thumb|Phobos probe model

The Phobos program () was an uncrewed space mission consisting of two probes launched by the Soviet Union to study Mars and its moon Phobos. Phobos 1 was launched on 7 July 1988, and Phobos 2 on 12 July 1988.

Phobos 1 suffered a terminal failure en route to Mars. Phobos 2 attained Mars orbit and made several passes collecting data on the Martian system, but contact was lost before the final phase, prior to deployment of the planned Phobos landers. By losing its lock on the Sun, the spacecraft could no longer properly orient its solar arrays, thus depleting its batteries.

Software instructions to turn off the probe's attitude control, normally a fatal operation, were part of a routine used when testing the spacecraft on the ground. Normally this routine would be removed before launch. However, the software was coded in PROMs, and so removing the test code would have required removing and replacing the entire computer. Because of time pressure from the impending launch, engineers decided to leave the command sequence in, though it should never be used. However, a single-character error in constructing an upload sequence resulted in the command executing, with subsequent loss of the spacecraft.

Phobos 2

thumbnail|Sample image taken by the Phobos 2 probe. Enhanced image released by the IKI. Taken 430 km away with a resolution of 80/420 m.

Phobos 2 was launched atop a Proton-K with a Blok D upper stage from Baikonur cosmodrome on July 12, 1988, and entered Mars orbit on January 29, 1989. Phobos 2 operated nominally throughout its cruise and Mars orbital insertion phases on January 29, 1989, gathering data on the Sun, the interplanetary medium, Mars, and Phobos. Phobos 2 investigated Mars's surface and atmosphere and returned 37 images of Phobos with a resolution of up to 40 meters. Communications were lost before planned deployment of a Phobos lander.

Systems and sensors

Phobos probes carried several instruments: solar x-ray and ultraviolet telescopes, a neutron spectrometer and the Grunt radar experiment designed to study the surface relief of Phobos.

The lander had an x-ray/alpha spectrometer to provide information on the chemical element composition of the surface of Phobos, a seismometer to determine the internal structure of Phobos, and the "Razrez" penetrator with temperature sensors and an accelerometer for testing the physical and mechanical properties of the surface.

The Phobos 2 infrared spectrometer (ISM) obtained 45000 spectra in the near infrared (from 0.75 to 3.2 μm) in the equatorial areas of Mars, with a spatial resolution ranging from 7 to 25 km, and 400 spectra of Phobos at 700 m resolution. These observations made it possible to retrieve the first mineralogical maps of the planet and its satellite, and to study the atmosphere of Mars. ISM was developed at IAS and DESPA (Paris Observatory) with support from CNES.

List of instruments:

  • "VSK" TV imaging system
  • PROP-F "hopping" lander. Only carried by Phobos 2.
  • ARS-FP automatic X-ray fluorescence spectrometer
  • ferroprobe magnetometer
  • Kappameter magnetic permeability / susceptibility sensor
  • gravimeter
  • temperature sensors
  • BISIN conductometer / tiltmeter
  • mechanical sensors (penetrometer, UIU accelerometer, sensors on hopping mechanism)
  • "DAS" (long-lived autonomous station) lander
  • TV camera
  • ALPHA-X Alpha-Proton-X-Ray Spectrometer
  • LIBRATION Sun sensor (also known as STENOPEE)
  • Seismometer
  • RAZREZ anchor penetrometer
  • Celestial mechanics experiment
  • "ISM" thermal infrared spectrometer/radiometer - 1–2 km resolution