1971 жылғы "Mariner 9" ғарыш кемесінің Марс саяхаты

Successful 1971 Mars robotic spacecraft

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 and at the highest resolutions (from 1 kilometer to 100 meters (1,100 to 110 yards) 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. Under original plans, a dual mission was to be flown like Mariners 6–7, however the launch failure of Mariner 8 ruined this scheme and forced NASA planners to fall back on a simpler one probe mission. NASA still held out hope that another Mariner probe and Atlas Centaur could be readied before the 1971 Mars launch window closed. A few logistical problems emerged, including the lack of an available Centaur payload shroud of the correct configuration for the Mariner probes, however there was a shroud in NASA's inventory which could be modified. Convair also had an available Centaur stage on hand and could have an Atlas readied in time, but the idea was ultimately abandoned for lack of funding. Mariner 9 was mated to Atlas Centaur AC 23 on May 9 with investigation into Mariner 8's failure ongoing. The malfunction was traced to a problem in the Centaur's pitch control servoamplifier and because it was not clear if the spacecraft itself had been responsible, RFI testing was conducted on Mariner 9 to ensure the probe was not releasing interference that could cause problems with the Centaur's electronics. All testing came back negative and on May 22, a tested and verified rate gyro package arrived from Convair and was installed in the Centaur. Liftoff took place on May 30 at 22:23:04 UT. All launch vehicle systems performed normally and the Mariner separated from the Centaur at 13 minutes and 18 seconds after launch.

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 a 500 watts in the orbit of Mars, the energy was stored in a 20 amp hr nickel cadmium battery. 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 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 2500 mile (4023 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 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).

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 forward error correcting code (FEC). Without FEC, noise would have made up roughly a quarter of a received image, while the FEC encoded the data in a redundant way which allowed for the reconstruction of most of the sent image data at reception. Since the flown hardware was constrained with regards to weight, power consumption, storage, and computing power, some considerations had to be put into choosing an FEC, and it was decided to use a Hadamard code for Mariner 9. Each image pixel was represented as a six bit binary value, which had 64 possible grayscale levels. 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 seven bits per each 32 bit 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 data 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.

As of February 2022, Mariner 9's location is unknown; it is either still in orbit, or has already burned up in the Martian atmosphere or crashed into the surface of Mars. NASA has provided multiple dates for when Mariner 9 could enter the Martian atmosphere. In 2011, NASA predicted that Mariner 9 would burn up or crash into Mars around 2022. However, a 2018 revision to the Mariner 9 mission page by NASA expected Mariner 9 would crash into Mars "sometime around 2020". At the time of the mission, Mariner 9 was left in an orbit that would not decay for at least 50 years, which placed the earliest date of atmospheric entry to October 2022. By August 2023, it is likely that Mariner 9 entered the Martian atmosphere and either burned up or impacted the surface.