Connect to a GO-TO GPS Telescope with Java™

May 1, 2003, VR (Updated Sept 11, 2003). The current generation of "go-to" GPS telescopes are an amazing technological innovation. They combine precise motor controls, position sensors, GPS receivers, and excellent optics into an telescopic instrument that can be enjoyed by both novice users and advanced amateur astronomers. The "go-to" telescope permits the user to view the moon, the planets, nebulas, galaxies, star clusters, and other celestial objects by simply pressing a few buttons. The functionality and ease of use of these telescopes can be futher extended by connecting them to your computer.

The telescope interface presented here will permit Java applications to instruct the telescope to slew or "go to" specified coordinates, to query the telescope's current position, and obtain other information such as slewing status, the GPS date and time, and the users geographic coordinate. The telescope interface is designed to be extensible, permitting connection from computers running various operating systems to telescopes from various manufactures. The telescope interface is a "pure" Java implementation. It utilizes the "javax.comm" api. (See the resources page at the end of this article for availability).

By using the telescope interface, applications such as star chart programs may be developed to control the telescope. More advanced applications such as augmented displays that combine digitized video output with graphic overlays are possible. Applications such as these will be the subject of future articles over the next several months.

 To connect to the Nexstar GPS telescope an adapter cable is required (Celestron Part Number 93920 available from telescope dealers and online suppliers such as Astronomics, Anacortes, A2Z Cables.com, and several others). The cable costs about $20 (US) plus shipping. The cable has a telephone handset plug at one end and a DB-9 connector on the other. The DB-9 Connector is connected to a COM port on the computer and the other is plugged into the end of the telescope hand controller. The telescope interface provides the RS232 communication functions described in Celestron Instruction manuals and a few additional functions such as accessing the GPS as well.