Understanding Our Universe, The Future of Photonics Is Written in the Stars

JUSTINE MURPHY, EDITOR, justine.murphy@photonics.com

Since NASA was established nearly 60 years ago, the average person’s understanding of the universe has grown, thanks to the efforts of untold numbers of scientists, researchers, engineers and others around the world. From America's first image of the moon — taken by NASA’s Ranger 7 spacecraft in 1964 — to the remarkably clear pictures of Pluto’s cratered, mountainous and glacial terrains — acquired by the New Horizons spacecraft within the last year — optics and photonics technologies are bringing us ever closer to the planets in our own solar system and all that lies beyond.

Global stereo mapping of Pluto’s surface is now possible, as images taken from multiple directions are downlinked from NASA’s New Horizons spacecraft.

Measuring stellar atmospheres

Today, light-based technologies are helping to improve our understanding of the universe. One such technology — optical spectrometry — is playing a role, according to Francesco Marsili, a microdevices engineer at NASA’s Jet Propulsion Laboratory. It has allowed engineers to measure the spectral content of a beam of light — specifically, how many photons of a certain color it contains.

“Applying this technique to astronomy, we’re able to gain a formidable amount of information about the universe, for instance by measuring what elements stars and planetary atmospheres contain and at which temperature and pressure they are,” he said. “Astronomy and photonics are now merging in the field of astrophotonics, which aims at using photonics to enhance astronomical instruments.”

This could mean that bulky free-space-coupled spectrometers may be replaced by miniaturized fiber-coupled, on-chip spectrometers.

Dark, narrow streaks on Martian slopes such as these at Hale Crater are inferred to be formed by seasonal flow of water on present-day Mars. Photo courtesy of NASA.

Hamamatsu Photonics KK in Japan has also been working with optical detection and sensing relating to aerospace. Koei Yamamoto, director of the company’s Solid State Division, said they are investigating low light-level detection in wavelengths that extend into the infrared. They have already developed — in conjunction with the National Astronomical Observatory of Japan (NAOJ), Osaka University and Kyoto University — CCD image sensors for use in the Hyper Suprime-Cam, which is an ultrawide field of view prime focus camera installed in the Subaru Telescope. Subaru is an 8.2-meter optical infrared telescope positioned at Mauna Kea, Hawaii, and operated by NAOJ, an association under Japan’s National Institutes of Natural Sciences.

Hamamatsu also developed and manufactured an optical sensor for the NASA Hayabusa (formerly Muses-C) mission, which was used to observe the surface condition of the Itokawa asteroid using light. According to Yamamoto, work such as this will drive the future of space exploration.

“New photonics technology is continuously required for research in this infinite space,” he said.

Live streaming from Mars

The dream of exploring Mars continues to captivate astronomers and engineers. NASA rovers are already on the Red Planet examining its surface and producing amazing images. However, further study will require updated communications systems incorporating optics technologies.

“The achievement that I am most excited to see in my lifetime is human exploration of Mars,” Marsili said. “Human exploration will rely on optical communications, which can support tens of times higher data rates than radio communications. With optical communications we could live stream from Mars.”

“Think of the pictures we are getting from the Mars rover,” he said. “Why are we not getting videos? The data rate that the [existing] DSN [Deep Space Network] can support is too low.”

NASA took an important step toward such innovation in 2013 when it demonstrated optical communication beyond Earth’s orbit with the Lunar Laser Communication Demonstration (LLCD). In it, the Lunar Atmosphere and Dust Environment Explorer (LADEE) spacecraft orbiting the Moon was able to downlink data to two receiver terminals using a laser beam.

Today, NASA communicates with its spacecraft primarily via radio waves, and the DSN relies on large antenna arrays around the globe. But engineers are working to switch to optical frequencies instead, which Marsili said will increase the data rate of the communication links. He compared the impending improvement to the difference between dial-up and high-speed Internet. What will become an optical DSN in the future will rely on technology such as lasers mounted to the spacecraft that are pointed at optical telescopes on Earth to downlink data.

Ball Aerospace & Technologies Corp. also cited laser communications as an important tool for understanding the universe. The Colorado-based company has developed and manufactured light-based components for many NASA initiatives, including Landsat 8, the Hubble Space Telescope, the New Horizons mission, the Mars Reconnaissance Orbiter, the Kepler/K2 mission and the James Webb Space Telescope. Their work with space exploration and Earth imaging has been recognized twice by the Colorado Photonics Industry Association.

“With the huge quantities of data from missions that are going farther and farther away from the Earth, we need higher bandwidth communications systems,” said Chip Barnes, chief engineer for the Ball Aerospace Civil Space business unit.

Advancing such communications systems will require development of optics and photonics technologies both on spacecraft and in ground terminals, according to Marsili.

But improving photonic technologies to better understand our universe doesn’t end there. Marsili says the future of space exploration will require not only advanced communications systems, but also more efficient lasers, vibration isolation systems, large-dish telescopes and single-photon detectors. He currently is developing ground receiver single-photon detectors that he says “are the most sensitive light detectors to date.”

Ball Aerospace has designed and manufactured many optical components for NASA, including the 18 beryllium primary mirror segments, secondary and tertiary mirrors, a fine steering mirror and several engineering development units for the James Webb Space Telescope, according to Barnes.

The Ralph camera is prepared for vibration testing to measure the instrument’s response to the launch of NASA’s New Horizons spacecraft on the mission to explore Pluto. White wires attached to Ralph’s detectors lead to accelerometers that will measure vibrations within the instrument. Photo courtesy of Ball Aerospace.

Technologies for exploration

Ball Aerospace has had a hand in NASA’s New Horizons mission that is exploring Pluto, by designing and building the Ralph camera installed on the New Horizons spacecraft. Ralph features seven charge-coupled devices and an infrared array detector, all of which provide color and black-and-white maps of the planet’s surface with a resolution of 250 meters (800 feet) per pixel. It is coupled with Alice, an ultraviolet imaging spectrometer created by the Southwest Research Institute in Texas — a device designed to image ultraviolet emissions and provide spectral images in the extreme- and far-ultraviolet passbands. The Ralph/Alice imaging system can also map the presence of nitrogen, methane, carbon monoxide, water and other materials across the surface of Pluto.

Together, these “honeymooners” are bringing us far beyond the moon, producing the closest, clearest images ever obtained of the dwarf planet.

Ball Aerospace also built the HiRISE camera on the Mars Reconnaissance Orbiter, which operates in visible wavelengths with a telescopic lens, producing images at resolutions “never before seen in planetary exploration missions,” according to NASA. HiRISE works at near-infrared wavelengths, as well, studying mineral groups that exist on the Mars surface. From as high as 400 km (about 250 miles), the camera acquires high-resolution images of layered materials, gullies and channels, and is identifying potential future landing sites.

The HiRISE camera, built by Ball Aerospace, is installed on the Mars Reconnaissance Orbiter and currently providing the images of predicted and unknown features on the Mars surface. Photo courtesy of Ball Aerospace.

“There is nothing more inspiring than the photographs,” Barnes said. “[And we can see things like] black holes by observing the impacts of photons around them.”

Space exploration and our understanding of the universe will continue to grow, thanks to the development of light-based technologies, Marsili said. An increasing number of discoveries in space have been made possible by optical techniques, including discoveries of exoplanets (planets orbiting other stars in our galaxy) and their properties. These can be detected and understood with optics technologies — from infrared, UV and visible imaging systems to spectrometers, telescopes and single-photon detectors — as they measure the periodic dimming in the starlight that happens when an exoplanet passes in front of a star.

Marsili may get his wish to see human exploration of Mars. Courtesy of NASA’s Orion spacecraft and its advanced optical systems, Mars is expected to get visitors within the next 10 years. The agency plans to send a crew there aboard the Orion in 2021.

Photonics technologies also extend beyond studying planets. Advancements could ultimately determine if there is life beyond Earth, something that Barnes and his team are eager to explore. But for now, there is an entire universe of information yet to be gathered and examined, and photonics is taking the front seat on the spacecraft.

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