Nathan, I agree that if the debate is phrased as "shuttle or nothing," shuttle will always win. But this is like saying of the defense budget, "Well, we can fund the new Godzilla attack helicopter even though it failed in tests, or we can surrender to Iraq. Those are the only choices." Shuttle prime contractors, the pork-barrel crowd on the Hill and the talking heads on the tube are the ones who phrase the debate as shuttle-or-nothing. People like me have spent years proposing alternatives that sustain the manned space program by replacing the shuttle with something better.
Your point that the shuttle lobby shouldn't care if this project was canceled, so long as a comparable initiative replaced it, is right in logical terms; the fact that the shuttle lobby does not think this way is revealing. At some level the faction that says shuttle-or-nothing—especially the shuttle "primes" and the congressional delegations from states and districts of NASA's flight centers and assembly facilities—fears that if the shuttle were canceled the replacement really should be nothing, or some dramatically retrenched mini-program, because they know in their hearts that current space research has hardly any value.
People like me are willing to assume space flight has value. A true rationalist might advocate shutting down almost everything until there is a propulsion breakthrough. The shuttle lobby fears this because it is not a squishy-lefty conclusion ("How can we be spending money to study pulsars in Andromeda if there is just one child who still does not have an MP3 player," etc.) but a rationalist conclusion.
I'll suggest one other reason why the space shuttle program lingers against common sense: because it has no objective. Its predecessors, the Mercury, Gemini, and Apollo programs, all had well-defined objectives and specific milestones. As each reached its well-defined objective, the program concluded. Nobody could have argued for endless funding for Gemini flights because the Gemini program was supposed to accomplish two specific objectives, the first American spacewalk and the first orbital rendezvous. It accomplished them, then sent its spare capsules to the Smithsonian and entered the history books.
Because the shuttle program has never had a defined objective, it cannot achieve its objective and therefore cannot end! Microsoft research projects, I suspect, have defined goals: "Make an X that does Y." If Microsoft started a program with a shuttle-like charge—"Make a really big, impressive, expensive, amazing-looking X"—that program would never come to a conclusion. Managers would endlessly say, "We can't stop now, it's not amazing enough yet." Arguing back "But what is it for?" would generate only blank stares. Without a defined objective, there would be nothing to judge results against.
Now I'd like to return to the question of whether there is any value to space flight. For the moment, there is almost none. That's the problem with your suggestion that NASA needs a "bold plan" or "compelling vision." Believe me, NASA would like to have a compelling vision. But when the agency debates this internally, as it often does, even the space cadets can't identify one. The two possible bold plans at the moment are the return to the Moon to establish a research base or sending men and women to Mars. It is very, very hard to justify either, and this is setting aside capital costs and risk to life.
A research base on the Moon? Surely Moon researchers would discover many things about the origins of the solar system that would be of interest to geologists. Maybe they'd make some stunning finding, like the wreckage of an alien space probe: sure to be stamped in all languages of the galaxy, contains no user-serviceable parts. If there is a monolith or similar artifact hidden on the Moon, by the logic of the Arthur C. Clarke story, we don't want that found. (Presumably, Moon-base personnel would be sternly instructed never to expose anything to sunlight.) Given that the nobody-knows-what-it's-for space station has cost $36 billion already, a manned base on the Moon, farther away and requiring extra descent and ascent energy, would cost at least three times as much. Odds are the yield in human knowledge would be small compared to, say, spending the same amount on medical research. And please don't tell me we would mine the Moon's resources. Almost all primary commodities are already in oversupply on Earth, while no one mines Antarctica, possible at a minute fraction of the cost of Moon mining.
A trip to Mars? Many advocates rhapsodize about flight to Mars now: Fantasize with them here at the Case for Mars Web site. But with current rocket motors, a Mars round trip would take about two years. Several automated missions delivering supplies, fuel, and equipment would have to arrive at Mars successfully before departure of the ship bearing crew. That crew vessel would need to be elaborately shielded against cosmic and solar radiation—not a threat to the Apollo astronauts, who were always within Earth's protective magnetic sphere—and there is no shielding solution that does not entail substantial weight. You'd need a full operating theater aboard the ship and at least two surgeons on the crew, because what if it's the surgeon who gets injured? Probably there would need to be two complete Mars vessels flying in tandem, in case one develops a fault during the transit. And you'd have to be confident that six to 10 people could live extremely close together—essentially, aboard a submarine—for two years without psychological conflict. Remember how well this plan worked out for the much more spacious Biosphere II.
Mars advocates talk about fast trajectories in cheap inflatable spacecraft and going to the red planet without fuel, then using a tiny nuclear reactor to manufacture carbon monoxide from the atmosphere as a propellant for the return trip. Aside from the fact that you could manufacture carbon monoxide from Earth's atmosphere as a propellant and no one does, maybe Edward Bass, godfather of Biosphere II, would sponsor the hurling of a fuelless inflatable spacecraft toward Mars. NASA would do this mission right or not at all. Doing it right would mean $100 billion to $200 billion, and that's assuming we first develop a shuttle replacement that can put all the mass—thousands of tons—into orbit affordably. I spoke at a Case for Mars conference once and sat in on the sessions. By the strangest coincidence, there was no discussion of launch cost.
Would men and women on Mars make interesting discoveries? That seems almost certain. There's a fighting chance of finding fossil remains of at least some form of microbial life. There could be much, much more. But $200 billion and tremendous risk doesn't seem like much of a vision when automated Martian probes could do most of what astronauts could accomplish for a small percent of the cost. If in the next few years NASA proposed Mars flight as a bold plan, it would be lampooned beyond belief. The agency already has several advanced, automated Mars landers in the works for launch this decade. Unless they find something really spectacular, they are likely to reduce the short-term argument for sending people to the fourth planet.
When I try to come up with a bold plan or compelling vision for NASA, under present circumstances the only one that really registers is a systematic search for asteroids and comets that might hit Earth—"near Earth objects," as astronomers call them—coupled with construction of some kind of spacecraft, perhaps manned, designed to intercept a killer rock and blow it up or knock it off course. Yes, this sounds like a movie, but protecting the planet from the unlikely, though totally real, threat of a horrifying impact is the only present way NASA and its astronauts can perform a service of clear value to taxpayers. Killer rocks and comets have hit Earth many times in the past and will hit again. Logic points you to this as NASA's prime concern. But asteroid defense is not a sexy mission and would itself be relentlessly lampooned.
Everything we're saying changes, of course, if there is a propulsion breakthrough. The Air Force has actually tinkered with antimatter combustion, which is wildly impractical now, but computers were wildly impractical once. A propulsion breakthrough that gets tons into orbit cheaply would alter the equations for the Moon and Mars as bold plans, and an antimatter drive capable of 1 percent of light speed would zip us anywhere in the solar system quite nicely. (Though, still be useless for travel even to the nearest extrasolar star.) So I'm for propulsion research, including more work on nuclear propulsion. But this has no application to NASA policy decisions at the moment.