Integrated LCRD Low-Earth Orbit User Modem and Amplifier Terminal (ILLUMA-T)
NASA’s Integrated LCRD Low-Earth-Orbit (LEO) User Modem and Amplifier Terminal (ILLUMA-T), targeted to launch in 2022, will provide astronauts and experiments aboard the International Space Station with enhanced data capabilities. The terminal will be mounted to the space station’s Japanese experiment module-exposed facility (JEM-EF), and will leverage optical communications to send high-resolution information from the space station to NASA’s first optical relay - the Laser Communications Relay Demonstration (LCRD), located in geosynchronous orbit (GEO).
ILLUMA-T will be LCRD’s first user, completing an end-to-end optical communications system, which is shown in the image below. After collecting data, ILLUMA-T will send the information to LCRD over 1.244 gigabits-per-second optical links. This data will then be beamed down to optical ground stations in Haleakala, Hawaii and Table Mountain, California, which were chosen for their minimal cloud coverage, as clouds can disrupt optical signals.
Optical communications systems are ideal for missions like the space station because they are smaller, weigh less, and use less power than current radio frequency systems. A smaller size means more room for science instruments. Less weight means a less expensive launch. Less power means less drain on the spacecraft’s batteries.
ILLUMA-T is being built by engineers at NASA’s Goddard Space Flight Center and the Massachusetts Institute of Technology – Lincoln Laboratory, a federally funded research and development center.
ILLUMA-T utilizes multiple laser sources housed within the modem module to create the specific wavelengths required to initialize the communication and then perform the high-speed data transfer. The modem module is based upon heritage from both the LCRD design and the laser terminal developed for the 2013 Lunar Laser Communications Demonstration, which displayed optical communications capabilities from an orbit around the Moon.
ILLUMA-T utilizes existing communication paths between the optical terminal and the International Space Station. The space station is also upgrading the internal network to create gigabit connections that will allow for full utilization of the optical link. This provides a direct path from the space station’s network to the ground via an optical communications link, which will increase both the uplink and downlink data rates over the current radio frequency capabilities.
There are five key subsystems in ILLUMA-T, and the details of the ILLUMA-T payload are shown in the picture below. It shows the relative positioning of the optical module with respect to the Payload Interface Unit (PIU), which is the interface between the terminal and the space station, as well as the H-fixture and grapple fixture, which are used for robotic transfer of the payload. The picture below also displays the various parts and subsystems of the ILLUMA-T payload:
- Optical Module: is responsible for both transmitting and receiving the laser signals carrying the information. On the transmitting side, it receives the amplified optical signal from the modem and directs it toward LCRD, while on the receiving side it collects the light signal, couples it to a fiber that will take it to the modem.
- Modem Subsystem: The subsystem where information received from the space station in the form of electrical signals and is modulated on laser signals, amplified, and then directed through fiber to the optical module. For the other direction, it receives the signal from the optical module, converts it to electrical signal, and sends it to the space station.
- Media Converter: This component is used as an interface between the space station and ILLUMA-T, and uses the existing fiber connection between the JEM-EF, where ILUMA-T will be mounted, and inside the pressurized section of the space station to enable high-speed data connections.
- Controller Electronics: This is responsible for controlling the optical terminal, accepts commands, gathers operational parameters and provide information to operators.
- Power Converter Unit: A unique subsystem responsible for converting the supplied power from the space station of 120V to 28V, which is common on unmanned spacecraft platforms. All other ILLUMA-T electronic boxes use a 28V power input which allows future unmanned missions to use the ILLUMA-T hardware without having to redesign the power interfaces.
Together, these systems will ensure the data transmission between the terminal and the space station will run smoothly. With ILLUMA-T onboard and leveraging optical communications, more data can be transmitted to Earth in single downlink. The terminal will allow for increase discovery from experiments and instruments on the space station!