Mars - Missions To Mars

After the Moon the planet Mars was the destination of choice during the early days of space travel. The Soviet Union was particularly eager to reach the Red Planet before the United States. A historical log of all Mars missions is presented in Table 7.1.

Many Failures

Historically, spacecraft have had a difficult time making it to Mars in working order and staying that way. As shown in Table 7.1, more than half of the missions intended for Mars have failed for one reason or another. Some were plagued by launch problems, while others suffered malfunctions during flight, descent, or landing.

Mars missions undertaken during the 1960s by the former Soviet Union were particularly trouble-prone. All six of them failed. Although the next decade showed some improvement, little usable data were obtained from the spacecraft that reached their destination. The one attempt to reach Mars by the Russian space agency, in 1996, failed when the spacecraft was unable to leave Earth orbit.

In contrast to the Soviet Union, most NASA Mars missions conducted during the 1960s achieved their objectives. There was also notable success over the next decade with the Viking spacecraft. There was a long lull after that in NASA's Mars exploration program.

During the 1990s NASA launched five separate missions to Mars. Their names were Mars Observer (1992), Mars Global Surveyor (1996), Mars Pathfinder (1996), Mars Climate Orbiter (1998), and Mars Polar Lander (1999). Only two of the missions were successful (Mars Global Surveyor and Mars Pathfinder). The other spacecraft were lost on arrival.

NASA lost contact with the Mars Observer just before it was to go into orbit around Mars. It is believed that some kind of fuel explosion destroyed the spacecraft as it began its maneuvering sequence. The Observer carried a highly sophisticated gamma-ray spectrometer designed to map the Martian surface composition from orbit. Failure of the mission resulted in a loss estimated at $1 billion. This was by far the most expensive of NASA's failed Mars missions.

In June 1999 the Mars Climate Orbiter was more than sixty miles off-course when it ran into the Martian atmosphere and was destroyed. The loss of the $85 million spacecraft was particularly embarrassing for NASA, because it was due to human error. An investigation revealed that flight controllers had made mistakes doing unit conversions between metric units and English system units. This resulted in erroneous steering commands being sent to the spacecraft. Outside investigators complained that the problem was larger than some mathematical errors. They blamed overconfidence and poor oversight by NASA management during the mission.

NASA's embarrassment deepened a few months later when the Mars Polar Lander was lost. The loss was attributed to a software problem that caused the spacecraft to think it had touched down on the surface even though it had not. The computer apparently shut down the engines during descent and let the spacecraft plummet at high speed into the ground, where it was destroyed. The cost of the failed spacecraft was estimated at $120 million.

The Polar Lander also carried a $30 million technology package known as Deep Space 2. Deep Space missions are part of a JPL program called New Millennium. The program was started during the mid-1990s to flight-test new technologies for possible use in future missions. For example, the Deep Space 1 mission conducted in 1998 included the test of an ion engine while a spacecraft was orbiting the sun. In-flight testing of experimental devices in space is preferable to conventional laboratory testing because space conditions are difficult to simulate on the ground.

The Deep Space 2 package was comprised of two small probes, each weighing about ten pounds. The probes were packed with miniaturized robotic instruments that were going to be tested under the harsh conditions on Mars. The probes were designed to impact the ground at a high rate of speed and penetrate beneath the sandy surface. Tiny sampling instruments were to gather soil for analysis of water content. The probes were equipped with data relays to transmit the results to the computer aboard the Global Surveyor already in orbit around the planet.

NASA hoped that successful operation of the micro-instrument packages would lead to development of micro-spacecraft. These small compact spacecraft would be much cheaper to build than conventional spacecraft and could be sent out in fleets to conduct scientific investigations. The loss of Deep Space 2 was a setback for the program. However, in 2004 NASA intends to test micro-components as part of another New Millennium project called Space Technology 5.