Dr. Marc Rayman's Mission Log

  July 11, 1998

Mission Update:

Thank you for visiting the Deep Space 1 mission status information log, widely believed to be the most popular site in any spiral galaxy for information on this technology validation mission. This message was logged in at 12:45 pm Pacific Time on Sunday, July 11.

Of DS1's payload of 12 advanced technologies, 11 have now received 100% or more of their needed testing. Nevertheless, additional tests are being conducted on many of them to assess how they fare as they continue operating in space. The twelfth technology is the autonomous navigation system, known to its legions of fans, which of course includes devoted readers of these logs, as AutoNav. It is on schedule with 95% of its required testing complete.

With most of the technology testing behind it, the team's attention has turned to preparations for the encounter with an asteroid with the charismatic yet refreshingly simple name 1992 KD. The primary objective of the event will be to provide that final 5% of the testing of AutoNav. As a bonus, now that we have already squeezed more out of this mission than was required -- or expected by many people -- we want to do still more. As fellow taxpayers, we can understand the desire to get as much out of this mission as possible. So the two science instruments that DS1 has tested will be used to gather exciting scientific data (including pictures) during the encounter with this intriguing body. But keep in mind that this is primarily an exceedingly challenging test for the small portion of AutoNav that can only be exercised by visiting a solar system target.

AutoNav continues to collect images of distant asteroids and stars to refine its estimate of where it is in the solar system using a method described in many earlier logs. But it is still too far away from 1992 KD to see that tiny asteroid, so for now it is simply using the best estimate of where the asteroid is. AutoNav will not be able to detect 1992 KD until about one day before it arrives. AutoNav has done a remarkable job calculating its position in the solar system, now routinely getting within 1000 km or under 600 miles of the position as determined by conventional radio tracking. Compared to its distance from the Sun this is impressive indeed. This accuracy is comparable to being anywhere in the continental United States and determining your position to within about 70 feet. When DS1 is traveling through most of the expansive emptiness of the solar system, this knowledge is more than adequate. But when it gets in the vicinity of 1992 KD, it needs to do even better. The principal limitation now in AutoNav's ability is the result of imperfections in the camera. Although AutoNav has sophisticated techniques to analyze the camera's pictures, it cannot fully compensate for the shortcomings of the camera. AutoNav's designers and testers are paying close attention now to see how well it can do.

The encounter with the asteroid will be relatively brief, as the spacecraft will be passing by at 15.5 kilometers/second, or nearly 35,000 miles/hour. The operations team has been developing the complex set of instructions that will govern the spacecraft, including the ones that give AutoNav the opportunity to design and execute maneuvers to correct the spacecraft's trajectory, the commands to the new technology science instruments to collect data, and directions to the attitude control system on how to turn the spacecraft at the moment of closest approach. Refining this unusually complex choreography, in which all the spacecraft systems including AutoNav need to work together, is the focus of the small operations team's work right now. A group of instructions is known as a sequence, and each day, the sequences covering the final 6 hours before the closest approach to 1992 KD are run through the Deep Space 1 test facility at JPL. This is a simulation of the spacecraft, created using some hardware similar to what is on the real spacecraft and some computer programs that emulate the behavior of other parts of the spacecraft. This allows the team to test, modify, and retest sequences, a cycle repeated now nearly every day. The test facility is certainly not identical to the spacecraft, so a successful test does not guarantee success on the spacecraft, but it does allow many of the bugs to be worked out. A rehearsal of the encounter using the actual spacecraft is planned for July 13. This will be an opportunity to compare the performance of the sequences in the test facility with the same sequences run on the spacecraft when it is not in the vicinity of 1992 KD. Following that, more tests will be run in the test facility. When DS1 takes the final test on the evening of July 28, it will be on its own. Its closest approach to the asteroid will occur at 9:47 pm PDT, and it will be several hours after that before it can begin reporting its results to Earth. Future logs will provide more details on the events to occur at encounter as well as progress in reaching the asteroid.

Deep Space 1 is still more than 23 million kilometers, or over 14 million miles, from 1992 KD. The spacecraft is now more than 15% farther away from Earth than the Sun is and over 450 times farther than the moon. At this distance of over 173 million kilometers, or almost 108 million miles, radio signals, traveling at the universal limit of the speed of light, take longer than 19 minutes to make the round trip.

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