Fobos 1, 2

Fobos 1 (cruise configuration)

Fobos 2 (orbital configuration)

Fobos 2 Hopper

Fobos 1 and 2 were nearly identical spacecraft to explore the martian moon Phobos. The mission included co-operation from 14 other nations including Sweden, Switzerland, Austria, France, West Germany, and the United States (who contributed the use of its Deep Space Network for tracking the twin spacecraft).

The objectives of the Fobos missions were to:

• conduct studies of the interplanetary environment;
• perform observations of the Sun;
• characterize the plasma environment in the Martian vicinity;
• conduct surface and atmospheric studies of Mars; and,
• 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.

Following instruments were on board of the probes:

• Automatic Space Plasma Experiment with Rotating Analyzer (ASPERA)
• Proton and Alpha Particle Spectrometer (TAUS)
• Energy, Mass, and Charge Spectrometer (SOVIKOMS)
• Energetic Charged-Particle Spectrometer (SLED)
• Solar Photometer (IPHIR)
• X-Ray Photometer (RF-15)
• Ultrasound Spectrometer (SUFR)
• Gamma-Ray Burst Spectrometer (LILAS)
• Gamma-Ray Burst Spectrometer (VGS)
• Videospectrometric System (VSK)
• Infrared Spectrometer (ISM)
• Gamma Ray Emission Spectrometer (APEX)
• Radar System (RLK)
• Laser Mass Spectrometer Analyzer (LIMA-D)
• Secondary Ion Mass Analyzer (DION)
• Optical Radiation Spectrometer (AUGUST)
• Flux Gate Magnetometer Mars (FGMM)
• Plasma Wave System (PWS)
• Ion and Electron Spectrometer (HARP)
• Magnetic Fields near Mars (MAGMA)
• Neutron Detector (IPNM) (only #1)
• Solar Telescope/Coronograph (TEREK) (only #1)
• Infrared Radiometer/Spectrometer (KRFM) (only #2)
• Scanning Infrared Radiometer (Thermoscan) (only #2)
• Energetic Particles (MSU-TASPD) (only #2)

Both probes carried a small solar-powered Phobos surface station called DAS, which carried panoramic stereo TV system, seismometer, magnetometer, X-ray fluorescence spectrometer, alpha particle scattering device and a penetrator.

Fobos-2 carried a unique lander called Hopper to make surface measurements on different locations on the surface of Phobos. This battery-powered lander would have had only a short lifetime. It featured spring powered "legs", which enabled the probe to align it self correctly after landing and perform up to 10 hops of about 20 m on the surface. It featured following instruments:

• a X-ray fluorescence-spectrometer
• a Penetrometer
• a Dynamometer
• a Magnetometer
• a Gravimeter

Fobos 1 operated nominally until an expected communications session on 2 September 1989 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.

Fobos 2 operated nominally throughout its cruise and Mars orbital insertion phases, gathering data on the Sun, interplanetary medium, Mars, and Phobos. Shortly before the final phase of the mission, during which the spacecraft was to approach within 50 m of Phobos' surface and release two landers, one a mobile `hopper', the other a stationary platform, contact with Fobos 2 was lost. The mission ended when the spacecraft signal failed to be successfully reacquired on 27 March 1989. The cause of the failure was determined to be a malfunction of the on-board computer.