One reason might be the very success of the rovers, which show that effective science can be done at a far lower price tag than the $400 billion requried for a manned mission. And the notable lack of public reaction and the generally negative response from the scientific community may have given the Administration pause.
Like many scientists, James Van Allen, best known for the discovery of the radiation belts that bear his name, is aghast at the Mars proposal. He points to the difficulty and the danger and the cost, all of them monstrous problems and notes that the budget the President proposed for the project is far too anemic to anywhere meet the need.
A manned mission to Mars, Van Allen notes, would require a minimum of a year and a half — six months to reach the Red Planet, six months of research on the surface and six months to return. Each astronaut would require about five pounds of food and water daily. They talk about growing broccoli and other vegetables on the spacecraft, he says dismissively, and recycling water. Still, for a five-man crew, a mission of that length would require carrying along some 20,000 pounds of food and water. Then, too, you have to bring along a good supply of oxygen and reconvert exhaled carbon dioxide to replenish it.
The risk would be great, the margin of error tiny, and any kind of rescue effort out of the question. A simple malfunction of equipment or, say, a micrometeorite impact that caused the spacecraft atmosphere to escape, could bring disaster. Some experts say that the first attempt to send a crew to Mars might well be a suicide mission. Yet Van Allen thinks there would be no shortage of volunteers. The present astronauts are a pretty daring bunch, he says.
But what about the total cost of the mission, which would include establishing a Moon base from which the spacecraft would be launched? Experts calculate that it would be in the neighborhood of a cool $400 billion, unwelcome news at a time when the national debt stands at $500 billion and isrising. In his proposal, President Bush insisted that a manned Mars mission was necessary because The human thirst for knowledge ultimately cannot be satisfied by even the most vivid pictures or the most detailed measurements, obviously referring to the twin rovers. But the editors of the prestigious journal Science disagreed. While acknowledging that human involvement in the space program initially fired the publics imagination as an adventure, they noted editorially that the more recent manned ventures were more like a version of extreme sport. And unlike the robotic missions to the planets, the space telescopes and remote-sensing Earth orbiters, manned missions have contributed little to our knowledge of the solar system and the universe.
Space exploration carries risks, the Science editorial concluded, and ensuring against accidents in human space travel is expensive; when tragedies occur, programs become stagnant Indeed, NASA, in the wake of the Columbia disaster, has suspended shuttle flight at least until 2005. On the other hand, the Science editors wrote, Failures of unmanned missions, while disappointing, tend to increase determination. That is most evident in the current spectacular exploits of Opportunity and Spirit, hard at work after the failure of earlier Mars missions.
Indeed the twin Mars rovers have apparently generated more interest in space exploration than any of the more recent missions. Their exploits and images, posted on NASAs web sites, have drawn 5.5 billion pageviews from an obviously fascinated public.
Van Allens final report card about the manned Mars mission proposal: I give the President an A for rhetoric, a D for arithmetic and a D for realism.