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.
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.
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.
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.
All information on this site, including text and images describing the Rover is copyright © 1997, Jet Propulsion Laboratory, California Institute of Technology and the National Aeronautics and Space Administration.
Solar Array Technical Information
Solar Cells
Type Gallium Arsenide on Germanium (GaAs/Ge)
Size 2 x 4 cm, 5.5 mil thick
Coverglass 3 mil, CMG
Efficiency >18% efficiency
Solar Array
Configuration 13 parallel strings, 18 series cells per string
Power 16.5 watts on Mars at noon
45 watts 1 sun/AMO (Earth)
Operating Voltage 14-18 volts
Substrate Nomex honeycomb
Weight 0.340 kg
Size 0.22 m2
Survival Temp -140 to +110 C
Solar Array Contractor Applied Solar Energy Corporation (ASEC)
City of Industry, CA
Battery Technical Information
Cells
Chemistry Lithium-Thionyl Chloride (Li-SOCl2)
Size D-Size
Weight 118 grams
Capacity +25C 12 amp-hrs
-20C 8 amp-hrs
Batteries
Number 3
Cells Per Battery 3 cells in series
Size 40 mm dia, 186 mm length
Weight 1.24 kg
Operating Voltage 8 - 11 volts
Cell Contractor SAFT America
Cockeysville, MD
Power Electronics Technical Information
Distribution Architecture Single string w/graceful degradation
User Voltages
Main bus 8 to 18 volts
Secondary +/-12v, 9v, +/-7.5v, 5v, +/-5v, 3.3v
Power Electronics Suppliers Pico Electronics, Power Trends,
Nation Semiconductor, Motorola, Semtech
Last Update: 24 June 1997 @ 10:00 am
