Rob Manning’s spirits soared as never before on July 4, 1997, when NASA’s ground-breaking Pathfinder spacecraft bounded onto the surface of Mars, successfully delivering a small robotic rover called Sojourner. “There was an incredible rush,” recalled Manning, who served as chief engineer for the $265 million mission developed by NASA’s Jet Propulsion Laboratory. “There’s all these different emotions you go through. It’s not just the success — that it’s working. It’s also this wonderful feeling of discovery, of feeling like, ‘Oh my gosh. I’m on Mars, now.'”