The Martian Wikia

"Houston, Be Advised: Rich Purnell is a Steely-Eyed Missile Man."

Rich Purnell is a physicist and rocket scientist who works for NASA.

He was the one to figure out that instead of sending supplies to Mars for Mark so he could stay alive until the scheduled landing of Ares IV they could use Earth's gravity to sling shot the Hermes and the Ares 3 crew back to Mars in order to pick up Mark Watney. This is known as the Rich Purnell Maneuver and was revealed during the meeting for 'Project Elrond'.

Rich is autistic, as confirmed by the author.