[3] As part of the Mars Surveyor '98 mission, a lander was sought as a way to gather climate data from the ground in conjunction with an orbiter.

NASA suspected that a large quantity of frozen water may exist under a thin layer of dust at the south pole.

In planning the Mars Polar Lander, the potential water content in the Martian south pole was the strongest determining factor for choosing a landing location.

[5] The primary objectives of the mission were to:[6] The Mars Polar Lander carried two small, identical impactor probes known as "Deep Space 2 A and B".

The probes were intended to strike the surface with a high velocity at approximately 73°S 210°W / 73°S 210°W / -73; -210 (Deep Space 2) to penetrate the Martian soil and study the subsurface composition up to a meter in depth.

[4][1][7] During the cruise stage, communications with the spacecraft were conducted over the X band using a medium-gain, horn-shaped antenna and redundant solid state power amplifiers.

With the orbiter lost on September 23, 1999, the lander would still be able to communicate directly to the NASA Deep Space Network through the Direct-To-Earth (DTE) link, an X band, steerable, medium-gain, parabolic antenna located on the deck.

Another two auxiliary solar arrays were located on the side to provide additional power for a total of an expected 200 watts and approximately eight to nine hours of operating time per day.

[4][1] While the Sun would not have set below the horizon during the primary mission, too little light would have reached the solar arrays to remain warm enough for certain electronics to continue functioning.

Traveling at 6.9 kilometers per second, the entry capsule entered the Martian atmosphere at 20:10:00 UTC, and was expected to land in the vicinity of 76°S 195°W / 76°S 195°W / -76; -195 (Mars Polar Lander) in a region known as Planum Australe.

Three minutes after entry, the spacecraft had slowed to 496 meters per second, signaling an 8.4-meter polyester parachute to deploy from a mortar, followed immediately by heat shield separation and MARDI powering on while 8.8 kilometers above the surface.

When the spacecraft had slowed to 80 meters per second, one minute after parachute deployment, the lander separated from the backshell and began a powered descent at 1.3 kilometers aloft.

Below 40 meters, the radar would become unreliable by raised dust and was switched off already at that height; for the final seconds, the thrust would be controlled by inertial sensors.

[4][6][1][7] Lander operations were to begin five minutes after touchdown, first unfolding the stowed solar arrays, followed by orienting the medium-gain, direct-to-Earth antenna to allow for the first communication with the NASA Deep Space Network.

On the following days, the spacecraft instruments would be checked by operators and science experiments were to begin on December 7 and last for at least the following 90 Martian Sols, with the possibility of an extended mission.

[4][6][1][7] On December 3, 1999, at 14:39:00 UTC, the last telemetry from Mars Polar Lander was sent, just prior to cruise stage separation and the subsequent atmospheric entry.

"[18] "A magnetic sensor is provided in each of the three landing legs to sense touchdown when the lander contacts the surface, initiating the shutdown of the descent engines.