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 was 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, provide 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, provide 22 newtons for controlling roll maneuvers. Of the hydrazine thrusters, eight provide 4.5 newtons to control orbit trim maneuvers; another eight provide 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.^[8][10]

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.^{[5][8][9][10]}

Power

Power was supplied to the spacecraft through a six panel solar array, measuring 7.0 meters wide and 3.7 meters tall, and 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.^{[5][8][9][10]}

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 random-access memory, 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, redundant digital tape recorders (DTR) were included and each capable of storing up to 187.5 megabytes, for later playback to the Deep Space Network.^[8]

Scientific instruments

More information Objectives ...

Mars Observer Camera (MOC)
-see diagram	Objectives[6] Obtain 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.[11] Principal investigator: Michael Malin / Arizona State University (website) reincorporated on Mars Global Surveyor
Mars Observer Laser Altimeter (MOLA)
-see diagram	Objectives[6] 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.[12] Principal investigator: David Smith / NASA Goddard Space Flight Center reincorporated on Mars Global Surveyor
Thermal Emission Spectrometer (TES)
-see diagram	Objectives[6] 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.[13] Principal investigator: Philip Christensen / Arizona State University reincorporated on Mars Global Surveyor
Pressure Modulator Infrared Radiometer (PMIRR)
	Objectives[6] 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.[14] Principal investigator: Daniel McCleese / JPL reincorporated on Mars Climate Orbiter and then further developed and flown on Mars Reconnaissance Orbiter
Gamma Ray Spectrometer (GRS)
-see diagram	Objectives[6] 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.[15] Principal investigator: William Boynton / University of Arizona / NASA Goddard Space Flight Center (HEASARC website) reincorporated on 2001 Mars Odyssey
Magnetometer and Electron Reflectometer (MAG/ER)
	Objectives[6] 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.[16] Principal investigator: Mario Acuna / NASA Goddard Space Flight Center reincorporated on Mars Global Surveyor
Radio Science experiment (RS)
	Objectives[6] 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. Determine both local and broad scale density structure and stress state of the Martian crust and upper mantle. Detect and measure temporal changes in low degree harmonics of the gravitational field. Collects data on the gravity field and the Martian atmospheric structure with a special emphasis on temporal changes near the polar regions.[17] Principal investigator: G. Tyler / Stanford University reincorporated on Mars Global Surveyor
Mars Balloon Relay (MBR)
	Planned as augmentation to return data from the penetrators and surface stations of the Russian Mars '94 mission and from penetrators, surface stations, a rover, and a balloon from the Mars '96 mission.[18] Principal investigator: Jacques Blamont / Centre National de la Recherche Scientifique reincorporated on Mars Global Surveyor

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Intended operations

On August 24, 1993, Mars Observer would turn 180-degrees and ignite the bipropellant thrusters to slow the spacecraft, entering into a highly elliptical orbit. Over the next three months, subsequent "transfer to lower orbit" (TLO) maneuvers would be performed as the spacecraft reached periapsis, eventually resulting in an approximately circular, 118-minute orbit around Mars.^[22]

The primary mission was to begin on November 23, 1993, collecting data during one Martian year (approximately 687 Earth days). The first global map was expected to be completed on December 16, followed by solar conjunction beginning on December 20, and lasting for nineteen days, ending on January 3, 1994; during this time, mission operations would be suspended as radio contact would not be possible.^[22]

Orbiting Mars at an approximate speed of 3.4 km/s, the spacecraft would travel around Mars in a north to south, polar orbit. As the spacecraft circles the planet, horizon sensors indicate the orientation of the spacecraft while the reaction wheels would maintain the orientation of the instruments, towards Mars. The chosen orbit was also Sun-synchronous, allowing the daylit side of Mars to always be captured during the mid-afternoon of each Martian Sol. While some instruments could provide a real-time data link when Earth was in view of the spacecraft, data would also be recorded to the digital tape recorders and played back to Earth each day. Over 75 gigabytes of scientific data was expected to be yielded during the primary mission, much more than any previous mission to Mars. The end of the operable life for the spacecraft was expected to be limited by the supply of propellant and the condition of the batteries.^[22]