The Mars Pathfinder is one of two NASA low-cost planet Discovery missions. The purpose of this mission, which was launched on December 5, 1996 aboard a Delta II launch vehicle, is to develop technologies and capabilities for low-cost exploration of the Martian surface. This means that this is the first NASA planetary surface exploration mission to the designed to adapt to different aspects of planetary exploration instead of being designed around specific scientific goals.
The scientific parameters of this mission are broad and include many of the aspects surrounding the landing of the rover on the surface of the Red planet. Unlike the Viking missions, which had as its goal atmospheric analyzes and soil analyzes in search for biological traces, the current mission to Mars includes atmospheric entry science and landing site characterization by an imaging system mounted on the landing pod. In this aspect, the Pathfinder mission design allows for last minute modifications as needed by instantaneous changes on the surface of the planet. Although there are scientific goals to be accomplished during the mission, the major focus of this mission is the adaptability of the rover to the Martian surface for its exploration.
The Mars Pathfinder mission is composed of two modules which cooperate for the conclusion of the mission. In contrast to the Viking missions, neither of the Pathfinder modules will remain in orbit to photograph the planet. All the images of this mission will be surface images. The two modules comprising the payload sent to Mars are a lander and a rover. This payload will be delivered to the Martian atmosphere in a space capsule-shaped vehicle similar to the package design used by the Viking missions.
Unlike the Viking missions, the payload of the Pathfinder mission will not enter a Martian orbit before commencing the landing procedures. On board instruments will detect entry into the atmosphere by the slowing down of the vehicle. This vehicle slows down, because of friction between the Martian atmosphere and the vehicle's heat shield. The friction between the atmosphere and the and the heat shield will decrease its velocity from 27,000 km per hour to 1,450 km per hour in a time period of two minutes. The decrease in vehicle velocity triggers the deployment of a parachute, which will decrease the velocity of the Pathfinder package to 250 km per hour. The other landing mechanism, air bags, will deploy to finish the landing process when the vehicle is 100 meters over the landing site. The air bags will cushion the landing of the capsule on the surface and in theory will minimize structural damage to the lander.
To aid in the landing of the capsule inside the air bag cocoon, a retrorocket will bring the velocity of the package to 0 km/hour at a height of 12 meters above the surface. At this moment another parachute deploys and the lander falls to the ground. Once on the ground, the lander module deploys and the rover leaves the package.
Throughout the duration of the mission, the major task of the lander will be to provide support for the rover. This means that this unit will image rover operations and function as a relay between the rover and mission control. Although part of the system is designed to function autonomously as a result of a 6 to 41 minute transmission delay between the Earth and Mars, the rover operation images generated by the lander are essential in providing the rover operator at mission control with references. Theses references will then be used to direct rover movements on the Martian surface.
The heart of the mission, the lander, will be powered by 2.5 sq. Meters of solar cells and rechargeable batteries. Solar power is also used on the rover in combination with non-rechargeable lithium thionyl chloride D-cell batteries for back up. The solar panels allow both units of the Mars Pathfinder to power up all systems for daytime operation.
The communication window of 12 hours between the Earth and the Mars forces all instructions for autonomous operation to be among the first things transmitted to the lander. These instructions are then relayed to the rover via UHF signals. Once all instructions are stored in both the lander and the rover, the Earth controlled operation of the rover begins.
The UHF communication system to be used between the lander and the rover will be thoroughly tested during the mission, because of its relative low cost and its possible employment in future missions to Mars. This system will be the life line of the rover and will be essential to it when exploration missions of over 30 sols begin. Failure of this system or lack of range will loose the rover.
The mission layout of the Mars Pathfinder has two major goals. The first goal is to continue the scientific experiments begun by the Viking lander in the late 1970's. This refers mostly to the analyzes of soil composition and to soil tests in search for biological traces. Also, in the scientific goal section of the mission is the analyzes of the atmosphere and of the seismic movements of the crust. The analyzes of these areas is the continuation of the experiments carried out by both Viking 1 and 2 in these fields.
The other part of the goals of the mission are the technical goals of it. These goals include the completion of all of the scientific goals plus some engineering goals. During the mission, the lander module will provide mission control with visual information to analyze the performance of the rover. Other technical information such as soil resistance, performance of the suspension system, and general movement of the vehicle will be relayed to Earth through the lander from instruments aboard the rover. The data gathered from the rover will then be analyzed and used in the design and possible construction of an efficient vehicle for the Martian surface.
All the questions surrounding the Mars Pathfinder mission, such as rover efficiency, will be answered on July 4, 1997 when Pathfinder reaches Mars.