Fermi Gamma-ray Space Telescope

Observing Timeline

In this section you can determine where Fermi pointed in the past and is scheduled to point in the future.

Timeline Utilities

The following are utilities that provide you with these capabilities:

  • Timeline posting - through this webpage you can determine Fermi's pointing history in the past, and find future observing plans. The most accurate observing information available is used.
  • ToO status - information on accepted ToO (Target-of-Opportunity) observations is reported here. Since ToO observations are not being performed following the March 16, 2018 anomaly this information is provided for historical reference.
  • Time system conversions - different utilities and tools use different time systems (e.g., Mission Elapsed Time, calendar date, modified Julian date). Note that Fermi and Swift use the same 'Mission Elapsed Time' conventions. This is a HEASARC tool.
  • Coordinate conversions - this utility can convert between source names and coordinates for single sources and lists of sources. This is a HEASARC tool.

Overview of the Timeline Process

Following the March 16, 2018 anomaly which prevents the movement of one of Fermi's solar arrays, a weekly observing timeline is created by the FSSC to schedule sky survey observations in three modes. The observing mode used depends on the angle between the spacecraft's orbital plane and the Sun, i.e. the beta angle. This angle varies on both a yearly timescale and with an approximate period of 46 days driven by the precession of Fermi's orbit. More information about beta angle dependent observing modes and sky coverage is available here.

Assigned a Fermi mission week number (e.g. 513), the weekly observing timeline is prepared starting with an preliminary draft to facilitate mission planning about 3 weeks before implementation. One week before upload to the observatory a final timeline is generated based on the preliminary draft. An as-flown timeline records the observations as performed. The latest version of the timelines will be posted.

The following table compares the different timelines.

If an observation is on this timeline... Then...
Preliminary weekly observing timeline The observation will most likely occur when scheduled, but could be rescheduled.
Final weekly observing timeline The observation will occur when scheduled, unless disrupted.
As-flown timeline Observation occurred at the reported time

The FSSC compares the timeline as actually implemented with the planned timeline and updates the observing timeline with the results.

For the forseeable future Fermi will be operated in a beta angle dependent sky survey mode.