| INSTRUMENT_HOST_DESC |
Instrument Host Overview
========================
For most Mars Odyssey 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 observations (such
as radio tracking) required that DSN hardware also participate
in data acquisition. The following sections provide an
overview first of the spacecraft and then of the DSN ground
system as both supported Mars Odyssey science activities.
Instrument Host Overview - Spacecraft
=====================================
The Mars Odyssey spacecraft was built by Lockheed Martin
Astronautics (LMA). The spacecraft structure was divided into
two modules: the equipment module and the propulsion module.
The shape was not uniform, but can be approximated by
envisioning a box 2.2 x 1.7 x 2.6 meters. The framework was
composed of aluminum and titanium. Most spacecraft systems
were redundant in order to provide backup should a device fail.
For more information, see [JPLD-16303].
Command and Data Handling
-------------------------
This subsystem handled all computing functions for Mars
Odyssey. It ran the flight software and controlled the
spacecraft through interface electronics. The system was
based around a RAD6000 computer with 128 megabytes of
random access memory (RAM) and 3 megabytes non-volatile
memory, which allowed data to be maintained by the system
in the event of a power failure. The interface
electronics were computer cards that communicated with
external peripherals. The cards fit into the computer's
main board. There were two identical sets of the
computer and interface electronics for back up in case
one failed. One card was not redundant. It was a one
gigabyte mass memory card that was used to store imaging
data.
Telecommunications
------------------
The telecommunication subsystem was composed of two parts.
The first was a radio system that operated in the X-band
microwave frequency range. It was used for communications
between Earth and the spacecraft. The other system operated
in the ultra high frequency (UHF) range for communications
between future Mars landers and Odyssey.
Communication between the spacecraft and Earth occurred
through the use of three antennas. The high-gain antenna was
a dish with 1.3 meter diameter (4.25 feet). It was used
during the late Cruise and Science and relay phases of the
mission when data rates were high. It simultaneously
received commands from Earth and transmitted science data to
Earth. The medium-gain antenna was a 7.1 cm (2.8 inch) wide
rectangular horn antenna that protruded through the high-gain
dish. The low-gain antenna was 4.4 cm (1.75 inches) and
provided wide- angle communications in emergencies or when
the high-gain antenna was not pointed directly at Earth.
Electrical Power
----------------
A 7 square meter (75 square feet) solar panel containing an
array of gallium arsenide cells generated power for the
spacecraft. The power distribution and drive unit sent power
to the electrical loads of the spacecraft through a system of
switches.
Guidance, Navigation and Control
--------------------------------
This subsystem used three redundant pairs of sensors to
determine the spacecraft's attitude. A star camera was used
to look at star fields and a sun sensor detected the position
of the Sun in order to back up the star camera. The inertial
measurement unit collected spacecraft orientation data
between star camera updates. The reaction wheels along with
the thrusters operated to control the attitude. There were
four reaction wheels - three primary and one for backup.
Odyssey was a three-axis stabilized spacecraft.
Propulsion
----------
The propulsion system comprised a main engine, which aided in
placing Odyssey in orbit around Mars, and sets of small
thrusters, which performed attitude control and trajectory
correction maneuvers. The main engine produced a thrust of
about 695 Newtons (156 pounds of force). Each of the four
attitude controlling thrusters produced a thrust of 0.9
Newtons (0.2 pounds of force) and the four spacecraft turning
thrusters produced a force of 22 Newtons (5 pounds of force).
The propulsion system also included one gaseous helium tank
used to pressurize the fuel and oxidizer tanks, miscellaneous
tubing, pyro valves, and filters.
Structures
----------
The spacecraft was composed of two modules - propulsion and
equipment. The propulsion module contained tanks, thrusters,
and associated plumbing. The equipment module consisted of
the equipment deck, which supported the Mars Radiation
Environment Experiment (MARIE), and engineering components.
The other component of the equipment module was the science
deck which housed the Thermal Emission Imaging System
(THEMIS), Gamma Ray Spectrometer (GRS), High-Energy Neutron
Detector (HEND), Neutron Spectrometer (NS), and star cameras
on top and engineering components and the GRS central
electronics box on the underside.
Thermal Control
---------------
A combination of heaters, radiators, louvers, blankets, and
thermal coatings maintained each spacecraft component's
temperature within its allowable limits.
Mechanisms
----------
Odyssey functioned via several mechanisms, many of which were
associated with the high-gain antenna. The antenna was
locked down during launch, cruise, and aerobraking through
three 'retention and release devices,' or latches. The
antenna was released and deployed with a motor-driven hinge
once the science orbit around Mars was attained. A two-axis
gimbal assembly controlled the position of the antenna. The
solar array used four latches which folded together and
locked down the panels during launch. After deployment, a
two-axis gimbal assembly controlled the solar array. The
last mechanism was a latch for the deployment of the 6-meter
GRS boom.
Flight Software
---------------
Odyssey received commands from Earth via radio and then
translated them into spacecraft actions. The flight software
had the capability to run many sequences concurrently in
addition to executing received commands immediately.
The data collection software was quite flexible. The science
and engineering data were collected and then put in a variety
of holding bins called Application Identifiers (APIDs). Ground
commands could easily modify the data routing and sampling
frequency.
A number of autonomous spacecraft performance functions were
part of the flight software. The spacecraft ran routines
to control attitude and orientation without commands sent
from Earth. The software also executed fault protection
routines to determine if any internal problem occurred. If
a problem was found, a number of automatic preset actions
would occur to resolve the problem and put the spacecraft
into a standby mode until ground controllers provided
further direction.
Coordinate System
-----------------
The spacecraft frame is defined with the X axis parallel to
the stowed HGA boresight, the Y axis normal to the stowed
solar arrays, and the Z axis in the direction of the main
engine thrust (see figure below). The origin of the frame
is centered on the launch vehicle separation plane.
_______________ HGA
\ /
Science .. `._________.'
Orbit || ._______________.
Velocity || | ^+Xsc | Science Deck
^. || | | |
`. || | | |
`. || +Ysc | |
||@| <-----o +Zsc (out of page)
|| | |
|| | |
|| | Science Deck |
Solar || ._______________.
Array ..
/
/
/
V Nadir
Instrument Host Overview - DSN
==============================
The Deep Space Network is a telecommunications facility managed
by the Jet Propulsion Laboratory of the California Institute of
Technology for the U.S. National Aeronautics and Space
Administration (NASA).
The primary function of the DSN is to provide two-way
communications between the Earth and spacecraft exploring the
solar system. To carry out this function it is equipped with
high-power transmitters, low-noise amplifiers and receivers,
and appropriate monitoring and control systems.
The DSN consists of three complexes situated at approximately
equally spaced longitudinal intervals around the globe at
Goldstone (near Barstow, California), Robledo (near Madrid,
Spain), and Tidbinbilla (near Canberra, Australia). Two of
the complexes are located in the Northern Hemisphere while the
third is in the Southern Hemisphere.
Each complex includes several antennas, defined by their
diameters, construction, or operational characteristics:
70-m diameter, standard 34-m diameter, high-efficiency 34-m
diameter (HEF), and 34-m beam waveguide (BWG).
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