The Space Shuttle and GPS: A Safety-Critical Navigation Upgrade

In 1993, the Space Shuttle Program selected an off-the-shelf Global Positioning System (GPS) receiver to eventually replace the three Tactical Air Navigation units on each space shuttle orbiter. A proven, large production base GPS receiver was believed to be the key to reducing integration, certification, and maintenance costs. More GPS software changes, shuttle flight software changes, and flight and ground testing were required than anticipated. This resulted in a 3-year slip in the shuttle GPS certification date. A close relationship with the GPS vendor, open communication among team members, Independent Verification and Validation of source code, and GPS receiver design insight were keys to successful certification of GPS for operational use by the space shuttle.