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?
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Timeline
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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.