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THE MISSION

Spacecraft Overview

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Interstellar Mission.  › larger image

The identical Voyager spacecraft are three-axis stabilized systems that use celestial or gyro referenced attitude control to maintain pointing of the high-gain antennas toward Earth. The prime mission science payload consisted of 10 instruments (11 investigations including radio science). Only five investigator teams are still supported, though data are collected for two additional instruments. With the exception of the Voyager 1 PLS instrument, all of the above are working well and are capable of continuing operations in the expected environment. In addition, data are collected from the Planetary Radio Astronomy (PRA) instrument and Voyager 1's Ultraviolet Spectrometer (UVS). The Flight Data Subsystem (FDS) and a single 8-track digital tape recorder (DTR) provide the data handling functions. The FDS configures each instrument and controls instrument operations. It also collects engineering and science data and formats the data for transmission. The DTR is used to record high-rate PWS data. Data are played back every six months.

INVESTIGATOR TEAMS INSTRUMENT MEASUREMENTS
Plasma Science (PLS) Properties and radial evolution of the solar wind (ions 10 eV - 6 keV, electrons 4 eV-6 keV)
Low-Energy Charged Particles (LECP) Energy spectrum of low-energy particles (electrons 10-10,000 keV, ions 10-150,000 keV/n)
Cosmic Ray Sub-system (CRS) Energy spectrum of high- and low-energy electrons (3-110 MeV) and cosmic ray nuclei (1-500 MeV/n)
Magnetometer (MAG) High (50,000 - 200,000 nT) and low (8-50,000 nT) magnetic field intensity
Plasma Wave Subsystem (PWS) Electrical field components of plasma waves in frequency range of 10 Hz to 56 kHz

The command computer subsystem (CCS) provides sequencing and control functions The CCS contains fixed routines such as command decoding and fault detection and corrective routines, antenna pointing information, and spacecraft sequencing information.

The Attitude and Articulation Control Subsystem (AACS) controls spacecraft orientation, maintains the pointing of the high gain antenna towards Earth, controls attitude maneuvers, and positions the scan platform.

Uplink communications is via S-band (16-bits/sec command rate) while an X-band transmitter provides downlink telemetry at 160 bits/sec normally and 1.4 kbps for playback of high-rate plasma wave data. All data are transmitted from and received at the spacecraft via the 3.7 meter high-gain antenna (HGA).

Electrical power is supplied by three Radioisotope Thermoelectric Generators (RTGs). The current power levels are about 315 watts for each spacecraft. As the electrical power decreases, power loads on the spacecraft must be turned off in order to avoid having demand exceed supply. As loads are turned off, some spacecraft capabilities are eliminated.

To date, the entire Voyager 2 scan platform, including all of the platform instruments, has been powered down. All platform instruments on Voyager 1, except the UVS, have been powered down. The Voyager 1 scan platform was scheduled to be powered down in late 2000, but will be left on at the request of the UVS investigator (with the concurrence of the Science Steering Group) to investigate an unexpected excess in UV from the upwind direction. The PLS experiment on Voyager 1 is currently turned off to accommodate UVS observations.