Terra Mission Status Update

Status Update Archive

June 15 - 21, 2007

Terra spacecraft and instrument subsystems are in nominal operations.

Terra spacecraft Ultra Stable Oscillator clock error jumped from -23 to -50 microseconds offset on May 31st, 2007 due to unknown cause and is still under investigation. Subsequently a ground commanded update to the clock control offset circuitry was planned and executed. This a routine process performed at least a dozen times a year. In this case extra analysis and deliberation were required due to new trend slope following the unexplained jumo. Several excel spreadsheets are utilized to log the previous commanded values and calculate the next values. It now appears that a formula error had been introduced into the spreadsheet during a previous session which yielded an incorrect value. The value was uploaded and subsequent monitoring showed unexpected clock performance. Investigation quickly located the error, a new correct value was calculated and uploaded. The spreadsheet structure has been now modified to correct a weakness in human factors logical flow. An additional improvement is being considered to lock down previous rows and cells.

The Terra ASTER SWIR Cryocooler completed a fourth week back at the 6mm compressor stroke length. The detector temperature continues to rise at the typical slope. Using this drift rate, the detector temp max will reach 83K on 6/26/07 and the detector temp average will reach 83K on 7/5/07 at which point the first science impact begins on bright scenes. An array of amplifier gain/offset adjustments are being considered for use in the coming 6 months. The Japanese instrument team is assessing the cost and schedule to modify existing algorithms to adjust for the degradation and eventual loss of the SWIR band.

The Terra predicted seven day orbital path is routinely screened by the Air Force for potential conjunctions with space debris based on their catalog and its updates. The findings are then reprocessed and analyzed by ESMO engineers to assess the probability of collision. The predictions have a fair amount of inaccuracy at the minus 7 day prediction limit, this improves both with time and with multiple screenings from multiple sites. Terra routinely conducts orbit maintenance to compensate for atmospheric drag. Terra has the option to conduct a small drag make up maneuver ahead of schedule if analysis shows a high probability of collision if Terra remains on its present path. The entire conjunction assessment and collision avoidance process is a new and maturing.