Mars Pathfinder was an American robotic 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, wheeled robotic Mars rover named Sojourner, the first rover to operate outside the Earth–Moon system. The mission terminated in 1998.
Launched on December 4, 1996, by NASA aboard a Delta II booster a month after the Mars Global Surveyor, it landed on July 4, 1997, on Mars's Ares Vallis. The region is called Chryse Planitia, a part of the Oxia Palus quadrangle. The lander carried a series of scientific instruments to analyze the Martian atmosphere, climate, and geology. Analysis of the rocks and soil was a key objective. It was the second project from NASA's Discovery Program, which promotes the use of low-cost spacecraft and frequent launches under the "cheaper, faster, and better" motto promoted by 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 Mars 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 program failed.
Mission objectives
The mission was originally conceived as the first of the Mars Environmental Survey (MESUR) program. Mars Pathfinder was "proof-of-concept" for various scientific technologies, such as airbag-mediated touchdown and automated obstacle avoidance, both later exploited by the Mars Exploration Rover mission. It also achieved low costs relative to other robotic space missions to Mars, a MESR goal.
To prove that the development of "faster, better and cheaper" spacecraft was possible (with three years for development and a cost under $150 million for the lander, and $25 million for the rover). 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 acted 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 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.
The rover was equipped with three CCD cameras, all manufactured by Eastman Kodak Company and controlled by the rover's CPU. The two front-facing monochrome cameras served navigation purposes and were coupled with five laser stripe projectors for stereoscopic hazard detection. These front cameras had a resolution of 484 vertical by 768 horizontal pixels, and an optical resolution capable of discerning details as small as across a range of . Images from these cameras could be compressed using the block truncation coding (BTC) algorithm.
The third camera, situated at the rear near the APXS, was used for color imaging. It shared the resolution of the front cameras but was rotated 90 degrees to capture images of both the APXS target area and the rover's tracks. This rear camera featured a 4x4 pixel block with specific color sensitivities: 12 pixels for green, two for red, and two for infrared. All cameras employed lenses made of zinc selenide, which blocks light wavelengths below 500 nm; as a result, the blue/infrared pixels effectively detected only infrared light. Each camera had auto-exposure and bad-pixel handling functions. Image parameters, such as exposure time and compression settings, were included in the transmitted image headers. If BTC compression was to be used on the rear camera, the color information would need to be discarded.
Pathfinder lander
Imager for Mars Pathfinder (IMP), (includes magnetometer and anemometer)
The IMP had a set of filters designed to record surface and atmospheric phenomena. There were two cameras, or eyes, allowing for stereoscopic imagery, with the set of filters being slightly different between them. +IMP filter characteristicsEye and FilterCenter Wavelength (nm)Bandwidth (nm)CategoryL044326Stereo, GeologyL567120Stereo, GeologyL680221GeologyL785834GeologyL889841GeologyL993127Stereo, Ranging, GeologyL10100329GeologyL1196831Stereo, Ranging, GeologyR044326Stereo, GeologyR567120Stereo, GeologyR675219GeologyR860021GeologyR953130Stereo, Ranging, GeologyR1048027GeologyR1196730Stereo, Ranging, GeologyL14505SolarL28836SolarL39255SolarL49355SolarR16705SolarR294644SolarR39365SolarR49895Solar
Atmospheric and meteorological sensors (ASI/MET).
The ASI/MET recorded temperature, pressure and wind data, during entry and descent, and once on the surface. It also housed electronics for sensor operation and data recording.
Landing site The landing site was an ancient flood plain in Mars's northern hemisphere called "Ares Vallis" ("the valley of Ares", the ancient Greek equivalent of the ancient Roman deity Mars) and is among the rockiest parts of Mars. Scientists chose it because they found it to be a relatively safe surface to land on and one that contained a wide variety of rocks deposited during a catastrophic flood. After the landing, at , succeeded, the lander received the name The Carl Sagan Memorial Station in honor of the astronomer. (See also List of extraterrestrial memorials)
Entry, descent and landing
The entire entry, descent and landing process was completed in four minutes. Mars Pathfinder entered the Martian atmosphere and landed using an innovative system involving an entry capsule, a supersonic parachute, followed by solid rockets and large airbags to cushion the impact. The entry was direct and retrograde, from a hyperbolic trajectory at using an atmospheric entry aeroshell (capsule) that was derived from the original Viking Mars lander design. The aeroshell consisted of a back shell and a specially designed ablative heatshield to slow to where a supersonic disk-gap-band parachute was inflated to slow its descent through the thin Martian atmosphere to .
The lander's on-board computer used redundant accelerometers to determine the timing of the parachute inflation. Twenty seconds later the heatshield was pyrotechnically released. Another twenty seconds later the lander was separated and lowered from the backshell on a bridle. When the lander reached above the surface, a radar was used by the on-board computer to determine altitude and descent velocity. This information was used to determine the precise timing of the landing events that followed.
Once the lander was above the ground, airbags were inflated in less than a second using three gas generators. The airbags were made of four inter-connected multi-layer vectran bags that surrounded the tetrahedron lander. They were designed and tested to accommodate grazing angle impacts as high as . However, as the airbags were designed for no more than about vertical impacts, three solid retrorockets were mounted above the lander in the backshell. These were fired at above the ground. The lander's on-board computer estimated the best time to fire the rockets and cut the bridle so that the lander velocity would be reduced to about zero between above the ground. After 2.3 seconds, while the rockets were still firing, the lander cut the bridle loose about above the ground and fell to the ground.
The rockets flew up and away with the backshell and parachute (they have since been sighted by orbital images). The lander impacted at and limited the impact to only 18 G of deceleration. The first bounce was high and the lander continued bouncing for at least 15 additional bounces (accelerometer data recording did not continue through all of the bounces).
Once the lander stopped rolling, the airbags deflated and retracted toward the lander using four winches mounted on the lander "petals". Designed to right itself from any initial orientation, the lander happened to roll right side up onto its base petal. Eighty-seven minutes after landing, the petals were deployed with Sojourner rover and the solar panels attached on the inside.
First day on Mars
The lander arrived at night at 2:56:55 Mars local solar time (16:56:55 UTC) on July 4, 1997. The lander had to wait until sunrise to send its first digital signals and images to Earth. The landing site was located at 19.30° north latitude and 33.52° west longitude in Ares Vallis, only southwest of the center of the wide landing site ellipse. During Sol 1, the first Martian solar day the lander spent on the planet, the lander took pictures and made some meteorological measurements. Once the data was received, the engineers realized that one of the airbags had not fully deflated and could be a problem for the forthcoming traverse of Sojourners descent ramp. To solve the problem, they sent commands to the lander to raise one of its petals and perform additional retraction to flatten the airbag. The procedure was a success and on Sol 2, Sojourner was released, stood up and backed down one of two ramps.
Rover operations
Sojourner components
Imaging system (three cameras: front B&W stereo, 1 rear color) Laser striper hazard detection system Alpha Proton X-ray Spectrometer (APXS) Wheel Abrasion Experiment Materials Adherence Experiment Accelerometers
Sojourner deployment The Sojourner rover departed from the lander on Sol 2, after its landing on July 4, 1997. As the next sols progressed it approached some rocks, which the scientists named "Barnacle Bill", "Yogi", and "Scooby-Doo", after famous cartoon characters. The rover made measurements of the elements found in those rocks and in the martian soil, while the lander took pictures of the Sojourner and the surrounding terrain, in addition to making climate observations.
The Sojourner is a six-wheeled, long vehicle, wide, tall and weighing . Its maximum speed reached . Sojourner travelled approximately in total, never more than from the Pathfinder station. During its 83 sols of operation, it sent 550 photographs to Earth and analyzed the chemical properties of 16 locations near the lander. (See also Space exploration rovers)
Sojourners rock analysis
The first analysis on a rock started on Sol 3 with Barnacle Bill. The Alpha Particle X-ray Spectrometer (APXS) was used to determine its composition, the spectrometer taking ten hours to make a full scan of the sample. It found all the elements except hydrogen, which constitutes just 0.1 percent of the rock's or soil's mass.