Instrument Host Information |
|
IDENTIFIER | urn:nasa:pds:context:instrument_host:spacecraft.mo::1.1 |
NAME |
MARS OBSERVER |
TYPE |
Spacecraft |
DESCRIPTION |
Mars Observer was launched September 25, 1992 from Cape Canaveral on a Titan III built by Martin Marietta Corporation, with an upper Transfer Orbit Stage from Orbital Sciences Corporation. Flight controllers lost contact with the spacecraft on August 21, 1993, effectively terminating the mission. For most Mars Observer experiments, data were to be collected by instruments on the spacecraft. Those data were then to be relayed via the telemetry system to stations of the NASA Deep Space Network (DSN) on the ground. Radio Science experiments (such as radio tracking of the spacecraft and bistatic radio scattering experiments) 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 Observer science activities. Instrument Host Overview - Spacecraft ===================================== The Mars Observer spacecraft provided a stabilized, nadir-oriented platform for continuous observations of Mars by an advanced set of science instruments.However, communication with the spacecraft was lost three days before it was scheduled to enter Mars orbit in late August 1993. Only data from Earth-Mars cruise and a very small amount of distant-encounter Mars data were obtained from Mars Observer. The spacecraft contract was originally won by the RCA Astro-Space Division (ASD), which subsequently became the General Electric Astro-Space Division when the two companies merged. The selection of RCA was intended to make maximum use of existing designs and technologies from DMSP/TIROS weather satellites and Satcom-K communication satellites. General Electric sold ASD to Martin Marietta Corporation at about the time Mars Observer was launched; Martin Marietta was the prime contractor when the spacecraft was lost. The dimensions of the rectangular bus were 2.1 x 1.5 x 1.1 m in the x-y-z dimensions. When fully deployed, the six-panel solar array was 7.0 x 3.7 meters, and would have developed over a kilowatt of power at Mars. The mass of the spacecraft was about 1028 kg, including 166 kg of payload but excluding the approximately 1346 kg of propellant required, most of which was intended for orbit insertion and orbit circularization at Mars. The propellant also included 63 kg of hydrazine, which would have been used for spacecraft control during mapping. At launch (25 September 1992), the solar panels and high-gain antenna were folded against the rectangular bus and the two science booms (Magnetometer and Gamma-Ray Spectrometer) were retracted. During early cruise the partially-deployed spacecraft was stabilized in a controlled 0.01-rpm roll about the y-axis; communications were conducted with Earth via a low-gain antenna. For trajectory correction and orbit insertion maneuvers the spacecraft was oriented under three- axis control and then returned to cruise attitude. In its mapping orbit, Mars Observer was to be controlled in three axes, using its horizon sensors to point the science instruments on the +Z face toward the nadir. The six-panel solar-array was to be fully deployed on a boom to track the Sun during each orbit, and the high-gain antenna boom was to be fully deployed to track the Earth around each orbit. Spacecraft pointing control was provided by four reaction wheels. Attitude information during mapping was to be provided by a Mars horizon sensor that defined the nadir direction, a star-mapper for inertial attitude, gyros and accelerometers for measuring angular rates and linear accelerations, and multiple sun sensors. The spacecraft was required to maintain adequate pointing control and to provide sufficient telemetry to allow reconstruction of the pointing after each orbit. The telemetry stream provided data from the sensors sufficient to characterize nadir and high-gain antenna pointing to within +/- 3 mrad (per axis, 3 sigma) and boom-mounted science instrument pointing to within +/- 25 mrad (per axis, 3 sigma). Two independent propulsion systems were provided. All major maneuvers, both in cruise and during orbit insertion, were to be accomplished by a hypergolic, bipropellant system. A hydrazine system was available for orbit trim maneuvers during the mapping period and some attitude control functions, including unloading of the momentum wheels. The hydrazine thrusters were chosen to minimize contamination of the instruments during the mapping period. Most instruments were rigidly mounted on a nadir-pointing spacecraft panel and, in general, provided simultaneous views of the same nadir area. No movable scan platform was provided; the spacecraft was to be continuously pointed toward nadir, rotating at the orbital rate. Those instruments that required scanning or multiple fields of view were constructed with internal scanning mechanisms. The Gamma Ray Spectrometer and Magnetometer sensor assemblies were mounted on individual booms on the spacecraft. The steerable high-gain antenna (used for radio science) was mounted on a third boom. For more information regarding the Mars Observer spacecraft, see [ALBEE&PALLUCONI1990] Instrument Host Overview - DSN ============================== The Mars Observer Radio Science investigations utilized instrumentation with elements both on the spacecraft and at the NASA Deep Space Network (DSN). Much of this is shared equipment, being used for routine telecommunications as well as for Radio Science. 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. 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 the DSN 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. The network comprises four subnets, each of which includes one antenna at each complex. The four subnets are defined according to the properties of their respective antennas: 70-m diameter, standard 34-m diameter, high-efficiency 34-m diameter, and 26-m diameter. These DSN complexes, in conjunction with telecommunications subsystems onboard planetary spacecraft, constitute the major elements of instrumentation for radio science investigations. For more information see [ASMAR&RENZETTI1993]. |
NAIF INSTRUMENT IDENTIFIER |
MO |
SERIAL NUMBER | |
REFERENCES |
Albee, A.L., and D.F. Palluconi, Mars Observers' Global Mapping Mission,
EOS, 71, 1099-1107, 1990. Asmar, S. W., N. A. Renzetti, The Deep Space Network as an instrument for radio science research, NASA Technical Reports Server, 1993STIN...9521456A, 1993. |