[Bender2]

My main complaint to your post was your saying “...half again as much propellant from liftoff to carry...” the ET to orbit.

From http://www.permanent.com/ext-tank.htm

“After the Boosters are detached early in the flight, the Main External Tank fuels the Shuttle Orbiter tail engines at full thrust to gain the high speed required for orbit. When more than 97% of orbital speed is attained, the External Tank is detached from the Shuttle Orbiter and directed to cross Earth’s atmosphere to burn up (Skylab-like) with remnants falling into a remote section of the Indian Ocean. The Main External Tank cannot be returned to Earth for reuse on later launches because it cannot be returned without burning up in Earth’s atmosphere, unlike the Boosters which detach themselves early before high speeds are attained. Currently, the Main External Tank is just thrown away.

“This wasteful procedure will eventually change. The questions are “when?” and “by who?” NASA has offered to deliver its tank to orbit for free to any entity capable of handling it properly.Notably, the External Tank, when separated from the Shuttle, still has some hydrogen and oxygen in it. This leftover fuel is about 1000 kilograms (roughly 2000 pounds) or 1 ton of hydrogen, and about 6,000 kilograms (13,000 pounds) or 6 tons of oxygen, which is 1% of its liftoff fuel. It also has 500 kilograms (245 pounds) of nitrogen (a refrigerant).

“The hydrogen and oxygen are useful combined as water (7,000 kilograms, or 15,000 pounds per tank). Humans and plants need water, nitrogen, oxygen, and hydrogen. (Oxygen is abundant in lunar soil — 44% of average lunar soil. But hydrogen and nitrogen are difficult to obtain in large quantities, except from asteroids or permanently shadowed lunar polar crater “hydrogen cold traps”.)

“Notably, if the tank is saved, the Space Shuttle can lift MORE payload up from Earth, or it can go up to a higher orbit. Why? Saving the tank would eliminate a maneuvering operation required to send the tank to burn up safely in a small target area at a remote spot in the Indian Ocean. This requires use of fuel on board the Shuttle, which is a compact but relatively heavy fuel (hydrazine), which is also used to propel the Shuttle to its final orbital velocity. Saving the tank would also allow more of the tank’s leftover fuel to be used (by a slow burn at lower tank pressure). An engineering study by the tank’s manufacturer, Martin Marietta, shows that the Shuttle can take an extra ton of cargo to orbit if the tank is saved.”

[anymouse]

There were some serious proposals back in the early 1990s to use the Shuttle External Tanks for orbital construction, but Gene Meyers and his Space Islands effort only muddied the waters on such prospects. Gene had me (and some other good people) sucked in pretty good for a while, but he is a hapless dreamer long on ideal and short on ability to get anything done.

[brityank]

Thanks for the info, and straightening me out; fortunately I'm not a rocket scientist. Pity that Permanent is not (seemingly) a viable site anymore, although a lot of the links still work. What a waste of both the tank and the opportunity to allow for better utilization. Lord knows we have the expertise and the technology to add a small OMS onto the tanks, why wasn't that considered to park the tanks for future use? Penny wise and pound foolish -- seems to be the mantra of the NASA bureaucracy.

We need to get onto the Moon and establish a civilian base, NASA won't do it so it's up to folks like Rutan, Ansari, and Branson to light the way.