Design of an inertially stabilized telescope for the LLCD
2011
The Lunar Laser Communication Demonstration (LLCD) program will demonstrate the first high-bandwidth
optical communication payload on a NASA space mission. The inertially stabilized 108 mm aperture
telescope will fly on NASA's LADEE spacecraft and is fabricated nearly entirely of beryllium, providing a
high stiffness-to-weight ratio. The telescope consists of a two-axis fine positioning stage using inertial
sensors and coarse and fine optical tracking. The stabilized telescope uses a two-axis coarse positioning
gimbal to provide a large field-of-regard. Inertial stabilization provides local disturbance rejection while
allowing modest optical uplink power to provide an absolute pointing reference. The telescope is a three-wavelength
design providing separate uplink acquisition and communication wavelengths, and a downlink
communication wavelength. Acquisition and coarse tracking of the uplink beacon is via a photodiode
quadrant detector, while fine tracking is via nutation tracking and piezoelectric actuation of the receive fiber.
Control of the downlink point-ahead angle is via piezoelectric actuation of the transmit fiber. The telescope is
thermally stabilized during normal operations. The transmit and receive beams are fiber-coupled to a separate
optoelectronic module and the telescope line-of-sight will be stabilized to better than 2.5 microradians during
normal operations. Provision for self-test and boresighting during on-orbit operations is provided.
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