Thought your Internet speeds were slow? Try being a space scientist for a day.
The vast distances involved will throttle data rates to a trickle.
You're lucky if a spacecraft can send more than a few megabits per
second (Mbps).
But we might be on the cusp of a change. Just as going from dial-up
to broadband revolutionized the Internet and made high-resolution photos
and streaming video a given, NASA may be ready to undergo a similar
"broadband" moment in coming years.
The key to that data revolution will be lasers. For almost 60 years,
the standard way to "talk" to spacecraft has been with radio waves,
which are ideal for long distances. But optical communications, in which
data is beamed over laser light, can increase that rate by as much as
10 to 100 times.
High data rates will allow researchers to gather science faster,
study sudden events like dust storms or spacecraft landings, and even
send video from the surface of other planets. The pinpoint precision of
laser communications is also well suited to the goals of NASA mission
planners, who are looking to send spacecraft farther out into the solar
system.
"Laser technology is ideal for boosting downlink communications from
deep space," said Abi Biswas, the supervisor of the Optical
Communications Systems group at NASA's Jet Propulsion Laboratory,
Pasadena, California. "It will eventually allow for applications like
giving each astronaut his or her own video feed, or sending back
higher-resolution, data-rich images faster."
Science at the speed of light
Both radio and lasers travel at the speed of light, but lasers travel
in a higher-frequency bandwidth. That allows them to carry more
information than radio waves, which is crucial when you're collecting
massive amounts of data and have narrow windows of time to send it back
to Earth.
A good example is NASA's Mars Reconnaissance Orbiter, which sends
science data at a blazing maximum of 6 Mbps. Biswas estimated that if
the orbiter used laser comms technology with a mass and power usage
comparable to its current radio system, it could probably increase the
maximum data rate to 250 Mbps.
On Earth, data is sent over far shorter distances and through
infrastructure that doesn't exist yet in space, so it travels even
faster.
Increasing data rates would allow scientists to spend more of their time on analysis than on spacecraft operations.
"It's perfect when things are happening fast and you want a dense
data set," said Dave Pieri, a JPL research scientist and volcanologist.
Pieri has led past research on how laser comms could be used to study
volcanic eruptions and wildfires in near real-time. "If you have a
volcano exploding in front of you, you want to assess its activity level
and propensity to keep erupting. The sooner you get and process that
data, the better."
That same technology could apply to erupting cryovolcanoes on icy
moons around other planets. Pieri noted that compared to radio
transmission of events like these, "laser comms would up the ante by an
order of magnitude."
Clouding the future of lasers
That's not to say the technology is perfect for every scenario.
Lasers are subject to more interference from clouds and other
atmospheric conditions than radio waves; pointing and timing are also
challenges.
Lasers also require ground infrastructure that doesn't yet exist.
NASA's Deep Space Network, a system of antenna arrays located across the
globe, is based entirely on radio technology. Ground stations would
have to be developed that could receive lasers in locations where skies
are reliably clear.
Radio technology won't be going away. It works in rain or shine, and
will continue to be effective for low-data uses like providing commands
to spacecraft.
Next steps
Two upcoming NASA missions will help engineers understand the
technical challenges involved in conducting laser communications in
space. What they'll learn will advance lasers toward becoming a common
form of space communication in the future.
The Laser Communications Relay Demonstration (LCRD), led by NASA's
Goddard Space Flight Center in Greenbelt, Maryland, is due to launch in
2019. LCRD will demonstrate the relay of data using laser and radio
frequency technology. It will beam laser signals almost 25,000 miles
(40,000 kilometers) from a ground station in California to a satellite
in geostationary orbit, then relay that signal to another ground
station. JPL is developing one of the ground stations at Table Mountain
in southern California. Testing laser communications in geostationary
orbit, as LCRD will do, has practical applications for data transfer on
Earth.
Deep Space Optical Communications (DSOC), led by JPL, is scheduled to
launch in 2023 as part of an upcoming NASA Discovery mission. That
mission, Psyche, will fly to a metallic asteroid, testing laser comms
from a much greater distance than LCRD.
The Psyche mission has been planned to carry the DSOC laser device
onboard the spacecraft. Effectively, the DSOC mission will try to hit a
bullseye using a deep space laser -- and because of the planet's
rotation, it will hit a moving target, as well.
http://go.nasa.gov/2gBzbyx
UPDATED AT 10:40 a.m. PST on 2/15/17 to clarify relative data speeds.
