NASA Spacecraft Temple 1

It's not exactly young love, but some might find it romantic. On Valentine's Day, an aging Lothario that has been flitting from beauty to beauty through the solar system will make his final stop, taking pictures of a battered dowager to send to the folks back home before disappearing forever.

The Stardust spacecraft, which has already taken images of asteroid Annefrank and captured interstellar dust from comet Wild 2, on Monday night will swing by comet Tempel 1. There, it will take new pictures of the devastation wrought on the comet by NASA's 2005 Deep Impact mission.

In that historic encounter six years ago, the Deep Impact spacecraft released an 820-pound probe that crashed into Tempel 1 at 23,000 mph, sending a luminous plume of debris into space and allowing researchers to determine what the comet was made of. There was so much debris, in fact, that the spacecraft could not get a clear look at the impact crater.

Now, Stardust will be able to obtain images of that crater up close for the first time. Moreover, in the nearly six years since that initial encounter, the comet has completed an orbit around the solar system, passing close to the sun.

"For the first time, we'll go back to see what happens to a comet" after it passes close to the sun, said Pete Schultz of Brown University, a scientist for the new mission, which has been dubbed Stardust-NExT.

Instruments on the spacecraft will also measure the size and distribution of particles flowing from Tempel 1 and analyze their composition, enabling scientists to get a better sense of what comets are made of.

The craft will fly within 124 miles of the comet, taking 72 pictures with its camera, a spare left over from the Voyager program, which produced the first spacecraft to reach the outer planets. Each image will require about 15 minutes to be beamed back to Earth.

The Tempel encounter was not part of Stardust's original mission. But after the craft returned dust particles from Wild 2 to Earth and was placed in a parking orbit, researchers looked for another mission and finally settled on the trip to Tempel 1. They concluded that the repurposed mission could be carried out for about a 10th of the cost of a completely new project.

After Tempel, no future missions seem likely. When Stardust was launched, it carried 22 gallons of hydrazine to power its rocket thrusters. Spacecraft don't have traditional fuel gauges, but the control team estimates that the craft's attitude and translational thrusters have each fired almost half a million times over the last 12 years.

That means there is probably about a cup of hydrazine left in the fuel tank, not enough for any meaningful maneuvers. After the aging Lothario sweeps by Tempel 1, it will simply keep going around and around the solar system on its own, and will probably be booted into deep space eventually.