A moon mission with science along the way

Phobos is the larger of Mars’s two moons. Phobos 1 and Phobos 2 were Soviet spacecraft launched in July 1988 to investigate the Mars system, with a final close encounter planned at that moon. The archive uses the transliteration Fobos-1 and Fobos-2 for the spacecraft. Neither name should be confused with the later Russian Phobos-Grunt sample-return project.

The scientific plan had several stages. Instruments could observe the Sun and interplanetary environment during cruise, study Mars and its surroundings from orbit, then make close measurements at Phobos. A mission can therefore return useful observations before reaching its most ambitious objective. Each stage needs its own description of intended and achieved work.

NASA’s project record describes an electronics section arranged around a central experiment section, propulsion equipment, solar panels and a three-axis attitude-control system. The museum model shown here represents that spacecraft design. Its visible panels and antennas help explain power and communication needs, but the display is not an identified flight article or a photograph of operations at Mars.

Pointing is a system requirement as well as a camera requirement. Solar panels need a suitable relationship to sunlight, antennas must support the communication link and instruments need their observing geometry. In an original operations review, a command that changes the spacecraft’s orientation must be checked against those other requirements, even when its immediate purpose concerns just one instrument.

The Swedish Institute of Space Physics supplied ASPERA, combining electron and ion measurements. CNES’s archive describes the plasma-wave investigation developed by ESA’s ESTEC, the French CNRS laboratory LPC2E and UCLA. French instrument teams also contributed ISM imaging spectroscopy. These roles made the Soviet-led program an international scientific effort without turning it into several independent national missions.

In an original payload table, give each instrument a measured quantity and an observing location. A charged-particle analyzer samples particles near the spacecraft; an imaging spectrometer receives light from a distant surface. Both can contribute to understanding Mars, but a result from one is not automatically a substitute for the other. The instrument method should remain attached to the claim.