Mars 4

Description

Mars 4, 5, 6, and 7 comprised an associated group of Soviet spacecraft launched towards Mars in July and August of 1973. The Mars 4 automatic station was intended to be a Mars orbiter mission. It was presumably very similar in design and intended mission to the Mars 5 orbiter launched 4 days later. The orbiter had a fully fueled launch mass of 3440 kg. It was put into Earth orbit by a Proton SL-12/D-1-e booster and launched from its orbital platform roughly an hour and a half later on a Mars trajectory. A mid-course correction burn was made on 30 July 1973. It reached Mars on 10 February 1974. Due to a flaw in the computer chip which resulted in degradation of the chip during the voyage to Mars, the retro-rockets never fired to slow the craft into Mars orbit, and Mars 4 flew by the planet at a range of 2200 km. It returned one swath of pictures and some radio occultation data which constituted the first detection of the nightside ionosphere on Mars. It continued to return interplanetary data from solar orbit after the flyby.

Scientific Instrumentation

Mars 4 was equipped with a television imaging system consisting of two cameras. One, called Vega, was f/2.8 with a focal length of 52 mm, a 23 x 22.5 mm frame, and a 35.7 degree look angle. The other camera, Zufar, was f/4.5 with a 350 mm focal length, 23 x 22.5 mm frame, and a 5.67 degree look angle. The images were taken through red filters and could be facsimile scanned at 1000 x 1000 or 2000 x 2000 pixels and transmitted to Earth. The cameras provided pictures with resolutions of 100 m to 1 km. In addition, there was a single-line scanning device with a 30 degree field of view to provide panoramic images in the visible and near-infrared.

The spacecraft was also equipped with a Lyman-Alpha photometer to search for hydrogen in the upper atmosphere, a magnetometer, plasma ion traps and a narrow angle electrostatic plasma sensor to study the solar wind, an infrared radiometer (8-40 microns) to measure surface temperature, a radio telescope polarimeter (3.5 cm) to probe the subsurface dielectric constant, two polarimeters (0.32-0.70 microns) to characterize surface texture, and a spectrometer (0.3 - 0.8 microns) to study emissions in the upper atmosphere.

There were four photometers on board: one for 2 carbon dioxide bands to obtain altitude profiles, one at 0.35 - 0.7 microns for albedo and color studies, one in the water vapor band (1.38 microns) to study water in the atmosphere, and a UV photometer (0.26 and 0.28 microns) to measure ozone. The probe was equipped with a radio-occultation experiment to profile atmospheric density and a dual-frequency radio occultation experiment to profile ionospheric density. The spacecraft also carried French experiments, one called Zhemo to study the distribution and intensity of fluxes of solar protons and electrons and one known as Stereo-2 to study solar radio emissions.