Mars Observer was an American robotic space probe launched by NASA on September 25, 1992, to study the surface, atmosphere, climate and magnetic field of Mars. The spacecraft was developed and managed by the Jet Propulsion Laboratory.
The project originated with a 1984 proposal for a new Mars mission, originally titled the Mars Geoscience Climatology Orbiter. As the first and ultimately only mission in the Planetary Observer program, its design was based on earlier Earth-orbiting satellites, including the TIROS and DMSP series. Seven scientific instruments were included.
On August 21, 1993, during the interplanetary cruise phase, communication with Mars Observer was lost, three days prior to its scheduled orbital insertion around Mars. Attempts to re-establish communications with the spacecraft were unsuccessful. Investigators concluded that the likely cause of the failure was a rupture of the fuel pressurization tank in the spacecraft's propulsion system. Several instruments designed for Mars Observer, including the Mars Orbiter Camera, were successfully flown on subsequent missions, beginning with Mars Global Surveyor in 1996.
Mission background
History In October 1984, NASA approved a new mission to Mars, considered high priority by the Solar System Exploration Committee. The original name of the mission was the Mars Geoscience Climatology Orbiter, emphasizing the scientific goals of geology, geophysics and climatology. The Martian orbiter was planned to expand on the information already gathered by the Viking program. Preliminary mission goals expected the probe to provide planetary magnetic field data, detection of certain spectral line signatures of minerals on the surface, images of the surface at 1 meter/pixel and global elevation data. The Jet Propulsion Laboratory managed the project for NASA, and was responsible for mission design, acquisition of science instruments, and direction of flight operations.
Mars Observer was originally planned to be launched in 1990 by a Space Shuttle orbiter. The possibility for an expendable rocket to be used was also suggested, if the spacecraft was designed to meet certain constraints. On March 12, 1987, the mission was rescheduled for launch in 1992, with NASA citing budget concerns over the cost of the launch vehicle. Other missions that had been backlogged after the Space Shuttle Challenger disaster, including Galileo, Magellan, and Ulysses, were given priority. Along with a launch delay, budget overruns necessitated the elimination of two instruments to meet the 1992 planned launch: a mapping spectrometer was removed for programmatic reasons, and a laser altimeter was substituted for the original, more complex radar altimeter. As the development matured, the primary science objectives were finalized as: Determine the global elemental and mineralogical character of the surface material. Define globally the topography and gravitational field. Establish the nature of the Martian magnetic field. Determine the temporal and spatial distribution, abundance, sources, and sinks of volatiles and dust over a seasonal cycle. Explore the structure and circulation of the atmosphere.
The program's total cost was estimated at $813 million.
Spacecraft design
The Mars Observer spacecraft had a mass of . Its bus measured 1.1 meters tall, 2.2 meters wide, and 1.6 meters deep. The spacecraft was based on previous satellite designs that were originally intended and developed to orbit Earth. The RCA AS-4000 Ku-band satellite design was used extensively for the spacecraft bus, propulsion, thermal protection, and solar array. RCA TIROS and DMSP Block 50-2 satellite designs were also utilized in implementing the Attitude and Articulation Control System (AACS), command and data handling subsystem, and power subsystem, into Mars Observer. Other elements such as the bipropellant components and high-gain antenna were designed specifically for the mission.
Attitude control and propulsion The spacecraft was three-axis stabilized with four reaction wheels and twenty-four thrusters with 1,346 kilograms of propellant. The propulsion system used a high thrust, monomethyl hydrazine/nitrogen tetroxide bipropellant system for larger maneuvers and a lower thrust hydrazine monopropellant system for minor orbital corrections during the mission. Of the bipropellant thrusters, four located on the aft provided 490 newtons of thrust for course corrections, control of the spacecraft during the Mars orbital insertion maneuver and large orbit corrections during the mission; another four, located on along the sides of the spacecraft, provided 22 newtons for controlling roll maneuvers. Of the hydrazine thrusters, eight provided 4.5 newtons to control orbit trim maneuvers; another eight provided 0.9 newtons for offsetting, or "desaturating", the reaction wheels. To determine the orientation of the spacecraft, a horizon sensor, a 6-slit star scanner, and five Sun sensors were included.
Communications
For telecommunications, the spacecraft included a two-axis gimbaled 1.5 meter, parabolic high-gain antenna, mounted to a 6 meter boom to communicate with the Deep Space Network across the X-band using two GFP NASA X-band transponders (NXTs) and two GFP command detector units (CDUs). An assembly of six low-gain antennas, and a single medium-gain antenna were also included, to be used during the cruise phase while the high-gain antenna remained stowed, and for contingency measures should communications through the high-gain antenna become restricted. When broadcasting to the Deep Space Network, a maximum of 10.66 kilobytes/second could be achieved while the spacecraft could receive commands at a maximum bandwidth of 62.5 bytes per second.
There was also a research payload, the Mars Observer Ka-Band Link Experiment (KABLE), designed to measure performance for possible future missions at Ka-band. It was very low power, intended only for measurements and not operational use. Proposal. Final report.
Power Power was supplied to the spacecraft through a six-panel solar array, measuring 7.0 meters wide and 3.7 meters tall, which would provide an average of 1,147 watts when in orbit. To power the spacecraft while occluded from the Sun, two 42 A·h nickel-cadmium batteries were included; the batteries would recharge as the solar array received sunlight.
Computer The computing system on the spacecraft was a retooling of the system used on the TIROS and DMSP satellites. The semiautonomous system was able to store up to 2,000 commands in the included 64 kilobytes of RAM, and execute them at a maximum rate of 12.5 commands/second; commands could also provide sufficient autonomous operation of the spacecraft for up to sixty days. To record data, two digital tape recorders (DTR) manufactured by Odetics were included, each of which were capable of storing up to 187.5 megabytes for later playback to the Deep Space Network.
Scientific instruments Mars Observer Camera (MOC) -see diagram ObjectivesObtain global synoptic views of the Martian atmosphere and surface to study meteorological, climatological, and related surface changes. Monitor surface and atmosphere features at moderate resolution for changes on time scales of hours, days, weeks, months and years. Systematically examine local areas at extremely high spatial resolution in order to quantify surface/atmosphere interactions and geological processes. Consists of narrow-angle and wide-angle telescopic cameras to study the meteorology/climatology and geoscience of Mars. Mars Observer Laser Altimeter (MOLA) -see diagram Objectives Provide topographic height measurements with a vertical resolution better than 0.5% of the elevation change within the footprint. Provide RMS slope information over the footprint. Provide surface brightness temperatures at 13.6 GHz with a precision of better than 2.5K. Provide well sampled radar return wave forms for precise range corrections and the characterization of surface properties. A laser altimeter used to define the topography of Mars. Thermal Emission Spectrometer (TES) -see diagram Objectives Determine and map the composition of surface minerals, rocks and ice. Study the composition, particle size, and spatial and tempora distribution of atmospheric dust. Locate water-ice and carbon dioxide condensate clouds and determine their temperature, height and condensate abundance. Study the growth, retreat and total energy balance of the polar cap deposits. Measure the thermophysical properties of the Martian surface (thermal inertia, albedo) used to derive surface particle size and rock abundance. Determine atmospheric temperature, pressure, water vapor, and ozone profiles, and seasonal pressure variations. Uses three sensors (Michelson interferometer, solar reflectance sensor, broadband radiance sensor) to measure thermal infrared emissions to map the mineral content of surface rocks, frosts and the composition of clouds. Pressure Modulator Infrared Radiometer (PMIRR) Objectives Map the three-dimensional and time-varying thermal structure of the atmosphere from the surface to 80 km altitude. Map the atmospheric dust loading and its global, vertical and temporal variation. Map the seasonal and spatial variation of the vertical distribution of atmospheric water vapor to an altitude of at least 35 km. Distinguish between atmospheric condensates and map their spatial and temporal variation. Map the seasonal and spatial variability of atmospheric pressure. Monitor the polar radiation balance. Uses narrow-band radiometric channels and two pressure modulation cells to measure atmospheric and surface emissions in the thermal infrared and a visible channel to measure dust particles and condensates in the atmosphere and on the surface at varying longitudes and seasons. Gamma Ray Spectrometer (GRS) -see diagram Objectives Determine the elemental composition of the surface of Mars with a spatial resolution of a few hundred kilometers through measurements of incident gamma-rays and albedo neutrons (H, 0, Mg, Al, Si, S, Cl, K, Fe, Th, U). Determine hydrogen depth dependence in the top tens of centimeters. Determine the atmospheric column density. Determine the arrival time and spectra of gamma-ray bursts. Records the spectrum of gamma rays and neutrons emitted by the radioactive decay of elements contained in the Martian surface. Magnetometer and Electron Reflectometer (MAG/ER) Objectives Establish the nature of the magnetic field of Mars. Develop models for its representation, which take into account the internal sources of magnetism and the effects of the interaction with the solar wind. Map the Martian crustal remanlint field using the fluxgate sensors and extend these in-situ measurements with the remote capability of the electron-reflectometer sensor. Characterize the solar wind/Mars plasma interaction. Remotely sense the Martian ionosphere. Uses the components of the on-board telecommunications system and the stations of the Deep Space Network to collect data on the nature of the magnetic field and interactions the field may have with solar wind. Radio Science experiment (RS) Objectives Atmosphere Determine profiles of refractive index, number density, temperature, and pressure at the natural experimental resolution (approx. 200 m) for the lowest few scale heights at high latitudes in both hemispheres on a daily basis. Monitor both short term and seasonal variation in atmospheric stratification. Characterize the thermal response of the atmosphere to dust loading. Explore the thermal structure of the boundary layer at high vertical resolution (approx. 10 m). Determine the height and peak plasma density of the daytime ionosphere. Characterize the small scale structure of the atmosphere and ionosphere. Gravity Develop a global, high-resolution model for the gravitational field.