OCTL Laser Beam Transmission Interruptions due to Aircraft and Predictive Avoidance
Abstract
Laser beam transmission from the Optical Communications Telescope Laboratory (OCTL) at Table Mountain, California, is required in order to provide a beacon source for optical link acquisition between spacecraft carrying laser communication terminals and OCTL. The laser transmission must be regulated in order to avoid inadvertent irradiation of overflying aircraft or spacecraft. In this article, we present an analysis and data to determine the frequency and duration of laser transmission interruptions so that future laser communication operations can be planned. A week's worth of aircraft flight-path data in the vicinity of OCTL was obtained from the Federal Aviation Administration (FAA). The FAA data were analyzed, along with simulated Lunar Atmospheric and Dust Environment Explorer (LADEE) spacecraft predicted orbital data, in order to determine the frequency of laser transmission interruptions. An upper bound of five interruptions per 15-min period was observed due to aircraft overflights. Under more favorable conditions, a 15-min pass to the LADEE spacecraft could encounter no interruptions due to aircraft. The analysis was corroborated with "ground-truth" measurements at OCTL, using the existing laser safety system sensors and radar, to monitor aircraft that intercept a plus-or-minus 2.5-deg exclusion zone around the boresight axis of the OCTL telescope. The frequency of interruptions obtained from this data was in agreement with the predictions obtained using the FAA data analysis. Furthermore, the ground observation confirmed typical interrupt durations of 3 to 5 s due to overflying aircraft. This sets a lower bound for the fractional duration of the shoot window to be approximately 98 percent. Predictive avoidance (PA) data obtained from the Laser Clearing House (LCH) for approximately one month with the Moon as a target was analyzed. Note that the difference between using the Moon as a target versus simulated LADEE spacecraft orbital data is that the Moon line of sight is continuous from moonrise to moonset, whereas the line of sight to the spacecraft is interrupted due to occultation of the spacecraft by the Moon. The limited LCH data analysis presented indicates that though greater than 90 percent of laser shoot windows can be accessed nearly two-thirds of the time, it can drop to 60 to 90 percent approximately one-third of the time, with a single instance when it dropped to 32 percent.
- Publication:
-
Interplanetary Network Progress Report
- Pub Date:
- November 2012
- Bibcode:
- 2012IPNPR.191B...1B