A Graceful Retirement for Envisat after 10 Years Watching over Our Planet

Following the unexpected loss of contact with Envisat on 08 April 2012 the European Space Agency (ESA) has spent the last month trying to re-establish communication. They have now declared the end of the mission that has been informing our understanding of the planet for a decade.

There were no signs of degradation before the loss of contact. This is despite having doubled it's planned life span, celebrating its 10th anniversary in orbit on 01 March 2012. A team of engineers has spent the last month attempting to regain control of Envisat, investigating possible reasons for the problem. Despite continuous commands sent from a widespread network of ground stations, there has been no reaction yet from the satellite.

The team has been collecting other information to help understand the satellite's condition. These include images from ground radar and the French Pleiades satellite which operated a remarkable feat of agility, turning to capture images of Envisat within 100km of it. With this information, the team has gradually elaborated possible failure scenarios. One is the loss of the power regulator, blocking telemetry and telecommands.

Another scenario is a short circuit, triggering a 'safe mode' - a special mode ensuring Envisat's survival. A second anomaly may have occurred during the transition to safe mode, leaving the satellite in an intermediate and unknown condition.

Although chances of recovering Envisat are extremely low, the investigation team will continue attempts to re-establish contact while considering failure scenarios for the next two months.

Envisat was a huge achievement in science as well as engineering. With ten sophisticated sensors Envisat is the largest Earth observation satellite ever built. Envisat has observed and monitored Earth's land, atmosphere, oceans and ice caps during its ten-year lifetime, delivering over a thousand terabytes of data. An estimated 2500 scientific publications so far have been based on the data produced by Envisat furthering our knowledge of the planet.

The outstanding performance of Envisat over the last decade led many to believe that it would be active for years to come, at least until the launch of the follow-on Sentinel missions. The technique of interferometry used in Envisat was developed based on the radar instruments which first became available from the European Remote Sensing missions, ERS-1 and -2. The data produced by the three missions has provided 20 years of continuous data. This archived data continue to prove useful for scientists and for disaster relief efforts.

Source: UK Space Agency