Mars-6

Orbiter

The main structural element to which the units are attached, including the propulsion system, solar panels, parabolic, directional and low-directional antennas, radiators of the cold and hot circuits of the thermal management system and the instrumentation part, is the unit of fuel tanks of the propulsion system. ^[one]

An important difference between the M-73S and M-73P modifications is the placement of scientific equipment on the orbiter: in the satellite version, the scientific equipment is installed in the upper part of the tank unit, in the variant with the descent vehicle - on a conical transition element connecting the instrument compartment and the tank unit.

For the vehicles of the 1973 expedition, the KTDU was modified. Instead of the main engine 11D425.000, 11D425A is installed, whose thrust in the low thrust mode is 1105 kgf (specific impulse - 293 seconds), and in the large thrust mode - 1926 kgf (specific impulse - 315 seconds). The block of tanks was replaced with a new one - of large dimensions and volume due to the cylindrical insert, while also increased consumable fuel tanks were used. Installed additional helium cylinders for pressurizing fuel tanks. The rest of the orbiters of the M-73 series in terms of the layout and composition of the onboard equipment, with a few exceptions, repeated the M-71 series. ^[one]

Descent vehicle

On the orbiters M-73P in the upper part of the block of fuel tanks of the propulsion system with the help of a cylindrical adapter and a connecting frame attached descent vehicle.

The descent vehicle includes:

• automatic Mars station (close to spherical in shape);
• aerodynamic (brake) screen;
• a container with a parachute- reactive system consisting of a parachute and a soft landing engine;
• a connecting frame with systems that control the movement of the device at the stage of its separation from the orbital compartment and its removal from the flight path to the "falling" one. After the maneuver to change the trajectory of the frame is separated from the descent vehicle.

The descent vehicle installed equipment for measuring the temperature and pressure of the atmosphere, mass spectrometric determination of the chemical composition of the atmosphere, measurement of wind speed, determination of the chemical composition and physicomechanical properties of the surface layer, as well as to obtain a panorama using television cameras. ^[one]

Mass

The total mass of the Mars-6 spacecraft was 3880 kg, of which the scientific equipment of the orbital compartment is 114 kg, the mass of the descent vehicle is 1000 kg. Corrective propulsion system is filled with 598.5 kg of fuel: 210.4 kg of fuel and 388.1 kg of oxidizer. The mass of the descent vehicle at entry into the atmosphere of Mars is 844 kg. The mass of the automatic Martian station after landing is 355 kg, of which the mass of scientific equipment is 19.1 kg.

Technological innovation of the project

For the first time in the practice of domestic cosmonautics, four automatic space vehicles simultaneously participated in a single interplanetary expedition. During the preparation of the expedition, the modernization of the ground-based experimental and test bases, the command-measuring ground complex commenced for the M-71 series vehicles was continued. ^[one]

So, to check and refine thermal calculations, special vacuum units were created, equipped with solar radiation simulators. The analogue of automatic spacecraft passed in them the full scope of complex thermal vacuum tests, the task of which was to verify the ability of the thermal control system to maintain the temperature regime within specified limits at all stages of operation. ^[one]

• Delivery of SA to the near-planet region and providing the required conditions for ballistics to penetrate the SA into the atmosphere of Mars;
• the implementation of the landing of the research probe (automatic Martian station - AMC) on the surface of the planet;
• the implementation of a scientific program. ^[one]

By flying machine

• studying the distribution of water vapor on the planet's disk;
• determination of the gas composition and density of the atmosphere ;
• surface topography study;
• determination of atmospheric brightness temperature and distribution of gas concentration in the atmosphere,
• determination of dielectric constant, polarization and temperature of the surface of the planet;
• measurement of the magnetic field along the flight route and near the planet;
• investigation of the electric field in the interplanetary medium and on the planet;
• the study of the spatial density of meteoric particles;
• study of solar wind during the flight;
• the study of the spectrum and composition of solar cosmic rays;
• registration of cosmic radiation and radiation belts of the planet. ^[one]

The descent vehicle

• measuring the density, pressure and temperature of the atmosphere in height;
• measurements related to the determination of the chemical composition of the atmosphere;
• studies of the type of surface rocks and the distribution of some elements in them;
• measuring wind speed and gas density;
• receiving two-color stereoscopic telepanorama landing AMC;
• determination of the mechanical characteristics of the surface layer of the soil. ^[one]

All spacecraft of the M-73 series successfully passed the entire cycle of ground tests. The launches of these automatic spacecraft in accordance with the Soviet program for the study of outer space and the planets of the solar system were carried out in July – August 1973. ^[1]

In flight, the spacecraft M-73P ("Mars-6 and 7"), intended for the delivery of the descent vehicle, repeats completely the scheme of separation and descent of the SA to the Martian surface, which was developed for the previous M-71 expedition. The most important stage of the expedition - landing on the Martian surface - is as follows. The entry of the descent vehicle into the atmosphere occurs in a given range of entry angles, at a speed of about 6 km / s. At the site of passive aerodynamic braking, the stability of the descent vehicle is ensured by its external shape and centering. ^[one]

The orbital (span) apparatus after separation of the SA and during the subsequent approach to Mars - this is the difference from the M-71 flight pattern - using a gyro platform, it turns out that the antennas of the meter range are rotated to receive the signal from the descent module, and the sharply directed antenna for information transfer to Earth. After completing work with an automatic Martian station, the device continues its flight in heliocentric orbit.

Flight Control

To work with the spacecraft of the M-73 series, the ground-based radio engineering complex “Pluto” , located on the NPC-16 near Evpatoria, was used. When receiving information from spacecraft at large distances, the summation of signals from two ADU 1000 antennas (K2 and K3) and one KTHA-200 (K-6) antenna was used to increase the potential of the radio link. Commands are issued via ADU 1000 (K1) and P 400P (K8) antennas at the second site of NPC-16. Both antennas are equipped with “Harpoon-4” decimeter range transmitters capable of emitting power up to 200 kW. ^[one]

From the point of view of the session control of the spacecraft, some changes have been made to the logic of the onboard systems: for the M-73P devices, a typical 6T session has been excluded, intended for braking and going into orbit of the Mars satellite.

The Mars-6 satellite (M-73P No. 50) was launched from the left launcher of the site No. 81 of the Baikonur cosmodrome on August 5, 1973 at 20:45:48 with the Proton-K launch vehicle. With the help of three stages of the Proton-K launch vehicle and the first start-up of the control unit of the spacecraft accelerating unit, the spacecraft launched an intermediate OISS with a height of 174.9-162.9 km By switching on the remote control of the upper stage after ~ 1 hour and 20 minutes of passive flight, the spacecraft moved to the flight path to Mars. At 22: 04: 09.6 the spacecraft separated from the upper stage. August 13, 1973 made the first correction of the trajectory of movement. When setting the settings, the readiness of the first channel of the on-board computer ACS was removed, however, it was restored during the correction session. The correction impulse was 5.17 m / s, the engine was running at low thrust - 3.4 seconds, and the fuel consumption was 11.2 kg. Almost immediately, the first set of the onboard tape recorder EA-035 refused. The situation was corrected by switching to the second set. However, only a month after the start, on September 3, 1973, telemetry failed on the device, as a result of which it became impossible to receive information in the direct transmission mode via the UHF channel, and via the centimeter one it was possible to transmit information only in the playback mode, and only information from the FTU and VCR. It was necessary to change the control technology, and during the whole flight to issue all the teams two or three times "blindly", controlling their passage only by indirect signs.

Fifteen minutes after separation, the CA brake engine worked, and after 3.5 hours the descent capsule entered the atmosphere of Mars at 09:05:53 at a speed of 5600 m / s (20160 km / h). The entry angle was −11.7 °. First, braking was due to the aerodynamic screen, and after 2.5 minutes, at a speed of 600 m / s (2160 km / h), the parachute system was put into action. At the stage of parachute descent at altitudes from 20 km to the surface and below, temperature and pressure measurements were made, and the chemical composition of the atmosphere was determined. Within 149.22 seconds, the results were transmitted to the flight apparatus, but useful information was extracted only from the signal from the radio complex CA. The signal from CD 1, turned on 25 minutes before entering the atmosphere, was very weak, so it was not possible to decipher the information from it.

The entire stretch of descent - from entering the atmosphere and aerodynamic braking to descending by parachute inclusive - lasted 5.2 minutes. The total time of descent by parachute from the moment of giving the signal to the input of the parachute system was 151.6 seconds. During the descent, there was no digital information from the MX 6408M, but using the Zubr, IT and ID devices, information was obtained about overloads, temperature and pressure changes. Immediately before landing, communication with the SA was lost. The last telemetry received from it confirmed the issuance of the command to turn on the engine soft landing . A new appearance of the signal was expected 143 seconds after the disappearance, but this did not happen.

The landing area of ​​the Mars-6 descent vehicle was selected in the low-lying part of the Eritrean Sea in the southern hemisphere of Mars. The coordinates of the aiming point are 25 ° S. W, 25 ° W. The descent vehicle, according to the data of the trajectory measurement carried out in 1974, landed in an area with nominal coordinates of 23.9 ° S. sh. and 19.5 ° C. d. ^[2] . (According to another processing of trajectory measurements carried out in 1974 in the Margaritifer Terra region with nominal coordinates of 23.54 ° S, 19.25 ° W. ^[3] ) The landing occurred in the calculated coordinate spread region.

Definitely the reason for the failure to work with the SA could not be determined. The most likely versions include:

• the apparatus crashed, including due to the failure of the radio complex, although the speed of the descent and the operation of the soft-fit engine corresponded to the calculated ones (the apparatus was designed for shock acceleration when landing 180 g, and in peripheral places up to 240 g);
• an emergency situation led to the excess of the amplitude of oscillations of the apparatus under the action of the Martian storm at the time of the inclusion of the soft landing engines.

Results

The flight program of the spacecraft "Mars-6" is partially implemented. The program of the descent vehicle ended in failure.

Scientific results

The Mars-6 descent module landed on the planet, first transmitting to the Earth data on the parameters of the Martian atmosphere obtained during the descent.

The Mars-6 descent vehicle measured the chemical composition of the Martian atmosphere using a radiofrequency-type mass spectrometer. Shortly after the opening of the main parachute, the analyzer opening mechanism worked, and the atmosphere of Mars gained access to the device. The mass spectra themselves should have been transmitted after landing and were not received on Earth, however, when analyzing the parameter, the current of the magnetic ionization pump of the mass spectrograph transmitted via the telemetry channel during a parachute descent, it was assumed that the argon content in the planet's atmosphere could be from 25% up to 45%. ^[four]

Pressure and ambient temperature measurements were also carried out on the descent vehicle; The results of these measurements are very important both for expanding knowledge of the planet and for identifying the conditions in which future Martian stations should operate.

Together with French scientists, a radio astronomy experiment was also performed - measurements of the radio emission of the Sun in the meter range. Receiving radiation simultaneously on Earth and aboard a spacecraft remote from our planet for hundreds of millions of kilometers makes it possible to reconstruct a three-dimensional picture of the process of generating radio waves and to obtain data on the fluxes of charged particles responsible for these processes. In this experiment, another problem was solved - the search for short-term bursts of radio emission, which can be expected to occur in distant space due to explosive-type phenomena in the nuclei of galaxies, during outbursts of supernova stars and other processes.

In 2014, astronautics fans led by renowned blogger and space explorer Vitaly Yegorov conducted a visual review and analysis of high-resolution images of the proposed landing zone, which were made by the Mars Reconnaissance Orbiter (MRO) satellite ^{[5] [6] [7]} .

In 2018, Russian researchers found a likely place where the descent vehicle crashed. Modeling ^[8] showed that Mars-6 was supposed to leave a crater with a diameter of about four meters when falling onto solid ground and with a diameter of about five meters when falling into soft ground; the station could also bounce on impact up to 99 meters. This is the crater that researchers found in the low-lying part of the Eritrean Sea in the southern hemisphere of the planet. ^[9]

• Mars-4 is the Soviet automatic interplanetary station from the M-73 series.
• Mars-5 is a Soviet automatic interplanetary station from the M-73 series.
• Mars-7 is the Soviet automatic interplanetary station from the M-73 series.

• AMC Series M-73 on the NPO them. Lavochkin (Neopr.) (Inaccessible link) . The appeal date was August 20, 2012. Archived July 23, 2015.
• VG Perminov The Difficult Road to Mars Memories of the developer AMC Mars and Venus
• TSB Yearbook 1975
• Expedition 1973 (Mars-4, Mars-5, Mars-6, Mars - 7)
• Mars-6 on NASA website
• Mars-6 on the NASA Solar System Exploration site (Unreferenced) (inaccessible link) . Archived September 22, 2008.
• Possible Crash Site of Mars 6 Orbiter / Lander in Samara Vallis PSP_003894_1560
• Samara Valles and Mars 6 Descent Area
• Found Mars 3?!, Search for Soviet descent vehicles on Mars
• We are looking for "Mars-6" on Mars
• We are looking for Mars-6