The concept of a realistic interstellar explorer has been addressed by the Johns Hopkins University Applied Physics Laboratory (JHU/APL) with support from the NASA Institute for Advanced Concepts (NIAC). This paper discusses the requirements, conceptual design and technology issues associated with the optical and RF communications systems envisioned for this mission, in which the spacecraft has a projected range of 1000 AU. Well before a range of 100 AU interactive control of the spacecraft becomes nearly impossible, necessitating a highly autonomous craft and one-way communications to Earth. An approach is taken in which the role of the optical downlink is emphasized for data transfer and that of the microwave uplink emphasized for commands. The communication system is strongly influenced by the large distances involved, the high velocities (20 AU/year or ~ 95 km/s) as well as the requirements for low-mass (~ 10 kg), low prime power (~ 15 W), reliability, and spacecraft autonomy. An optical terminal concept is described that has low mass and prime power in a highly integrated and novel architecture, but new technologies are needed to meet the range, mass, and power requirements. These include high-power, wall-plug efficient diode-pumped fiber lasers; compact, lightweight, and low-power micro-electromechanical (MEM) beam steering elements; and lightweight diffractive quasi-membrane optics. In addition, a very accurate star tracking mechanism must be fully integrated with the laser downlink to achieve unprecedented pointing accuracy (~ 400 nrad RMS). The essential optical, structural, mechanical, and electronic subsystems are described that meet the mission requirements, and the key features of advanced technologies that need to be developed are discussed. The conclusion from this preliminary effort is that an optical communications downlink out to 1000 astronomical units (AU) is within the realm of technical feasibility in the next 5-10 years if the identified technical risks for the new technologies can be retired.
Proceedings Title: Free-Space Laser Communication and Laser Imaging, Conference | 2nd | , Conference | 2nd | Free-Space Laser Communication and Laser Imaging II | SPIE
Conference Dates: July 7-11, 2002
Conference Title: Proceedings of SPIE--the International Society for Optical Engineering
Pub Type: Conferences
diffractive optics, interstellar explorer, link analysis, optical communications, RF tone-tracking