Page 25 - EngineerIt May 2021

SPACE SCIENCES

How it works laser communications capabilities
Both radio waves and infrared light are electromagnetic radiation with wavelengths with numerous experiments to refine
at different points on the electromagnetic spectrum. Like radio waves, infrared light laser technologies further, increasing
is invisible to the human eye, but we encounter it every day with things like television our knowledge about potential future
remotes and heat lamps. applications.
Missions modulate their data onto the electromagnetic signals to traverse the distances LCRD’s initial experiment phase will
between spacecraft and ground stations on Earth. As the communication travels, the leverage the mission’s ground stations
waves spread out. in California and Hawaii, Optical Ground
The infrared light used for laser communications differs from radio waves because the Station 1 and 2, as simulated users. This
infrared light packs the data into significantly tighter waves, meaning ground stations can will allow NASA to evaluate atmospheric
receive more data at once. While laser communications aren’t necessarily faster, more disturbances on lasers and practice
data can be transmitted in one downlink. switching support from one user to
Laser communication terminals in space use narrower beam widths than radio the next. After the experiment phase,
frequency systems, providing smaller “footprints” that can minimise interference or improve LCRD will transition to supporting space
security by drastically reducing the geographic area where someone could intercept a missions, sending and receiving data to
communications link. However, a laser communications telescope pointing to a ground and from satellites over infrared lasers
station must be exact when broadcasting from thousands or millions of miles away. A to demonstrate the benefits of a laser
deviation of even a fraction of a degree can result in the laser missing its target entirely. communications relay system.
Like a quarterback throwing a football to a receiver, the quarterback needs to know where The first in-space user of LCRD
to send the football, i.e. the signal, so that the receiver can catch the ball in stride. NASA’s will be NASA’s Integrated LCRD low-
laser communications engineers have intricately designed laser missions to ensure this earth orbit user modem and amplifier
connection can happen. terminal (ILLUMA-T), which is set to
launch to the International Space Station
Laser communications relay demonstration in 2022. The terminal will receive high-
Located in geosynchronous orbit, about 35 000 km above Earth, LCRD will be able to quality science data from experiments
support missions in the near-Earth region. LCRD will spend its first two years testing and instruments onboard the space
station and then transfer
this data to LCRD at
1.2 gigabits per second.
LCRD will then transmit
it to ground stations at
the same rate.
LCRD and ILLUMA-T
follow the ground
breaking 2013 lunar
laser communications
demonstration, which
downlinked data
over a laser signal
at 622 megabits-per-
second, proving the
capabilities of laser
systems on the Moon.
NASA has many other
laser communications
missions currently
in different stages of
development. Each
of these missions will
increase our knowledge
about the benefits and
challenges of laser
communications and
further standardise the
technology.
LCRD is slated to
launch as a payload
on a US Department of
Defence spacecraft on
June 23, 2021. n