You know what’s the coolest thing ever?
Not that we can send spacecraft to distant
planets but that we can get hi-res images
back!
Yeah.
Awesomesauce.
Hello, everyone, Amy getting nerdy about SPACE
today with you on DNews!
Every spacecraft, telescope, probe, or lander
we’ve ever sent into space has to communicate
with the Earth to both receive commands and
return data.
Since 1957, when the Soviet Union launched
the first ever satellite, Sputnik, they’ve
all used radio waves.
A radio wave has a regular pattern, so data
is encoded by either changing the amplitude,
more simply the height of the wave, or the
frequency, which is how close the peaks are
together, a value measured in Hertz.
If we’re changing the amplitude, for example,
some peaks can be higher than others and we
can assign values to them so the higher peaks
are 1s and the lower peaks are 0s.
If we’re changing the frequency, 1s can
be waves that are closer together and 0s waves
that are further apart.
These patterns are received by radio dishes
and interpreted by mission scientists.
The process of encoding data and sending it
on radio waves is the same regardless of what
the spacecraft is sending home, so that could
include voice transmissions, spacecraft data,
and pictures.
Modern spacecraft have digital cameras on
board.
The core of the camera is a small device made
up of light-sensitive pixels on a sensor.
Every pixel has an assigned number to denote
its position on the sensor.
When the camera takes a picture, each pixel
then measures the brightness of its specific
part of the scene.
The measured brightness is also given a corresponding
numeric value.
So basically the image is broken down into
numbers, one for brightness and one for the
location of the pixel on the sensor.
Getting the picture back is then a simple
process of sending those numbers back to Earth
on radio waves.
Radio waves are easy enough to receive with
radio dishes, just as long as the spacecraft
and the dish can “see” one another -- meaning
that there aren’t any large bodies like
planets and moons blocking the wave’s path.
Then it’s just a matter of the mission scientist
translating pixel information into an image!
So if we have pictures beaming down from all
over the solar system, why don't we have video
yet?
It comes down to how much information radio
waves can carry.
The limiting factor in radio communications
is the bandwidth, or the frequency of a wave.
Higher frequency waves can carry more data,
but radio waves can only have so high a frequency,
even if they’re manipulated to encode data.
The shortest radio waves are only 300 GHz.
The frequency can get higher, the thing is,
at that point, it becomes visible light.
So to have a communications system that can
carry more data, you need optical communications.
More data can be held in a laser beam than
a radio wave because the laser’s frequency
is much higher.
But there's a tradeoff.
Radio waves are so big they're easy to receive.
Laser beams are narrow and have to be perfectly
aimed at a receiver.
But NASA is working on it!
In 2013, scientists beamed a picture of the
Mona Lisa to the Lunar Reconnaissance Orbiter’s
LOLA instrument, marking the first optical
communications beyond Earth orbit.
Closer to home, the OPALS mission use lasers
to beam a video to Earth from the International
Space Station.
So for now we can only have videos from space
made out of images put together to simulate
motion.
But soon we could have live video from Mars!
With the light time delay, of course.
But this is all how modern cameras work.
Back in the 1960s, there were no digital cameras;
Apollo astronauts used film on the Moon and
then developed it back on Earth.
So how did we get live footage of Neil Armstrong
landing on the Moon?
I’ve got a look at how we saw those historic
first steps over on my own channel Vintage
Space.
But what about colour data?
The story of modern images from space gets
a little more complicated when we talk about
how we know what colour things are in space.
I’ve got more detail on what colour the
planets really are in this episode of DNews
right here.
What pictures from deep space do you guys
love?
Let us know in the comments below and be sure
to check back for a new episode of DNews every
day of the week.
