5 000lb approx.|
|Specific Impulse||400 lb.sec/sec|
|Two boost phases:|
|Boost||3 500lb for 8 minutes|
|Cruise||44lb for 2 hours|
|from Saunders Roe publication SP510|
They concluded that such a design could actually put 900lbs into a 5 000NM orbit or 600lb into a 9 000NM orbit.
However, the nature of the second stage is very undefined, since by this time it was clear that Black Prince probably was to be replaced by some form of Anglo French laucher.
There was one rather novel proposal in the design: the boost phase was to use the main motors [see layout above] with turbo pumps. The cruise phase then used the 2 small motors at a very low chamber pressure [perhaps 2 atmospheres], thus dispensing with the pump. In the vacuum of space, the low combustion chamber preesure is no drawback. The tanks would be pressurised by using a heat exchanger from the motors back to the tank in order to keep the hydrogen boiling!
Although a good idea, it does mean carrying the dead weight of the large chambers and pump up to altitude. It is a proposal with possibilities, but needs thinking through more carefully.
This cruise phase would mean then that the stage would spiral up to its final orbit after another 2 hours!
2nd February 2000
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