Fermi Observation Types

The Fermi observatory supports a variety of different types of observations. The most common mode for the spacecraft is all-sky survey, where the observatory scans across one hemisphere of the sky for one orbit, then rocks to the other hemisphere to scan for the second orbit. This mode of operations provides about 30 minutes of livetime at any point on the sky approximately every 3 hours (two orbits).

In early 2018 the Fermi spacecraft experienced an anomaly with its -Y Solar Array Drive Assembly (SADA), which left the -Y solar panel unable to rotate and necessitated the creation of a new observing strategy in order to maintain sufficient spacecraft power and thermal control. Please see Post-Anomaly Observations for more information regarding the event and Fermi's current survey observation strategy.

The observatory has three different modes of pointed observations: autonomus repoint requests (ARRs) occur in response to interesting gamma-ray bursts (not performed since the SADA anomaly in 2018), a target of opportunity (ToO) pointed observation may be requested by any member of the Fermi science community (disabled in 2018, restarted in 2025), and pre-scheduled pointed observations may be part of the normal science timeline.

In addition, the observing plan may combine several different observing modes. For example, the observatory can switch between pointing at different targets, or, more commonly, will perform a portion of sky-survey while the pointed target is occulted. The history of Fermi observations and the upcoming planned observations are available in the posted timeline. More complete descriptions of the various observing modes are available at the links below.