NASA's Deep Space 1 spacecraft, sailing through the solar system today, has taken delivery of a new cargo: the latest software for its ambitious encounter with Comet Borrelly this September.

After successfully finishing its primary mission in 1999 as a testing ground for important new technologies, NASA approved a risky bonus mission to Comet Borrelly for Deep Space 1. There the spacecraft will take black-and-white pictures, use infrared pictures to find out the nature of the comet's surface, measure and identify the gases coming from the comet, and measure the interaction of solar wind with the comet. To take pictures of the comet, Deep Space 1 must upgrade its software's pointing system to turn the spacecraft from a testbed for advanced technologies to a chronicler of Comet Borrelly.

"Deep Space 1's previous version of software, which was transmitted to the spacecraft eight months ago, has proven itself during the surprisingly successful flight through the solar system since then, but now we're giving the probe a new assignment," said Dr. Marc Rayman, the project manager. "And in order to prepare for this exciting and daring comet encounter, the software needs to be upgraded."

The spacecraft team will be checking the software, radioed to Deep Space 1 throughout the week of March 5. The first check came when the team actually received a signal from the spacecraft after it shut the main computer off and restarted it. Since the software sent by the team works well, the spacecraft sent a signal indicating it is healthy. Now engineers are giving the spacecraft's new software a thorough physical checkup.

"The process of transmitting the new software to the spacecraft, rebooting the on-board computer to begin running it, verifying that the spacecraft is working properly with the new software and restoring the craft to its cruise configuration, all when the spacecraft is 318 million kilometers (197 million miles) away, is a complex and tricky operation, " said Daniel Eldred, the Deep Space 1 mission manager.

The new software contains capabilities that will be needed when the spacecraft gets to Borrelly. The new commands will include lessons that Deep Space 1 learned in its 1999 encounter with asteroid Braille about the behavior of the spacecraft when it gets close to a solar system object.

The spacecraft carries a device, part of the successful new technology system, which holds two cameras. One uses a conventional charge-coupled device detector, the other a new technology detector. The test camera, though performing its initial tests successfully, wasn't equipped to deal with the very dark object that Braille turned out to be. Small bodies like asteroids and comets are still a mystery. Since they're so small and distant, their exact size and shape can't usually be determined from Earth. Deep Space 1 plans to use its tried-and-true CCD camera to try to snap photos of Borrelly. The team will send commands to the new software to stop using the test camera and start using the CCD camera, which will take a larger picture with more light.

In late 1999, after the successful end of its primary mission, Deep Space 1 lost its star tracker, and the spacecraft had to be reconfigured to use the photographic camera to orient itself by the stars around it. In order to take pictures of Borrelly, the camera can't align the spacecraft and snap photos of the comet at the same time. Instead, the spacecraft will have to rely on its fiber-optic gyroscopes to help maintain its orientation. But the gyros are not accurate enough by themselves, so the new software will try to correct for those inaccuracies. The new software is designed to help the camera stay pointed at the comet's nucleus during the 15 minutes that the camera will attempt to observe the comet.