What would constitute rational budget priorities for NASA? The agency's first emphasis should be research about Earth and the sun. That's the sole area in which NASA spending is odds-on to produce immediate returns for taxpayers. Second, NASA should fund more automated probes and satellites to study this solar system and close-by star systems—the parts of space that might have some effect on us. Almost all NASA findings since the moon program have come from automated probes such as Cassini, which a few weeks ago discovered what appears to be a water vent on a moon of Saturn. Most probe projects cost less than a single launch of the space shuttle. Third, the agency should cancel the shuttle program and use the funds to research new propulsion systems that might fundamentally reduce the price of access to space. A fundamental propulsion breakthrough must come before grand visions like a Mars mission. Currently NASA is working on a new launcher to replace the shuttle, but that system will be cobbled together from existing engines and hardware and won't notably differ from rockets of the 1960s.
Fourth, NASA needs a serious program for searching nearby space for asteroids and comets that might strike Earth and figuring out how to deflect any big rock headed this way. Asteroids and comets large enough to cause devastation may strike Earth distressingly often; for instance, it is believed thousands of people were killed by a smallish space rock that hit China in 1490. (Here is more on the chance of a calamitous comet or asteroid impact.) Even if asteroid and comet strikes only happen in intervals of thousands of years, that doesn't change the chances that a space rock is headed our way right now, in the same sense that a coin coming up heads 10 times in a row has no bearing on what the next flip will produce. If NASA protected Earth against a strike from space, that might be, let's say, the most significant accomplishment in human history. Yet NASA has only a minor program to search for "near-Earth objects" and no program to figure out what to do about them. Preventing comet strikes would give taxpayers a return on their money, and we can't have that! The new budget request suggests that no one in the agency's hidebound, turf-obsessed upper management wants to think about what NASA can do to actually benefit the public.