Mariner 9
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The Mariner 9 probe was used as part of the Mariner program for the exploration of Mars. Mariner 9 was launched towards its destination on May 30, 1971, arriving at Mars on November 13 of the same year, becoming the first spacecraft to orbit another planet. Scientifically, it constituted a continuation of the observations of Mars acquired by the Mariner 6 and 7 probes, showing clear photographs of the Martian surface hidden at the beginning of the mission by large sand storms.
Introduction
The Mariner Mars 71 project was a mission made up of two ships that were to orbit Mars on complementary missions, but due to the failure of Mariner 8 at launch, it could only be carried out with one probe. The Mariner 9 spacecraft picked up the objectives of the failed mission (map 70% of the Martian surface) and its own objectives (study temporal changes in the atmosphere and surface). Mariner 9 was the first probe to successfully orbit another planet.
The planetary surface of Mars had to be mapped with the same resolution planned for the initial mission, although the resolution of the images of the polar regions had to decrease due to the greater distance to the surface of this probe compared to the Mariner 8.
The ship
The Mariner 9 probe was built on an octagonal magnesium structure, 45.7 cm high and 138.4 cm diagonally. Mounted on top of the structure were two propulsion tanks with fuel, the orbital maneuvering engine, a 1.44 m long low gain antenna, and a satellite dish for communications with Earth.
A mobile platform was mounted in the lower part of the structure, where the scientific instruments (wide and narrow angle TV cameras, infrared radiometer, ultraviolet spectrometer and infrared interferometer spectrometer) were attached.
The total height of the ship was 2.28 m and the mass at the time of launch was 974 kg, of which 415 kg were fuel. The scientific instrumentation had a total weight of 63.1 kg. The electronics for communications, commands and control of the probe were within the main structure.
To obtain electricity, the probe had 4 solar panels with dimensions of 90 x 215 cm, extended from the top of the structure. Each group of two solar panels measures 6.89 m from side to side. The ship's energy was provided by a total of 14,742 solar cells in the 4 panels with a total area of 7.7 m². Electricity production reached 800 W on Earth and 500 W in Martian orbit. The energy was stored in nickel-cadmium batteries with a capacity of 20 Ah.
Propulsion was obtained by means of an engine with a maximum thrust of 1340 N and which could be restarted more than 5 times. The propellant was monomethyl hydrazine and nitrogen tetroxide. Two sets of six nitrogen gas orientation nozzles were placed at the end of the solar panels.
Orientation was obtained with localization carried out by a solar sensor, a star tracker, gyroscopes and an inertial reference unit together with an accelerometer. The probe had a passive thermal control system based on the use of mobile panels on the eight sides of the ship and thermal insulators.
Control of the probe was carried out by a central computer and a sequencer that had a memory of up to 512 words. The command system was programmed with 86 direct commands, 4 quantitative commands and 5 control commands. The data were stored on a reel to reel digital tape recorder. The 168 m, 8-track tape could store 180 million recorded bits at a speed of 132 kbits/s. The data could be sent to Earth at 16, 8, 4, 2 and 1 kbit/s, using two tracks at the same time.
Telecommunications are carried out by two S-band transmitters of 10 and 20 W and received by a receiver through the high-gain satellite dish, the medium-gain horn antenna or the omnidirectional low-gain antenna..
The mission
The probe was launched on a direct trajectory to Mars of 398 million km by an Atlas-Centaur SLV-3C (AC-23) rocket. The rocket separation occurred at 22:36 GMT, about 13 minutes after takeoff. The four solar panels were deployed at 22:40 GMT and the sensors found the Sun around 23:16 GMT, shortly after the probe left the Earth's shadow. The acquisition of the Canopus star occurred at 02:26 GMT on May 31.
The first trajectory correction maneuver took place on June 5. The Mariner 9 spacecraft arrived at Mars on November 13, 1971 after 166 days of flight. A main engine burn of 15 min and 23 s placed the spacecraft in Martian orbit, thus making this probe the first to orbit another planet. The spacecraft was placed in an orbit that had a periapsis of 1,398 km and a period of 12 hours and 34 minutes. Two days later, a 6 s engine firing changed the orbital period to 12 h with a periapsis of 1,387 km. A trajectory correction maneuver was performed on December 30 during orbit 94 that raised the periapsis to 1,650 km and left the orbital period at 11 h, 59 min and 28 s so that synchronized data transmissions could be made with Goldstone's 64m antenna.
The taking of photographs of the surface of Mars was delayed indefinitely due to a large Martian storm that had begun on September 22, 1971 in the Noachis region. The storm quickly grew to become the largest sandstorm ever observed on Mars. When the ship arrived at the planet, no detail of the surface could be seen, except for the peaks of Olympus Mons and the three volcanoes of Tharsis. The storm disappeared during November and December so that normal operations of the probe could begin.
The spacecraft's instruments obtained extensive data on pressures, densities and composition of the atmosphere, as well as the composition, temperature, gravity and topography of the surface. In total, 54 billion bits of scientific data were sent to Earth, including 7,329 photographs that covered the entire planet. After exhausting the gas to control the ship's orientation, the ship was turned off on October 27, 1972, after almost a year of operations. Mariner 9 was left in Martian orbit, which will not decay until after 50 years, when the probe will enter the atmosphere of the red planet.
The Mariner 9 mission was a resounding success as it produced the first global map of Mars, including the first detailed views of the volcanoes, Valle Marineris, the polar caps, and the Phobos and Deimos satellites. It also provided information on global dust storms, the variable gravitational field by area and evidence of erosive activity by the wind.
Instruments
Television photography
It consisted of a 5 cm vidicon television camera that transmitted photographs from Mars. It was capable of transmitting low-resolution filtered photographs and high-resolution unfiltered photographs. Each image had a total of 700 by 380 pixels and its resolution varied between 500 m/TV line to 50 m/TV line if they were taken at an altitude of about 2,000 km. In total he obtained more than 7,300 photographs of the Martian surface, its satellites, Saturn and some stars.
Infrared Radiometer (IRR)
The infrared radiometer of Mariner 9 was designed to study the surface of Mars, the soil temperatures depending on the local time, measuring the radiated energy between 8-12 microns and 18-25 microns, which allowed us to know the energy flows and possible 'hot zones' due to thermal springs and the cold zones of the poles. It operated normally throughout the mission.
S-Band Concealment
The Doppler shift of the S-band telemetry signal that occurred during the occultation of the probe by Mars provided information on the vertical distribution of the refractive index of the Martian atmosphere, which allowed us to know the vertical distribution of ions and neutral molecules.
Celestial Mechanics
A celestial mechanics experiment was carried out to analyze the orbital trajectory through the tracking data. This made it possible to obtain the characteristics of the gravity field of Mars and the ephemeris with high precision.
Infrared Interferometer Spectrometer (IRIS)
It was designed to provide information about the vertical structure, composition and dynamics of the atmosphere and the properties of the planet's surface. Measurements were made between 6 and 50 microns, using a modified Michelson interferometer. The instrument was mounted at the bottom of the ship on a mobile platform. The instrument obtained excellent data during the mission.
Ultraviolet Spectrometer (UVS)
This experiment was designed to receive ultraviolet radiation between 1100 and 3520 A from the Martian surface and atmosphere, observing selected bands of this radiation and providing information on local atmospheric pressure, ozone concentrations, variations in surface structures and variations in oxygen and ozone as possible signals of biological activity.
It also allowed us to detect the rate of escape of atomic hydrogen from the exosphere and the presence of auroras in the UV induced by the planet's magnetic field. It operated normally throughout the mission.
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