Phobos 1

Description

Phobos 1, and its companion spacecraft Phobos 2, were the next-generation in the Venera-type planetary missions, succeeding those last used during the Vega 1 and 2 missions to comet P/Halley. The objectives of the Phobos missions were to: (1) conduct studies of the interplanetary environment; (2) perform observations of the Sun; (3) characterize the plasma environment in the Martian vicinity; (4) conduct surface and atmospheric studies of Mars; and, (5) study the surface composition of the Martian satellite Phobos. The main section of the spacecraft consisted of a pressurized toroidal electronics section surrounding a modular cylindrical experiment section. Below these were mounted four spherical tanks containing hydrazine for attitude control and, after the main propulsion module was to be jettisoned, orbit adjustment. A total of 28 thrusters (twenty-four 50 N thrusters and four 10 N thrusters) were mounted on the spherical tanks with additional thrusters mounted on the spacecraft body and solar panels. Attitude was maintained through the use of a three-axis control system with pointing maintained with sun and star sensors. Phobos 1 operated nominally until an expected communications session on 2 September 1979 failed to occur. The failure of controllers to regain contact with the spacecraft was traced to an error in the software uploaded on 29/30 August which had deactivated the attitude thrusters. This resulted in a loss of lock on the Sun, resulting in the spacecraft orienting the solar arrays away from the Sun, thus depleting the batteries.