Mars Surveyor '98

The Mars Surveyor '98 program was comprised of two spacecraft launched separately, the Mars Climate Orbiter and the Mars Polar Lander. The two missions were to study the Martian weather, climate, water and carbon dioxide.

Mars Climate Orbiter

The Mars Climate Orbiter’s objectives included:

1. monitoring daily weather and atmospheric conditions

2. recording changes on the Martian surface due to wind and other atmospheric effects

3. determining temperature profiles of the atmosphere

4. monitoring the water vapor and dust content of the atmosphere

5. looking for evidence of past climate change.

The orbiter had two instruments to carry out these investigations; the Mars Climate Orbiter color imager used to acquire daily atmospheric weather images and high-resolution surface images and an infrared radiometer to allow measurement of the atmospheric temperature, water vapor abundance, and dust concentration. The orbiter would have served as a data relay satellite for the Mars Polar Lander and for other future NASA and international lander missions to Mars. Click here for an animation of the Mars Climate Orbiter.

The spacecraft’s propulsion fuel was hydrazine/nitrogen tetroxide. Spacecraft power was provided by three panels of solar cells on a 5.5-meter long single-wing solar array. Power was stored in nickel-hydride batteries. Communications with Earth were through a high-gain antenna for uplink and downlink, a medium-gain transmitting antenna, and a low-gain receiving antenna.

The Mars Climate Orbiter was launched on a Delta launch vehicle on December 11, 1998. The spacecraft reached Mars and executed an orbit insertion main engine burn on September 23, 1999. It then passed behind Mars and was to reemerge and reestablish radio contact with Earth ten minutes after the burn was completed.

Contact was never reestablished and no signal was ever received from the spacecraft. Findings of the failure review board indicate that a navigation error resulted from some spacecraft commands being sent in English units instead of being converted to metric units. This caused the spacecraft to miss its intended 140 - 150 kilometers altitude above Mars during orbit insertion. It instead entered the Martian atmosphere at about 57 kilometers.   The spacecraft would have been destroyed by atmospheric stresses and friction at this low altitude.

Mars Polar Lander

The Mars Polar Lander was to touch down on the southern polar layered terrain, less than 1000 km from the Martian south pole, near the edge of the carbon dioxide ice cap in Mars' late southern spring.

The Mars Polar Lander had a number of scientific instruments, including an instrument package comprised of a robotic arm and attached camera, an imager, a meteorology package, and a gas analyzer. In addition, the Mars descent imager was planned to capture images from parachute deployment (at about 8 km altitude) down to the landing. The Russian Space Agency provided a laser ranger package for the lander that would be used to measure dust and haze in the Martian atmosphere. A miniature microphone was also onboard to record, for the first time, sounds on Mars. Attached to the lander spacecraft were a pair of small probes, the Deep Space 2 Mars microprobes, which were to be deployed to fall and penetrate beneath the Martian surface when the spacecraft reached Mars.

During surface operations, communications would have been via the Mars Climate Surveyor orbiter which would have functioned as a relay to Earth. Power was provided during cruise phase by two solar array wings. After landing, solar arrays would have deployed. Power would have been stored in nickel-hydride batteries for peak load operations and nighttime heating.

At approximately six 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 further 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 three or four 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 pre-launch 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.

Deep Space 2 Microprobes

Named after polar explorers Roald Amundsen and Robert Falcon Scott , the Deep Space 2/Mars microprobes would have penetrated the surface of Mars near the south pole to a depth of up to 3 feet in order to search for evidence of water or ice.
	An aeroshell that encased the probe was designed to protect the probe from the heat of atmospheric entry. The aeroshell was made of a ceramic material designed to shatter on impact with the surface.
The probe itself consisted of two parts, an aft body and a forebody. The aft body was designed to remain above the surface after impact to provide radio communications. The forebody, or penetrator, was a long thin cylinder.  At the center of the cylinder were the drill, the soil sample chamber, and the heating and ice and water vapor detection equipment. Both parts of the probe were designed to withstand extreme decelerations.

Before deployment, the probes were mounted on the cruise stage of the Mars Polar Lander under the solar panels. The probes were each powered by two non-rechargeable lithium-thionyl chloride batteries. The batteries were expected to provide power for 1 to 3 days, but they may have lasted longer. Technology tests included survivability of small science instruments, and of the aeroshell and its accompanying components.

The two probes were to be separated from the cruise stage of the Mars Polar Lander by mechanical pyros. The probes had no active control or propulsion systems, but they were designed to passively orient themselves during free fall with the forebody front forward. On impact, the aeroshell would shatter, and the forebody would separate from the aft body and would penetrate 0.3 to 1 meter below the surface depending on the surface material. The impacts were planned to occur about 15 to 20 seconds before the Mars Polar Lander touchdown on December 3. Light travel time from Mars at that point was approximately 14 minutes. However, no signals were received from the probes after landing or over the following days. The reason for the probes' failure is not known. The total cost of development of the Deep Space 2 probes was $29.2 million.

Questions to think about:

• The two teams that were working on this mission were using different units of measurement. What does the loss of this spacecraft have to say about cultural biases towards using a common frame of reference?
• Are you learning the metric system in school (the one used by most people around the world)? Is it harder or easier to use than English measures?
• What do you think were the most important lessons to come out of the loss of the Mars Climate Orbiter, Mars Polar Lander and the Deep Space 2 missions?

Next... 2001 Odyssey (pg. 9 of 12)