NASA's Mars Pathfinder

• Mars Pathfinder

  Mars Pathfinder (MESUR Pathfinder) was an American spacecraft that landed a base station with a roving probe on Mars in 1997. It consisted of a lander, renamed the Carl Sagan Memorial Station, and a lightweight (10.6 kg/23 lb) wheeled robotic Mars rover named Sojourner.
  
  
  
  
  Launched on December 4, 1996 by NASA aboard a Delta II booster a month after the Mars Global Surveyor was launched, it landed on July 4, 1997 on Mars's Ares Vallis, in a region called Chryse Planitia in the Oxia Palus quadrangle. The lander then opened, exposing the rover which conducted many experiments on the Martian surface. The mission carried a series of scientific instruments to analyze the Martian atmosphere, climate, geology and the composition of its rocks and soil. It was the second project from NASA's Discovery Program, which promotes the use of low-cost spacecraft and frequent launches under the motto "cheaper, faster and better" promoted by the then administrator, Daniel Goldin. The mission was directed by the Jet Propulsion Laboratory (JPL), a division of the California Institute of Technology, responsible for NASA's Mars Exploration Program. The project manager was JPL's Tony Spear.
  
  
  This mission was the first of a series of missions to Mars that included rovers, and was the first successful lander since the two Vikings landed on the red planet in 1976. Although the Soviet Union successfully sent rovers to the Moon as part of the Lunokhod program in the 1970s, its attempts to use rovers in its Mars probe program failed.
  
  
  In addition to scientific objectives, the Mars Pathfinder mission was also a "proof-of-concept" for various technologies, such as airbag-mediated touchdown and automated obstacle avoidance, both later exploited by the Mars Exploration Rover mission. The Mars Pathfinder was also remarkable for its extremely low cost relative to other unmanned space missions to Mars. Originally, the mission was conceived as the first of the Mars Environmental Survey (MESUR) program.
  
  

  • Mission objectives

  

  Sojourner rover on Mars on sol 22

• To prove that the development of "faster, better and cheaper" spacecraft was possible (with three years for development and a cost under $150 million).
• To show that it was possible to send a load of scientific instruments to another planet with a simple system and at one fifteenth the cost of a Viking mission. (For comparison, the Viking missions cost $935 million in 1974 or $3.5 billion in 1997 dollars)
• To demonstrate NASA's commitment to low-cost planetary exploration by finishing the mission with a total expenditure of $280 million, including the launch vehicle and mission operations.  

• Science experiments

• The Mars Pathfinder conducted different investigations on the Martian soil using three scientific instruments. The lander contained a stereoscopic camera with spatial filters on an expandable pole called Imager for Mars Pathfinder (IMP), and the Atmospheric Structure Instrument/Meteorology Package (ASI/MET) which acts as a Mars meteorological station, collecting data about pressure, temperature, and winds. The MET structure included three windsocks mounted at three heights on a pole, the topmost at about one meter (yard) and generally registered winds from the West.

• The Sojourner rover had an Alpha Proton X-ray Spectrometer (APXS), which was used to analyze the components of the rocks and soil. The rover also had two black-and-white cameras and a color one. These instruments could investigate the geology of the Martian surface from just a few millimeters to many hundreds of meters, the geochemistry and evolutionary history of the rocks and surface, the magnetic and mechanical properties of the land, as well as the magnetic properties of the dust, atmosphere and the rotational and orbital dynamics of the planet.
  Three cameras were onboard of the rover: Two black and white 0.3-megapixel cameras were located on the front (768 horizontal pixels × 484 vertical pixels configured in 4×4 pixel blocks), coupled with five laser stripe projectors, which enabled stereoscopic images to be taken along with measurements for hazard detection on the rover's path. A third camera with the same resolution but taking colour images was located on the back, near the APXS, and rotated by 90°. It provided images of the APXS's target area and the rover's tracks on the ground. The pixels of this colour camera were arranged in such a way, that out of the 16 pixel of a 4×4 pixel block, 12 pixel were sensitive to green, 2 pixel to red and 2 pixel were sensitive to infrared as well as blue. As all cameras had lenses made out of zinc-selenide, which blocks light below a wavelength of 500 nm, no blue light actually reached these "blue/infrared" pixels, which therefore recorded only infrared.
  All three cameras were CCDs manufactured by Eastman Kodak Company, and were controlled by the rover's CPU. They all had auto-exposure and capabilities for handling bad pixels, and the image parameters (exposure time, compression used, etc.) were included in the transmitted images as part of the image header. The rover could compress the front cameras' images using the block truncation coding (BTC) algorithm, but it could only do the same for the back camera's images only if the colour information was discarded. The cameras' optical resolution was sufficient to resolve 0.6 cm details across a 0.65 m range.
  
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