I'm not normally a big agitator for unmanned planetary missions. I'm not opposed to them, but I don't find them all that urgent and compelling. Generally, I agree with Proxmire's famous statement, "Mars will still be there..."

But in this case I think that the cancellation of this particular mission is a travesty and a tragedy. In the context of the total NASA budget, a mission to Pluto doesn't cost that much, and it's one of the cases in which it isn't true that "it will still be there." Pluto has an orbit such that it will get much more difficult to reach it if the launch doesn't occur in the next few years, perhaps to the point that it will be decades before we have an opportunity to explore it (assuming, of course, no major advances in deep-space propulsion, admittedly a brave assumption).

Unfortunately, the problems aren't just penny pinching--they're political (what a surprise--politics in a government space program). First, they've designed to launch the mission on a new launch vehicle that may not be adequately tested to NASA's satisfaction by the time the launch window closes. This problem could be resolved by using a Russian launcher, but that's not poltically acceptable.

The other problem is that a mission that far away from the sun can only be done with a nuclear power source, called a radioisotope thermal generator (RTG). This isn't a reactor--it's just a lump of plutonium that generates heat as it decays, which is then converted to electricity. We've been using such power sources safely since the beginning if the space program, but the last few missions that required such power sources (most notably the Cassini mission to Saturn) have had to run a gauntlet of environmental approvals and hysterical and ignorant protestors, and there is fear that the delays from this for the Pluto mission could end up pushing it out beyond its date of viability.

So, barring some technological breakthrough, we may not see Pluto up close for many decades.

I'm still peeved at the astronomers who discovered Pluto's moon, Charon. "Charon"?!? The obvious choice should have been Persephone.

In February of this year, NASA announced a new nuke-power initiative. Word within the Agency is that the Bush administration is a big believer in using RTGs to explore the solar system, and RTGs have for a while been the favored propulsion engine among engineers for such missions. Rather than view the Pluto mission as killed, which would be a pity, the RTG initiative may get us there faster with a heftier instrument payload. If we can keep the uninformed enviromentalist and anti-nuke protesters from stealing the airwaves, that is.

Hi Rand -- I thought the motivation for a Pluto mission soon was not that the planet would get too far away, but that its atmosphere will freeze when it gets more distant from the Sun.

You may be right--as I said, I don't follow planetary science all that closely. But if you're going to use gravity assists to get there, (and it's pretty hard to do it otherwise without radically new propulsion methods) there are also launch windows with times between them of decades, given how slowly all the outer planets move.

It is my understanding that "Charon" was named in part for Charlene, the wife of the discoverer, and is therefore usually pronounced with an initial "sh" sound, rather than the more technically correct "ch" or "kh" sounds.

For NASA's Nuclear Systems Initiative, see http://avoyagetoarcturus.blogspot.com/2002_03_01_avoyagetoarcturus_archive.html#75010622.

The "date-related motivation," to use a new business buzzphrase, for the Pluto mission is indeed that the atmosphere is expected to freeze out over the next decade or two, rendering it unavailable for study for another couple of centuries.

Perhaps I am mistaken, but I believe that NASA's nuclear initiative is focused on reactors, not RTGs. This would have a (positive) profound impact on future exploration, but alas, will probably run afoul of the usual Luddites...