Phobos program

Lore & Background

Phobos 1 operated nominally until a few weeks into its cruise to Mars, when an expected communications session on September 2, 1988, failed to occur. The failure was traced to a software error uploaded on August 29/August 30 that deactivated the attitude thrusters. The spacecraft lost its lock on the Sun, could not orient its solar arrays, and depleted its batteries. The fatal command was part of test code left in the PROMs due to time pressure before launch; a single-character error in an upload sequence caused its execution.

Phobos 2 was launched on July 12, 1988, and entered Mars orbit on January 29, 1989. It operated nominally throughout its cruise and orbital insertion, gathering data on the Sun, interplanetary medium, Mars, and Phobos. It returned 37 images of Phobos with resolution up to 40 meters and obtained 45000 spectra of Mars and 400 spectra of Phobos. Communications were lost before the planned deployment of a Phobos lander.

The spacecraft design featured a pressurized toroidal electronics section surrounding a modular cylindrical experiment section, with four spherical tanks containing hydrazine for attitude control and orbit adjustment. A total of 28 thrusters were mounted on the tanks, spacecraft body, and solar panels. Attitude was maintained via a three-axis control system with Sun and star sensors.

Reader's Guide

The Phobos program represents a significant but ultimately incomplete Soviet effort to explore Mars and its moon Phobos. Despite the loss of both spacecraft, the missions contributed valuable scientific data. Phobos 2 successfully entered Mars orbit and returned 37 high-resolution images of Phobos, as well as infrared spectra that enabled the first mineralogical maps of Mars and its satellite. The program demonstrated international cooperation, with 14 nations contributing instruments or support, including the use of NASA's Deep Space Network for tracking. The failure of Phobos 1 due to a software error highlighted the risks of leaving test code in flight software under time pressure. The program's legacy includes the data returned by Phobos 2 and the technical lessons learned, which influenced later planetary missions. The planned Phobos landers, carrying instruments such as an X-ray/alpha spectrometer, seismometer, and penetrometer, were never deployed, leaving questions about Phobos' composition and internal structure unanswered.

Did You Know?

• Phobos 1 was lost due to a single-character error in an upload sequence that activated test code left in the PROMs.
• The Phobos program featured cooperation from 14 nations, including the United States via the NASA Deep Space Network.
• Each Phobos probe had a mass of 2600 kg (6220 kg fully fueled launch mass including propellant and propulsion module) and was launched on a Proton-K rocket.