  High power Earth and orbital-based directed energy (DE) systems pose a
potential hazard to Earth orbiting spacecraft. The use of very high power,
large aperture DE systems to propel spacecraft is being pursued as the only
known, feasible method to achieve relativistic flight in our NASA Starlight and
Breakthrough Starshot programs. In addition, other beamed power mission
scenarios, such as orbital debris removal and our NASA program using DE for
powering high performance ion engine missions, pose similar concerns. It is
critical to quantify the probability and rates of interception of the DE beam
with the approximately 2000 active Earth orbiting spacecraft. We have modeled
the interception of the beam with satellites by using their orbital parameters
and computing the likelihood of interception for many of the scenarios of the
proposed systems we are working on. We are able to simulate both the absolute
interception as well as the distance and angle from the beam to the spacecraft,
and have modeled a number of scenarios to obtain general probabilities. We have
established that the probability of beam interception of any active satellite,
including its orbital position uncertainty, during any of the proposed mission
scenarios is low ($\approx10^{-4}$). The outcome of this work gives us the
ability to predict when to energize the beam without intercept, as well as the
capability to turn off the DE as needed for extended mission scenarios. As
additional satellites are launched, our work can be readily extended to
accommodate them. Our work can also be used to predict interception of
astronomical adaptive optics guide-star lasers as well as more general laser
use.
