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Boeing, Ball Aerospace Collaborate on Satellite Communications System

Photonics Spectra
Jul 2003
Brent D. Johnson

Boeing Space and Intelligence Systems, a unit of Boeing Integrated Defense Systems, and Ball Aerospace & Technologies Corp. are collaborating to develop a laser communications satellite system for the US armed forces. The system is expected to improve the efficiency of satellite communications by a factor of 10.

Laser-based Satellite Communications System

A laser-based satellite communications system under development for the US armed forces is expected to improve the efficiency of satellite communications by a factor of 10. Courtesy of Ball Aerospace & Technologies Corp.

The two aerospace giants had a prior relationship working on Teledesic -- the Internet-in-the-sky. The satellite system, developed by Teledesic LLC of Bellevue, Wash., included Ball Aerospace's optical head composed of a telescope, optical bench and line-of-sight pointing system, and a transceiver containing the high-power, high-data-rate laser transmitter and sensitive optical receiver from Boeing (then Hughes Space & Communications).

In this latest endeavor, Boeing is developing the transceiver portion, the communications interface and data switching subsystems. Ball Aerospace's experience in flight payloads, developed to support IR astronomy as well as other scientific and defense applications, incorporates many of the same subsystems used in laser communications terminals. These applications include diffraction-limited telescopes, stable optical bench assemblies, payload-control and sensor-processing electronics, and precision line-of-sight pointing and control assemblies.

Ball Aerospace senior optical engineer Robert Kaliski and systems engineer Robert Marshalek say that several laser transceiver approaches have been investigated over the past 40 years, ranging from AlGaAs semiconductor diode lasers to Nd:YAG solid-state lasers to erbium-doped fiber amplifiers.

The optimal choice for a given link is driven mainly by the data rate and range requirements, including the potential for growth. Recent high-data-rate development efforts, such as those completed for Teledesic and Celestri, have investigated both coherent-detection Nd:YAG and direct-detection erbium-doped fiber amplifier approaches. Celestri is Motorola Inc.'s satellite system, which has been incorporated into Teledesic.

Ball Aerospace's Teledesic activity, for example, developed a laser transceiver method that is very similar to that used in terrestrial fiber optic transmission systems. Leveraging such commercially available technologies requires development of space-based transceivers that use high-power amplifiers to boost the transmitted signal above 1 W, and low-noise optical amplifiers to improve the detection sensitivity in the receiver.

Three areas present significant technical challenges to this engineering team. The first is in acquisition, pointing and tracking, because a narrow diffraction-limited transmit beam must be accurately pointed between linked assets amid the base disturbances present on the host platforms. The integrated disturbances can greatly exceed the transmitted beam width, which means that they must be attenuated by a precision line-of-sight control subsystem. The second challenge lies within the high-data-rate communications subsystem, particularly regarding the ability to provide reliable operations amid the space environments encountered over a mission lifetime that can range from one to 15 years. Finally, to perform integrated acquisition, pointing and tracking and high-data-rate-communications functions throughout the lifetime of the spacecraft requires a payload that is reliable and stable and that does not degrade significantly in harsh radiation environments. Data rates of up to 40 Gb/s are under consideration for near-Earth communications applications such as low or geosynchronous Earth orbit, or airborne host platforms.

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