December 18, 2001

Mission Update:

Thank you for visiting the Deep Space 1 mission status information site, for 1151 days the most popular site anywhere in the 4 dimensional space-time continuum for information on this historic mission. This message was logged at 2:45 pm Pacific Time on Tuesday, December 18, 2001.

With highly successful primary, extended, and hyperextended missions behind it, the Deep Space 1 mission is over. The spacecraft continues to function, but engineers held a bittersweet retirement party for the veteran explorer today. The guest of honor was, of course, unable to attend because of travel commitments.

The hyperextended mission was completed last week, meeting all of its objectives. During this intensive period following the return of data from the comet encounter (the end of the extended mission), all 9 hardware technologies that were tested during the primary mission, which concluded successfully in September 1999, were exercised again.

The hyperextended mission has been as intensive as any part of the mission for the shrinking team. We have focused on ion propulsion system tests, repeating some from 1998 and 1999 to measure the aging of the thruster, and undertaking others to explore different operating regimes of the system. By the time the spacecraft retired, the ion propulsion system had accumulated 677 days of operation and expended 90% of the xenon it carried at launch.

Probably just to keep us from taking it for granted, on December 2 the probe lost lock on its reference star. We considered not struggling to return it to normal operations as we did in the 4 times that this occurred during the extended mission. The spacecraft was stable but in the wrong orientation; had we left it, the final ion engine and solar array tests would not have been possible. In addition, this close to the end, it would have been a shame to give up: we wanted to let the spacecraft retire with dignity and honor. The crack operations team was successful in restoring the spacecraft to its normal operational configuration.

Now with no further technology objectives and no further science objectives, there is not sufficient justification for keeping the spacecraft operating. We squeezed far far more out of Deep Space 1 than we expected, and now the most responsible way to use NASA's precious resources is to turn our attention to other missions. And this way we have the joy of saying goodbye to Deep Space 1 on our terms, at a time of our choosing, when we are ready.

Before the decision to end the mission was made, we did consider other options. We had what I liked to call an ultraextended mission, which would have targeted an encounter in August 2002 with an asteroid tantalizingly named 1999 KK1. We had some clever ideas that would have given the aged spacecraft a chance of reaching this tiny asteroid and returning some data. But as intriguing as that might have been, it would not have been an efficient use of your tax dollars or mine. The mission would have been very risky for a variety of reasons (some different from the comet encounter), and the reward would not have been great enough. Some pictures of a little asteroid, while perhaps fun and interesting, just could not be justified given the many exciting and important missions NASA has on its manifest.

During the past week, the reconfiguration of the spacecraft for its retirement was begun. We conducted final read-outs of some of the files and other data on board, we stored certain parameters to ensure that if the computer reboots it will come back up in the state we want, and we performed other preparations to allow DS1 to operate indefinitely without hearing from or reporting to Earth (or anywhere else for that matter). In addition, some members of the team gathered for a parting shot, spelling out DS1 for a spacecraft's eye view.

Protective software always operates on board, ready to take action if it detects a problem. For many problems, one part of its response is to turn the power for many systems off and then on again. This was modified so that it would never turn the transmitter on again. The Deep Space Network had requested that we do this to guarantee that the weak signal from the distant craft could not interfere with any of the DSN's exquisitely sensitive communications with other interplanetary probes.

One of the many possible problems the spacecraft is always alert for is that it has been too long since it heard from Earth. It keeps track of what we call the command loss timer as a measure of how long it has been since it has communicated with controllers. If the time is too long, the craft has many steps it goes through in case, for example, it is pointed in a direction that makes contact impossible, or there is a problem with an antenna, the radio receiver, or other systems that might have prevented communication. Normally we reset the timer to about 2 weeks, but now it is set for more than 50 years.

On December 18, many of the people who worked on this project before and after launch gathered in mission control to wish DS1 well. Before the final transmission, the 9905th sent to the spacecraft during its journey, your on-the-scene correspondent took one final poll of all subsystems and systems (which in this case really meant everyone who was jammed into the room), and then gave the wistful final "go to radiate Sierra Quebec 8 7 9 X-ray 0 1." This command triggered a set of instructions that were stored on board last week. One by one, they prevented the accumulation of various kinds of data that, without the opportunity to be transmitted to Earth, might cause data overflow problems some time in the future. The last instruction (FP_RUN_STBSSA) told it to turn off nonessential subsystems, stop using its main antenna and switch to one of its 3 auxiliary antennas (that can work even when it is not pointed directly to Earth), and perform other reconfigurations. Although the receiver was kept on, the transmitter was turned off.

While the radio signal carrying the last command was racing to the spacecraft and then while it was executing those instructions, team members gathered to share in remembrances of their experiences working on this terrific project. We reminisced over Middle Eastern comestibles, with enough goodies to satisfy all carnivores, herbivores, omnivores, and kabobivores on the team. (The lunch also provided a nice opportunity to wish everyone on the team happy holidays, including a very Borrelly Christmas!) Then we returned to mission control to watch the displays revealing the strength of the radio signal received by the Deep Space Network. Right on schedule, at 1:00:09 pm PST, the line traced on the graph dropped, and the normally calming and gentle green display changed, unemotionally indicating "Carrier Loop Mode: Out of Lock" in what looked to me to be a harsh shade of red. Radio signals, traveling at the universal limit of the speed of light, will no longer make the round trip.

What fate awaits our distant friend? It will remain in orbit about the Sun, as surely as a planet, asteroid, or comet. Should someone wish to contact it, it will be waiting patiently, constantly listening for the gentle whisper of a radio signal that contains a message from the planet it left behind years ago. In all likelihood, it will never hear from its family again. (If this were a movie instead of reality, we would learn later that a comet was on a collision course with Earth, and only DS1 was in position to intervene in time to save us. Then the team would be reassembled to reactivate the craft.)

Long before the command loss timer expires, the final puffs of rocket propellant used to hold the spacecraft stable in the frictionless zero gravity of space will be exhausted. Conserving this hydrazine to give DS1 a chance at the bold encounter with comet Borrelly was one of the myriad enormous challenges of the past few years. But the hard work paid off, and some hydrazine remains, perhaps enough for 3 to 12 months of operation. When the last of the hydrazine is gone, the spacecraft will no longer be able to point its solar arrays at the Sun, and it will have to rely on its battery. But the energy stored in the battery will only power the probe for about 3 hours. During that time, it will struggle to conserve power and to point the arrays at the Sun, but its efforts will prove futile.

DS1 will become an inert piece of cosmic flotsam. But perhaps it will be something more than that, as it will remain a monument to humanity's most noble spirit of adventure, sense of wonder, desire to explore, and tenacious creativity.

Well before launch, I decided to make DS1 something of a time capsule. The New Millennium Program, of which Deep Space 1 was the first mission, had formed a partnership with the Boys' & Girls' Clubs of America. One of the activities we conducted with them in 1997 was called Picture Yourself in the New Millennium. We provided the clubs with some educational materials that included some information on what humankind had accomplished in the preceding millennium and encouraged the youngsters to think about what life might be like in the new millennium. They were invited to write or draw their views of the future (see them at The Space Place website), and over 800 of these are on a CD-ROM that is on the spacecraft. Perhaps, many decades from now, one of these youngsters will be involved in the retrieval of that CD. Also included are some personal thoughts and hopes of some of the people who worked on the mission.

The wealth of science and engineering data returned by this mission will be analyzed and used for years to come. The testing of high risk, advanced technologies means that many important future missions that otherwise would have been unaffordable or even impossible now are within our grasp. And as all macroscopic readers know, the rich scientific harvest from comet Borrelly is providing scientists fascinating new insights into these important members of the solar system family. From a high-tech testbed to a bold cometary explorer (and recovering from a crippling and potentially fatal injury in between), DS1 has been lucky enough to have a tremendously varied space adventure, with bonuses on top of bonuses. And now with its place in history secure, it continues to travel, silent and alone in the cold emptiness of space.

Should we be sad that the Deep Space 1 mission has concluded? Perhaps. But rather than be sad it has ended, I am happy that it accomplished so much. I think the orbiting relic will serve as a celestial testimony to NASA at its best -- bold, exciting, resourceful, and productive! And for a lifelong space buff, working on this mission has been nothing short of a dream-come-true.

On an even more personal note, this is my final mission log (unless we have to reactivate DS1 to save Earth). With its tiny budget, DS1 had no funds for what NASA calls outreach -- communicating with the public. But I felt that the Deep Space 1 mission was a true human adventure, and what's the point in conducting such an adventure without sharing it with other humans (my apologies to our many nonhuman readers)? Still, the logs always were written in what otherwise would have been my spare time, and each one was composed in a hurry. I am very disappointed that with Deep Space 1 keeping me so busy, I never was able to devote as much time to any of these (including this one) as I would have liked. Nevertheless, I did enjoy writing them and thus spending time with loyal readers throughout the cosmos, and I hope all of you felt a part of the greater Deep Space 1 team.

Thanks again for visiting!