This paper describes a new six degree of freedom navigation and guidance system. The first such system, developed for the USAF, provides a precise real-time measure of the relative position (two pointing angles and range) and relative orientation (three Euler angles) of the pilots head (LOS), relative to the aircraft body frame. This aircraft cockpit system employs the electromagnetic near-field. A longer-range system (10 m to over 100 km) operates cooperatively and symmetrically between two bodies employing the EM far-field. It also provides in each body a precise real-time measure of the relative position and orientation of the other body. One operational mode of this longer range system allows one-body to "handoff" its local measure of the vector that locates a third point in the space. This HANDOFF or OFFSET GUIDANCE vector, which identifies the position of the third point in the frame of one body, is defined immediately and-precisely as a vector in the frame of the remote other body. This OFFSET GUIDANCE or HANDOFF capability is discussed in the context of an application, namely, the "blind" landing of a helicopter on an offshore platform. The system is described and the algorithms that compute this guidance vector are derived and discussed.


The term "synchro" is familiar to those concerned with the navigation, guidance, and control of physical systems as a one (1) degree-of-freedom, electromechanical, angle-measuring transducer that has a rotor and a stator.

The SPASYN is a new navigation and guidance system, a six degree-of-freedom transducer, which measures the relative position and the relative orientation between two independent bodies. SPASYN measures, in each body, the two pointing angles and range plus the three Euler angles, of the other body. The SPASYN is also a synchro, a space synchro. It, like its predecessor the synchro has a rotor (called the Sensor) and a stator (called the Radiator). The three-axis radiator, which is fixed in one body, electromagnetically tracks the three-axis sensor, which is fixed in the remote other body. The result is that, with appropriate signal processing, SPASYN measures the angles that define the "generalized" relative rotation and position between the stator (radiator) and the remote rotor (sensor).

The first SPASYN application employs the EM near-field of the radiator, which is fixed in the cockpit, to track the sensor on the pilot's helmet. The head position and the pilot LOS are thereby determined relative to the aircraft body frame. This very short range, hard-wire feedback, SPASYN system application1 is all-attitude and provides a closed loop measure of the angles defining the relative position and the relative orientation. This very short-range navigation and guidm1ce SPASYN system, operating in the cockpit, has successfully passed extensive flight-testing by the USAF, US Navy, and the US Army.

The longer-range SPASYN employs the electromagnetic far-field. It operates cooperatively and symmetrically in a transponding or multiplexed fashion, between the two relatively remote independent bodies.

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