Flight Test Evaluation of a New GPS Attitude Determination Algorithm

A new Global Positioning System (GPS) Attitude Determination Algorithm (GADA) is proposed, featuring the capability to keep its accuracy, even when the line-of-sight angle (LOS) of a given satellite vehicle (SV) is below the GPS horizontal antenna plane (HAP). The GADA model has been developed and evaluated through simulations and flight test campaigns, which comprised static and dynamic flight profiles, to best characterize the algorithm performance. As attitude reference a complete flight tests instrumentation (FTI) system was integrated into the testbed for the flight test campaign. The attitude measurements given by GADA and REQUEST algorithms are compared with those given by FTI (i.e., reference system). The results show that GADA accuracy is significantly better than that of REQUEST, for all flight conditions.     

Optimization of transfers under constraints on the thrust direction: I

Transfers with a low thrust are considered under constraints imposed on the thrust vector direction. These constraints can be caused by peculiarities of the attitude control system and the mode of stabilization of a spacecraft, and, in the general case, they are functions of the time and state vector. The constraints specified by equalities and inequalities are investigated. It is shown that the optimal thrust is directed along the projection of the Lawden’s primer vector onto the restricting set.     

Results from the Energetic Gamma-Ray Experiment Telescope (EGRET) on the Compton Observatory

The Energetic Gamma-Ray Experiment Telescope (EGRET) on the Compton Gamma Ray Observatory covers the high energy gamma ray energy range, approximately 30 MeV to 30 GeV, with a sensitivity considerably greater than earlier high energy gamma-ray satellites. Thus far, 4 pulsars have been detected and their properties measured, including in 3 cases the energy spectrum as a function of phase. The details of the galactic plane are being mapped and a spectra of the center region has been obtained in good agreement with that expected from cosmic ray interactions. The Magellanic clouds have been examined with the Large Magellanic Cloud having been detected at a level consistent with it having a cosmic ray density compatible with quasi-stable equilibrium. Sixteen Active Galactic Nuclei (AGN's) have been seen thus far with a high degree of certainty including 12 quasars and 4 BL Lac objects, but no Seyferts. Time variation has been detected in some of these AGN's.