Mars 3

Description

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 3 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 solar radiation, the solar wind and the interplanetary and martian magnetic fields, and act as a communications relay to send signals from the lander to Earth.

Spacecraft and Subsystems

The attached orbiter/bus and descent module had a mass of approximately 4650 kg at launch (including fuel) and was 4.1 meters high, 5.9 meters across the two solar panel wings, and had a base diameter of 2 meters. The mass of the orbiter/bus was about 3440 kg fully fueled, and the fueled mass of the descent/lander module was about 1210 kg. 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 meter 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.

Scientific Instrumentation

For scientific experiments (most mounted in a hermetically sealed compartment) the Mars 3 orbital bus carried: a 1 kg infrared radiometer with an 8- to 40-micron range to determine the temperature of the martian surface to -100 degrees 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 microns; a radiotelescope and radiometer instrument to determine the reflectivity of the surface and atmosphere in the visible (0.3 to 0.6 microns) 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 micron 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 degree 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 1000 x 1000 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 3 orbiter also carried a French-built experiment which was not carried on Mars 2. Called Spectrum 1, the instrument measured solar radiation at metric wavelengths in conjunction with Earth-based receivers to study the cause of solar outbursts. The Spectrum 1 antenna was mounted on one of the solar panels.

Mission Profile

Mars 3 was launched towards Mars from a Tyazheliy Sputnik (71-049C) Earth orbiting platform. A mid-course correction was made on 8 June. The descent module (71-049F) was released at 09:14 UT on 2 December 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 degrees). 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 22 August 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.