On Tuesday, February 7, Landsat 7's Flight Operations Team fired the spacecraft's 1-pound thrusters for about 13 minutes. After a pause of about 7.5 hours, the thrusters fired a second time for about 13 minutes.This was the last such maneuver for Landsat 7 and the beginning of the end for the satellite, which has provided images of the earth's changing resources for more than 17 years.
The two burns exhausted the satellite's fuel for any more burns with the exception of the final burns to deorbit the satellite. The maneuver to reposition Landsat 7 for its 20th and final time executed exactly as intended.
The thruster burns were part of a necessary routine to ensure that the satellite always crosses the equator at 10 a.m. plus-or-minus 15 minutes local time as it orbits from the North Pole to the South Pole. Scientists want the sun's angle on the landscape they're studying to be the same image to image, month to month, year to year. So it's important that Landsat 7 crosses a given point on the globe at roughly the same time each time.
This maneuver, called an inclination maneuver, pushes the satellite toward its outermost boundary of 10:15 local time. The spacecraft will hit a peak of 10:14:55 on or about August 11, 2017, before it begins to drift back reaching its 9:45 threshold by early 2020.
If Landsat 7 is still healthy, its science mission will continue until it reaches 9:15 in mid-2021. The goal is to overlap Landsat 7 science operations with the Landsat 9 launch -- planned for late 2020 -- to continue the record of 8-day repeat coverage of the earth for science. Pushing the threshold to 9:15 gives Landsat 9 until the middle of 2021 to launch. Beyond that, the spacecraft's science data will no longer be valid and its science mission will likely end.
Landsat 7 will likely move to a lower altitude one to two months before Landsat 9 launches to allow Landsat 9 to take Landsat 7's orbital place at 438 miles above Earth. At that lower altitude, Landsat 7 will not provide science data, and Landsat 8 will likely be the sole provider of Landsat science data while Landsat 9 progresses through its on-orbit test and checkout.