Sojourner Truth

On the 30th anniversary of robotic exploration of Mars, NASA has selected the name "Sojourner" for the first rover to explore the Red Planet. The 25-pound, six-wheeled robotic explorer, after the Mars Pathfinder lander touched down on the planet's surface on July 4, 1997, was deployed to roam on Ares Vallis, an ancient Martian flood plain.
The U.S. spacecraft Mariner 4 initiated humanity's study of the Red Planet 30 years ago today, when it flew by Mars at a distance of about 6,000 miles (9,656 Km) on July 14, 1965, taking the first close-up images of another planet.

The name Sojourner was chosen for the Mars Pathfinder rover after a year-long, worldwide competition in which students up to 18 years old were invited to select a heroine and submit an essay about her historical accomplishments. The students were asked to address in their essays how a planetary rover named for their heroine would translate these accomplishments to the Martian environment.

Valerie Ambroise, 12, of Bridgeport, Connecticut, submitted the winning essay about Sojourner Truth, an African-American reformist who lived during the Civil War era. An abolitionist and champion of women's rights, Sojourner Truth, whose legal name was Isabella Van Wagener, made it her mission to "travel up and down the land", advocating the rights of all people to be free and the rights of women to participate fully in society. The name Sojourner was selected because it means "traveler". JPL scientists and engineers working on the Mars Pathfinder project and Planetary Society staff members reviewed the 3,500 total entries received from all over the world, including essays from students living in Canada, India, Israel, Japan, Mexico, Poland and Russia.

The Rover Sojourner

Sojourner is a small, six-wheel robotic vehicle built at the Jet Propulsion Laboratory. She weighs in at a sleek 11.5 kg (25 lbs) and is about the size of a milk crate (65 cm (26 inches) long by 18 cm (7 inches) tall), Sojourner landed on Mars aboard the Pathfinder Spacecraft, but quickly stroke 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 -120°C) 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 provided power for periodic Rover communications ("health checks") during the seven month cruise from Earth.

The three batteries are 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.

"Six wheels on soil!" The image above was taken by the IMP camera on July 5, 1997 (Sol 2). Sojourner's descent down the rear rover deployment ramp was successful. The microrover's seven month journey from Earth to Mars is complete. The soil beneath Sojourner (with tracks showing behind the right rear wheel) will be the first target of the Alpha Proton X-Ray Spectrometer.

The image above shows the Sojurner Rover conducting its examination of "Barnacle Bill" with the APXS. This image was taken by the fully deployed (1.8 meters) IMP camera on Sol 4 (7 July 1997).

In the image above, taken with the Imager for Mars Pathfinder (IMP) at 8:45 p.m. PDT on Sol 6 (10 July 1997), Sojourner has made contact with the rock Yogi. The rover's left rear wheel has driven up onto the Yogi's surface in an attempt to get as close as possible to the rock's surface. Note the tracks left by the rover as it turned around to get closer.
Sojourner will later use its Alpha Proton X-Ray Spectrometer (APXS) instrument to conduct a study of Yogi's chemical composition.

In the image above, taken with the Imager for Mars Pathfinder (IMP), on Sol 18 (21 July 1997), Sojourner has made contact with the rock Yogi. It clearly shows the "two-toned" surface of this large rock. The nature of this color difference is not known, however. It might consist of wind-blown dust accumulated on the surface (the rock is leaning into the prevailing wind) or might be evidence of a break from a larger boulder as it was deposited in the ancient flood that scoured this area.
Note the tracks left by the rover as it turned around to get closer.
Sojourner has used its Alpha Proton X-Ray Spectrometer (APXS) instrument to conduct a study of Yogi's chemical composition.

A different, higher-resolution version of this image (65KB) can be obtained from the Mars Pathfinder pages at: Mars Pathfinder Mission (NASA-JPL and all mirror sites)

In the image above, taken by the Rover Sojourner, you can see the Mars Pathfinder lander with its airbags. The dish-shaped object is the high-gain antenna, the bright vertical cilinder is the low-gain antenna, the lower part of the IMP camera's mast is to its left, the wind-socks mast is further to the left.
The 'Mini Matterhorn' rock is to the left side. The shadows in the foreground bottom are from the edge of the rover's solar panel and its antenna. The rock Yogi is to right, behind the airbags.

A different, higher-resolution version of this image (146 KB) can be obtained from the Mars Pathfinder pages at: Mars Pathfinder Mission (NASA-JPL and all mirror sites)

Updated: July 31 '97

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