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.
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 |
|
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.
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.