Thursday, July 21, 2011

RIP Shuttle

kw: space flight, shuttle, requiem

Thus ends an era. The 135th and last mission of the NASA Shuttle program landed this morning. This CNET News article has more details. Now it is official. The United States has no means of sending astronauts off earth. We must rely on "partners" to ferry personnel to and from the International Space Station.

Growing up as a Cold War Kid, I'd never have dreamed that we'd be in such a position: We must rent space on Russian rockets to continue our manned space program. I remember at age ten, going outside every evening with binoculars and the newspaper orbit listings, trying to see Sputnik (too small for binoculars), and later the various Explorers and Echo's, and also various Russian satellites. We feared the Russians in the 1950s and '60s. They had The Bomb, and Stalin was crazy enough to use it. Khrushchev was even crazier, but fortunately, we learned later, less murderous of his own citizens.

Twelve years after the Ham operators picked up the "beep . . . beep" from Sputnik I, we had a man on the moon. Boy, were we proud! We'd grown up reading about going to the moon, but not one of my boyhood books predicted that America would watch that "small step" on color TV! In less than four years, it was all over; we had only sent men there six times. Anybody under the age of thirty-nine was born after we quit going to the moon!!

Forty years hence, will the U.S. manned space program be equally a thing of the past; will there be eighty-year-olds who have never known the thrill of seeing someone walk on another world? What happened?

Money happened. Without a significant technological breakthrough, it will continue to cost about $10,000 per kilogram to inject payloads into low Earth orbit (LEO). Medium Earth orbit (MEO), higher than 1,000km, costs about twice as much. The current estimate for a lunar mission is around $100 Million per kilogram that makes the round trip. The brick wall that stopped progress is called Specific Impulse.

Specific Impulse is measured in Seconds. In other words, it is the number of seconds that an engine can produce a kilogram of thrust using a kilogram of fuel. The Shuttle, and the Saturn V and Saturn Ib before it, had engines with a SI of around 500 seconds. That sounds impressive, but you have to thrust against a rather deep gravity well to get off Earth, and it takes about 15 kg of fuel to put 1 kg of stuff into orbit. If SI could be raised to about 6,000 seconds, you'd be pretty close to the much more economical goal of using a kilogram of fuel per kilogram of payload. (Any reader who has more accurate figures is welcome to comment; these were back-of-envelope figuration, and my calculus is getting rusty.) Until much higher SI is achieved, putting people into orbit, even littler ones that weigh no more than 50kg each, will be a very costly proposition.

In the middle of an economic meltdown, with belt-tightening everywhere but between our President's ears, the current NASA proposal for spending around $160 Billion to return to the Moon is DoA. I wonder if I should take bets on how many countries get to the moon before the U.S. does… Goodbye, Shuttle program. You were beautiful, but you were a very expensive date.

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