The Optical Communications Telescope Laboratory (OCTL) is a laboratory that was built to support research and development of FSO communications from space. The OCTL facility is located at the Table Mountain Observatory near Wrightwood, CA. A second ground station is located in Maui, Hawaii and houses a 60 cm receive aperture and a 15 cm transmit aperture. The terminal is housed within an approximately 5.5 meter diameter dome.
OCTL is located at JPL’s Table Mountain Facility in the San Gabriel Mountains near Wrightwood, California. The site can fully support optical telescope operations with 24/7 availability and accommodations for sleeping. The location is convenient to JPL since it is only about a 1.5 hour drive away. OCTL has line of sight to numerous ground locations which permit point to point field testing with ranges of a few hundred meters to a few kilometers. The telescope laboratory is equipped with a full suite of optical, electronic and mechanical tools and test equipment. The networking capability at OCTL was recently upgraded from standard internet access to a secure JPL mission connection. This upgrade included dedicated router hardware and controlled building access through a badge reader. A local computer with a firewall to the JPL Mission Operations Center acts as a data server to both transmit and receive data at rates up to a few hundred kilobits/second that are limited by the T1 internet service. Secure voice connection is also possible using VOIP over this connection. The OCTL telescope itself has a 1m diameter primary mirror mounted on a fast-tracking elevation over azimuth gimbal with a coudé path that sends the collected light signal into a controlled laboratory area. The focal ratio of the telescope is F/76 (F/ represents the focal ratio) with a near diffraction limited field-of-view (FOV) of over 500 µrad (38 mm at the telescope focus) and a seeing limited unvignetted FOV of approximately 2.6 mrad (200mm at focus). By translating the secondary mirror, the telescope is capable of being focused at conjugate distances ranging from infinity down to less than 1 km. Table Mountain Observatory is located (34.4°N latitude, 242.3E longitude) at nearly 2300 meters. The telescope has a clear view of the sky at all azimuth angles above 0 to 10 degrees elevation, with the local tree line restricting 0-degree viewing at some azimuthal angles. Weather and astronomical seeing information is available from instruments located at the site. The gimbal can slew at up to 20 degrees/sec in azimuth and 10 degrees/sec in elevation. The all sky blind pointing error is less than 17 µrad (1σ). The telescope also has a co-aligned 20 cm diameter, F/7.5 Classical Newtonian acquisition telescope which can accommodate auxiliary instrumentation. This telescope provides an unvignetted FOV at the focal plane of 5 mrad. Co-alignment of this telescope with the main OCTL telescope is usually better than 100 urad, which easily supports acquiring and guiding sources into the main telescope field of view. Both electrical and fiber optic cables and fiber optic cables that wrap through the telescope mount service loop connect the telescope to the operator control room. Telescope operations can take place both during day and night and the telescope can point to within 5 degrees of the sun without any solar damage. The final mirror in the telescope coudé path (M7, see Figure 1b below) can rotate to four different positions which each lead to separate optical benches. This allows concurrent development, integration and testing of four different optical receive/transmit assemblies (more if space allows the sharing of an optical bench). Furthermore multiple mission operations can be supported in the same time period as long as they do not occur simultaneously. An AR-coated fused silica window in the optical path prevents the exchange of air between the telescope dome and the coudè room, and prevents the potential chimney effect from degrading the telescope seeing.