Instrument Host Information
IDENTIFIER urn:nasa:pds:context:instrument_host:spacecraft.ody::1.3
NAME 2001 MARS ODYSSEY
TYPE Spacecraft
DESCRIPTION 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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REFERENCES Mars Surveyor 2001, Mission Plan, Revision B (MSP 722-201), JPL Document D-16303, Jet Propulsion Laboratory, Pasadena, CA, 2000.