The debate over what kind of rocket to use for NASA's exploration program has become so clouded by politics and salesmanship that it's hard for outsiders to tell any more which approach would be best, or even if it's still possible to send people beyond Earth orbit. The Augustine commission says it isn't, at least not without more money. Meanwhile, former NASA Administrator Mike Griffin continues (as in this recent Congressional testimony) to defend the agency's proposed Ares launchers against all criticisms.
Based on the presentations at a recent workshop on advanced Earth-to-orbit concepts, it doesn't appear that anyone has cracked the basic, decades-old problem of space economics: It still costs thousands of dollars per pound to deliver stuff to orbit, whether that stuff is astronauts, weather satellites or water. The only agreed way to bring down launch costs—and this applies to today's chemical rockets as well as tomorrow's space elevators—is to increase the traffic rates.
NASA's current plan, though, is to build large, expensive rockets that would seldom be used—just as it did with the Saturn V in the 1960s.
Another approach, championed most recently in a series of papers posted by United Launch Alliance (the Boeing-Lockheed Martin joint venture that builds and operates Delta and Atlas rockets), would be to use a lot of launchers to carry the tons of supplies required for a lunar mission—75 percent of which is fuel—to orbit. The fuel would be stored in orbital propellant depots, a scheme that ULA's mission architects claim would allow moon landings by 2018 without busting the budget.
Orbital gas stations are hardly a new idea. But ULA says it has found a way to make them simple and relatively cheap in the near term, by adapting existing upper stages. If true, it would be quite an advance. The Augustine commission was high on the concept of orbital refueling, at least in principle:
All of the options would benefit from the development of in-space refueling, and the smaller rockets would benefit most of all. The potential government-guaranteed market for fuel in low-Earth orbit would create a stimulus to the commercial launch industry.Griffin, though, is skeptical. In his Congressional testimony he said:
An architectural approach based upon the use of numerous smaller vehicles to stock a fuel depot is inevitably more expensive than putting the necessary payload up in larger pieces. Further, a fuel depot requires a presently non‐existent technology—the ability to maintain cryogenic fuels in the necessary thermodynamic state for very long periods in space. This technology is a holy grail of deep‐space exploration, because it is necessary for both chemical‐ and nuclear‐powered upper stages. To embrace an architecture based upon a non‐existent technology at the very beginning of beyond‐LEO operations is unwise.Who's right? Who knows? Griffin often criticizes engineering "solutions" based on vague promises. "Your vugraphs will always beat my hardware," he's fond of saying. Fair enough. But ULA's Deltas and Atlases have launched 850 payloads into space in the past half century, while the Ares V is still just a vugraph.
If the nation's most experienced launch company steps forward with a near-term concept that could potentially change the economics of spaceflight, why wouldn't we at least pay for a couple of test flights to see if it works? The ULA authors say they could have a proof-of-concept depot ready to fly by 2011.