Landsat Missions

Landsat Satellite Maneuvers

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In order to maintain a consistent equatorial crossing time, the Landsat spacecrafts must occasionally undergo maneuvers using the satellite's propulsion subsystem to fire thrusters and bring about a change in the orbital elements. There are three types of maneuvers that each Landsat satellite makes:

  • Inclination Adjustment Maneuver (IAM): An IAM is commonly referred to as a Delta-Inclination (Delta-I) maneuver. The maneuver is performed in the cross-track direction (i.e. perpindicular to the direction the spacecraft is moving.) An IAM changes the angle of the equatorial plane to the orbital plane. This type of maneuver is performed periodically (nominally once per year) to maintain the mission's Mean Local Time (MLT). Landsat has a requirement for a MLT equatorial crossing of 10:00 AM +/- 15 minutes.
  • Drag Make-Up (DMU) Maneuver: This type of maneuver may also be referred to as a Delta-Velocity (Delta-V) maneuver (or an orbit altitude adjustment maneuver). It is used to raise (or lower) the orbit's semi-major axis. A DMU is a specific type of Delta-V (positive) which increases the orbital velocity thus increasing the orbital altitude and is used to counteract the effects of atmospheric drag on the spacecraft and maintain orbit circulation as well as maintain the strict constraints on the projected spacecraft ground track. (A negative "DMU" is a retrograde maneuver to lower the altitude. However, Landsat 8 has not performed one of these operationally.)
  • Risk Mitigation Maneuver (RMM): This type of maneuver is also a Delta-V maneuver to change the orbit altitude. An RMM is executed to avoid orbital debris and may be either a velocity increase (prograde maneuver - semi-major axis increase) or a velocity decrease (retrograde maneuver - semi-major axis decrease). An RMM is only performed if the flight operations team determines the Probability of Collision (Pc) meets certain thresholds as determined by complex conjunction assessments.

 

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Landsat represents the world's longest continuously acquired collection of space-based moderate-resolution land remote sensing data. Four decades of imagery provides a unique resource for those who work in agriculture, geology, forestry, regional planning, education, mapping, and global change research. Landsat images are also invaluable for emergency response and disaster relief.

 

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The Landsat Update is an informal communication tool, prepared periodically and distributed electronically to USGS Landsat partners, to provide information about Landsat activities and related topics of interest.

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