Landsat 5 has been collecting global data sets continuously since it was launched in March 1984.
The satellite has had a series of anomalies and has lost redundancy in onboard systems, but continues to collect high-quality data.
Early Saturday, October 6, 2007, the Landsat 5 Flight Operations Team (FOT) noted that battery #2 was automatically taken off-line the previous evening. All imaging was stopped in order to conserve power. Landsat 5 has three 22-cell Nickel Cadmium batteries. During the non-sunlit part of each orbit, the batteries provide power to sustain the satellite’s electrical needs. During the day-lit period of the orbit, the solar array re-charges the batteries and meets the electrical demands of the satellite. Previously, on May 21, 2004, Landsat 5’s battery #1 was taken offline following an anomaly. With the loss of battery #2, Landsat 5’s remaining battery may have sufficient capacity to maintain the health and safety of the spacecraft and potentially continue with some level of day-lit imaging operations. Although the mission can operate with only 1 healthy battery, the potential loss of battery #2 would mean a loss in the level of redundancy.
The satellite continues to operate on battery #3, but is not collecting imagery. In this configuration, battery #3 appears to be operating normally and maintaining an adequate charge to operate the mission to required health and safety standards. Also, the FOT has uplinked a new command load that ensures health and safety of the spacecraft operating with only one battery. It is expected that the spacecraft can operate indefinitely in this configuration (barring any further complications).
Three phases to the investigation and recovery activity are underway. Each successive phase will be dependent on the outcome of the previous phase. The tentative plan includes:
Phase 1 - Maintain and ensure the continued operation of Landsat 5 utilizing only battery #3.
Phase 2 - Determine the optimum charging profile with battery #2 and battery #3 on-line. Bring battery # 2 back on-line and monitor performance. If battery #2 and battery #3 can be charged to produce sufficient power, there is a potential to operate in this configuration.
Phase 3 - Investigate bringing battery #1 back into service.
Over the last 3 weeks the FOT, with additional battery expertise from industry, has been working through these phases. The team is currently working on Phase 2 of the plan and will work with battery experts in mid-November to bring battery #2 back on-line. By the end of November, the team will have sufficient information to make a recommendation on the Landsat 5 mission concept – return to full operations or a more limited operations concept.