In the human bid to explore the solar system, Mars has always been a critical destination. Orbiters, landers and robots are asking the same questions: Does the planet have water, and has it ever supported life?
The U.S. space program has put people in space and on the moon, helped build the International Space Station, and sent unmanned vehicles to Mars, Saturn and beyond. Here are a few highlights from the opening chapters of the human journey to the stars.