Phobos program

• 1. Introduction

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  The Phobos program was a Soviet mission unlike almost any before it: two spacecraft, each weighing 2,600 kilograms, launched within days of each other in the summer of 1988, bound for Mars and its mysterious inner moon. Their names were Phobos 1 and Phobos 2. Their purpose was ambitious. They would study the Sun, the interplanetary medium, the Martian atmosphere, and the surface of the small, lumpy moon for which the mission was named. They were the product of cooperation between fifteen nations. They carried instruments built in Sweden, France, and across Europe. And both of them failed before completing their missions. What went wrong, and how close did they come to success?

• 2. A New Spacecraft

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  The 1F design that powered both probes was genuinely new hardware. Soviet planetary missions of the previous decade had flown on the 4MV type, and the Vega 1 and Vega 2 probes that visited Comet Halley had used the 5VK design. The Phobos spacecraft stepped beyond both. At the core sat a pressurized toroidal electronics section surrounding a modular cylindrical experiment section. Four spherical tanks below carried hydrazine, which fed twenty-four 50-newton thrusters and four 10-newton thrusters for attitude control. A three-axis control system kept the spacecraft pointed correctly, with Sun and star sensors as its guides. Each probe needed all of that pointing precision to keep its solar arrays generating power across the long cruise to Mars.

• 3. The Fatal Upload

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  On the 2nd of September 1988, mission controllers expected a routine communications session with Phobos 1. The session never came. Investigators traced the silence back to a software upload on the 29th or the 30th of August, which had deactivated the attitude thrusters. Without attitude control, Phobos 1 lost its lock on the Sun, its solar arrays drifted out of alignment, and its batteries drained. The sequence that killed the spacecraft had originally existed for ground testing only. It should have been removed before launch, but the software was coded into PROMs, and replacing the test code would have meant replacing the entire computer. Under time pressure ahead of launch, engineers chose to leave the sequence in and rely on operators never sending it. A single wrong character in an upload command executed the forbidden instruction instead.

• 4. Phobos 2 at Mars

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  Phobos 2 launched on the 12th of July 1988 from Baikonur cosmodrome atop a Proton-K with a Blok D upper stage. On the 29th of January 1989, it entered Mars orbit. The probe collected data on the Sun, the interplanetary medium, Mars itself, and its moon during a cruise phase that gave no trouble at all. In Mars orbit it returned 37 images of Phobos at a resolution of up to 40 meters. Its infrared spectrometer, built at IAS and DESPA at Paris Observatory with support from CNES, gathered 45,000 spectra in the near-infrared range from 0.75 to 3.2 micrometers across equatorial areas of Mars, with a spatial resolution ranging from 7 to 25 kilometers. Those measurements allowed scientists to produce the first mineralogical maps of both Mars and Phobos. Then, before controllers could deploy the planned landers onto the surface of Phobos, contact was lost.

• 5. Instruments and Landers

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  The science payload on the Phobos probes was international in scope and extraordinary in variety. The Lima-D laser experiment was designed to vaporize material directly off the surface of Phobos so a mass spectrometer could analyze its chemistry. The ASPERA instrument, an electron spectrometer and ion mass analyzer from the Swedish Institute of Space Physics, would probe the plasma environment around Mars. The Grunt imaging radar, carried only by Phobos 1, was built to map the surface relief of Phobos. Each lander carried an x-ray/alpha spectrometer to identify the chemical elements in the surface material, a seismometer to probe the moon's interior, and a device called the Razrez penetrator, fitted with temperature sensors and an accelerometer to test the physical properties of the surface. One lander, the PROP-F, was a hopping lander carried only by Phobos 2, built to bounce across the low-gravity surface of the tiny moon.

• 6. International Partnership

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  Fourteen nations contributed to the Phobos program alongside the Soviet Union. Sweden, Switzerland, Austria, France, and West Germany all provided instruments or expertise. The United States, despite the Cold War context of the era, contributed access to its NASA Deep Space Network, the global antenna system used to track and communicate with the twin probes across deep space. That level of cooperation, a Soviet mission relying on American infrastructure for tracking, reflected how deeply scientific goals could cut across political divisions. The program's objectives ranged from basic solar and interplanetary observations to detailed surface chemistry at a moon most planetary scientists had barely studied. The hopping lander intended for Phobos's surface would have been the first device ever to move across that body, a goal that remained unreached.