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Right now, the Perseverance rover is located inside the Jezero crater on Mars, roughly
363 million kilometres away from us.
And yet, despite this distance, Perseverance is sending us thousands of images, videos,
and scientific data from its various sensors and instruments.
If you think that’s far away, the Voyager spacecraft took and sent the famous Pale blue
dot image from 6 billion kilometres from Earth.
That is 40 times the distance between Earth and the Sun.
We currently use radio waves to transmit data to and from spacecraft.
That’s right, the same kind of waves used to listen to the radio.
However, at interplanetary distances, even with the incredible and expensive technology
in use today, data transfer speeds can be far slower than dial-up internet.
This severely limits how much data a probe can capture, as well as the speed in which
it’s received.
Which is why NASA has something new up its sleeve.
I’m Alex McColgan and you are watching Astrum.
Join with me today as we understand how NASA stays in contact with spacecraft billions
of kilometres away and explore the new kinds of technology NASA have just launched in the
field of deep space communication.
Unsurprisingly, the probes and rovers of NASA missions do not have extremely powerful radio
antennas themselves, they simply aren’t big enough or powerful enough to house them.
They have small, but directional and efficient antennas which transmit their data.
This means most of the heavy lifting needs to come from huge radio antennas on the Earth
itself.
NASA uses something called the Deep Space Network to communicate with its spacecraft.
The Deep Space Network is the largest and most sensitive scientific telecommunications
system in the world.
The DSN received and relayed to the world the first TV images of astronaut Neil Armstrong
setting foot on the surface of the moon in 1969.
It was called on to support the nerve-wracking Apollo 13 mission after the rupture of an
oxygen tank which forced NASA to abort the planned lunar landing.
During the critical re-entry of the capsule, it was essential that engineers on the ground
maintained contact with the astronauts on board.
The spacecraft's minimal power was needed for re-entry, with little left over for communications.
The DSN was able to capture these “whispers from space,” and it helped bring the astronauts
home.
And of course, the DSN maintains contact with every ongoing deep space NASA mission.
It can even talk to the rovers on Mars.
In fact, each antenna can receive multiple incoming signals at the same time, however
it only has the capability to transmit one at a time.
So, how does it work?
Well, it’s a network of three facilities containing multiple giant radio telescopes,
with facilities located in California, Spain, and Australia.
Each facility has multiple antennas.
And while the size of the antennas is important, it isn’t the only factor to consider.
Their placement is actually very important too.
They are all equidistant from each other and are approximately 120 degrees apart in longitude,
with each facility situated in semi-mountainous, bowl-shaped terrain to help shield against
radio frequency interference.
The location of the three sites means that at any given moment in the Earth’s rotation,
almost every area of the sky is covered by an antenna, so there aren’t many communication
blackouts with ongoing missions.
The DSN helps gather the science data acquired by the spacecraft, it transmits commands and
uploads software modifications to spacecraft.
While the DSN tracks, sends commands to and receives data from all NASA spacecraft beyond
the moon, the network also supports other international space agencies like the European
Space Agency ESA, Japanese space agency JAXA and the Indian space agency ISRO.
However, there are downsides to this system too.
They require large antennas on Earth, ultra-sensitive receivers, and powerful transmitters in order
to maintain contact over the vast distances involved.
And as incredible and as versatile as the DSN is, it is showing its age.
It’s been the only communication system for NASA for decades.
Replacing major components can cause problems, as it can leave an antenna out of service
for months at a time.
Plus, the older 70m antennas are reaching the end of their lives.
At some point these will need to be replaced.
And, in reality, they are not really very efficient when it comes to interplanetary
missions.
As I mentioned, at tremendous distances, the data transfer rate is painfully slow.
It took New Horizons over 2 years to send back all the data it collected from just the
one Pluto flyby.
So, what can be done better?
Well, this is where the Laser Communications Relay Demonstration mission comes into play.
Since the dawn of space exploration, NASA has used radio frequency systems to communicate
with astronauts and spacecraft, but the LCRD will demonstrate the capabilities of optical
communications.
Launched on 7th December 2021, this space relay is a new, better, faster and more advanced
way of transmitting data in space, using infrared laser communications rather than radio waves.
Infrared light has higher frequencies when compared to radio waves, and that means more
data can be packed into each transmission.
This antenna in space can send data to Earth from geosynchronous orbit at 1.2 gigabits-per-second.
With it, it’s almost like NASA is upgrading from ADSL to fibre internet.
Including the benefits of the increased data transfer speeds, the LCRD will also help NASA
remove the need for missions to have direct line-of-sight to antennas on Earth.
And its geostationary orbit will mean it is always in view of the ground stations on Earth.
A geostationary orbit means the spacecraft is orbiting Earth the same speed as Earth’s
rotation, meaning the same side of Earth is always in its view.
Now, this is a technology demonstration mission, but it is hoped that LCRD will prove the capabilities
of optical communications in space.
Using this system, we should have a bandwidth increase of 10 to 100 times more than radio
frequency systems.
Additionally, optical communication instruments are smaller in size, and they weigh less than
radio instruments.
So, for a spacecraft using optical communications, that would mean there would be more room for
science instruments, or simply a less expensive launch due to its lower weight.
In fact, the entire LCRD payload itself is only the size of a standard king-size mattress,
compared to the 70m behemoth radio antennas the DSN currently utilise.
Helpfully, optical communications systems are also very power efficient.
But the major downside of using optical signals is that they cannot easily penetrate cloud
coverage, so NASA must still build a system flexible enough to avoid interruptions due
to weather on Earth.
LCRD will test this by transmitting data to two ground stations, one of which is located
in California, with the other in Hawaii.
These locations were chosen for their minimal cloud coverage.
So, what will the LCRD actually be used for?
As part of the technology demonstration, it will be able to relay data from the ISS to
Earth at much greater speeds than are currently possible.
Because the ISS is orbiting so close to Earth, it’s only ever in view of ground stations
for very short periods of time.
However, if it is relaying data to the LCRD which is high above the Earth, it will remain
in view of the LCRD for half of its orbit and so can relay data to it for much longer
periods of time.
And assuming LCRD is proven a success, we do have some upcoming missions that will utilise
this new optical capability.
The Orion Artemis II mission which is planned to launch in 2024 is set to transfer ultra-high-definition
video over infrared light to Earth, which will show Artemis II astronauts exploring
the moon in a definition we’ve never seen before.
In addition, the Psyche mission, which is planned to be launched in 2026, will go to
an asteroid over 240 million kilometres away from Earth.
Psyche will carry the Deep Space Optical Communication payload to test laser communications at this
distance.
These missions will help pave a way for laser communication in the space field.
The increase in bandwidth will fix one of the major bottlenecks of science collection
that has really hindered missions in the past.
Being able to transmit ultra-high definition video from planets and asteroids going forward
seems like an incredibly exciting prospect, and honestly, I just can’t wait.
Plus, should we explore the far reaches of the solar system again, hopefully this time
we won’t have to wait years at a time for all the data to reach us!
So, there we have it.
Almost everything you would want to know about deep space communication systems, and how
future missions may enjoy a bandwidth we’ve never experienced before!
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