[QUOTE=Squink]
Other than that, no, there’s only so much energy in a chemical bond, and H[sub]2[/sub]/O[sub]2[/sub] rockets aren’t going to get any more powerful, ever.
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No, but they can become more efficient, cheaper to build and maintain, and reliable. Fixed geometry rocket nozzles have a peak efficiency at one particular ambient pressure which drops off rapidly as external pressure decreases. This is because the exhaust expands more rapidly with less ambient pressure (due to either higher altitude or increasing velocity) and thus does less work on the nozzle, translating into less impulse to the motor. Variable geometry nozzles (like the aerospike engine) give greater efficiency and use less fuel, thus increasing specific impulse and the fuel mass fraction for a given payload. While a LOX/H2 reaction gives the greatest specific energy output (H[sub]2[/sub] has a specific heat of 1.75 kcal/kg-K at the boiling point) it has a relatively low molecular mass relative to heavier propellents and thus exhibits high chamber pressures and sensitivity to nozzle configuration, whereas hydrocarbon bipropellent fuels like kerosense offer more thrust in a compact, reasonable pressure motor and not being cryogenic are easier to store (hence, the use of kerosene and LOX on the Saturn I, IB, and IC first stages, as well as Atlas, Delta family, Titan, Energia-Zenit boosters, et cetera.
Frankly, the biggest cost in performing a space launch isn’t the cost of the fuel–which for common fuels comes in at a few dollars a pound–or the materials used to construct the vehicle, but the development costs and operational/maintainence labor. This is particularly true of NASA, which has an entrenched bureaucracy to feed, and the aerospace contractors for whom the first priority is to spend the available budget rather than produce a viable product, which goes a long way to explaining the exorbiant budget of the CEV/Orion system, which consists largely of existing production components (STS-SRBs, RS-68 engine) and familiar technologies (blunt cone capsule, ablative heat shield) which shouldn’t require expensive development. (In the press conference following the CEV award announcement, one person questioned NASA’s selection of Lockheed-Martin SSC based upon their past performance and experience with space launch systems, which was an amusingly pithy observation as LMSSC has a reputation in the aerospace industry of repeatedly overspending development budgets and then failing to fly hardware.) In contrast, the Russian Space Agency launches of the manned Soyuz system cost an estimated $10-$16M per, illustrating the economy of using a relatively simple, mature system, albeit one that can’t be readily expanded to more extensive missions. However, the example demonstrates that space launches can be done far more cost-effectively than Apollo and the STS would indicate. Indeed, launches of the Gemini system atop a Titan II were a fraction of the cost of comperable Apollo earth orbit missions (albeit subsidized by using surplus Air Force ICBMs rather than a dedicated booster) and the cost estimates for Big Gemini, which would have accomodated a crew of six were substantially lower than Apollo.
The problem with the Shuttle was that there was really no focus on keeping launch costs minimized during design; the thrust of the effort was to keeping within the projected development costs (unlike the blank cheque policy during Apollo development, the STS was expected, upon threat of cancellation, to stay tightly within budget estimates) while having the system ready for deployment on schedule (1979) and meeting the myriad of expectations and capabilities laid upon it, including being the primary–and as it turned out, exclusive–heavy lift vehicle, having the cross-range for polar orbit launches for the Air Force and NRO, acting as a delivery truck for modules for the then-Space Station Alpha (the much grander concept that eventually became the ISS). and so forth. The many flaws, needless complexities, and labor-intensive operations were ignored in favor of getting something out the door on time, meeting specifications, and within budget. (Two out of three ain’t bad, I guess.)
As for Orion as the basis of a Mars mission, that is neither in the spec for CEV nor is it suited for such a mission. We have exactly zero experience with long term manned interplanetary missions, so to suggest that “we have the technology” is disingenous at best. We certainly have the ability–at enormous expense–to send a vessel to, say, Mars, but we lack the ability and experience to minimize radiation hazards outside of the Earth’s magnetosphere, nor do we have the experience to reduce the risks of long-duration missions to an acceptible level when rescue or assistance cannot be rendered. A vessel for eventual manned interplanetary exploration will be much different from CEV, and will require the development and maturity of technologies that are not even conceptually part of the CEV program.
At any rate, objective of Mars is, from both a technical and scientific standpoint, a poor return on investment. We can advance the prospect of a permanent, self-sustaining human presence in space, as well as acquire much valuable scientific information about the formation of the Solar System by first venturing to Near Earth Asteroids and later going to the outsystem (Jupiter, Saturn, the asteroid belt). Mars has some potential for planetologists and (perhaps) xenobiology, but the combination of inaccessability, low exploitability, and limited science prospects (compared to the exotic and diverse Jovian and Saturnian systems) renders the focus of landing on Mars as little more than a brazen stunt to attract attention and deflect criticism of the Shuttle and other unrelated current government policies.
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