Fermi GLAST

The Fermi GLAST was launched on June 11, 2008. The NMDB provided prelaunch analysis and on-orbit support during the Launch & Early Orbit (L&EO) phase of the mission. The Flight Dynamics Facility (FDF) provided orbit determination and Space Network (SN) acquisition data support for the first week of the mission. All Flight Dynamics operations were transitioned to the MOC on June 18.

Fermi GLAST flies a redundant pair of Motorola Viceroy GPS receivers that provide the spacecraft with time, position, and velocity. Prior to Viceroy initialization and verification, FDF provided orbit determination solutions to the Mission Operations Center (MOC) based on Differenced One-Way Doppler (DOWD) tracking data acquired from the SN. The GLAST Omni antenna uses Left Hand Circular Polarization (LHCP) and Spread Spectrum, thus we were able to take advantage of using the TDRS Multiple Access Return (MAR) link for DOWD. The DOWD orbit solutions were accurate to better than 20 meters.

The NMDB provided technical support to the Flight Operations Team (FOT) by tuning the Kalman filter and smoother in Orbit Determination Tool Kit (ODTK), a COTS product provided by Analytical Graphics Incorporated (AGI). The Viceroy receiver specifications indicate that the point solutions are accurate to 30 m (1 Sigma) and 20 cm/s (1 Sigma). By processing the Viceroy telemetry in ODTK, the smoother provided accuracies to 1.67 m (1 Sigma) and 0.17 cm/s (1 Sigma). Filter-smoothing the Viceroy data in the MOC was critical to allow the FOT to perform accurate 42-day predictions for mission planning.