BOX 3.4 The Phobos Hopper
The Phobos mission, launched by the Soviet Union in 1988, consisted of two identical spacecraft equipped to carry out detailed investigations of Mars and its small moon, Phobos. Although both spacecraft suffered failures before they could begin close-up studies of Phobos, the low-gravity environment of the small, asteroid-like moon enabled a unique lander architecture and approach to mobility. Each craft was equipped with a "hopper" lander that was to be jettisoned toward Phobos from a cruising height above it of ~50 m. The relative free-fall approach velocity of the 50-kg, semispherically shaped lander was designed to be a few meters per second.1 Upon touchdown on the surface of the moon, two mechanical rods, or levers, would release and work to position the lander so that its instruments faced Phobos's surface (Figure 3.4.1). Each hopper carried several instruments, including an x-ray fluorescence spectrometer, a magnetometer, a gravimeter, and a penetrometer.2,3 After measurements were made at one location, two spring-loaded "legs" would extend and the hopper would literally jump to a new location up to 20 m away, using no chemical propulsion. With each hop, the position control levers would correct the hopper's attitude after landing. The hopper was designed to sample 10 sites during its 4-hour, battery-powered lifetime.4
FIGURE 3.4.1
Hopping is an appealing means of providing mobility in a low-gravity environment. The former Soviet Union planned to use hoppers to undertake multipoint measurements on the martian moon, Phobos, in the late 1980s as part of the ambitious, but unsuccessful, Phobos program. Although their parent spacecraft failed before they could be released, these 60-cm-by-90-cm (approximate) hoppers were designed to leap from one site to another up to 20 m away and were outfitted with an array of scientific instruments, including an x-ray fluorescence spectrometer, a magnetometer, and a gravimeter. The two mechanical rods used to position the device are visible to the left of the semispherical hopper. This photograph of one of the engineering test models and its mounting adaptor (upper left) is courtesy of Valery Gromov and Alexander Zakharov.
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1
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Space Research Institute, Phobos: Exploration of Phobos, Mars, Sun and Interplanetary Space, Academy of Science of the USSR, Moscow, 1987, p. 7.
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2
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Space Research Institute, 1987, p. 12.
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3
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"Soviets Will Use Venera Follow-on in Mars Mission," Aviation Week and Space Technology, April 14, 1997, p. 125.
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4
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Space Research Institute, 1987, p. 12.
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