Mars Microrover Power Subsystems
Mars
Pathfinder is a NASA Mission targeted for the Ares Vallis region on the surface of
Mars. The spacecraft was launched out of Florida's Kennedy Space Center in December of
1996, and will land on the Red Planet on July 4th 1997. One of the payloads carried by the
spacecraft is a Mars Microrover named Sojourner.
Sojourner is a small, six-wheel robotic vehicle built here at the Jet Propulsion Laboratory. She weighs in at a sleek 11.5kg (25lbs) and is about the size of a milk crate. Sojourner will land on Mars aboard the Pathfinder Spacecraft, but will quickly strike out on her own to traverse the Martian terrain, perform science and technology experiments, and transmit images and data back to the Lander spacecraft. The Lander will then relay the information back to the scientists and engineers waiting on Earth. Although Sojourner needs only about four days to complete her primary mission, she is designed to survive the cold Martian nights (which dip down to a chilly -120C) for many months.
Rover Solar Array
Of course, all of Sojourner's equipment, including her computers,
lasers, motors, and radio modem require power. Sojourner generates most of her power using
a lightweight solar array. The array is easily visible as a flat panel mounted on the top
of the Rover.
The panel is actually made up of an "array" of over two hundred photovoltaic solar cells. Each cell is about the size and width of a double-edge razor blade. The cells are very light, thin, and fragile.
By electrically connecting these cells together in strings, the solar array will provide Sojourner with around 16 watts of power at noon on Mars. That's equivalent to the power used by a oven light, yet it allows the power-efficient Rover to perform almost all her nominal mission activities.
Rover Batteries
During the times when there is either too little or no sunlight for the solar array,
Sojourner can use batteries to power the Rover hardware. Battery power is used cautiously
since the batteries store only a limited amount of energy and once depleted, cannot be
recharged. They are primarily used for night time experiments and early morning operations
on Mars, but also provide power for periodic Rover communications ("health
checks") during the seven month cruise from Earth.
The three batteries are normally out of sight inside the Rover's gold-colored electronics box mounted under the solar panel. Each battery looks something like a black flashlight tube (without end caps) and each tube has three D-size cells inside it. The tubes are strapped together around the Rover's suspension axle which runs through the middle of the electronics box.
Should either the batteries or the solar array fail, the Rover can complete its primary mission using the other power source.
Power Electronics
The power generated by the solar array and batteries is conditioned and
distributed using a complex arrangement of Power Electronics. The electronics are fully
integrated with the navigation and computer electronics to save money, space, and mass,
and yet still provide more than ten different voltages to the various Rover hardware. Most
of the power electronic components used are commercially available.