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method, the aircraft is tracked continuously by theodolites at two 
ground stations. The aircraft flies across the line connecting the 
two stations at a small angle, and the readings of the theodolite dials 
are recorded on film. Radio pulses from the aircraft synchronize the 
camera exposures of theodolite readings at the two stations. The azi 
muth reference between the two stations is then reduced from the film 
records by the ground computer. 
The Flashing Light Method technique requires that the star 
fields be visible from the ground. As the aircraft flies directly across 
the line between the two stations, ballistic cameras record the light 
flashes against a background of stars. The x, y coordinates of the 
stars and the flashes of the light are measured by a precise compara 
tor. With the assistance of star catalogues and astronomical formulas, 
the azimuth determination of the ground station can be computed. 
The light source provides two beams of light displaced 180° in 
azimuth from each other. The lamps are xenon arc, and will deliver 
100, 000 lumens when operating at maximum design input power of 2250 
watts. Each beam is rectangular with a 20° horizontal width and a 10° 
vertical width. The average intensity of each light beam when projec 
ted through the transparent plastic bubble is 300, 000 candlepower mini 
mum when the arc lamp is operating at full power and when the intensity 
control (iris diaphragm) is fully opened. 
A high speed shutter is used to generate the required flashes of 
each light beam. One shutter blade assembly is mounted in eachbeam- 
ing device, and a common shutter drive mechanism provides simultan 
eous operation of the two blade assemblies. When operating in the 
flashing mode, the flash duration is three milliseconds. The shutter 
provides three different intervals between flashes; 1/2 second, 1 second 
and 2 seconds. 
A servomechanism positions the azimuth of the point light 
source over a range of 35 degrees counterclockwise to 115 degrees 
clockwise from the fore and aft position. The slewing rate is 150°