May 20, 2000

Mission Update:


Thank you for visiting the Deep Space 1 mission status information site, now recognized as the most popular and the most authoritative site among a clear majority of spiral galaxies for information on this bold mission of exploration. This message was logged in at 8:30 pm Pacific Time on Saturday, May 20. This log is an edited transcript of a telephone recording. If you would like to access the same information from any place with a telephone, please call 1-800-391-6654 and select option 3.

Deep Space 1 is about to undergo a significant refurbishment while over twice as far from Earth as the Sun. Faithful readers know that the little craft has been traveling through space without the benefit of one of its primary sensors. The star tracker, so memorably named in honor of its function of tracking stars, stopped working in November, but the operations team devised remarkable new ways of controlling the craft, described in song and story as well as recent mission logs. And now the team is going to attempt to upgrade Deep Space 1 so that it can do even more -- and do it with much less direct supervision from far-away Earth.

This is NASA at its best. In its triumphant and exciting primary mission, which concluded in September, Deep Space 1 met or exceeded all of its "mission success criteria." But JPL and NASA decided to squeeze as much out of the mission as possible, so DS1 was allowed to continue operating. Later, when its star tracker stopped, by all rights the mission should have been over. All spacecraft (all machines, for that matter) reach the end of their operating lives sooner or later, usually triggered by some critical component failing. With an enviable record of accomplishments behind it, DS1 could have been retired to rest on its many laurels. But engineers saw a hope for rejuvenating the distant craft to allow it to continue its solar system journey. By redesigning it with new computer programs, the team has developed a method to have the camera replace the star tracker.

There are many differences between the star tracker and the camera. Among them is the amount of sky they view, an important difference which you terrestrial readers may be able to visualize. The camera sees an area only a bit larger than the full moon as viewed from Earth, but the star tracker covered well over 100 times as much area. Both can see stars fainter than the unaided human eye can detect, but the next time you enjoy the beautiful sights of your nighttime sky, imagine being able to search for stars in a patch of sky only as large as the moon instead of one comparable in size to the bowl of the Big Dipper. The star tracker told the spacecraft computer its orientation in space, based on the patterns of stars it saw, and it did so 4 times every second. The camera, on the other hand, simply produces a computer file containing a picture, and it takes more than 20 seconds to transfer one picture to the computer. Then the picture has to be analyzed. (There has not been time to design a brand new system to extract the needed information from the picture, but there is no need to -- that will be taken care of through the expertise of the on-board navigation system that performed so brilliantly during the primary mission.) Engineers have invented new techniques for flying the spacecraft to account for these and other differences.

This is an extremely difficult task, with an enormous number of complex and important engineering problems to solve, but the opportunity to bring technical knowledge from a variety of disciplines, creativity, and teamwork to this challenge is one of the great rewards of such work. The Deep Space 1 team chose to aim for the ambitious goal of completing the job in time to resume thrusting with the advanced ion propulsion system in July to propel the craft to an encounter with Comet Borrelly in September 2001. This has made the schedule extremely tight and the chances for success less certain. If the team had taken about two months longer to complete the task, we could be much more confident the new software would be up to the job, but then the opportunity to travel to the comet would be lost. So setting its sights high, the team is taking its best shot at the biggest prize. If it works, the resurrected probe will have a second chance for carrying humankind to a new destination in the solar system. And even if it does not work, the new methods developed along the way stand as more impressive accomplishments in the mission of Deep Space 1.

To try to be ready for ion powered flight again in July, the team will begin radioing the new software to Deep Space 1 on May 30, a complex process in itself that will span about 8 days. It would be essentially impossible to transmit all this software to the spacecraft without the innovative technique the operations team devised for helping Deep Space 1 point its main antenna at Earth without the use of the star tracker. To begin running the software, the spacecraft's main computer, which is responsible for keeping the craft healthy and running smoothly, needs to be rebooted. After the software is on board, controllers will command the spacecraft through carefully designed steps to prepare it for that event, and then send the final command to reboot. It will take DS1 a few minutes to begin operating again, and then when it resumes transmitting signals to Earth, watchful controllers at JPL will be ready to verify that the new software is working correctly. Over a period of two days, DS1's engineers will reactivate systems turned off during the reboot.

Then the next challenge begins. The new features of the software will be tested to determine whether the spacecraft can indeed hold a fixed orientation by itself, turn reliably from one direction to another, and provide a stable platform for using the ion propulsion system, all by using pictures of a star with its camera instead of signals from its star tracker. This log will be updated once the testing is underway.

Deep Space 1 is now nearly twice as far from Earth as the Sun is and over 760 times as far as the moon. At this distance of almost 292 million kilometers, or over 181 million miles, radio signals, traveling at the universal limit of the speed of light, take about 32 and a half minutes to make the round trip.

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