Instrument Host Overview
For most Galileo Orbiter experiments, data were collected by instruments on the spacecraft; those data were then relayed via the telemetry system to stations of the NASA Deep Space Network (DSN) on the ground. Radio Science also required that DSN hardware participate in data acquisition on the ground. The following sections provide an overview, first of the Orbiter and then of the DSN ground system as bothsupported Galileo Orbiter science activities.
Instrument Host Overview - Spacecraft
Launched 1989-10-18 by the Space Shuttle Atlantis, Galileo was the first spacecraft to use a dual-spin attitude stabilization system. The rotor (or spun section) turned at approximately three revolutions per minute while the stator(or despun section) maintained a fixed orientation in space.
This design accommodated the different requirements of remote sensing instruments (mounted on the stator) and fields and particles instruments (mounted on the rotor); spacecraft engineering subsystems were also mounted on the rotor. The rotor and stator were connected by a spin bearing assembly, which conducted power via slip rings and data signals viarotary transformers.
There were eleven subsystems and nine scientific instruments on the orbiter. The spacecraft power source was a pair of radioisotope thermoelectric generators. Propulsion was provided by a bipropellant system of twelve 10-newton thrusters and one 400 newton engine. The command and data subsubsystem consisted of multiple microprocessors and a high-speed data bus. The telecommunications subsystem was designed to transmit data to Earth at rates ranging from 10 bps to a maximum of 134 kilobits per second at S-band and X-band frequencies. The rotor had one 4.8 meter high-gain antenna and two low-gain antennas, but the high-gain antenna never deployed properly so data were returned from Jupiter atrates far below the design maxima using the low-gain antennas.
The stator contained a radio relay antenna operating at L band for receiving data from the atmospheric probe, which isdescribed elsewhere.
Science instruments fell into two general categories. Remote sensing instruments included: PPR Photopolarimeter Radiometer NIMS Near-Infrared Mapping Spectrom