AbstractUntil recently, space programs such as Viking used the “block redundancy” concept for spacecraft navigation/control, whereby multiple navigation units of the same configuration were packaged in different locations on the spacecraft. The desire for a more efficient and cost effective approach to redundant spacecraft navigation systems prompted NASA to fund the development of a redundant Inertial Reference Unit (DRIRU I) based on the utilization of three dry, tuned‐gimbal, two‐degree‐of‐freedom gyroscopes. Each gyroscope, together with its associated electronics and power supply, comprises a “gyro channel” which provides two axes of angular rate information and is totally independent from the other two gyro channels. The first of these systems was successfully flown on the Voyager Program.More demanding space programs of the late 1970's and through the 1980's, such as SOLAR MAX, LANDSAT, ASPS, and SPACE TELESCOPE, have prompted the further development of a standardized high accuracy IRU (DRIRU II) based on the same design concepts and objectives stated above.This paper provides a comprehensive discussion of the system design configuration, performance capability, and environmental capability of the NASA Standard Redundant Dry Rotor Inertial Reference Unit (DRIRU II). Further, the design flexibility of the DRIRU II is discussed to allow potential users to consider adaptation of the unit to their unique space progr