In situ made simple: The Planetary Object Geophysical Observer (POGO) power system

Planetary Object Geophysical Observer (POGO) is an M&M®-shaped hopping lander with an integrated payload to measure the composition and temperature of a small planetary body's surface. It is designed to be dropped off by a host spacecraft at the target and conduct a series of random samples by “hopping” around the body's surface. The ability to “hop” is achieved through a unique utilization of a voice coil to provide an upward impulse on the structure of the lander. If POGO lands on an unsuitable measurement location for the instruments, it activates a “shimmy” mode to attempt to reseat the structure in the surface. Thorough testing has been conducted to verify the voice coil can propel POGO provided the gravity of the planetary body and the losses in the regolith are small. The power system on POGO is simple in design but unique in utilization. Since batteries provide the only energy source for POGO, multiple trades and tests have been performed of different cell options. Currently, thorough life testing of various cells is being conducted to ensure the batteries survive the long cruise to the selected planetary body. The voice coil is actuated by discharging a bank of capacitors at high voltage through the voice coil. The capacitor bank is charged up with a charge pump, which is a unique combination of a standard boost converter and a Cockroft-Walton voltage multiplier. The direction of discharge into the voice coil is controlled with a MOSFET H-bridge. The H-bridge is driven with a pair of half-bridge gate drivers which have a floating bootstrap topology for the high side driver. This gives the H-bridge a wide range of capacitor bank operating voltages while providing the fast control necessary for “shimmy” mode. Although there are many benefits to the floating bootstrap topology, there are several drawbacks that must be accounted for in the design and control of the H-bridge.