Solar System exploration had been virtually stalled since the Eighties due Shuttle's development problems and an increasing leakage of funds to a virtual spacestation. Part of NASA's frantic strategy to ensure that the Shuttle monopolized the U.S. launch industry, and that expendable rockets were eliminated, was to make sure that all planetary exploration spacecraft -- and as many Earth-orbiting scientific spacecraft as possible -- were as big and complicated as possible, with NASA dubbing them "flagship" missions.

But their chief characteristic was that they were simply too big and heavy to be launched on any vehicle but the Shuttle or the Titan. And while some planetary missions, such as the Magellan radar mapping mission of Venus can't be chopped up into a set of smaller and cheaper spacecraft that can be launched at more frequent intervals -- but most of them can.

For example, Galileo and Cassini could each have been easily subdivided into two -- or even three -- smaller spacecraft, with very little science loss.

The Challenger disaster returned expendable launch vehicles -- including smaller ones, such as the Delta -- to their original position of prominence and thus forced NASA to consider again the possible benefits of smaller scientific spacecraft, which its new Administrator Dan Goldin was willing to do.

And the 1993 failure of Mars Observer confirmed that smaller spacecraft had an important role to play in planetary exploration. The Clementine and NEAR missions were launched before Pathfinder -- but Clementine was a partial failure, while NEAR is still traveling a long road before reaching its asteroid target following a rocket malfunction last December.

But Pathfinder -- and now Lunar Prospector -- have proven that the new philosophy can pay off in a big way. True, the failures of the Lewis, WIRE and ABRIXAS satellites -- and the troubles experienced on Clementine, NEAR and the Mars Global Surveyor -- have shown that it is possible to economize too much on designing and testing a spacecraft -- "faster and cheaper" doesn't always mean "better".

But even so, small scientific spacecraft have two big advantages. First, if a small spacecraft fails because of a design error (as Mars Observer did), you haven't lost nearly as much and can correct the flaw in later spacecraft (unless you've launched them all at the same time).

Second, the plain fact is that some scientific experiments are always going to be more valuable than others -- and so, when you divide them up among several spacecraft, you can launch the highest-priority experiments first and get their data earlier than when you had to lug all of them along at the same time (and often the data from those highest-priority experiments has been invaluable in causing us to redesign our later explorations of a planet or moon).

But Pathfinder had another effect on space exploration, which I think will be much more important in the long run. Ever since the end of the Apollo program, NASA (like any government agency) has been obsessed with maintaining its budget at as high a level as possible.

This means that it is obsessed with emphasizing the continuing preeminence of manned rather than unmanned space missions -- even when manned missions are uneconomical or flat-out absurd -- simply because they are far more expensive.

And one of the main arguments it has been using to publicly justify the importance of manned missions is that the public, and therefore Congress, has no real interest in space exploration unless it involves astronauts --"No bucks without Buck Rogers", the saying has gone.

The public's interest in the Voyager missions and the Hubble Telescope had already called that philosophy into question -- but the public's fascination with Pathfinder, which approached the level of adoration, blew it to smithereens.

No astronaut since Sally Ride had inspired as much public interest and affection as the 10-kg robot Sojourner did. The Pathfinder Web site recorded an incredible 600 million hits during the first month after landing, and a recent poll of American newspaper editors listed the landing as among the hundred most noteworthy news stories of the entire 20th century (albeit 97th).

It turned out, in short, that the public is not so much interested in who or what is exploring space as in whatever interesting things they see and learn when they get there.

Why go to the trouble and expense of sending the rest of our bodies into space when we can send our eyes and minds there? This was perhaps predictable -- one aerospace engineer suggested that Lewis and Clark would cheerfully have explored the western U.S. by remote-control robots if they had had the technology -- but after Pathfinder it was simply impossible for NASA to publicly deny it.

NASA is now limited to trying to pump up enthusiasm for manned space flight by pure stunts -- first John Glenn's reflight, now the ridiculous talk of an all-female Shuttle flight.

One wonders what might come next -- perhaps putting a teenager into orbit, a la Anakin Skywalker? There were rumors that the Soviet Union seriously considered that idea during the Eighties.

But the number of such stunts is inevitably limited -- and the public seems unlikely to ever be significantly interested in the Space Station, for the simple reason that the Station can never do anything really interesting (or very important scientifically).

The Station is, I think the last hurrah for wasteful manned space exploration; after it ends (and however it ends), human beings henceforth will enter space only when there is a good and practical reason for them to do so.

And that lurch toward scientific and fiscal sanity -- that first step toward really rational and sensible space exploration -- was made possible primarily by Pathfinder.