Acquisition and pointing for a Mars optical access link

Optical characteristics can potentially benefit communication links transmitting data from the surface of Mars to orbiting assets because of their high gain and modulation bandwidth compared to radio frequency (RF) links. Furthermore, optical systems can achieve higher data rates and be realized with lower mass and power, enabling the streaming of high definition imagery. In this paper we present a conceptual design for a low complexity, autonomous optical communications link for returning data at up to 250 Mb/s from the Martian surface. The pointing control is simplified because the short distance (400-1200 Km) allows us to use relatively wide (0.6 milliradian) transmitted laser beams. Link acquisition is based on the orbiter transceiver (OT) ldquoblind pointingrdquo a laser beam to illuminate the lander transceiver (LT) on the surface. The LT acquires the link with a spectrally-filtered, wide-field-of-view camera and subsequently tracks the OT with a two-axis, stepper-motor-actuator, to send back a laser modulated with high-rate data. The system design also has a provision for the OT transitioning from blind-pointing to closed loop tracking once it acquires the signal from the lander transceiver. Results from successful ground-based demonstrations performed at JPL, in which the pointing rate required to track an orbiter was emulated by mounting both transceivers on rotating stages, and in which we transmitted live video and pseudo-random data streams, are presented.