By George Leopold

NASA plans to launch a pair of laser communications missions over the next nine months that would demonstrate high-bandwidth optical relays capable of someday transmitting streaming HD video and other data from planetary probes.

The launch of the Laser Communications Relay Demonstration (LCRD) scheduled for Dec. 4 will be followed as early as August 2022 by the launch of the Deep Space Optical Communications flight demonstration, program officials said this week. LCRD, testing laser communications from geosynchronous orbit, is managed by NASA’s Goddard Space Flight Center. The Jet Propulsion Laboratory (JPL) is overseeing development of the deep space mission that will operate between the orbits of Mars and Jupiter as part of NASA mission to study a giant metal asteroid.

The LCRD payload consists of two optical terminals, each with bi-directional optical communications capability along with switching circuitry that enables one terminal to receive signals, switch data to the second terminal and relay it in real time to one of two ground stations in California and Hawaii.

The NASA demonstrations differs from current commercial satellite optical links in that they focus on space-to-ground links. “The challenge with optical back to the ground is that the earth’s atmosphere and the clouds [attenuate signals], and we can’t turn up the power and get past the bad weather like you can on an RF link,” said Dave Israel, LCRD principal investigator.

That means laser beams must be steered to the relatively clear skies over ground stations located at Table Mountain, Calif., or Haleakalā, Hawaii. “So, we need to get a lot of operational experience before we’re able to used optical communications for our missions,” Israel added. The goal is establishing “trunk lines” from the moon and Mars capable of transferring data at rates as much as 100 times faster than current RF links and at rates up to 1.2 gigabits per second.

Once the LCRD payload is maneuvered to its proper geostationary orbit, NASA will begin demonstrating the optical link next year using a relay terminal to be installed aboard the International Space Station.

Common channel

The $320 million laser communications demonstration also reflects NASA’s efforts to promote commercial space activities in low-earth orbit as the space agency pivots to planetary exploration. While addressing commercial demand for more bandwidth, “The optical domain will provide a common channel for all [users] to communicate,” said Badri Younes, NASA’s deputy associate administrator for space communications and navigation.

Unlike RF, Younes noted that optical frequencies are unregulated. That means near-infrared spectrum is more widely available than constrained RF frequencies. The primary requirement for optical-communications interoperability among government or commercial systems is a common waveform.

NASA also touts optical links as a way to relieve pressure on crowded RF spectrum while promoting interoperability among private sector users.

Meanwhile, the LCRD ground station sites were selected for their favorable weather conditions. Among the ground station upgrades were replacing mirrors to boost reflectivity and higher laser thresholds to enable telescopes to receive and send laser signals to and from the LCRD payload.

LCRD ground station. (Source: NASA Goddard)

“We are a pathfinder to what the next generation of NASA communications can look like,” said Miriam Wennersten, LCRD ground segment manager at NASA Goddard.

Building on the low-earth orbit demonstration is next year’s launch of the Deep Space Optical Communications (DOSC) mission. JPL has delivered the payload that is being integrated with an asteroid probe for environmental testing. The deep space transmitter using high-powered lasers is located at the Table Mountain, Calif., ground station; the ground receiving station is at the Palomar Observatory near San Diego.

Abi Biswas, JPL’s deep space optical communications technologist, said the receiver has been integrated with Palomar’s 5-meter telescope. His team is currently calibrating receiver electronics that will detect and process faint photon signals from deep space.

“We’re testing all of our receive electronics and detectors by looking at asteroids and stars, and tracking them,” Biswas said. Among the potential capabilities provided by high-bandwidth laser communications are livestreams of high-definition video from Mars rovers, he added.