Mission profile

The Mars Polar Lander and the attached Deep Space 2 probes were launched on a Delta launch vehicle on January 3, 1999. After an 11-month cruise, the Mars Polar Lander reached Mars on December 3, 1999.

At approximately 6 minutes before atmospheric entry, an 80-second thruster firing was to turn the craft to the proper orientation.  The upper cruise stage was to be jettisoned and, about 18 seconds later, the microprobes were to be dropped. Due to complete lack of future communication, it is not known at this time whether any of these steps were executed as designed. The Mars Surveyor '98 Program spacecraft development cost $193.1 million dollars. Launch costs are estimated at $91.7 million dollars and mission operations at $42.8 million dollars.

A design flaw may have been the cause of the failure of the Mars Polar Lander. Previous U.S. unmanned lunar and Mars landers used radar to sense when they were 3 or 4 meters above the surface and to shut off their engines then. For this mission, JPL decided to equip each of the lander's legs with a switch to sense when the leg was starting to flex upward after hitting the surface. As soon as any of the three legs sensed this, the engines would have been turned off. It was discovered that when the landing legs first swing down to lock into position after the heat shield is released, they do this with sufficient force that the flexible part of the leg "bounces" slightly upwards again -- triggering the contact switch and setting a crucial "bit" in the craft's computer memory which indicates that ground contact has occurred.

Apparently it was never detected during the Mars Polar Lander's prelaunch tests because the leg fold-down procedure was tested by a team separate from the team that tested the craft's behavior during the remainder of the landing sequence. As soon as it switched over to its own guidance, the spacecraft would have begun monitoring the status of the "ground-contact" bit. It would have then concluded that it had already landed and immediately switched the engines off, falling the remaining 40 meters to the surface of Mars. While we will never know for certain - due to no telemetry - this is the single most likely cause for the failure according to the NASA Failure Review Board.

Questions to think about:

• What might be some of the benefits and hazards of landing near the south pole region?
• Some scientists believe the terrain in this region is unstable. Think of some reasons why this might be so.
• What missions could you design that could test the stability of the terrain without great expense?

Mars Surveyor '98: Deep Space 2 Microprobes