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Mission Operations/Recovery Status

TERRIERS launched successfully from VAFB on May 18 05:09:47 GMT. It hit a nearly perfect orbit (550 X 530 km and an inclination of about 97.72 degrees). To see the TERRIERS position go to the position page. For a quick update on the TERRIERS status see the mission operations log below .

Mission operations for TERRIERS are taking place at Boston University's Center for Space Physics. TERRIERS operations began on 5-18-99 with the first contact of the spacecraft around 7:07 EDT. Unfortunately, after the first 3 contacts it was clear that the the spacecraft's attitude control system was not functioning properly, since the solar array was pointing away from the sun and the system was nutating. Sometime shortly thereafter the spacecraft ran out of battery power and effectively went to sleep.

That week a recovery team was formed by NASA/USRA to devise and implement a plan to wake the spacecraft and get it back to the original mission. Led by Steve Battel, the team took on several tasks in pursuing this goal:

  • Determine the cause of the ACS problem,
  • Assess the state of the system and its ability to wake up, and
  • Model the spacecraft dynamics to determine if and when the solar array will be illuminated due to natural disturbances
  • Devise and test a command load that will aide in the recovery of the satellite.

Within a week or so we had pruned our fault tree down to the lone cause of the failure: a sign flip in one of the 3 torque coil actuators. The fix for this is fairly simple given the flexibility of the flight software.

All the telemetry from the spacecraft indicates that it was working properly, except for the sign flip. Furthermore, the system should not degrade much in its current configuration, since the spacecraft is powered down and in a reasonable thermal state. The big question is whether the system can reboot itself from this state. Simulations on our engineering system were run and it appears there is a good probability the system will reboot.

Unfortunately the dynamics of the spacecraft was not easy to model, due to uncertainties in TERRIERS' inherent magnetic moment, center of pressure, and eddy current/hysteresis damping characteristics. Initially we thought that the gravity gradient torque would tie our angular momentum vector (and solar array vector) towards the orbit normal, which is always pointed away from the sun. However, data points taken by NORAD of our angular momentum direction and spin period showed that this model was not adequate. Further modeling efforts over the weeks have not been able to match the data either. However, we could see simply from the data that TERRIERS was spinning down at a linear rate and that in about 70 days (late July) from launch, its motion should become "erratic" such that the solar panel should get illuminated for periods on the order of 10 minutes.

Based on the analyses described above, we devised and tested a set of commands which will correct the sign error. We also modified and tested the TERRIERS ground station code to include a mode in which we can transmit only, so that we can upload the commands as soon as contact is established. Furthermore, we set up another ground station at Poker Flats, Alaska to increase our coverage.

Through July and August we received no "truly" positive indications that the spacecraft had booted. We had support from Poker for about 3 weeks during this time as well. Analysis assuming that we were tumbling randomly across the sky, indicated that the spacecraft would be in a power positive position above a ground station once every few days. This led us to believe that the spacecraft was either phase locked away from the sun (a small possibility given our simulations) or something else had failed.

In September, Michael Comberiate at GSFC suggested that the south pole albedo during Antarctic summer, might be enough to boot the spacecraft. The idea seemed plausible and preparations began shortly thereafter to send some equipment down to the McMurdo ground station to attempt contact in December, 1999.

The TERRIERS, south pole recovery effort took place between December 15th and December 24, 1999. This was the culmination of efforts by Michael Comberiate (GSFC), Greg Huffman (BU RF engineer), and GSFC Wallops and McMurdo personnel. It was sponsored in combination by USRA, NASA and NSF.

The team assembled and tested TERRIERS ground station specific equipment at Wallops Flight Facility in mid November. The equipment was subsequently packed up and then delivered to NASA's McMurdo Ground Station (MGS). Mike Comberiate and Greg Huffman arrived at MGS on December 15, 1999 to integrate the equipment into the GS. They were able to get the system up and running in only a few hours. Thanks to the excellent support from the McMurdo GS team, they covered nearly 60 passes over the 9 day period. Unfortunately, in all attempts to contact and receive date from the spacecraft, no sign of a downlink was detected from TERRIERS. A more detailed report ( pdf format or ps format ) of the operations was written by Greg Huffman.

From the operation, we can conclude that the spacecraft did not boot in response to the Antarctic albedo during the height of Antarctic summer. This is either because there is not enough energy coming from the surface or there is something else preventing the spacecraft from communicating. In his report, Greg presents a calculation of the albedo, which indicates that there may not have been enough reflected sunlight for the spacecraft to boot. However, there should have been enough energy for the transmitter to send a carrier signal even if the system was in a browned out state. Test data indicate that this is highly likely to happen. Because this signal was not detected, it is more likely that there is something else preventing the spacecraft from booting.

At this point, the probability of recovery has dropped significantly. Our hope was that the spacecraft was phase locked away from the sun and that the albedo would have provided the needed energy to allow us to communicate with it. Since this did not happen, we have some evidence that TERRIERS is not phase locked away from the sun as previous ACS simulations suggest. If this is the case, we can conclude that the spacecraft attitude (solar array position with respect to the sun), is not the only thing preventing it from communicating with us. Thus, there is very little hope for recovery. We will continue to automated passes from the BU ground station, but, at this point, no further actions are planned.

As of updating this page (1-24-99), we have not reestablished direct contact with the spacecraft. Below is a summary of the mission operations to date.

Mission Operations Log

Items are put in reverse chronological order for quick access to the latest information.
   Date    Time Activity Activity Details/Status
1-23-00 07:03 EST Boston Signal The GS Mac at Boston indicates another possible brief contact with the spacecraft, but no data is transferred.
1-23-00 06:17 EST Boston Signal The GS Mac at Boston indicates a possible brief contact with a fake spacecraft in an orbit 180 degrees out of phase with TERRIERS. This puts more doubt on all the other "possible brief contacts."
1-11-00 21:32 EST Boston Signal The GS Mac at Boston indicates another possible brief contact with the spacecraft, but no data is transferred.
1-9-00 21:44 EST Boston Signal The GS Mac at Boston indicates another possible brief contact with the spacecraft, but no data is transferred.
1-8-00 19:23 EST Boston Signal The GS Mac at Boston indicates a possible brief contact with a fake spacecraft in an orbit 180 degrees out of phase with TERRIERS. This puts more doubt on all the other "possible brief contacts."
12-27-99 20:17 EST Boston Signal The GS Mac at Boston indicates another possible brief contact with the spacecraft, but no data is transferred.
12-26-99 07:31 EST Boston Signal The GS Mac at Boston indicates a possible brief contact with a fake spacecraft in an orbit 180 degrees out of phase with TERRIERS. This puts more doubt on all the other "possible brief contacts."
12-24-99 12:00 EST South Pole Ops Greg Huffman leaves MGS. The operation fails to receive any indication that the spacecraft is alive. TERRIERS hopes for recovery are all but gone. Automated contacts continue at BU only.
12-22-99 20:17 EST Boston Signal The GS Mac at Boston indicates another possible brief contact with the spacecraft, but no data is transferred.
12-17-99 19:14 EST Boston Signal The GS Mac at Boston indicates another possible brief contact with the spacecraft, but no data is transferred.
12-15-99 08:00 EST South Pole Ops Michael Comberiate (GSFC) and Greg Huffman arrive at McMurdo Station in Antartica to attempt to contact TERRIERS from the NASA facility (MGS) there. They set up things in a couple of hours and make their first attempt later in the day.
12-16-99 21:48 EST Boston Signal The GS Mac at Boston indicates a possible brief contact with a fake spacecraft in an orbit 180 degrees out of phase with TERRIERS. This puts more doubt on all the other "possible brief contacts."
12-14-99 21:05 EST Boston Signal The GS Mac at Boston indicates another possible brief contact with the spacecraft, but no data is transferred.
12-13-99 08:52 EST Boston Signal The GS Mac at Boston indicates a possible brief contact with a fake spacecraft in an orbit 180 degrees out of phase with TERRIERS. This puts doubt on all the other "possible brief contacts."
12-1-99 20:55 EST Boston Signal The GS Mac at Boston indicates another possible brief contact with the spacecraft, but no data is transferred.
12-1-99 07:42 EST Boston Signal The GS Mac at Boston indicates another possible brief contact with the spacecraft, but no data is transferred.
11-29-99 07:51 EST Boston Signal The GS Mac at Boston indicates another possible brief contact with the spacecraft, but no data is transferred.
11-26-99 17:51 EST Boston Signal The GS Mac at Boston indicates another possible brief contact with the spacecraft, but no data is transferred.
11-23-99 21:50 EST Boston Signal The GS Mac at Boston indicates another possible brief contact with the spacecraft, but no data is transferred.
11-17-99 19:06 EST Boston Signal The GS Mac at Boston indicates another possible brief contact with the spacecraft, but no data is transferred.
11-17-99 08:59 EST Boston Signal The GS Mac at Boston indicates another possible brief contact with the spacecraft, but no data is transferred.
11-11-99 21:10 EST Boston Signal The GS Mac at Boston indicates another possible brief contact with the spacecraft, but no data is transferred.
11-6-99 20:11 EST Boston Signal The GS Mac at Boston indicates another possible brief contact with the spacecraft, but no data is transferred.
10-29-99 07:09 EDT Boston Signal The GS Mac at Boston indicates another possible brief contact with the spacecraft, but no data is transferred.
10-23-99 22:25 EDT Boston Signal The GS Mac at Boston indicates another possible brief contact with the spacecraft, but no data is transferred.
10-6-99 09:36 EDT GS Jammed It's discovered that The GS receiver is jammed by an unknown signal all day. It appears to be internal to the system, but disappears the next day.
9-30-99 22:56 EDT Boston Signal The GS Mac at Boston indicates another possible brief contact with the spacecraft, but no data is transferred.
9-28-99 09:52 EDT Boston Signal The GS Mac at Boston indicates another possible brief contact with the spacecraft, but no data is transferred.
9-17-99 10:00 EDT Recovery Meeting The latest data point - taken on 9-14 - shows that the spacecraft has spun down to a very slow rate and it is estimated to be about 1 revolution per orbit. This is consistent with a gravity gradient lock or previous simulations showing "erratic" behavior. It is decided during the meeting we need one more data point and a few other simulations to determine this. In any case, it is a clear that the spacecraft has not come up for any length of time in the last 4-6 weeks, our expected window of opportunity. Automatic contacts will continue at BU, but no further efforts will be employed at this time unless something turns up.
9-7-99 13:15 EDT Boston GS We switched to the transmit only ground station code and a command load which minimizes power on the spacecraft. The hope is that by shutting down many of the systems aboard the spacecraft, we will increase our probablility of making contact.
8-29-99 22:36 EDT Boston Signal We get a lot of activity on the receiver and bit synch for a couple minutes, but no link is established.
8-17-99 10:35 EDT Boston Signal The GS Mac at Boston indicates another possible brief contact with the spacecraft, but no data is transferred.
8-16-99 10:39 EDT Boston Signal The GS Mac at Boston indicates another possible brief contact with the spacecraft, but no data is transferred.
8-10-99 01:53 EDT Poker Signal The GS Mac at Poker indicates another possible brief contact with the spacecraft, but no data is transferred.
8-6-99 09:30 EDT Boston Signal The Bit Synch at the Boston site glitched with the receiver power for less than a second, but no link was established.
8-5-99 11:42 EDT Poker Signal The GS Mac at Poker indicates another possible brief contact with the spacecraft, but no data is transferred.
8-2-99 10:30 EDT Poker Signal Poker reports a 2dB signal above the noise for one minute at the appropriate frequency on the last pass. No data was collected by the ground station computer however.
8-1-99 07:22 EDT Poker Signal The GS Mac at Poker indicates another possible brief contact with the spacecraft, but no data is transferred.
7-29-99 04:30 EDT Poker Signal The GS Mac at Poker indicates another possible brief contact with the spacecraft, but no data was passed.
7-26-99 08:00 EDT Poker Support To support the latest opportunity, Poker schedules about 6 contacts a day. We now have about 60-70% of the passes for the next few weeks.
7-25-99 09:24 EDT Boston Signal The GS Mac at Boston indicates another possible brief contact with the spacecraft, but nothing was detected by the operators at the ground station, and no data was passed.
7-14-99 20:15 EDT Boston Signal The GS Mac at Boston indicates a possible brief contact with the spacecraft, but nothing was detected by the operators at the ground station, and no data was passed.
7-14-99 08:00 EDT 3rd Recovery Meeting The latest data from NORAD shows that we are spinning down at a rate such that in a week or two we will be slow enough such that the gyro inertia will not control the system. This means that TERRIERS will get spotty illumination of the solar array after this time for several weeks and perhaps longer. Simulations of the expected start up sequence performed by Aeroastro are analyzed and a new upload scheme is devised based on these analyses.
6-23-99 10:00 EDT QuikScat Launches Poker supports the Quikscat launch and initial maneuvers so we lose the Poker support for the time being.
6-17-99 10:00 EDT SC Status An analysis is performed to determine any long term negative effects that may occur from the spacecraft in its current unpowered and backwards position. The conclusion is that the system can survive time scales on the order of 6-12 months in its current situation.
6-9-99 03:00 EDT Poker installation Passes are now automated in terms of the TERRIERS equipment. The installation team flys home. The NORAD data shows large inconsistencies with our model. We are also spinning down quite rapidly and expect to go into an erratic type motion in a couple months, illuminating the solar array for short periods of time.
6-4-99 03:00 EDT Poker installation First passes are run at Poker about 3 hours after team arrives and sets up the equipment. All the bugs get worked out over the next couple of days and by the end of 5 days we have a fully operational system.
6-4-99 15:00 EDT Poker installation First passes are run at Poker about 3 hours after team arrives and sets up the equipment. All the bugs get worked out over the next couple of days and by the end of 5 days we have a fully operational system.
6-2-99 08:00 EDT 2nd Recovery Meeting Failure analysis is closed and we develop plan to install hardware up at NASA's Poker flat facility to increase our coverage. A new upload load is devised to take advantage of a possible opportunity now predicted by the GSFC models and NORAD data in the next few days. Furthermore, data comes in today that indicates the spacecraft may have spun up somewhat. This later turns out to be noise in the data, but it accelerates our work to get the Poker site up and working.
5-28-99 10:00 EDT Failure Analysis Simulations and test data all point towards a sign flip in the Y (spin axis) torque coil actuator as the cause of the ACS failure.
5-24-99 08:00 EDT 1st Recover Meeting First recovery team meeting. The data is analyzed and all systems appear to check out. Initial dynamic model results show that the spacecraft is phase locked with the orbit and that it might never see the sun. The failure analysis branches to 12 possible faults. We start, investigating possible locations for other ground stations, analysis on restart scenarios, and continue to attempt contacting the spacecraft from the Boston GS.
5-18-99 20:14 EDT 4th Pass No contact with the spacecraft. The spacecraft has most likely run out of power.
5-18-99 10:14 EDT 3rd Pass Uplink commands to try to force the spacecraft into sun pointing mode and switch to the backup magnetometer. The data for the last 1.5 hours shows no improvement on our power and pointing status.
5-18-99 08:38 EDT 2nd Pass Second contact is picture perfect until the data reveals that the batteries are draining and we are not sun pointed.
5-18-99 07:09 EDT 1st Pass First contact with the spacecraft. No data is passed, but the link indicates that the spacecraft is alive and most likely spinning correctly.
 
 
24 January 2000
Prepared by Dan Cotton
Center for Space Physics
Boston University