The Soviet space mission Mars 5, consisted in the launch, together with its twin Mars 4, of a probe destined to enter orbit around the planet Mars with the task of taking photos, collecting information on the atmosphere and on the surface of the planet and acting as a repeater to earth of the signals sent by the Mars 6 and Mars 7 rovers. Unlike its twin, Mars 5 reached Mars and entered correctly into orbit, starting its mission. Due to an internal fault, the probe lost communication with the Earth after only 22.81 days of "work".
Mars 5, like Mars 4 as twin probes, was equipped with a television system consisting of two cameras. One, named Vega, with a focal length of 52mm, a focal ratio of f / 2.8 and an angular aperture of 35.7 degrees. The other, called Zufar, has a focal length of 350 mm, a focal ratio of f / 4.5 and an angular aperture of 5.67 degrees. The images were taken through a red filter and may have had a pixel resolution of 1000x1000 or 2000x2000 when they were transmitted to Earth. The resolution of the photos ranged from 100 meters to the kilometer and the device for digitizing the footage was able to generate panoramic images in the visible and near infrared.
On board the probe were also installed a Lyman-Alph photometer, capable of detecting hydrogen in the upper atmosphere, a magnetometer, ion plasma detectors, an electrostatic plasma sensor to study the solar wind, an infrared radiometer to acquire the temperature of the Martian surface, a radio polarimeter to detect the dielectric constant inside the planet, two polarimeters to study the characteristics of the Martian surface and a spectrometer to investigate the emissions of particles in the upper atmosphere.
In addition to this scientific instrumentation on board, two photometers were also installed, one designed to search for water in the atmosphere and the other to detect ozone. In addition, the probe was equipped with instrumentation capable of performing radio-occultation experiments to discover the density of the atmosphere and the ionosphere. In addition, Mars 5 housed instruments created in France to study solar emissions and their intensity.
Mars 5 was launched into orbit via the Proton vector on July 25, 1973 at 14:55:48 UTC and placed on the route to the red planet at 20:15 UTC on the same day. After a course correction performed on August 3, Mars 5 reached Mars on February 12, 1974 at 15:45:00 UTC and entered an elliptical orbit of 1,755 km x 32,555 km inclined by 35.33 ° and lasting 24.87. hours. Mars 5 collected data for 22 orbits before a pressure loss in the data transmission system container interrupted the mission. In total, 43 usable photographs were transmitted to earth depicting an area south of the Valles Marineris ranging from 5 ° N, 330 ° W to 20 ° S, 130 ° O plus 5 panoramas of the red planet. Also in this area were carried out the other scientific measurements that the probe was able to perform.
Data collected by the infrared radiometer showed a maximum surface temperature of 272 Kelvin, 230 near the terminator and 200 in the nocturnal hemisphere. The thermal inertia of the soil proved to be consistent with the existence of dust with a particle size of 0.1 to 0.5 mm, while the data from the polarimeters showed wind deposits with a particle size smaller than 0.04 mm. Femic-type rocks with a composition similar to terrestrial ones were detected. The dielectric constant measured ranged from 2.5 to 4 for a depth of several tens of centimeters. Water vapor was also detected in interesting quantities south of the Tharsis region. In addition, a thin (one hundredth of the Earth's) ozone layer was discovered at an altitude of 40 km. Radio occultation experiments confirmed the few data detected by Mars 4, demonstrating the existence of an ionosphere in the nocturnal hemisphere with a maximum electron density of 4,600 per cubic centimeter at an altitude of 110 km and an atmospheric pressure near the surface of 6.7 mbar.
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