Exploration of the Red Planet has resumed nine years after the last Viking obiter transmitted data to Earth and 14 years after the last Viking lander sent information from the surface of Mars. On Nov. 7 Mars Global Surveyor was successfully launched from Cape Canaveral and Mars Pathfinder is scheduled to be sent aloft during a launch window extending from Dec. 2 to 31. Mars 96, a third probe, was launched from the Baikonur cosmodrome in Russia on Nov. 16, but it fell back to Earth after its fourth stage failed to ignite and put it on a trajectory to Mars. This probe contained an orbiter, two soft-landers and two surface penetrators.
Despite its launch a month later, Pathfinder is scheduled to reach Mars first. On July 4, 1997, this lander will enter Mars' atmosphere directly from its interplanetary trajectory rather than orbiting Mars first, as the Viking landers did. A parachute will begin slowing its descent. Then rockets will fire to slow it even more. Finally, air bags will be inflated around it to cushion the lander's final fall from a height of less than 100 feet. After bouncing and coming to rest, the air bags will be deflated and the top three "petals" of the tetrahedron that is the lander will open to allow deployment of its instruments.
One item in the lander's payload is a six-wheeled rover named Sojourner. Sojourner is two feet long, 1 ½ feet wide, 1 foot high, and weighs 22 pounds. It moves at just under 2 feet per minute. Sojourner's mission is to take pictures of its surroundings, test the soil structure, and carry out chemical analyses of the soil and rocks as it travels up to a few tens of yards from the lander. The duration of its primary mission is only 7 days. Scientists fear that the extreme range of temperatures to which the electronics will be subjected may cause it to cease functioning in this short time. If Sojourner operates longer, it will be used to make close-up images of any damage to the lander and to make images of the path made by the bouncing and tumbling lander in its initial contacts with the surface. If Sojourner performs exceptionally well in this extended mission, it may even be sent beyond the lander's horizon.
The lander has a primary mission lasting 30 days that includes imaging the Martian surface, measuring winds at several heights above the lander, measuring the atmospheric temperature, density and pressure, and measuring any magnetic field associated with the planet. For the first 7 days, though, it will devote much of its time to support of Sojourner's primary mission.
Mars Global Surveyor (MGS) will be captured in a Martian orbit as its retro-rockets fire for more than 20 minutes on September 11, 1997. Mars will capture MGS in a very elongated, 48-hour orbit. For about four months, each time MGS is closest to Mars, it will be slowed slightly by the thin atmosphere of the planet in a technique called "aerobraking."; This aerobraking will nearly circularize the orbit and will reduce the orbital period to about 2 hours. The final polar orbit will be used to map the surface for an entire Martian year of 687 Earth days -- over a complete cycle of seasons -- beginning about March 15, 1998. Cameras will image details as small as 6 to 10 feet across. A laser altimeter will map variations in the height of the planetary surface and a magnetometer will measure magnetic fields in the vicinity of the planet.
Lander and orbiter pairs are planned for 1998 and 2001. Additional future missions are under consideration, including a possible return with Martian samples in 2003 or 2005. The projected cost for each of these future missions is approximately $200 million, about $45 million more than the cost of the current missions.
Information gained from our neighbor Mars will help us understand more about the formation and evolution of the solar system and Earth.
