Launch Date: 05 December 1996
The Mars Pathfinder will be the second of NASA's low-cost planetary Discovery missions. The mission will comprise a lander and a small surface rover, launched in late 1996. The mission is intended to develop technology and capabilities for low-cost landings on and exploration of the martian surface rather than being driven primarily by specific science goals
The scientific objectives are, however, quite broad including atmospheric entry science, and detailed characterization of the landing site by an advanced imaging system and a chemical analysis experiment mounted on the rover. The spacecraft will enter the martian atmosphere directly (i.e. without first going into orbit around the planet as Viking did) and, after losing most of its energy in the upper atmosphere, will land on Mars with the aid of parachutes, rockets and airbags. After landing, the spacecraft will unfold itself from within a tetrahedral structure that has three triangular solar panels (see picture above.)
The lander will first transmit the engineering and science data collected during entry and landing after which the stereo/color imaging system will obtain a panoramic view of the landing area and transmit it to Earth. Finally, the rover will be deployed to examine and measure the composition of individual rocks near the lander.
Much of the lander's task will be to support the rover by imaging rover operations and relaying data from the rover to Earth. Over 2.5 sq. meters of solar cells, in combination with rechargeable batteries, will power the lander. The main lander components are held in a tetrahedral shaped unit in the center of the three petals, with three low-gain antennas extending from three corners of the box and the camera extending up from the center. The rover is stowed against one of the petals.
A landing site has been chosen for the Mars Pathfinder in the Ares Vallis region.
The rover, "Sojourner" (previously known as Rocky IV), is a six-wheeled vehicle, 280 mm high, 630 mm long, and 480 mm wide with a ground clearance of 130 mm, mounted on a "rocker-bogie" suspension. The rover is stowed on the lander at a height of 180 mm. At deployment, the rover will extend to its full height and roll down a deployment ramp. The rover will be controlled by an Earth-based operator, who will use images obtained by both the rover and lander systems. Note that the time delay will be between 6 and 41 minutes depending on the relative position of Earth and Mars, requiring some autonomous control by the rover.
The on-board control system is built around an Intel 80C85 processor, selected for its low cost and resistance to single-event upsets from certain types of radiation. It is an 8- bit processor which runs at about 100,000 instructions per second (100 kips). Development to date indicates that this is ample for rover needs, provided that rover motion remains slow.The computer is capable of compressing and storing a single image on-board. The rover is powered by 0.2 square meters of solar cells, which will provide energy for several hours of operations per sol (1 Martian day = 24.6 Earth hours). Non-rechargeable lithium thionyl chloride (LiSOCl2) D-cell batteries provide backup. The rover is equipped with a black and white imaging system which will be used to image the lander in order to assess it's condition after touchdown. The goal is to acquire three black and white images spaced 120 degrees apart of the lander. Close-up images of any damaged areas may also be done. Images of the surrounding terrain will also be acquired to study size and distribution of soils and rocks, as well as locations of larger features. Imaging of the rover wheel tracks will be used to estimate soil properties.
The rover's performance will be monitored to determine tracking capabilities, drive performance, thermal behavior, and sensor performance. UHF Communications between the rover and lander will be studied to determine the effectiveness of the link between the rover and lander as the rover moves away from the lander. Assessments of rock and soil mechanics will be made based on abrasion of the wheels and adherence of dust. An alpha-proton-X-ray spectrometer (APXS) is on-board the rover to assess the composition of rocks and soil. Images of all samples tested will be transmitted to Earth. The primary objectives are scheduled for the first seven sols, all within about 10 meters of the lander. The extended mission will include longer trips away from the lander over about 30 sols.
The rover is primarily a technology experiment itself, designed to determine micro-rover performance in the poorly understood Martian terrain so that future rovers may be designed to be effective in navigating and moving about the surface of Mars. MFEX has three main mission objectives: technology experiments, science experiments and mission experiments.
Because of cost constraints, both the lander and rover have limited
redundancy. Also, the Martian environment is harsh, with temperatures averaging about 0 to -100 C (32 to -148 F) daily. Therefore, the surface mission is designed to achieve the important objectives in a relatively short time.
The rover is controlled by an Earth-based operator, but because of the time delay between Earth and Mars (variously from 6 to 41 minutes) some autonomy is needed in the rover. The direct communications link between the lander to Earth is limited to a few hundred bits per second. The landing site only faces Earth for 12 hours per day or less.
The operator on Earth views the work station with a stereo display of the lander's image of the terrain through three-dimensional glasses. The work station's software places an icon of the rover in the scene and the coordinates of the placement are determined. Those coordinates form the basis of the rover commands to traverse the surface. Other commands, which enable the rover to perform tasks, are interspersed with traverse commands.
The commands will be sent shortly after sun and Earth rise on Mars and are received first by the lander which stores them until notified by the rover it is ready to receive the data. The rover then stores the commands until ready for execution.
The rover control system features operator designation of targets and autonomous control to reach the targets and perform the tasks.
Like Viking, the Pathfinder lander will arrive at Mars packaged inside a space capsule-shaped entry vehicle. Hitting the thin upper atmosphere of Mars at more than 17,000 miles per hour (27,000 kilometers per hour), the entry vehicle's heat shield will slow the craft to 900 miles per hour (1,450 kilometers per hour) in about two minutes. An onboard computer will sense the slow-down in speed and then deploy a large parachute. The parachute can slow the lander down to about 155 miles per hour (250 kilometers per hour) in the rarified atmosphere of Mars, which is only 1/100th as dense as Earth's.
An onboard radar altimeter inside the lander will monitor the distance to the ground. At about 330 feet (100 meters) above the surface, the computer will inflate the air bags.
Seconds later, three solid rocket motors placed inside the top half of the entry vehicle above the lander will be fired. In approximately two seconds, the rockets will bring the lander to a stop some 40 feet (12 meters) above the Martian ground. The parachute will be released, and the lander, nestled inside its protective air bag cocoon, will fall to the ground, bouncing and rolling until it stops.
Within about an hour, the air bags will be deflated and partially retracted toward the lander. Pathfinder will then open its three metallic petals and stand itself right side up from any side that it happens to be lying on. The microrover, attached to the inside of one of the petals, will be exposed to the Martian terrain for the first time. After the lander camera has taken a photograph of its position on the Martian surface, engineers will instruct the rover to drive off and begin exploring the immediate surroundings.
See also the Pathfinder Landing Site Page.
Return to the Landing Site Catalog