Mariner 9 (Mariner Mars '71 / Mariner-I) was a robotic spacecraft that contributed greatly to the exploration of Mars and was part of the NASA Mariner program. Mariner 9 was launched toward Mars on May 30, 1971, from LC-36B at Cape Canaveral Air Force Station, Florida, and reached the planet on November 14 of the same year, becoming the first spacecraft to orbit another planet – only narrowly beating the Soviet probes Mars 2 (launched May 19) and Mars 3 (launched May 28), both of which arrived at Mars only weeks later. After the occurrence of dust storms on the planet for several months following its arrival, the orbiter managed to send back clear pictures of the surface. Mariner 9 successfully returned 7,329 images, covering 85% of Mars's surface, over the course of its mission, which concluded in October 1972.
Spacecraft and subsystems
Mariner 9 carried an instrument payload similar to Mariners 6 and 7, but because of the need for a larger propulsion system to control the spacecraft in Martian orbit, it weighed more than Mariners 6 and 7 combined (Mariner 6 and Mariner 7 weighed 413 kilograms while Mariner 9 weighed 997.9 kilograms).
Power The power for the spacecraft was provided by a total of 14,742 solar cells, being distributed between 4 solar panels, which in total resulted in 7.7 meters of solar panels being present in the spacecraft. The solar panels produced 500 watts in the orbit of Mars. The energy was stored in a 20 amp-hour (Ah) nickel-cadmium battery.
Propulsion Propulsion was provided by the RS-2101a engine, which could produce 1340 N thrust, and in total could have 5 restarts. The engine was fueled by monomethyl hydrazine and nitrogen tetroxide. For attitude control, the spacecraft contained 2 sets of 6 nitrogen jets on the tip of the solar panels. Attitude knowledge was provided by a Sun sensor, a Canopus star tracker, gyroscopes, an inertial reference unit, and an accelerometer. The thermal control was achieved by the use of louvers on the eight sides of the frame and thermal blankets.
Instruments and experiments
Ultraviolet Spectrometer (UVS)
The Ultraviolet Spectrometer (UVS) studied the composition and density of Mars's upper atmosphere, detecting hydrogen, oxygen, and ozone. It worked on a wavelength range of 110–340 nm with a spectral resolution of 2.5 nm. The instrument identified atomic hydrogen and oxygen in the upper atmosphere; provided data on the escape rates of these elements, influencing Mars's atmospheric evolution and mapped ozone distribution, showing seasonal variations. The UVS was constructed by the Laboratory for Atmospheric and Space Physics at the University of Colorado, Boulder, Colorado. The ultraviolet spectrometer team was led by Professor Charles Barth.
Infrared Interferometer Spectrometer (IRIS)
The Infrared Interferometer Spectrometer (IRIS) measured thermal radiation emitted by Mars to analyze atmospheric composition, surface temperature, and dust properties. It worked on a wavelength range of 6–50 μm with a spectral resolution of 2.4 cm−1. The instrument confirmed the presence of CO2 as the dominant atmospheric gas; detected water vapor in the Martian atmosphere; measured surface and atmospheric temperatures and provided insights into dust storms' thermal properties. The IRIS team was led by Dr. Rudolf A. Hanel from NASA Goddard Spaceflight Center (GSFC). The IRIS instrument was built by Texas Instruments, Dallas, Texas.
Celestial Mechanics The Celestial Mechanics Experiment was not a separate instrument. It used radio tracking to determine Mars's gravitational field and refine its mass estimates. It was based on analysis of Doppler shifts in the spacecraft's radio signals and measuring range and range rate to track Mariner 9's precise motion. The experiment improved the understanding of Mars's gravitational field, provided more accurate estimates of Mars's mass and shape and helped refine the planet's rotational parameters.
S-Band Occultation The S-Band Occultation Experiment was not a separate instrument. It used Mariner 9's radio signal at 2.295 GHz (S-band) passing through Mars's atmosphere to study its density, pressure, and temperature profiles. The experiment measured vertical profiles of temperature and pressure in the Martian atmosphere, detected variations in the ionosphere and confirmed the presence of CO2 as the main atmospheric component.
Infrared Radiometer (IRR)
The Infrared Radiometer (IRR) measured surface and atmospheric temperatures using infrared radiation. It worked on a wavelength range of 10–12 μm with a field of view of 1.7° × 1.7°. The instrument provided surface temperature maps of Mars, monitored thermal properties of dust storms and identified temperature variations between day and night cycles. The IRR team was led by Professor Gerald Neugebauer from the California Institute of Technology (Caltech).
Visual Imaging System
The Visual Imaging System captured high-resolution images of Mars's surface, weather patterns, and moons. It employed two vidicon television cameras, with a resolution of 832 by 700 pixels. In a lower orbit, half that of Mariner 6 and Mariner 7 flyby missions, and with a vastly improved imaging system, Mariner 9 achieved a resolution of 98 metres (320 ft) per pixel, whereas previous Martian probes had achieved only approximately 790 metres (2,600 ft) per pixel. It used broadband filters of various wavelengths optimized for surface and atmospheric studies. The wide-angle Camera A produced pictures using eight selectable colored filters: Minus Blue/ Yellow, Orange, Polarized 0°, Green, Polarized 60°, Blue, Polarized 120° and Violet. From a periapsis altitude of 2000 km each image covered an area of 11° × 14°. The narrow-angle Camera B didn't use any filters, but had a response equivalent to camera A's Minus Blue / Yellow filter. From a periapsis altitude of 2000 km each image covered an area of 1.1° × 1.4°. The following table summarizes characteristics of both cameras:
The instrument provided the first global mapping of Mars's surface; discovered volcanoes, valleys, and dried riverbeds, suggesting past water activity; captured dust storms covering the entire planet and mapped Phobos and Deimos, Mars's two moons.
Mission
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