||This article contains orbital elements but does not include an epoch, or date when those elements, which typically vary over time, were correct.|
The Mariner 9 spacecraft
|Mission type||Mars orbiter|
|Mission duration||1 year, 4 months, 27 days|
|Manufacturer||Jet Propulsion Laboratory|
|Launch mass||997.9 kilograms (2,200 lb)|
|Dry mass||558.8 kilograms (1,232 lb)|
|Start of mission|
|Launch date||May 30, 1971, 22:23:04UTC|
|Rocket||Atlas SLV-3C Centaur-D|
|Launch site||Cape Canaveral LC-36B|
|End of mission|
|Deactivated||October 27, 1972|
|Periareion||1,650 kilometres (1,030 mi)|
|Apoareion||16,860 kilometres (10,480 mi)|
|Orbital insertion||November 14, 1971, 00:42:00 UTC|
Mariner 9 (Mariner Mars '71 / Mariner-I) was an unmanned NASA space probe that contributed greatly to the exploration of Mars and was part of the Mariner program. Mariner 9 was launched toward Mars on May 30, 1971 from Cape Canaveral Air Force Station and reached the planet on November 14 of the same year, becoming the first spacecraft to orbit another planet  — only narrowly beating Soviet Mars 2 and Mars 3, which both arrived within a month. After months of dust storms it managed to send back clear pictures of the surface.
Mariner 9 returned 7329 images over the course of its mission, which concluded in October 1972.
Mariner 9 was designed to continue the atmospheric studies begun by Mariner 6 and 7, and to map over 70% of the Martian surface from the lowest altitude (1,500 kilometers (930 mi) and at the highest resolutions (from 1 kilometer per pixel to 100 meters per pixel) of any Mars mission up to that point. An infrared radiometer was included to detect heat sources in search of evidence of volcanic activity. It was to study temporal changes in the Martian atmosphere and surface. Mars' two moons were also to be analyzed. Mariner 9 more than met its objectives.
Mariner 9 was the first spacecraft to orbit another planet. It 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.
When Mariner 9 arrived at Mars on November 14, 1971, planetary scientists were surprised to find the atmosphere was thick with "a planet-wide robe of dust, the largest storm ever observed." The surface was totally obscured. Mariner 9's computer was thus reprogrammed from Earth to delay imaging of the surface for a couple of months until the dust settled. The main surface imaging did not get underway until mid-January 1972. However, surface-obscured images did contribute to the collection of Mars science, including understanding of the existence of several huge high-altitude volcanoes of the Tharsis Bulge that gradually became visible as the dust storm abated. This unexpected situation made a strong case for the desirability of studying a planet from orbit rather than merely flying past. 
After 349 days in orbit, Mariner 9 had transmitted 7,329 images, covering 100% of Mars' surface, whereas previous flyby missions had returned less than one thousand images covering only a small portion of the planetary surface.
The images revealed river beds, craters, massive extinct volcanoes (such as Olympus Mons, the largest known volcano in the Solar System; Mariner 9 led directly to its reclassification from Nix Olympica), canyons (including the Valles Marineris, a system of canyons over about 2,500 miles (4,020 km) long), evidence of wind and water erosion and deposition, weather fronts, fogs, and more. Mars' small moons, Phobos and Deimos, were also photographed.
After depleting its supply of attitude control gas, the spacecraft was turned off on October 27, 1972.
The ultraviolet spectrometer aboard Mariner 9 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.
The Infrared Radiometer (IRR) team was led by Professor Gerald Neugebauer from the California Institute of Technology (Caltech).
To control for errors in the reception of the grayscale image data sent by Mariner 9 (caused by a low signal-to-noise ratio), the data had to be encoded before transmission using a so-called error-correcting code (ECC). Without ECC, noise would have made up roughly a quarter of a received image, while the ECC encoded the data in a redundant way which allowed for the reconstruction of the sent image data at reception.
As the flown hardware was constrained with regards to weight, power consumption, storage and computing power, some considerations had to be put into choosing an error-correcting code, and it was decided to use a Hadamard code for Mariner 9. The data words used during this mission were 6 bits long, which represented 64 grayscale values. Because of limitations of the transmitter, the maximum useful data length was about 30 bits. Instead of using a repetition code, a [32, 6, 16] Hadamard code was used. Errors of up to 7 bits per word could be corrected using this scheme. Compared to a five-repetition code, the error correcting properties of this Hadamard code were much better, yet its rate was comparable. The efficient decoding algorithm was an important factor in the decision to use this code. The circuitry used was called the "Green Machine", which employed the fast Fourier transform, increasing the decoding speed by a factor of three.
Mariner 9 remains a derelict satellite in Mars orbit. It is expected to remain in orbit until approximately 2022, when the spacecraft is projected to enter the Martian atmosphere and either burn up or crash into the planet's surface.