interleave-55day: Pointing/Attitude/Livetime History

The pointing/attitude/livetime history (FT2) file was generated using orbit 17. The orbit is circular with 565 km altitude and 25.4 deg inclination, and the precession period is somewhat less than 55 days.

The attitude profile of this simulation was designed to represent a reasonable scenario for observations in the last few weeks in LEO and the first few weeks of normal ops. (See Launch and Early Ops Planning.)This includes an extensive period of pointed observations in a two-target mode, several weeks of survey mode observations and a set of 5 hour single target observations (providing an opportunity to study limb following mode).

We decided to perform some autonomous repoints (ARR). These were 5-hour pointed observations at a GRB location following detection by the GBM. The criterion used to trigger ARRs was to require that a well-detected, GBM-detected GRB happen within the LAT FoV (although, in reality, we will repoint to some outside the FoV too). So, by definition, the GRB was already in the LAT FoV at the time of the burst, and the purpose of the pointed observation is to enable more sensitive high energy afterglow searches.

The first two weeks of the simulation are in pointed mode. The LAT alternates between the Vela region (265.00 -44.00) and the PSR 1706-44 region (120.8 -45.0), moving from one target to the other when the Earth's limb reaches 30 deg from Vela (rising or setting). This means that for some parts of the orbit we perform a short earth avoidance maneuver during the PSR 1706 pointing, while waiting for Vela to move away from the Earth. The remainder of the simulation is survey mode (35 deg rocking angle) interrupted with a few ARRs (as described above).

An animation of switching between 2 targets for that pointing history is posted on the Looking at pointing histories page in Confluence under "Pointing with 2 targets".

Also See

• orbit and attitude profiles

• orbit 17 details