Mariner 9

Mariner 9

The Mariner 9 spacecraft
Mission type	Mars orbiter
Operator	NASA/JPL
COSPAR ID	1971-051A
SATCAT №	5261
Mission duration	1 year, 4 months, 27 days
Spacecraft properties
Manufacturer	Jet Propulsion Laboratory
Launch mass	997.9 kilograms (2,200 lb)
Dry mass	558.8 kilograms (1,232 lb)
Power	500 watts
Start of mission
Launch date	May 30, 1971, 22:23:04 (1971-05-30UTC22:23:04Z) UTC
Rocket	Atlas SLV-3C Centaur-D
Launch site	Cape Canaveral LC-36B
End of mission
Disposal	Decommissioned
Deactivated	October 27, 1972 (1972-10-28)
Orbital parameters
Reference system	Areocentric
Periareion	1,650 kilometres (1,030 mi)
Apoareion	16,860 kilometres (10,480 mi)
Inclination	64.4°
Period	719.47 minutes
Mars orbiter
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 the Soviets' 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.

Objectives

Mariner 9 launch

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.

Experiments

1. Ultraviolet Spectrometer (UVS)
2. Infrared Interferometer Spectrometer (IRIS)
3. Celestial Mechanics (not a separate instrument; it relied upon tracking measurements including range, range rate, and Doppler)
4. S-Band Occultation (not a separate instrument; experiment observed the attenuation of the communication signal as the orbiting satellite passed out of view)
5. Infrared Radiometer (IRR)
6. Visual Imaging System – at the lower orbit of Mariner 9, half that of Mariner 6 and Mariner 7 flyby missions, and a vastly improved imaging system, Mariner 9 achieved a resolution of 320 feet (98 m) per pixel, whereas previous Martian probes had achieved only approximately 2,600 feet (790 m) per pixel.

Achievements

Mariner 9 view of the Noctis Labyrinthus "labyrinth" at the western end of Valles Marineris.

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. It is also important to have flexible mission software. The Soviet Union's Mars 2 and Mars 3 probes, which arrived during the same dust storm, were unable to adapt to the unexpected conditions, which severely limited the amount of data that they were able to collect.

After 349 days in orbit, Mariner 9 had transmitted 7,329 images, covering 85% 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.

The findings from the Mariner 9 mission underpinned the later Viking program.

The enormous Valles Marineris canyon system is named after Mariner 9 in honor of its achievements.

After depleting its supply of attitude control gas, the spacecraft was turned off on October 27, 1972.

Construction

A schematic of Mariner 9, showing the major components and features

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 Interferometer Spectrometer (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.

The Infrared Radiometer (IRR) team was led by Professor Gerald Neugebauer from the California Institute of Technology (Caltech).

Error-Correction Codes achievements

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, which is also a 1st-order Reed-Muller code. 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.

Present location

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.

See also

• Exploration of Mars
• Space exploration
• Unmanned space missions
• Timeline of artificial satellites and space probes
• List of Mars orbiters

External links

• Mariner 9 Mission Profile by NASA's Solar System Exploration
• NSSDC Master Catalog: Spacecraft – Mariner 9
• NASA-JPL Guide to Mariner 9
• some Mariner 9 images of Mars
• Mariner 9 approaching Mars movie
• Mariner 9 images, including dust storm
• Mariner 9 view of Phobos (hosted by The Planetary Society)