Editing SpaceShipOne (section)

===Spaceplane navigation===
The core of the spacecraft [[avionics]] is the '''System Navigation Unit''' ('''SNU'''). Together with the '''Flight Director Display''' ('''FDD'''), it comprises the '''Flight Navigation Unit'''. The unit was developed jointly by [[Fundamental Technology Systems]] and [[Scaled Composites]].

The SNU is a [[GPS]]-based inertial navigation system, which processes spacecraft sensor data and subsystem health data. It downlinks telemetry data by [[radio]] to mission control.

The FDD displays data from the SNU on a color [[LCD]]. It has several distinct display modes for different phases of flight, including the boost phase, [[coast phase|coast]], reentry, and gliding. The FDD is particularly important to the pilot during the boost and coast phase in order to "turn the corner" and null rates caused by asymmetric thrust. A mix of commercial and bespoke software is used in the FDD.