Some of the most sophisticated robots ever built are currently on missions to explore our solar system - and more are being designed and built to extend our reach farther from Earth. These unmanned explorers travel to remote and hostile environments where the secrets of our origins and destiny are hidden.
Robotic explorers must be able to endure long journeys and long flights in the vacuum of space, yet carry the power and tools to retrieve the scientific data that make the mission worthwhile. Mission plans are structured to build on success to enable the next generation of robots to go farther.
The wagon-sized Sojourner rover of the 1997 Mars Pathfinder mission led to the development of the sturdy twin Mars Exploration Rovers - Spirit and Opportunity - who will be replaced on the Red Planet by the next-generation Mars Science Laboratory, a larger, more powerful rover. Each mission, combined with data from orbiting satellites, has revolutionized our understanding of the Martian climate and will help us understand if humans can ever safely live on Mars.
Some missions are developed just to prove a technology. NASA's Deep Space 1 provided a successful test of highly-efficient ion engines which are now powering NASA's Dawn on its long journey to asteroid Vesta and the dwarf planet Ceres.
Robotic missions are structured over decades of planning to complement each other. Flyby spacecraft conduct the initial reconnaissance, followed by orbiters and, in many cases landers. Sometimes spacecraft are deliberately crashed into a planet or object, but only after careful consideration of potential contamination.
This layered approach is what put humans on the Moon. Ranger probes perfected the trajectory, Ranger impactors worked out some of the kinks and provided the first detailed photographs and Surveyor robots proved the landing technologies. The mission successes led to Apollo 11 -- America's historic Moon landing in 1969.
Current Mars exploration efforts are using the same techniques with 21st century machines.
In the outer solar system, the initial flybys of the Pioneer 10 and 11 and Voyager 1 and Voyager 2 , led to the advanced Galileo and Cassini-Huygens missions that revealed Jupiter, Saturn and their intriguing moons in stunning detail.
Future solar system exploration missions will experience an even wider range of possible conditions, from the comparatively benign environment of Mars, to the intense radiation environment around Jupiter's Europa, to the intense heat and crushing pressure within the atmosphere of Venus.