In May 2022, the TeraByte InfraRed Delivery (TBIRD) payload on a small CubeSat satellite was launched into orbit 300 miles above the Earth’s surface. Since then, TBIRD has transmitted terabytes of data via optical communications links to receivers on the ground in California at record speeds of up to 100 gigabits per second—100 times faster than the fastest Internet speeds in most cities. data. This data rate is more than 1,000 times higher than radio frequency links traditionally used for satellite communications, and is the highest data rate ever achieved for a laser link from space to the ground. And these record speeds were all achieved with a communications payload about the size of a tissue box.
MIT Lincoln Laboratory conceptualized the TBIRD mission in 2014 as a means to provide scientific missions with unprecedented capabilities at low cost. Scientific instruments in space today typically generate more data than can be returned to Earth via typical space-to-ground communications links. With small, low-cost space and ground-based terminals, TBIRD could allow scientists around the world to take full advantage of laser communications to download all the data they could ever dream of.
The TBIRD communications payload, designed and built at Lincoln Laboratory, was integrated onto a Terran Orbital-built CubeSat as part of NASA’s Pathfinder technology demonstration program. NASA Ames Research Center developed the program to develop CubeSat buses (the “vehicles” that power and steer payloads) to get science and technology demonstrators into orbit faster and cheaper. Weighing about 25 pounds and about the size of two stacked cereal boxes, the CubeSat launched into low-Earth orbit (LEO ). The optical ground station is on Table Mountain, California, where most of the weather occurs below the summit, making this part of the sky relatively clear for laser communications. The ground station utilizes a one-meter telescope and adaptive optics (to correct for distortions caused by atmospheric turbulence) from NASA’s Jet Propulsion Laboratory’s Optical Communications Telescope Laboratory, and Lincoln Laboratory provides TBIRD’s dedicated ground communications hardware.
“We demonstrated higher-than-ever data rates in a smaller package than ever before,” said the lab’s program manager for TBIRD payloads and ground communications and assistant leader of the Optical and Quantum Communications Technology Group Jade Wang said. “While using lasers to send data from space sounds futuristic, the same technological concept is behind the fiber-optic internet we use every day. The difference is that laser transmission occurs in the open atmosphere, rather than in closed optical fibers. “
From radio waves to lasers
Whether it’s video conferencing, gaming, or streaming movies in HD, you’re using high data-rate links spanning fiber optics made of glass (and sometimes plastic). The fibers, about the diameter of a human hair, are bundled into cables that transmit data via rapidly traveling pulses of light from lasers or other sources. Fiber-optic communications are essential to the Internet age, where vast amounts of data must be distributed quickly and reliably across the globe every day.
However, for satellites, high-speed internet based on laser communications does not yet exist. Since the beginning of spaceflight in the 1950s, missions have relied on radio frequencies to send data to and from space. Infrared light used in laser communications has a higher frequency (or shorter wavelength) than radio waves, allowing more data to be packed with each transmission. Laser communications will allow scientists to send 100 to 1,000 times more data than today’s radio-frequency systems—similar to how we switch from dial-up to high-speed Internet on the ground.
Many scientific missions, from Earth observation to space exploration, will benefit from this acceleration, especially as instrument capabilities increase to capture larger volumes of high-resolution data, experiments involve more remote control, and spacecraft travel further from Earth to deep space.
However, laser-based space communication presents some engineering challenges. Unlike radio waves, lasers form narrow beams. In order to transmit data successfully, this narrow beam must be pointed precisely at a receiver (eg, a telescope) located on the ground. Although lasers can travel great distances in space, due to atmospheric influences and weather conditions, laser beams can become distorted. This distortion causes the beam to lose power, resulting in data loss.
Over the past 40 years, Lincoln Laboratory has been addressing these and related challenges through a variety of programs. To date, these challenges have been reliably addressed, and laser communication is rapidly gaining widespread adoption. The industry has already begun using laser communications to expand LEO cross-links with the aim of augmenting the existing terrestrial backbone and providing a potential Internet backbone to serve users in rural areas. Last year, NASA unveiled the Laser Communications Relay Demonstration (LCRD), a two-way optical communication system based on a laboratory design. On an upcoming mission, the lab-developed laser communications terminal will be launched to the International Space Station, where it will “talk” to the LCRD and support Artemis II, a mission that will fly past the moon ahead of future crewed flights. manned mission to the moon.
“As interest in and development of space-based laser communications expands, Lincoln Laboratory continues to push the limits of what’s possible,” Wang said. “TBIRD heralds a new approach that has the potential to further increase data rate capabilities; reduce size, weight, and power; and reduce the cost of laser communication missions.”
One way TBIRD aims to reduce these costs is by utilizing commercial off-the-shelf components originally developed for terrestrial fiber optic networks. However, ground components are not designed to survive the harshness of space, and their operation can be affected by atmospheric effects. With TBIRD, the lab developed solutions to both of these challenges.
Commercial components adapted to the space
The TBIRD payload integrates three key commercial-off-the-shelf components: a high-speed optical modem, a large high-speed storage drive, and an optical signal amplifier.
All of these hardware components are subjected to shock and vibration, thermal vacuum, and radiation testing to see how the hardware will perform in space, where it is subjected to intense forces, extreme temperatures, and high radiation levels. When the team first tested the amplifier through thermal tests that simulate the space environment, the fibers melted. In a vacuum, as Wang explained, there is no atmosphere, so heat is trapped and cannot be released by convection. The team worked with suppliers to modify the amplifier to release heat by conduction instead.
In response to data loss due to atmospheric influences, the lab developed its own version of Automatic Repeat Request (ARQ), a protocol for controlling data transmission errors on communication links. With ARQ, the receiver (in this case, a ground terminal) alerts the sender (satellite) to retransmit any lost or corrupted data blocks (frames) via a low-rate uplink signal.
“If the signal is lost, the data can be retransmitted, but if it’s inefficient — meaning you spend all your time sending duplicate data instead of new data — you can lose a lot of throughput,” explains Curt Schieler, systems engineer at TBIRD. Quantity.” Wang’s research group technical staff. “Using our ARQ protocol, the receiver tells the load which frames it received correctly, so the load knows which frames to retransmit.”
Another new aspect of TBIRD is that it lacks a gimbal, a mechanism used to point narrow laser beams. Instead, TBIRD relies on a lab-developed error signal concept to pinpoint the main body of the spacecraft. The error signal is fed to the CubeSat bus so it knows exactly how to point the entire body of the satellite at the ground station. Without the gimbal, the payload can be further miniaturized.
“We intend to demonstrate a low-cost technology capable of rapidly downlinking large amounts of data from LEO to Earth to support scientific missions,” Wang said. “In just a few weeks of operation, we have achieved this goal, achieving an unprecedented transfer rate of up to 100 gigabits per second. Next, we plan to practice other functions of the TBIRD system, including increasing the rate to 100 gigabits per second. 200 gigabits per second, enabling the downlink of more than 2 terabytes of data — the equivalent of 1,000 high-definition movies — to pass in a single 5-minute pass from the ground station.”
Lincoln Laboratory collaborated with NASA Goddard Space Flight Center to develop the TBIRD mission and technology.