Soviet Craft

Mars (1960-1974)

The USSR Mars program collectively included 13 missions, all bound for Mars. Four failed, two were doubled as Sputniks (and listed on that page), while seven were successful. Just as with other early Soviet missions, the Mars program included several firsts. One was that it was the first to deliver a probe to the surface of Mars with the Mars 2 lander.

Also called Marsnik 1 and Korabl 4
Launched October 10, 1960 at 14:27:49 UTC
Orbital Mass: 650 kg

Mars 1960A was reported by the NASA Administrator to Congress in 1962 to be an attempt at a Mars probe. Some Soviet scientists involved with the program at that time claim no knowledge of this mission, stating that only the launch on October 14 (Marsnik 2) was an intended Mars mission. However V.G. Perminov, the leading designer of planetary spacecraft at the Lavochkin design bureau, states that this mission was indeed intended for Mars, was identical to Marsnik 2, and was launched unsuccessfully in October 1960.

This would have been the Soviet Union's first attempt at a planetary probe. The objectives of the mission were to investigate interplanetary space between Earth and Mars, study Mars and return surface images from a flyby trajectory, and study the effects of extended spaceflight on onboard instruments and provide radio communications from long distances. After launch, the third stage pumps were unable to develop enough thrust to commence ignition, so Earth parking orbit was not achieved. The spacecraft reached an altitude of 120 km before reentry.

See Mars 1960B for information on the spacecraft itself.

Also called Marsnik 2 and Korabl 5
Launched October 14, 1960 at 13:51:03 UTC
Orbital Mass: 650 kg

Marsnik 2, an intended Mars flyby mission, was either the Soviet Union's first or second attempt at a planetary probe, depending on whether the probe designated as Marsnik 1 reputedly launched four days earlier was actually designed to go to Mars. The objectives of the mission were to investigate interplanetary space between Earth and Mars, study Mars and return surface images from a flyby trajectory, and study the effects of extended spaceflight on onboard instruments and provide radio communications from long distances. After launch, the third stage pumps were unable to develop enough thrust to commence ignition, so Earth parking orbit was not achieved. The spacecraft reached an altitude of 120 km before reentry.

The spacecraft was similar to the Venera 1 design, a cylindrical body about 2 m high with two solar panel wings, a 2.33 m high-gain net antenna, and a long antenna arm. It carried a 10 kg science payload consisting of a magnetometer on a boom, cosmic ray counter, plasma-ion trap, a radiometer, a micrometeorite detector, and a spectroreflectometer to study the CH band, a possible indicator of life on Mars. These instruments were mounted on the outside of the spacecraft. A photo-television camera was held in a sealed module in the spacecraft and could take pictures through a viewport when a sensor indicated the Sun-illuminated martian surface was in view.

Attitude was controlled by a Sun-star sensor with attitude correction performed by a dimethylhydrazine/nitric acid binary propellant engine. The spacecraft orientation was to be maintained so that the solar panels faced the sun throughout the flight. Power was provided by the two-square meter solar panels which charged silver-zinc batteries. Radio communications were made using a decimeter band transmitter via the high gain antenna for spacecraft commands and telemetry. Radio bearing was used to maintain the antennas orientation to Earth. Images were to be transferred using an 8-cm wavelength transmitter through the high-gain antenna. A fourth stage was added to the booster, the Molniya or 8K78, the new launcher was designated SL-6/A-2-e.

Also called Sputnik 22 and Korabl 11
Originally called Sputnik 29 in the U.S. Naval Space Command Satellite Situation Summary
Launched October 24, 1962 at 17:55:04 UTC
Orbital Mass: 6500 kg including the 893.5 kg probe

Sputnik 22 was an attempted Mars flyby mission, presumably similar to the Mars 1 mission launched 8 days later. The spacecraft and attached upper stage were launched by an SL-6 into a 180x485 km Earth parking orbit with an inclination of 64.9° and either broke up as they were going into Earth orbit or had the upper stage explode in orbit during the burn to put the spacecraft into Mars trajectory. In either case, the spacecraft broke into many pieces, some of which apparently remained in Earth orbit for a few days.

This occurred during the Cuban missile crisis. The debris was detected by the U.S. Ballistic Missile Early Warning System radar in Alaska and was momentarily feared to be the start of a Soviet nuclear ICBM attack.

Also called Sputnik 23, 1962 Beta Nu 1, and Mars 2MV-4
Originally called Sputnik 30 in the U.S. Naval Space Command Satellite Situation Summary
Launched November 1, 1962 at 16:14:16 UTC
Orbital Mass: 893.5 kg

Mars 1 was an automatic interplanetary station launched in the direction of Mars, with the intent of flying by the planet at a distance of about 11,000 km. It was designed to image the surface and send back data on cosmic radiation, micrometeoroid impacts and Mars' magnetic field, radiation environment, atmospheric structure, and possible organic compounds. After leaving Earth orbit, the spacecraft and the booster fourth stage separated and the solar panels were deployed. Early telemetry indicated that there was a leak in one of the gas valves in the orientation system so the spacecraft was transferred to gyroscopic stabilization. Sixty-one radio transmissions were held, initially at two day intervals and later at 5 days in which a large amount of interplanetary data were collected. On March 21, 1963, when the spacecraft was at a distance of 106,760,000 km from Earth on its way to Mars communications ceased, probably due to failure of the spacecraft orientation system. Mars 1 closest approach to Mars occurred on June 19, 1963 at a distance of approximately 193,000 km, after which the spacecraft entered a heliocentric orbit.

Mars 1 was a modified Venera-type spacecraft in the shape of a cylinder 3.3 m long and 1.0 m in diameter. The spacecraft measured 4 m across with the solar panels and radiators deployed. The cylinder was divided into two compartments. The upper 2.7 m, the orbital module, contained guidance and on-board propulsion systems. The experiment module, containing the scientific instrumentation, comprised the bottom 0.6 m of the cylinder. A 1.7 m parabolic high gain antenna was used for communication, along with an omnidirectional antenna and a semi-directional antenna. Power was supplied by two solar panel wings with a total area of 2.6 square meters affixed to opposite sides of the spacecraft. Power was stored in a 42 A-hr cadmium-nickel battery.

Communications were via a decimeter wavelength radio transmitter mounted in the orbital module which used the high-gain antenna. This was supplemented by a meter wavelength range transmitter through the omnidirectional antenna. An 8 centimeter wavelength transmitter mounted in the experiment module was designed to transmit the TV images. Also mounted in the experiment module was a 5-cm range impulse transmitter. Temperature control was achieved using a binary gas-liquid system and hemispherical radiators mounted on the ends of the solar panels. The craft carried various scientific instruments including a magnetometer probe, television photographic equipment, a spectroreflexometer, radiation sensors (gas-discharge and scintillation counters), a spectrograph to study ozone absorption bands, and a micrometeoroid instrument.

The probe recorded one micrometeorite strike every two minutes at altitudes ranging from 6000 to 40,000 km due to the Taurids meteor shower and also recorded similar densities at distances from 20 to 40 million km. Magnetic field intensities of 3-4 gammas with peaks as high as 6-9 gammas were measured in interplanetary space and the solar wind was detected. Measurements of cosmic rays showed that their intensity had almost doubled since 1959. The radiation zones around the Earth were detected and their magnitude confirmed.

Also called Mars 69A
Launched March 27, 1969 at 10:40:45 UTC
Orbital Mass: 4850 kg

This Soviet Mars mission was never officially announced but has since been identified as a planned orbiter. After successful operation of the first two stages, the third stage of the Proton SL-12/D-1-e (8K82K, #240-01 + 11S824) launcher experienced a malfunction in a rotor bearing which caused the turbopump to catch fire. The engine shut down 438.66 seconds after launch and exploded, the remains of the craft landing in the Altai mountains.

The nominal mission plan was to use the first three stages of the Proton booster and the Block-D upper stage to place the spacecraft into Earth parking orbit. The upper stage would then be reignited after one orbit to begin the escape sequence. The spacecraft main engine would then be used for the final boost to put the spacecraft into Mars trajectory. The main engine would also be used for two trajectory correction maneuvers during the 6 month cruise to Mars. The main engine would then be used to put the spacecraft into a 1700x34,000 km capture orbit around Mars with an inclination of 40° and a period of 24 hours. Photography and other experiments would take place from this orbit. Then the periapsis would be lowered to 500 to 700 km for a nominal three month session of imaging and data collection from orbit.

This mission was one of two identical probes launched in the spring of 1969. The payload was an M-69 class probe (#521). The probe was built around a spherical propellant compartment with an inner baffle to separate it into two isolated partitions. Two solar panel wings with a total surface area of 7 square meters were mounted on either side of the compartment. A 2.8 m diameter parabolic dish antenna was mounted near the top of the probe, along with three pressurized compartments, the top compartment holding electronics, the second the radio and navigation systems, and the third cameras, a battery, and telemetry devices. Also mounted on the outside of the spacecraft were two conical antennas and a suite of scientific sensors.

The main engine was mounted at the bottom of the probe and used a turbopump to run on the nitrogen tetroxide and unsymmetrical dimethyl hydrazine (UDMH) contained in the main propellant compartment. Eight thrusters with their own fuel tanks and 9 helium pressurization tanks controlled pitch (2 thrusters), yaw (2), and roll (4). Three-axis stabilization and orientation were achieved using 2 Sun sensors, 2 Earth sensors, 2 Mars sensors, a Canopus sensor, gyros, and small thrusters using pressurized nitrogen gas stored in ten tanks. Power at 12 amps was supplied by the solar panels and used to run the spacecraft directly and charge a hermetically sealed cadmium-nickel 110 amp-hour storage battery.

Communications were via two transmitters in the centimeter band (6 GHz) which operated at 25,000 W and transmitted at 6000 bits/s and two transmitters and three receivers in the decimeter band (790-940 MHz) at 100 W and 128 bits/s and a 500 channel telemetry system. The parabolic dish was a directional high-gain antenna for use as the spacecraft neared Mars and the low-gain conical antennas were semi-directional. Thermal control was achieved through passive screen-vacuum insulation and through an active system in the pressurized compartments which consisted of a ventilation and air circulation unit which could run through radiators exposed to sunlight or in shadow.

The spacecraft scientific payload consisted primarily of three television cameras designed to image the surface of Mars. The cameras had three color filters and two lenses, a 50-mm lens with a nominal field of view of 1500x1500 km and a 350-mm lens which had a field of 100x100 km. An image was 1024x1024 pixels for a maximum resolution of 200 to 500 meters. The camera system consisted of film, a processing unit, an exposure unit, and a data encoder to prepare the images for transmission. The camera could store 160 images. The spacecraft also carried a radiometer, water vapor detector, ultraviolet and infrared spectrometers, a radiation detector, gamma spectrometer, hydrogen/helium mass spectrometer, solar plasma spectrometer, and a low-energy ion spectrometer.

Also called Mars 69B
Launched March 27, 1969 at 10:40:45 UTC
Orbital Mass: 4850 kg

This Soviet Mars mission was never officially announced but has since been identified as a planned orbiter. The first stage of the Proton SL-12/D-1-e (8K82K, #233-01 + 11S824) launcher failed almost immediately. At 0.02 seconds after liftoff, one of the six 11D43 first stage rockets exploded. The control system initially compensated for the lost engine and the launch proceeded on 5 engines until 25 seconds after liftoff at approximately 1 km altitude the rocket began to tip over to a horizontal position. The five engines shut down and the rocket impacted and exploded 41 seconds after liftoff approximately 3 km from the launch pad.

The nominal mission plan was to use the first three stages of the Proton booster and the Block-D upper stage to place the spacecraft into earth parking orbit. The upper stage would then be reignited after one orbit to begin the escape sequence. The spacecraft main engine would then be used for the final boost to put the spacecraft into Mars trajectory. The main engine would also be used for two trajectory correction maneuvers during the 6 month cruise to Mars. The main engine would then be used to put the spacecraft into a 1700x34,000 km capture orbit around Mars with an inclination of 40° and a period of 24 hours. Photography and other experiments would take place from this orbit. Then the periapsis would be lowered to 500 to 700 km for a nominal three month session of imaging and data collection from orbit.

See the above Mars 1969A mission for information on the spacecraft.

Launched May 19 and 28, 1971 at 16:22:44 UTC and 15:26:30 UTC, respectively
Orbital Mass (each): 4650 kg including the 3440 kg fully fueled orbiter/bus and the 1210 kg fully fueled descent/lander module

Missions

The Mars 2 and Mars 3 missions consisted of identical spacecraft, each with a bus/orbiter module and an attached descent/lander module. The primary scientific objectives of the Mars 2 orbiter were to image the martian surface and clouds, determine the temperature on Mars, study the topography, composition and physical properties of the surface, measure properties of the atmosphere, monitor the solar wind and the interplanetary and martian magnetic fields, and act as a communications relay to send signals from the lander to Earth.

Mars 2 was launched towards Mars from a Tyazheliy Sputnik (71-045C) Earth orbiting platform. Mid-course corrections were made on June 17 and November 20. Mars 2 released the descent module (71-045D) 4.5 hours before reaching Mars on November 27, 1971. The descent module entered the martian atmosphere at roughly 6.0 km/s at a steeper angle than planned. The descent system malfunctioned and the lander crashed at 45° S, 302° W, delivering the Soviet Union coat of arms to the surface. The cause of the failure may have been related to the extremely powerful martian dust storm taking place at the time. Mars 2 was the first manmade object to reach the surface of Mars. Meanwhile, the orbiter engine performed a burn to put the spacecraft into a 1380x24,940 km, 18 hour orbit about Mars with an inclination of 48.9°. Scientific instruments were generally turned on for about 30 minutes near periapsis.

Mars 3 was launched towards Mars from a Tyazheliy Sputnik (71-049C) Earth orbiting platform. A mid-course correction was made on June 8. The descent module (71-049F) was released at 09:14±3 UT on December 2, 1971, 4 hours 35 minutes before reaching Mars. The descent module entered the martian atmosphere at roughly 5.7 km/s. Through aerodynamic braking, parachutes, and retro-rockets, the lander achieved a soft landing at 45° S, 158° W and began operations. However, after 20 sec the instruments stopped working for unknown reasons, perhaps as a result of the massive surface dust storms raging at the time of landing. Meanwhile, the orbiter had suffered from a partial loss of fuel and did not have enough to put itself into a planned 25 hour orbit. The engine instead performed a truncated burn to put the spacecraft into a long 12 day, 19 hour period orbit about Mars with an inclination thought to be similar to that of Mars 2 (48.9°).

Fifteen minutes after the Mars 3 descent module was released, the descent engine was fired to point the aeroshield forward. At 13:47 UT the module entered the martian atmosphere at 5.7 km/sec at an angle less than 10°. The braking parachute was then deployed, followed by the main chute which was reefed until the craft dropped below supersonic velocity, at which time it was fully deployed, the heat shield was ejected, and the radar altimeter was turned on. At an altitude of 20 to 30 meters at a velocity of 60-110 m/s the main parachute was disconnected and a small rocket propelled it off to the side. Simultaneously the lander retrorockets were fired. The entire atmospheric entry sequence took a little over 3 minutes.

Mars 3 impacted the surface at a reported 20.7 m/s at 13:50:35 UT. Shock absorbers inside the capsule were designed to prevent damage to the instruments. The four petal shaped covers opened and the capsule began transmitting to the Mars 3 orbiter at 13:52:05 UT, 90 seconds after landing. After 20 seconds, at 13:52:25, transmission stopped for unknown reasons and no further signals were received at Earth from the martian surface. It is not known whether the fault originated with the lander or the communications relay on the orbiter. A partial panoramic image returned showed no detail and a very low illumination of 50 lux. The cause of the failure may have been related to the extremely powerful martian dust storm taking place at the time, which would also explain the poor image lighting. (It has also been suggested that the 20 second transmission never occurred and was simply propaganda to allow the Soviets to claim the first Mars soft landing.)

The Mars 2 and 3 orbiters sent back a large volume of data covering the period from December 1971 to March 1972, although transmissions continued through August. It was announced that Mars 2 and 3 had completed their missions by August 22, 1972, after 362 orbits completed by Mars 2 and 20 orbits by Mars 3. The probes sent back a total of 60 pictures. The images and data revealed mountains as high as 22 km, atomic hydrogen and oxygen in the upper atmosphere, surface temperatures ranging from -110 °C to +13 °C, surface pressures of 5.5 to 6 mb, water vapor concentrations 5000 times less than in Earth's atmosphere, the base of the ionosphere starting at 80 to 110 km altitude, and grains from dust storms as high as 7 km in the atmosphere. The data enabled creation of surface relief maps, and gave information on the martian gravity and magnetic fields.

Spacecraft

The attached orbiter/bus and descent module was 4.1 m high, 5.9 m across the two solar panel wings, and had a base diameter of 2 m. The propulsion system was situated at the bottom of the cylindrical spacecraft body and was the main structural element of the orbiter. It consisted of a cylindrical fuel tank divided into separate compartments for fuel and oxidizer. The central part of the main body was composed primarily of this fuel tank. The engine was mounted on a gimbal on the lower surface of the tank. The descent module was mounted on top of the orbiter bus. The two solar arrays extended from the sides of the cylinder and a 2.5 m diameter parabolic high-gain communications antenna and radiators were also mounted on the side. Telemetry was transmitted by the spacecraft at 928.4 MHz. The instruments and navigation system were located around the bottom of the craft. Antennae for communications with the lander were affixed to the solar panels. Three low power directional antennae extended from the main body near the parabolic antenna.

For scientific experiments (most mounted in a hermetically sealed compartment) the Mars 2 orbital bus carried: a 1 kg infrared radiometer with an 8- to 40-µm range to determine the temperature of the martian surface to -100 °C; a photometer to conduct spectral analysis by absorption of atmospheric water vapor concentrations in the 1.38-micron line; an infrared photometer; an ultraviolet photometer to detect atomic hydrogen, oxygen, and argon; a Lyman-alpha sensor to detect hydrogen in the upper atmosphere; a visible range photometer covering six narrow ranges between 0.35 and 0.70 µm; a radiotelescope and radiometer instrument to determine the reflectivity of the surface and atmosphere in the visible (0.3 to 0.6 µm) and the radio-reflectivity of the surface in the 3.4 cm range and the dielectric permeability to give a temperature estimate to a depth of 35 to 50 cm below the surface; and an infrared spectrometer to measure the 2.06 µm carbon dioxide absorption band, allowing an estimate of the abundance along a line of sight to determine the optical thickness of the atmosphere and hence the surface relief.

Additionally, the craft carried a phototelevision unit with one 350 mm focal length 4° narrow angle camera and one 52 mm focal length wide angle camera, on the same axis and having several light filters, including red, green, blue, and UV. The imaging system returned 1000x1000 element scanned pictures with a resolution of 10 to 100 meters by facsimile after development in an automatic onboard laboratory. Radio occultation experiments were also performed when communications transmissions passed through the martian atmosphere in which the refraction of the signals gave information on the atmospheric structure. During the flight to Mars, measurements were made of galactic cosmic rays and solar corpuscular radiation. Eight separate narrow angle electrostatic plasma sensors were on board to determine the speed, temperature, and composition of the solar wind in the range 30 to 10,000 eV. A three axis magnetometer to measure the interplanetary and martian fields was mounted on a boom extending from one of the solar panels.

The Mars descent module was mounted on the bus/orbiter opposite the propulsion system. It consisted of a spherical 1.2 m diameter landing capsule, a 2.9 m diameter conical aerodynamic braking shield, a parachute system and retro-rockets. The entire descent module had a fueled mass of 1210 kg, the spherical landing capsule accounted for 358 kg of this. An automatic control system consisting of gas micro-engines and pressurized nitrogen containers provided attitude control. Four "gunpowder" engines were mounted to the outer edge of the cone to control pitch and yaw. The main and auxiliary parachutes, the engine to initiate the landing, and the radar altimeter were mounted on the top section of the lander. Foam was used to absorb shock within the descent module. The landing capsule had four triangular petals which would open after landing, righting the spacecraft and exposing the instrumentation.

The lander was equipped with two television cameras with a 360° view of the surface as well as a mass spectrometer to study atmospheric composition; temperature, pressure, and wind sensors; and devices to measure mechanical and chemical properties of the surface, including a mechanical scoop to search for organic materials and signs of life. It also contained a pennant with the Soviet coat of arms. Four aerials protruded from the top of the sphere to provide communications with the orbiter via an onboard radio system. The equipment was powered by batteries which were charged by the orbiter prior to separation. Temperature control was maintained through thermal insulation and a system of radiators. The landing capsule was sterilized before launch to prevent contamination of the martian environment.

The Mars 2 and 3 landers carried a small walking robot called PROP-M. The robot had a mass of 4.5 kg and was tethered to the lander by a cable for direct communication. The rover was designed to "walk" on a pair of skis to the limit of the 15 m cable length. The rover carried a dynamic penetrometer and a radiation densitometer. The main PROP-M frame was a squat box with a small protrusion at the center. The frame was supported on two wide flat skis, one extending down from each side elevating the frame slightly above the surface. At the front of the box were obstacle detection bars. The rover was planned to be placed on the surface after landing by a manipulator arm and to move in the field of view of the television cameras and stop to make measurements every 1.5 m. The traces of movement in the martian soil would also be recorded to determine material properties.

Launched July 21, 1973 at 19:30:59 UTC
Orbital Mass: 2270 kg

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 night side ionosphere on Mars. It continued to return interplanetary data from solar orbit after the flyby.

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 23x22.5 mm frame, and a 35.7° look angle. The other camera, Zufar, was f/4.5 with a 350 mm focal length, 23x22.5 mm frame, and a 5.67° look angle. The images were taken through red filters and could be facsimile scanned at 1000x1000 or 2000x2000 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° 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 µm) to measure surface temperature, a radio telescope polarimeter (3.5 cm) to probe the subsurface dielectric constant, two polarimeters (0.32-0.70 µm) to characterize surface texture, and a spectrometer (0.3-0.8 µm) 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 µm for albedo and color studies, one in the water vapor band (1.38 µm) to study water in the atmosphere, and a UV photometer (0.26 and 0.28 µm) 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.

Launched July 25, 1973 at 18:55:48 UTC
Orbital Mass: 2270 kg

Mars 4, 5, 6, and 7 comprised an associated group of Soviet spacecraft launched towards Mars in July and August of 1973. The Mars 5 automatic station was designed to orbit Mars and return information on the composition, structure, and properties of the martian atmosphere and surface. The spacecraft was also designed to act as a communications link to the Mars 6 and 7 landers. The orbiter operated only a few days and returned atmospheric data and images of a small portion of the martian southern hemisphere.

Mars 5 was launched into Earth orbit by a Proton SL-12/D-1-e booster, and propelled from its orbital platform into a Mars transfer trajectory at 20:15 UT on July 25, 1973. The fully fueled launch mass of the orbiter was 3440 kg. After a mid-course correction burn on August 3, the spacecraft reached Mars on February 12, 1974 at 15:45 UT and was inserted into an elliptical 1755x32,555 km, 24 hr, 53 min. orbit with an inclination of 35.3°. Mars 5 collected data for 22 orbits until a loss of pressurization in the transmitter housing ended the mission. About 60 images were returned over a nine day period showing swaths of the area south of Valles Marineris, from 5 N, 330 W to 20 S, 130 W. Measurements by other instruments were made near periapsis along 7 adjacent arcs in this same region.

Mars 5 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 23x22.5 mm frame, and a 35.7° look angle. The other camera, Zufar, was f/4.5 with a 350 mm focal length, 23x22.5 mm frame, and a 5.67° look angle. The images were taken through blue, red, and green filters in addition to a special orange filter and could be facsimile scanned at 1000x1000 or 2000x2000 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.

Data returned from orbit by the Mars 5 infrared radiometer showed a maximum surface temperature of 272 K, 230 K near the terminator and 200 K at night. Thermal inertia of soil was consistent with grain sizes of 0.1 to 0.5 mm, polarization data showed grain sizes smaller than 0.04 mm in aeolian deposits. Six altitude profiles were measured by the CO₂ photometer. U, Th, and K composition similar to terrestrial mafic rocks were found. A dielectric constant from 2.5 to 4 was measured at depths of several tens of cm. A high water vapor content (100 precipitable µm) was found south of Tharsis region. An ozone layer was detected at 40 km altitude with about one-thousandth the concentration of Earth's. The exosphere temperature was measured at 295-355 K, 10 K lower temperatures were found from 200 to 87 km. A small magnetic field was postulated, about .0003 Earth's. Mars 5 also performed a radio occultation experiment and the results, in concert with results from Mars 4 and 6 occultation measurements, showed the existence of a night side ionosphere with a maximum electron density of 4600 per cubic cm at an altitude of 110 km and a near surface atmospheric pressure of 6.7 mbar.

Launched August 5, 1973 at 17:45:48 UTC
Orbital Mass: 3260 kg including the 635 kg lander

Mars 4, 5, 6, and 7 comprised an associated group of Soviet spacecraft launched towards Mars in July and August of 1973. The Mars 6 interplanetary station consisted of a flyby bus and an attached descent module. The descent module separated from the bus on reaching Mars and was designed to enter the martian atmosphere and make in-situ studies of the Mars atmosphere and surface.

Mars 6 successfully lifted off into an intermediate Earth orbit on a Proton SL-12/D-1-e booster and then launched into a Mars transfer trajectory. After one course correction burn on August 13, 1973, it reached Mars on March 12, 1974. The descent module separated from the bus at a distance of 48,000 km from Mars. The bus continued on into a heliocentric orbit after passing within 1600 km of Mars. The descent module entered the atmosphere at 09:05:53 UT at a speed of 5.6 km/s. The parachute opened at 09:08:32 UT after the module had slowed its speed to 600 m/s by aerobraking. During this time the craft was collecting data and transmitting it directly to the bus for immediate relay to Earth. Contact with the descent module was lost at 09:11:05 UT in "direct proximity to the surface", probably either when the retrorockets fired or when it hit the surface at an estimated 61 m/s. Mars 6 landed at 23.90 S, 19.42 W in the Margaritifer Sinus region of Mars. The descent module transmitted 224 seconds of data before transmissions ceased, the first data returned from the atmosphere of Mars. Unfortunately, much of the data were unreadable due to a flaw in a computer chip which led to degradation of the system during its journey to Mars.

The Mars 6 Descent Module carried a panoramic telephotometer to image the martian surface around the lander, atmospheric temperature, pressure, density, and wind sensors, an accelerometer to measure atmospheric density during the descent, a mass spectrometer to estimate atmospheric composition, a radio altimeter, an activation analysis experiment to study soil composition, and mechanical properties soil sensors. The flyby module contained a telephotometer to image Mars, a Lyman alpha sensor to search for hydrogen in the upper atmosphere, a magnetometer, an ion trap and narrow angle electrostatic plasma sensor to study the solar wind and its interaction with Mars, solar cosmic ray sensors, micrometeorite sensors, and a French-supplied solar radiometer to measure solar long-wavelength radio emissions. It was also equipped to perform a radio occultation experiment to profile the atmosphere and ionosphere.

Data returned by the Mars 6 descent module allowed a profile of tropospheric structure from the base of the stratosphere at 25 km altitude at 150 K to the surface at 230 K and atmospheric density from 82 km to 12 km. A surface pressure of 6 mb and temperature of 230 K were measured. Instruments also indicated "several times" more atmospheric water vapor than previously reported. The mass spectrometer data were stored on-board during the descent and scheduled to be transmitted after landing and were therefore lost. The current to the vacuum pump was transmitted as an engineering parameter, however, and a steep increase in current was found. It was hypothesized to indicate an inert gas which could not be removed by the pump, leading to an estimate of argon abundance in the atmosphere of 25% to 45%. (The actual value is now known to be about 1.6%.) The Mars 6 flyby bus performed a radio occultation experiment and the results, in concert with results from Mars 4 and 5 occultation measurements, showed the existence of a night side ionosphere with a maximum electron density of 4600 per cubic cm at an altitude of 110 km and a near surface atmospheric pressure of 6.7 mbar.

Launched August 9, 1973 at 17:00:17 UTC
Orbital Mass: 3260 kg including the 635 kg lander

Mars 4, 5, 6, and 7 comprised an associated group of Soviet spacecraft launched towards Mars in July and August of 1973. The Mars 7 interplanetary station was intended to be a Mars lander. It consisted of a flyby bus and a descent module. The descent module was designed to enter the martian atmosphere and make in-situ studies of the atmosphere and surface, but a malfunction on board caused the lander to miss the planet.

Mars 7 successfully lifted off into an intermediate Earth orbit on a Proton SL-12/D-1-e booster and then launched into a Mars transfer trajectory. After one course correction burn on August 16, 1973, it reached Mars on March 9, 1974. Due to a problem in the operation of one of the onboard systems (attitude control or retro-rockets) the landing probe separated prematurely (4 hours before encounter) and missed the planet by 1300 km. The early separation was probably due to a computer chip error which resulted in degradation of the systems during the trip to Mars. The intended landing site was 50 S, 28 W. The lander and bus continued on into heliocentric orbits.

The Mars 7 Descent Module carried a panoramic telephotometer to image the martian surface around the lander, atmospheric temperature, pressure, density, and wind sensors, an accelerometer to measure atmospheric density during the descent, a mass spectrometer to estimate atmospheric composition, a radio altimeter, an activation analysis experiment to study soil composition, and mechanical properties soil sensors. The flyby module contained a telephotometer to image Mars, a Lyman alpha sensor to search for hydrogen in the upper atmosphere, a magnetometer, an ion trap and narrow angle electrostatic plasma sensor to study the solar wind and its interaction with Mars, solar cosmic ray sensors, micrometeorite sensors, and a French-supplied solar radiometer to measure solar long-wavelength radio emissions. It was also equipped to perform a radio occultation experiment to profile the atmosphere and ionosphere.