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 objective of the Mars 3 descent module was to perform a soft landing on Mars, return images from the surface, and return data on meteorological conditions, atmospheric composition, and mechanical and chemical properties of the soil. Mars 3 was the first spacecraft to make a successful soft landing on Mars.

Spacecraft and Subsystems

The Mars 3 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 degree 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.

Prop-M Rover

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 meters. The traces of movement in the martian soil would also be recorded to determine material properties.

Mission Profile

The descent module was separated from the orbiter on 2 December 1971 at 09:14 UT. (There is an uncertainty in the absolute times stated here of about 3 minutes.) Fifteen minutes later 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 degrees. 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 approximately 45 degrees S, 158 degrees W, 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 may have induced a coronal discharge, damaging the communications system. The dust storm would also explain the poor image lighting.