"Emilio" wrote in message
...
Remember VenurStar? http://www.fas.org/spp/guide/usa/launch/x-33.htm It
was built by Skunkworks in the late 1990s. The project was canceled after
the propulsion tank failed the test. The tank had to have very complex
shape because it had to fit with in the airframe that resemble flattened
cone. To cut weight, they had to used Graphite composite. The Graphite
composite simply didn't work too well at the liquid Hydrogen temperature.
I mean they had to push the envelop of technology in every area to achieve
single stage to orbit. To date we don't have the material to build such
space ship.

The most efficient single stage vehicle ever built was in 1960s. It was
Atlas. It had 1% throw weight and the tank was made out of .030 inch
stainless steel. Unless the tank was filled with fuel or pressurized the
whole thing would crumple down to scrap metal!

Emilio

The Atlas remains in production to this day in the form of the II,III
and V but the design has been continually updated since the
60's and the Atlas now has the highly efficient Russian designed
RD-180 engine.

The RD-180 is a closed cycle engine meaning that the expanding
O2 used to power the fuel pumps is used in the combustion chamber
rather than dumped outboard as is the practise in American engines.

This makes the engine much more efficient. The engine is also
much more powerful than the US engines it replaces and its
throttlable and cheaper. Indeed the RD-180 is likley to power
the new Expendable Launch Vehicles for the USAF

Keith