Originating Technology/NASA Contribution
In 1992, on a gravity assist flyby of Earth that would help propel it along its mission to Jupiter, NASA’s Galileo probe detected a line of light pulses emerging from Earth’s night-darkened hemisphere. Over the next few days, Galileo’s camera imaged similar signals—even though the probe was hurtling through space nearly 4 million miles from the planet.
The pulses Galileo detected were powerful laser bursts from telescopes at NASA’s Table Mountain Observatory in Wrightwood, California, and the U.S. Air Force Phillips Laboratory Starfire Optical Range near Albuquerque. The lasers, firing bursts in the range of tens of megawatts, were part of the Jet Propulsion Laboratory (JPL) Galileo Optical Experiment (GOPEX) that gave a glimpse into the future of communications—and how a Mars colonist might one day phone home.
As the scope of NASA’s missions have expanded in reach, unprecedented levels of data have flooded in from increasingly powerful sensors, and as manned missions and possible colonies on the Moon and Mars have inched closer to becoming viable realities, the Agency has seen the need for more efficient and effective means of communicating across the expanses of space. In addition, the practical demands of space exploration require further reductions in spacecraft size and weight, making smaller, lighter, more energy-efficient communications equipment a priority. GOPEX demonstrated the potential of free space (no physical connection) optical communications.
JPL’s Optical Communications Group has been tackling the challenge of enabling space missions to return 10–100 times more data while reducing antenna area to 1 percent of its current size—all while also employing less mass and power. Optical laser communication presents a host of benefits in these regards. It offers high-bandwidth, low mass, and low power consumption, allowing missions to communicate deeper into space. Optical communications are to radio frequency communications as a dart is to a shotgun blast; a radio signal from Mars spreads out to about 100 times Earth’s diameter by the time it reaches the planet, while an optical signal pinpoints a spot about one-tenth of the Earth’s diameter. This kind of precision enhances the security of the communicated data, but there are significant difficulties in acquiring, tracking, and pointing optical signals accurately over such incredible distances. As such, JPL continues to explore increasingly powerful sensor technologies that can help detect even the faintest light signals, helping enable NASA’s effort to establish interplanetary communications networks and a virtual presence throughout the solar system. One company has assisted JPL in this mission by developing a light sensor that has multiple applications on Earth, as well.
Brooklyn, New York-based Amplification Technologies Inc. (ATI), a subsidiary of PowerSafe Technology, received Phase I and II Small Business Innovation Research (SBIR) contracts with JPL to pursue the development of a solid-state photomultiplier capable of detecting light down to its most reduced form—particles called photons. Photomultipliers are highly sensitive light sensors that boost the signals of even the faintest light to detectable levels. ATI, an advanced developer of photon detection technology, had already developed its patented Discrete Amplification Photon Detector (DAPD), a solid-state, silicon-based photomultiplier that can detect visible light wavelengths down to a single photon. JPL was looking for photomultipliers that could detect individual photons in the near infrared (NIR) light wavelengths, specifically in the bands of 1060 and 1550 nanometers (nm) that the Center is exploring for use in free space optical communications. ATI employed its SBIR funding to implement a new indium-gallium-arsenide base for its DAPD technology, leading to a photomultiplier that detects single photon levels in the NIR range of 950 nm to 1700 nm. JPL used the device in its laser communications module, and it is now emerging as a commercial product with a variety of terrestrial uses.