Within six months of the announcement of the discovery of possible life on ancient Mars, three spacecraft will be on their way to the Red Planet. However, these spacecraft will not be a response to the discovery, but rather the first wave in a ten-year plan for robotic exploration of Mars.
       While a plan is already in place, NASA Administrator Dan Goldin acknowledged Wednesday that the discovery may force a revision in those plans, including moving up the date of a Mars sample return mission, if it can be scientifically justified.
       The armada begins this November, with the launch of Mars Global Surveyor from Cape Canaveral atop a Delta II rocket. The 665-kg (1,460-lb.) spacecraft is a partial replacement for the Mars Observer spacecraft, which failed shorly before arriving at Mars in August 1993.
       Mars Global Surveyor will cruise for 10 months before entering into polar orbit around Mars. after it achieves its final orbit around the planet in earl 1998, it will start a systematic study of the planet using its six on-board instruments, which include a high-resolution camera, magnetometer, laser altimeter, thermal emission spectrometer, and ultra-stable oscillator for radio science experiments.
       The following month, NASA will launch the Mars Pathfinder mission. One of the original Discovery-class low-cost missions, the small spacecraft will race ahead of Mars Global Surveyor and arrive at Mars on July 4, 1997.
       The spacecraft will then land on the planet, using a combination of parachutes and airbags to slow its descent and cushion its landing on the planet. The spacecraft carries three instruments -- a camera, an alpha proton x-ray spectrometer, and a meteorology package -- to study the planet.
       In addition to the instruments, Mars Pathfinder carries a microrover named Sojourner. The 16-kg (35-lb.) rover, named after abolitionlist Sojourner Truth in a student contest last year, will use the spacecrafts spectrometer to sample rocks and determine their chemical composition.
       Because Mars is too far away from Earth to allow for real-time navigation of the rover, Sojourner has its own autonomous navigation system that allows it to move around rocks and other obstacles and avoid any dangerous regions.
       While the Americans launch two spacecraft, Russia restarts its Mars exploration program with the Mars 96 mission. An all-purpose mission, the spacecraft includes an orbiter, two landers, and two surface penetrators.
       As part of the growing international cooperation among the world's space agencies, American and Russian scientists will be working on the Mars 96 project, and the Mars Global Surveyor spacecraft will help relay data from the Mars 96 surface spacecraft back to Earth using a dedicated relay mounted on the spacecraft.
       The next wave of Mars spacecraft will launch in 1998. They include Mars Surveyor '98 Orbiter, a follow-up mission to Mars Global Surveyor; Mars Surveyor '98 Lander; which is planned to be the first spacecraft to land on Mars's polar caps; and Planet B, the first Japanese mission to Mars.
       Future American missions are planned for the launch opportunities in 2001, 2003, and 2005, cumulating in 2005 with the launch of a sample return mission.
       Wednesday's announcement of possible life on ancient Mars may move the launch date of a sample return mission up by several years, however. NASA Administrator Goldin acknowledged that the sample return mission may be moved up if there is a scientific justification for it.
       "We may have to accelerate some activities," he said, saying a sample return mission could be moved up to as early as 2001.
       Goldin also supported international cooperation in future robotic missions to Mars. "I believe it [a sample return mission] will be a worldwide mission," he said.