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Dr. Marc Rayman's Deep Space 1 Mission Log

Mission Update:

Thank you for visiting the Deep Space 1 mission status information site, occasionally spoken of and frequently thought of as the most authoritative source in the solar system for information on this technology validation mission. This message was logged in at 1:30 pm Pacific Time on Sunday, July 18.

With its mission of testing high risk, important new technologies having exceeded expectations, Deep Space 1 is now making final preparations for a very very challenging encounter with an asteroid with the simple yet somehow noble name 1992 KD. This asteroid was discovered 7 years ago by JPL astronomers Eleanor Helin and Ken Lawrence as part of an extensive and productive effort to locate and study asteroids. 1992 KD is so small that it can only barely be seen through large telescopes, so very little is known about it. It is believed to be about 1 or 2 km (perhaps a mile or so) in diameter. It apparently rotates very slowly, taking nearly 10 Earth days to complete one turn. Although DS1 was designed to test technologies, it will attempt to make scientific measurements when it flies past 1992 KD. Black and white pictures may reveal the asteroid's size and shape and show craters, hills, valleys, and other topography. Infrared measurements may help scientists determine the minerals that make up the surface. By searching for changes in the solar wind, the stream of charged particles flowing from the Sun, in the vicinity of the asteroid, it may be possible to determine if it has a magnetic field. Perhaps the solar wind or sunlight even cause surface material to be slowly eroded from the asteroid and flung into space, in which case the spacecraft may directly measure the resulting free atoms.

To get close enough to make all these measurements, AutoNav will attempt to bring DS1 closer to 1992 KD than any spacecraft has ever come to a solar system body without actually landing on it. Speeding by at 15.5 km/s, or nearly 35,000 miles/hour, the spacecraft will pass by more than 50 times faster than a commercial jet and more than twice as fast as the space shuttle. But it will come a mere 15 kilometers from the center of the asteroid, or less than 9 miles from the surface. This is a great challenge to AutoNav and to the operations team, but if it works it should be exciting indeed.

The small 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, directions to the attitude control system on how to turn the spacecraft as it nears the asteroid, and instructions on how to transfer, manipulate, and store the large volume of data to be collected. Refining this unusually complex choreography, in which all the spacecraft systems including AutoNav need to work together, is the focus of the 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 was conducted on July 13. DS1 flew by an imaginary asteroid affectionately named Spoof2. For AutoNav to find this asteroid, special computer files were sent to the spacecraft that contained the orbit of Spoof2. Whenever AutoNav took a picture for navigation information, a special computer program intercepted the picture, added Spoof2 to it, and then sent it on its way for AutoNav to analyze. Under AutoNav's guidance then, DS1 executed two course corrections with its small thrusters and did correctly fly past the elusive Spoof2. The complex test went well. After analyzing data on how the spacecraft handled the sequences, the operations team is making a number of changes, and revised sequences continue to be tested 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 approximately 9:46 pm PDT, and it will be several hours after that before it can begin reporting its results to Earth. Returning all the data will then require several days.

In the meantime, 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 900 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 shortcomings in the camera. AutoNav's designers and testers are paying close attention now to see how well it can do.

Deep Space 1 is still nearly 14 million kilometers, or over 8.6 million miles, from 1992 KD. The spacecraft is now 20% farther away from Earth than the Sun is and almost 470 times as far as the moon. At this distance of over 179 million kilometers, or more than 111 million miles, radio signals, traveling at the universal limit of the speed of light, take almost 20 minutes to make the round trip.

Thanks again for logging in!

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