NASA's International Space Apps Challenge convenes global citizens through open data to solve mission challenges. It is NASA's program to spur innovation by fulfilling mandates to open data. Since 2012, the challenge has grown from hosting 75 events to over 770 events in 2015, producing thousands of solutions. The challenge brings technologists and domain experts together to build solutions from well-specified tasks and maintain engagement through regular meetups, documentation, and tying projects to upcoming space missions. Organizers must ensure participation remains diverse and inclusive, prevent a loss of motivation, and continue evangelizing to engage new users.