PDS_VERSION_ID = PDS3 RECORD_TYPE = FIXED_LENGTH RECORD_BYTES = 80 OBJECT = TEXT PUBLICATION_DATE = 2000-05-29 NOTE = "Description of MGS spacecraft antennas, software, and kernels needed to reconstruct their positions and orientations. Formatted with up to 78 constant width characters per line." END_OBJECT = TEXT END This document describes the high- and low-gain antennas on the Mars Global Surveyor (MGS) spacecraft (s/c), how their locations and pointing can be described, and the software and kernel files produced by the Navigation and Ancillary Information Facility (NAIF) at JPL that allow users to reconstruct these quantities. Most of the material which follows has been adapted (copied) from documentation provided by Boris Semenov JPL/NAIF. ============================================================================== MGS Antenna Descriptions ============================================================================== The MGS spacecraft was equipped with one high-gain antenna (HGA) and four low-gain antennas (LGA), two for transmit and two for receive. The HGA was mounted on a boom attached by a hinge to the +X side of the AFT deck of the spacecraft propulsion module. The HGA boresight direction was fixed and co-aligned with the spacecraft +X axis when the antenna was in the stowed configuration (during Cruise and Orbit Insertion phases of the mission, and during the first month of the Mapping phase). After the HGA was deployed for Mapping operations, it was pointed by rotation of the azimuth and elevation gimbals. Both transmitting LGA's were mounted on the TWA Enclosure Box which was itself mounted on the HGA reflector. One of the transmit LGA's (LGT1) was co-aligned with the HGA boresight (nominally in the +X direction while the antenna was stowed), while the other's (LGT2) boresight was oriented approximately 160 degrees away from this axis (near the -X axis while the HGA was stowed). The two receive LGAs were mounted on the -X panel of the equipment module (LGR2) and the +X side of the propulsion module (LGR1). ============================================================================== MGS HGA Boom/Gimbal Diagram ============================================================================== The diagram below illustrates relative locations of the HGA hinge, gimbal, and boresight frame centers (frames will be discussed more extensively below). The antenna is shown as if it were fully extended along the s/c +X axis in the s/c XY plane; dimensions are given in inches (1 inch = 2.54 cm): Top view (+Zsc view): --------------------- * * * * * * * * * * * * * * * * * ---------------------------- * o * ^ * * | * * | 27.33" * * | * * | * * | * *____ v * __| |_____ ------------------------------------ * * o__*___| ___ o| ^ |_____| | | | azimuth _|_|_ | ______ gimbal | | elev. | 14.33" | | | gimbal | |____ |_____| v | |___________________________________| | --------------- | o _____________________________________| | |_____| ------ o | deployment ^ | hinge | 13.00" | | |