spase://CNES/Observatory/CDPP-Archive/PHOBOS-1

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 Vega 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
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, once the main propulsion module had been jettisoned, orbit adjustment. A total of 28 thrusters with 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 1988 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.