Engineers at Celestron (www.celestron.com) are known for producing precision optical telescopes. The fact that many on the design team are amateur astronomers allows them to approach product performance from the customer's point of view.
According to Manishi Gupta, VP of engineering and quality assurance, "We stress quality components. It starts with good optics and you don't want your other components (mechanical systems, electronics for control, and software) to work against the optics." One of these critical areas is the drive system for pointing the telescope and maintaining precise positioning to track celestial objects.
Celestron engineers chose Pittman (www.pittman.com) 8000 Series dc brush motors and optical encoders for their latest NexStar 11GPS telescope. Gupta says the motors must function smoothly and allow a useful speed range. "The computer directs the telescope to find objects, which it must then track as the Earth turns. It has to move from star A to star B quickly, say 3 deg/sec, and then track at speeds the order of arc seconds/sec. Pittman had the dynamic speed range and uniform motor response to allow easier development of the control electronics," he notes. Part of the latter was low electrical noise that could cause EMI problems. The motors are also quiet.
ROSE (reflective optical sensing encoder) units (which sense 256 counts/rev plus quadrature) on both the azimuth and elevation motors provide a resolution of 1,024 counts per motor revolution. Coupled with the ratio of bronze worm gear drive with stainless steel worm, the total combination gives about 11 arc seconds of resolution, which, according to Gupta, allows enhanced time exposure photography.
With such precise control and motion smoothness, coupled with GPS and computerized "star tour" programs, backyard astronomy can concentrate more on the sky rather than on setting up the equipment.
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