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Mars Pathfinder

Mars Pathfinder was the first mission since Viking to land on Mars. It was truly a "pathfinder" in this aspect, paving the way for future missions to Mars. Launched on December 4, 1996 by a Delta II rocket, the Pathfinder lander rocketed to Mars in its cruise stage capsule with a mini-rover, Sojourner, snug inside. The mission was a success, landing at Ares Vallis (Mars Valley), an ancient floodplain, on July 4, 1997 -- to the favorability of the Americans. The versatile Sojourner rover traversed off the lander to "sniff" out the composition of the Martian surface. The final communications with Pathfinder happened in October, when the electronics are believed to have broken because of the bitter cold of the upcoming Martian winter or because of the degradation of the rechargeable batteries. Although the communications failure was a disappointment, Pathfinder had completed all of its science goals except for the Super Panorama image which was 83% done. Pathfinder had exceeded its one month lifespan by three times.

Pathfinder Lander

The Pathfinder lander -- now renamed the Sagan Memorial Station after the late astronomer, Carl Sagan -- was built to take images and carry out a few experiments on the Martian surface. Another job was to communicate with the Sojourner rover. It then relayed information via a high or low-gain antenna to one of Earth's tracking stations, called the Deep Space Network. Pathfinder landed on Mars mid-morning July 4 when its airbags were deployed for the 870 kg craft to bounce to a stop on the surface. After a few minutes, the airbags deflated and the petals were opened, revealing the Sojourner rover perched on top one of the petals.

Pathfinder is made up of three hexagonal-shaped petals attached to a base. On the base are the Instrument Electronics Assemblies which housed the electronics. They were also the white cover that supported the low and high-gain antennas and the IMP (imager). To insulate the electronics, 2 inch thick phenolic honeycomb, ecofoam and graphite epoxy face sheets were used. The assemblies were then painted with a substance called "flame-master white" to absorb and keep heat in. On each of the petals, solar panels were installed. These panels, along with the rechargeable batteries, were used to power the lander.


One of the instruments on Pathfinder was the IMP (Imager for Mars Pathfinder). It was a black and white, and color camera set on a deployable mast 1 metre high. The camera's resolution was 256 x 524 pixels and included 12 filter wheels. Its mission was to take pictures of the Martian surface, keep track of and communicate with the rover, and to image the magnetic experiments and windsocks. The magnetic experiments consisted of a magnet attached to various points of the lander; if there were any magnetic particles in the Martian dust, it would be imaged by the IMP. The IMP provided excellent resolution of the nearby area, and was assigned the job to take the "super-pan" which was nearly completed.


ASI/MET (Atmospheric Structure Instrument/Meteorology Package) are the weather instruments. They contain pressure sensors, thermocouples and windsocks. The pressure sensors measured the atmospheric pressure at landing and on the surface. Three thermocouples -- placed at 25, 50 and 100 cm intervals -- on a mast measured the surface temperature. The three windsocks, also spaced out on the mast, were hard cones. Windsocks that are used on Earth would be too soft to detect the light Martian wind. To find out the wind speed, the IMP was used to image the windsocks.

Sojourner Rover

The Sojourner rover was an example of innovative technology. Made at a cost of only $25 million US, Sojourner ambled out onto the Martian floodplain, inspecting and imaging the nearby landscape. It was to demonstrate low-cost rovers made with materials you could easily find at an electronics shop. Being only 23 pounds and 65 x 48 cm in dimension, the foot high rover seemed midget the large boulders. In addition to its minute size, the communications were quite simple, with a UHF link and a 9600 baud modem; the computer had a 80C85 processor and 0.5 megabyte of RAM, which is considerably slower than most people's computers. It is powered by 0.25 m2 of solar panels (16 watt hours) and non-rechargeable batteries (150 watt hours). Because of the low power, Sojourner was only able to travel at about 1 cm/s and only from 10 a.m. to 2 p.m. on each sol (Martian day). Because the rover could only communicate with the lander via the antenna, it could not stray off within the lander's line of sight.

Although Sojourner was quite simple in ways, the rover did have some high-tech technology. Its aluminum wheels, three on each side, were each powered by a motor. The "rocker-bogie" suspension system allowed each wheel to follow the contour of the landscape to prevent tip-overs. Also, Sojourner was semi-autonomous (could partly run by itself). There were 5 lasers at the front of the rover (side opposite the APXS) which detected any hazards the rover could encounter. If an obstacle was in the way, Sojourner would just back up and take a different route. This way, the engineers at JPL did not have to always keep track and "drive" the rover. They told it where to go and it would find a way to get there itself. Engineers used the IMP to tell where the rover had gone. One of the science instruments was the APXS, which was used to determine the composition of the Martian surface. Furthermore, there were three cameras mounted on the rover; two black and white cameras were on the front to make stereo images and one color camera was on the back. To roll off the lander petal, Sojourner had to traverse down one of two ramps which unfurled on the lander.

Sojourner's mission was a success, lasting 12 times its expected week-long lifetime. Its mission was cut off by the failure of the lander. Perhaps, the rover could still be driving around the lander, trying to communicate with its "mother-ship."


The WEB (Warm Electronics Box) is the gold-foiled box of the rover. It, like the Instrument Electronics Assemblies of the the lander, contained the electronics of the rover. The WEB is made out of 1.5 inches of aerogel (a lightweight smoke-like solid) and low-density silicon to insulate the rover. Gold foil was used on the outside of the box to absorb any reflected heat.


The APXS (Alpha Proton X-Ray Spectrometer) is the main science instrument on the rover. It is retractable from the back chassis of Sojourner. The purpose of the APXS was to determine the composition of the Martian rocks and soil by use of X-rays provided by alpha particle radiation. This 560 g and 0.4 watt spectrometer measured all the elements except hydrogen (a constituent of water). The APXS was powerful, measuring up to 1/10 of a percent of a rock's composition when it was deployed up on to it.

Wheel Abrasion Experiment

Sojourner was involved with the Wheel Abrasion Experiment. This experiment consisted of imaging the reflectivity of a special rover wheel to see how abrasive the soil was. A low reflectivity meant abrasive soil. Also, at times, all the rover wheels except the special one were stalled to increase the abrasion of the special wheel digging into the soil.

Material Adherence Experiment

The Material Adherence Experiment is located at one of the corners of Sojourner's solar arrays. It has a solar cell which measures the amount of dust that settled on the solar cells. The less light, the more dust. There was also a mass sensitive crystal on it which measured the mass of the dust on the cell.


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