Jet Propulsion Laboratory (U.S.). Mars Pathfinder Project.

The Mars Pathfinder was launched to Mars at 1: 58 am. EST on December 4, 1996 after a twenty-year hiatus of lander missions to Mars. It was the first spacecraft ever to send a robotic rover out to independently explore the Martian landscape. Mars Pathfinder also was the second of NASA's planetary Discovery missions designed to foster low-cost spacecraft with highly focused science objectives.

The Mars Pathfinder (formerly known as the Mars Environmental Survey, or MESUR, Pathfinder) was launched atop a McDonnell Douglas Delta II 7925 from the launch complex 17B at Cape Canaveral, Florida. The Delta II Lite launch vehicle was equipped with nine strapped-on solid-rocket boosters an a Star 48 PAM-D upper third stage booster.

The basic design of the Mars Pathfinder spacecraft involved an aeroshell, parachute, solid rocket, and an air bag entry, descent and landing system. It contained a self-righting tetrahedral lander with heater units. It also carried a free-ranging microrover. The Integrated Attitude and Information Management System (AIM) handled the command and data for the spacecraft.

Pathfinder utilized an R6000 computer with a VME bus. The MPE (Mars Pathfinder) computer had a 32-bit architecture that executed anywhere from 2.5 to 20 million instructions per second (mips) for computation. The mass memory the computer could hold 128 million bytes. Power was received in the cruise stage and lander through gallium arsenide/germanium solar cells. Cruise power was 250-460 watts with 1080-watt hours of daily energy available on the surface.

For surface operations, the telemetry rate via the High Gain Antenna/X-band was 1.2 to 12kbps for the 70-m Deep Space Network antenna. The command rate via HGA/X-band was 250b/s. The Deep Space Network's 70-meter (230-foot) and 34-meter (110-foot) antennas in Madrid, Spain were used to support entry commuications.

For propulsion, the spacecraft carried monopropellant hydrazine used for cruise and eight 4.4 Newton thrusters.

The robotic rover official name was Microrover Flight Experiment, (later named Sojourner, after African-American Civil War abolitionist Sojourner Truth; who lived during the tumultuous era of the American Civil War, in 1861-1865). Sojourner weighed less than 14kg (31 lbs.) including its mounting and deloyment equipment. Its mobile mass was 11.5kg (25 lbs.) including the Alpha Proton X-ray Spectrometer (APXS) deployment mechanism and APXS instrument. The Lander-Mounted Rover Equipment Mass was 4.5 kg (10 lbs.) including an ultra-high frequency (UHF) modem and support structure.

The onboard autonomus navigation utilized laser striping to detect obstacles. A six wheel, rocker-bogie suspension was chosen for this vehicle. A UHF link with the lander provided command and telemetry for the rover. Among its payload were three cameras, the APXS instrument, and the APXS deployment mechanism. The rover was able to get power via 0.25-square-meter solar panels, which produced a peak power of 16 watts hours. Its primary battery provided 150-watt hours. Included were there radioisotope heater units necessary for temperature control. Its computer was a 0.5 kg. 80c85 that executed 0.1 mips with a 0.5 megabyte RAM mass storage. Surface operation was expected to occur from 10 a.m. to 2 p.m. each Martian day.

The rover was controlled remotely from Earth. There was a workstation with a stereo display, a sort of 3-D display where images of the surrounding terrain taken from the lander were viewed.

The cruise stage was jettisoned 30 minutes before atmospheric entry trajectory at 26,460 kilometers per hour (16,600 miles per hour) and a mean flight path of 14.2 degrees. The lander took atmospheric measurements as it descented. The entry vehicle's heat shield slowed the craft to 400 m/s in about 160 seconds. A 12.5-meter billowing parachute was deployed at that time, slowing the craft to about 70 m/s. The heat shield was released 20 seconds after parachute deployment, and the bridle, a 20-meter long braided Kevlar tether, deployed below the spacecraft.

The lander separated from the backshell and slid down to the bottom of the bridle over about 25 seconds, at an altitude of about 1.6-km. The radar altimeter acquired the ground and about 10 seconds before landing, four air bags inflated in about 0.3 seconds forming a 5.2 meter diameter protective 'ball' around the lander. Four seconds later at an altitude of 98 meters, the three solid rockets, mounted in the back-shell, fired to slow the descent and about two seconds later the bridle was cut 21.5 meters above the ground, releasing the airbag-encased lander.

The lander dropped to the ground in 3.8 seconds impacted at a velocity of 18 m/s, approximately 14 m/s vertical and 12 m/s horizontal. Pathfinder rebounded about 12 meters (40 feet) into the air and bounced at least another 15 times before coming to rest approximately 2.5 minutes after impact and about 1 km from the intitial impact site.

After landing, the airbags deflated and retracted. Pathfinder opened its three metallic triangular solar panels (petals) 87 minutes after landing. The lander first transmitted the engineering and atmospheric science data collected during entry and landing, the first signal being received at Earth at 2:34 p.m. EDT. The imaging system obtained views of the rover and immediate surroundings and a panoramic view of the landing area and transmitted it to Earth.

The landing site, Ares Vallis, was chosen because scientists believe it was a relatively safe surface to land on and contained a wide variety of rocks washed down into this flood basin during a catastrophic flood. During its exploration of the surface, Sojourner did rely on the lander primarily for communications with Earth and for imaging support. After some maneuvers to clear an airbag out of the way, ramps were deployed and the rover, stowed against one of the petals, rolled onto the surface on 6 July 1997 at about 1:40 a.m. EDT. This began the exploration of the Martian northern lowlands.

The Pathfinder Lander and the Sojourner Rover were great successes in July and August 1997. During its initial thirty-day mission, the lander returned 2.3 gigabits of data and 16,500 images. Sojourner returned 550 images. On September 27, 1997, communication was lost with the Pathfinder, after meeting the August predictions that its battery would be the first thing to fail. Pathfinder had a design lifetime of thirty days, Sojourner of seven days, Both exceeded expectations.

The Mars Pathfinder mission cost approximately $265 million including launch and operations. Development and construction of the lander cost $150 million and the rover about $25 million.

Missions operations for Mars Pathfinder were conducted at the Jet Propulsion Laboratory; Dr. Matthew Golombek was project scientist; John Wellman was MPF Science and Instruments Manager and Tom Tomey was Science and Instrument System Engineer. Science data, both raw and processed, was transferred after a period of validation to NASA's Planetary Data System.

From the description of Mars Pathfinder Science and Instruments Design Test Documents Collection, 1993-1997. (Jet Propulsion Laboratory Library and Archives). WorldCat record id: 733102092