On 18 December 2009, Landsat-5 experienced an anomaly with its image data transmitter. Thanks to the assiduous work of United States Geological Survey (USGS) personnel, Landsat-5 resumed transmissions on 7 January 2010 with a test downlink to Sioux Falls, USA. Geoscience Australia successfully received a test downlink on 8 January 2010.
The failure was in the travelling wave tube amplifier (TWTA). The failed unit was the redundant TWTA, which has been in service since 1987. On a number of occasions in the past several years the redundant TWTA tripped a protection circuit. With a great deal of skill and ingenuity, and using additional mission telemetry data received through Geoscience Australia's facility at Alice Springs, USGS personnel modified the operational protocols to successfully extend the life of the redundant TWTA by several years. The application of these techniques has enabled recovery of the primary TWTA.
While the initial test downlinks cannot be processed, test downlinks received from 11 January should be able to be processed on receipt of an updated calibration parameter file, which is expected in late January. We anticipate that Landsat-5 will return to normal operations shortly.
The continued operation of this mission is a remarkable achievement. It has provided the world with high-quality imagery for 26 years despite an initial design life of three years. While we hope for operations to continue until the launch of the Landsat Data Continuity Mission (LDCM) in December 2012, the reported characteristics of the primary TWTA lead us to believe that continued operations may not occur. Landsat-7, however, continues to provide extremely stable, very well calibrated image data. Apart from the scan-line corrector failure, Landsat-7 is in extremely good condition and is expected to continue to supply data until after the launch of LDCM, which will provide an on-orbit cross calibration validation with LDCM.
As part of Geoscience Australia's contingency plan for Landsat-5 failure, we are receiving as much data from the Indian Resourcesat-1 (IRS-P6) as possible. Unfortunately, because of duty cycle limitations, IRS-P6 is not able to provide reliable coverage and we now envisage Landsat-7 will be the primary fall-back should Landsat-5 fail. During the remainder of 2009-10 we also will examine the cost, availability and quality of data from the DMCii constellation.