Mars Observer (TOS-21H)

Launch data: Designation  22136 / 92063A Launch date  25 Sep 1992 - 17:05:01 UT Launch site  CC, LC-40 Launch vehicle  Commercial-Titan-3 (#CT-4) Mission  Mars probe Satellite type   Mars orbit on: Perigee / Apogee   km Eccentricity   Inclination  ° Period   min

Spacecraft data: Prime contractor  GE Astro Space Operator  NASA, JPL Platform   Mass at launch  2573 kg Dry Mass   kg Basic shape   Dimension  3.2 m total length, 2.9 m max dia Solar array   Stabilization  3-axis stabilised DC power

Description:

• Mars Observer was a NASA mission to study the surface, atmosphere, interior and magnetic field of Mars from Martian orbit. The mission was designed to operate for one full Martian year (687 Earth days) to permit observations of the planet through its four seasons. The mission specific objectives were to (1) determine the global elemental and mineralogical character of Mars' surface material, (2) define the planet's global topography and gravitational field, (3) establish the nature of the Martian magnetic field, (4) determine the time and space distribution, abundance, sources and sinks of volatile material and dust over a seasonal cycle, (5) explore the structure and aspects of the circulation of the Martian atmosphere. The spacecraft also carried a radio relay package designed to receive information from the planned Mars Balloon Experiment carried on the planned Soviet Mars '94 mission for retransmission back to Earth.
• Spacecraft: Design based on Earth-orbiting spacecraft (DMSP and TIROS).3-axis stabilised, zero momentum bias using reaction wheels. Communications with Earth using X-band system and 1.5 m articulated HGA mounted on 6-meter boom. Deployed 3.7 x 6.5 meter solar array generated 1.1 - 1.5 kW. Hydrazine and bi-propellant propulsion systems to perform trajectory manoeuvres, Mars orbit capture and circularisation, and orbit maintenance. Deployable booms for instruments.
• Payload: Gamma-ray spectrometer (GRS) - designed to measure the abundance of elements (uranium, thorium, potassium, iron and silicon, for example) on the surface of Mars. Thermal-emission spectrometer (TES) - intended to map the mineral content of surface rocks, frosts and the composition of clouds. Mars Observer Camera (MOC) - a line-scan camera designed to take low-resolution images of Mars on a daily basis for studies of the climate, and medium- and high-resolution images of selected areas to study surface geology and interactions between the surface and the atmosphere. Laser altimeter - intended to measure the topographic relief of the Martian surface. Pressure-modulator infrared radiometer (PMIRR) - designed to measure dust and condensates in the atmosphere, as well as profiles of temperature, water vapour and dust opacity as they change with latitude, longitude and season. Radio-science investigation - planned to use the spacecraft radio with an ultrastable oscillator to measure atmospheric refractivity as it varies with altitude to determine the temperature profile of the atmosphere, and will use tracking data to measure the gravity field of Mars. Magnetometer and electron reflectometer - designed to determine the nature of the magnetic field of Mars, and its interactions with the solar wind.

Mission details:

• Mars Observer was launched by Titan III CT-4 from LC40 at Cape Canaveral at 17:05 UTC on Sep 25, 1992. The MO/TOS combination was placed in low earth orbit by the Titan second stage, which was deboosted shortly afterwards. The TOS (Orbital Sciences Corp. Transfer Orbit Stage) meanwhile ignited to place the Mars Observer on an escape trajectory. TOS then executed an avoidance maneuver to make sure it will not impact Mars. No TOS telemetry was transmitted, leaving flight controllers unsure of the launch's success until Mars Observer started transmitting about 1.5 hours after launch. Mars Observer will reach Mars orbit in Aug 1993.
• Mars Observer completed its third trajectory correction manoeuvre (TCM) on Mar 18, 1993.
• Communications was lost with the spacecraft on August 22, 1993 as it was preparing to go into orbit around Mars, and no significant scientific data was returned. Later investigation indicated this was due to a propulsion system explosion caused by propellants leaking past faulty valves.
• Solar Orbit (Heliocentric).