Exo-atmospheric telescopes for deep space optical communications

For deep space optical communications, optical telescopes located above the Earth's atmosphere would have significant performance advantages over telescopes mounted on the Earth's surface. Link outages due to cloud cover would be eliminated, atmospheric attenuation would be eliminated, and signal degradation due to stray light would be reduced. A study has been conducted to compare various exo-atmospheric platforms for the Earth end of the optical link. The three most promising platforms among many initially considered were selected for detailed study: satellites, free-flying airships and tethered airships. System configurations were compared that would have data rate capability comparable to a 6-m to 10-m diameter ground-mounted telescope, 100 percent line-of-sight coverage to a deep space spacecraft in the ecliptic, and at least 80 percent coverage in the event of failure of one Earth terminal. Based upon technical feasibility and readiness, life-cycle cost, performance and risk, a satellite platform is recommended. However, it is noted that airship technology may be advanced in the next decade or so to a level where airships should be reconsidered. Finally, this study provides a basis for a future study to compare systems using Earth-mounted and exo-atmospheric telescopes.