he planned scuttling of the U.S. Defense Department’s Orbital Express satellites stands out in stark contrast to NASA’s assignment of new missions to its Stardust and Deep Impact probes. In one case, two unique satellites, seemingly with plenty left to offer, are being

put out to pasture; in the other, NASA demonstrated both ingenuity and creativity in coming up with ways to maximize the scientific return from spacecraft that had completed their original missions.

That NASA unveiled the new itineraries for Stardust and Deep Impact as the U.S. Air Force was preparing to take irreversible steps to decommission the Orbital Express satellites – just days after they had completed a very successful demonstration of in-orbit spacecraft servicing techniques – is ironic, to say the least.

The Air Force’s decision on Orbital Express, which it co-sponsored with the U.S. Defense Advanced Research Projects Agency (DARPA), is puzzling. The mission’s Astro and NextSat satellites have fulfilled the goals set out for their planned 90-day demonstration, during which they exchanged fuel and hardware and performed other synchronized maneuvers, but are still in good working order. Meanwhile, there clearly was interest within some NASA quarters in taking over the satellites, whose orbital acrobatics had relevancy to a number of missions being planned or contemplated by the space agency. Two that come to mind are a Mars sample return mission and some of the automated in-orbit docking maneuvers envisioned as part of NASA’s plan to return astronauts to the Moon.

Yet somehow, NASA and the Air Force could not work out a deal to make it happen. As of press time July 6, the service was still planning to decommission the spacecraft, a process that involves emptying their fuel tanks and turning off their computers.

NASA declined to criticize the Air Force for ending the mission and said there was never any dispute in the matter. But knowledgeable sources have said NASA and DARPA quietly asked the Air Force not to pull the trigger, only to be rebuffed.

It could well be that getting the Air Force to comply would have required a bureaucratic campaign that NASA’s top management simply didn’t have the will or the energy to wage. If that’s the case, it would be understandable – NASA Administrator Mike Griffin has enough headaches to deal with, most of which stem from the fundamental problem of too many missions and not enough money.

Of course, the perpetual mismatch between missions and resources would seem to be all the more reason to try and extract some additional utility from satellites in which the U.S. government had invested some $300 million, $25 million of which came from NASA.

If thrift and resourcefulness did not carry the day on Orbital Express, both were on full display with NASA’s July 5 announcement of new assignments for its Deep Impact and Stardust spacecraft, which completed their primary missions in 2005 and 2006, respectively. Deep Impact, which wowed the public with photos it snapped of a projectile that it had dispatched smashing into the comet Tempel 1, will now go on to make observations of another comet and study known planets outside our solar system. The planned December 2008 flyby of the short-period comet Boethin will help make up for the failure of the Comet Nucleus Tour, or Contour, mission back in 2002.

Meanwhile, Stardust, which launched all the way back in 1999 and sampled material from the comet Wild 2 in 2004, will be directed to revisit Tempel 1 so scientists can study changes to a comet’s nucleus that result from its close approach to the sun. The flyby, slated to occur in 2011, will mark the first time a comet has been closely observed by separate spacecraft.

According to Alan Stern, who heads NASA’s cash-strapped Science Mission Directorate, these new investigations will be carried out at about 15 percent of the cost of starting dedicated missions from scratch. In addition, using these veteran spacecraft eliminates much of the technical risk associated with new missions, such as the risk of launch failure.

The end of any successful NASA mission almost invariably brings calls from scientists and other interested parties for an extended tour. Unfortunately,

NASA cannot afford to do this in all or even most instances, but with Stardust and Deep Impact the agency will be conducting compelling new science that is well worth the cost.

One can only wonder whether the technical knowledge NASA could have gained by taking over the Orbital Express satellites would have been equally compelling.