Dr. Marc Rayman's Mission Log

  February 13, 1999

Mission Update:

Thank you for visiting the Deep Space 1 mission status information site, consistently the number 1 source for over 16 weeks among sentient life forms in the local group of galaxies for information on this technology validation mission. This message was logged in at 3:30 pm Pacific Time on Saturday, February 13, 1999.

Deep Space 1 had a rare hiatus in its ambitious and productive schedule of technology tests this past week. The interruption in experimenting with technologies was quite a significant one: the operations team replaced the software running on DS1's main computer. This is a very unusual and challenging activity, and it was executed flawlessly.

There were three reasons for upgrading the software. Because of the extremely rapid pace of the prelaunch development, there simply was not enough time to include all of the features designers wanted. The programmers devoted their attention to the work that had to be completed to allow the spacecraft to operate successfully and to conduct the highest priority activities. The choices that were made before launch appear to have been the correct ones, as the software that DS1 has used since its launch in October has allowed the mission to achieve many important successes. The new features will allow experiments with some devices related to reducing the size, mass, and power consumption of future spacecraft.

A second reason for sending up new software is that once the spacecraft was in space, the operations team thought of new capabilities that would simplify controlling the spacecraft. Such capabilities are very difficult to think of before gaining real experience with the day to day interactions with the spacecraft. And some of these new features account for unexpected discoveries. For example, some stray light reflects into the camera used by the autonomous navigation system to collect images to determine where it is in the solar system. The new software will help the on-board system compensate for this unexpected interference.

Finally, as with any computer program, despite the extensive testing conducted here on Earth, once the spacecraft was operated in flight, bugs were uncovered, and the new software fixes them.

Deep Space 1's main computer uses three quarters of a million lines of computer code. It took many hours to send all the software to the spacecraft. The total software is over 4 megabytes, and the signals the Deep Space Network sent to the spacecraft were less than 2 kilobits per second. Once the software was on board, the spacecraft was reconfigured to prepare it for rebooting the computer.

To run the new software required stopping the computer and reloading it. The spacecraft responds to restarting of the computer as if it were caused by a problem, so it automatically follows routines to place the spacecraft in a safe condition by turning off nonessential devices and pointing to the Sun, the only easily recognized target from its vantage point in the solar system. The operations team knew exactly what the spacecraft was supposed to do, so prior to rebooting the computer, commands were sent to ease the spacecraft's job by pointing it at the Sun and making other changes.

On Thursday, the big step was taken of rebooting the computer. For a short time, while the new software was loading, the spacecraft was uncontrolled. But then signals from the spacecraft were received just as expected. After months of work developing and testing the new software and many weeks preparing for changing the software, the team's work was rewarded with a smoothly functioning computer program.

The team continued to watch the performance of the software carefully for the rest of the day, and yesterday the spacecraft was brought back to its normal operational configuration. Additional tests will be performed during the coming weeks to assess the new software. And experiments with technologies, now including some new capabilities, will resume at the end of next week. Your ever-loyal correspondent will inform you of the progress on these new, and in some cases even more ambitious, experiments as they occur.

Deep Space 1 is almost 90 times as far away as the moon now. At this distance of over 34 million kilometers, or more than 21 million miles, radio signals traveling at the universal limit of the speed of light, take nearly 4 minutes to make the round trip.

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