Mars Pathfinder, a NASA Discovery program mission designed to deliver a lander, camera and instrument-laden rover to the Martian surface on July 4, 1997, has successfully completed an initial series of engineering tests intended to validate the spacecraft's unique atmospheric entry, descent and landing techniques.
Mars Pathfinder will employ a new and unconventional approach to placing a lander on the surface of Mars, in keeping with NASA's new "faster, better and cheaper" philosophy of planetary exploration, said Tony Spear, Pathfinder project manager at NASA's Jet Propulsion Laboratory.
"This series of diverse tests has given us great confidence that the spacecraft will arrive safely and securely on Mars," Spear said. "A truly exciting scientific mission will then be ready to unfold."
The Viking 1 and 2 Mars landers of the mid-1970s used a complex, computer-controlled liquid retrorocket system to achieve a soft landing at about 8 kilometers per hour (5 miles per hour). In contrast, the smaller, tetrahedral-shaped Pathfinder lander will instead use a combination of parachutes, solid rockets and inflatable air bags to perform a safe, relatively hard landing of about 56 kilometers per hour (35 miles per hour).
Recent parachute drop stability tests were performed by Pioneer Aerospace of Windsor, Conn., in the desert near Yuma, Ariz. These tests successfully demonstrated the parachute configuration that will be used to bring the lander gracefully through the thin Martian atmosphere, said Ann Mauritz, JPL lead subsystem engineer.
Another element of the spacecraft's descent subsystems, the solid rocket motors, were tested at the China Lake Naval Weapons Center in Ridgecrest, Calif. These tests involved dropping a simulated lander on a parachute from a helicopter and then firing three prototype solid rockets to further slow the craft's fall toward the surface.
The tests went just as predicted, said Dr. Les Compton, JPL lead subsystem engineer, with the simulated lander essentially coming to a dead stop in mid-air while at the same time maintaining a stable orientation with respect to the ground.
Full-scale rocket prototypes, recently tested by Thiokol Corporation at Elkton, Md., will be used in full-scale subsystem tests to be carried out at China Lake later this summer.
Pathfinder's landing will be cushioned by four large air bags attached to the outside of each of the lander's four metallic exterior "petals." The air bag-based soft landing was recently demonstrated by the air bag designers, ILC Dover of Frederica, Del., inside a 36.5-meter (120-foot) vacuum chamber at the NASA Lewis Research Center's Plum Brook Station near Sandusky, Ohio. The vacuum chamber provides a way to simulate the very thin atmosphere of Mars, and the tests demonstrated the viability of the air bag design in softening the force of the impact on the lander and its delicate payload.
The air bag was dropped from a height of 21 meters (70 feet) onto a 12-meter (40-foot) platform containing many large rocks similar to those found on Mars, said Tom Rivellini, JPL lead subsystem engineer.
"Initial full-scale prototype drop tests were very successful," Rivellini said. "Engineers were able to test several air bag fabric construction techniques simultaneously. The tests showed that air bags constructed of a double-layered fabric will be necessary to provide a sufficiently rugged cushioning effect." A second phase of prototype drop testing later this year will demonstrate the durability of the new double-layered air bags at even higher impact levels.
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 27,000 kilometers per hour (17,000 miles per hour), the entry vehicle's heat shield will slow the craft to a relatively paltry 1,450 kilometers per hour (900 miles per hour) in about two minutes. An onboard computer will sense the slow-down in speed and then eject a large parachute. The parachute can slow the lander down to about 250 kilometers per hour (155 miles per hour) in the rarified atmosphere of Mars, which is only 1/100th as dense as Earth's atmosphere.
An onboard radar altimeter inside the lander will monitor the distance to the ground. At about 100 meters (330 feet) above the surface, the computer will inflate the air bags.
Seconds later, three 3/4-ton-thrust 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 dead stop some 12 meters (40 feet) 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 decide which exit ramp the rover should roll down and instruct it to drive off and begin exploring the immediate surroundings, part of an ancient Martian flood plain known as Ares Vallis.
Scheduled for launch in December 1996, Mars Pathfinder is part of a new generation of low-cost spacecraft with highly focused science goals designed to explore planets and other celestial bodies of the solar system. Discovery missions are capped at $150 million each and must be developed and readied for launch within 36 months.
Mars Pathfinder is managed by the Jet Propulsion Laboratory for NASA's Office of Space Science, Washington, D.C.
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