How Is There Internet On The Space Station?

What about the internet in the space station and NASA communication with spaceships??
The radio and satellite communications network allows ISS crews to talk to the ground control centers and the orbiter. It also enables ground control to monitor and maintain ISS systems and operate payloads, and it permits flight controllers to send commands to those systems. The network routes payload data to the different control centers around the world. Image credit: NASA

The radio and satellite communications network allows ISS crews to talk to the
ground control centers and the orbiter. It also enables ground control to monitor and
maintain ISS systems and operate payloads, and it permits flight controllers to send
commands to those systems. The network routes payload data to the different control
centers around the world. Image credit: NASA

Originally posted at Forbes!

We covered some of the tricks behind NASA’s communication with spaceships a little while back, but the International Space Station’s internet access is pretty interesting. There are some significant challenges with getting the internet set up in space, beginning with not being able to run a fiber-optic cable from ground to space, and we still don’t have a planetary scale wifi network yet, so getting a wifi hotspot in space is still a challenge.

The vast majority of communication with the ISS happens via radio. Radio is a pretty straightforward means of broadcasting information, and we’re pretty familiar with radio for audio recordings. (Your cars almost certainly still have radios in them, even if you plug them directly into an mp3 player instead.) Radio is pretty easy to set up, as you just need to have an antenna and a transmitter. Even more helpfully, the atmosphere doesn’t block radio waves, so you don’t have to worry about the air absorbing the signal you’d like to send out. This also means that the atmosphere won’t get in the way of shooting a signal up into space from the ground.

In fact, radio waves are so straightforward that this is also how we communicate with most of our artificial satellites. We use a very narrow range of the available radio frequencies for the kinds of radio stations that your cars are sensitive to, but there’s a lot of other frequencies that we can use for other things. And, as is our way, we have used these other radio frequencies for other things. A GPS satellite, for instance, uses the radio to communicate with the ground. These satellites use a frequency range called “L band”, which ranges from 1GHz to 2GHz, which in turn works out to wavelengths of tens of centimeters and longer.

JAXA astronaut Kimiya Yui captured this photograph from the Japanese Experiment Module (JEM) window on the International Space Station on Dec. 6, 2015. JEM, also called Kibo – which means “hope” in Japanese – is Japan’s first human space facility and enhances the unique research capabilities of the International Space Station. Image credit: NASA/JAXA

JAXA astronaut Kimiya Yui captured this photograph from the Japanese Experiment Module (JEM) window on the International Space Station on Dec. 6, 2015. JEM, also called Kibo – which means “hope” in Japanese – is Japan’s first human space facility and enhances the unique research capabilities of the International Space Station. Image credit: NASA/JAXA

Going from a GPS ping to sending data along the radio wave is relatively straightforward – and if you’ve got a data plan on your cell phone, you’re already doing it. The LTE network in the US is also roughly an L-band connection between cell phone and tower. The L-band is also of interest to astronomers, as it illuminates neutral hydrogen gas in nearby galaxies. This overlap in frequencies is one reason you’re not allowed to bring your cell phone near a telescope which is trying to observe in the L-band; you’d interfere with someone’s science data.

The radio connection to the ISS isn’t L-band, it’s Ku band (12-18 GHz) and S band (2-4 GHz), but the principle is the same. We can beam a signal up to the ISS, which has an antenna which lets them receive it, and then their computers can download an email. To be more precise, typically we beam a signal up to a satellite and the satellite slings it over in the direction of the space station. However, there are limitations to how fast your radio-based connection can communicate, and one of the issues is distance from the source. When you’re beaming a signal to space, and power drops with distance, the rate at which you can communicate also drops. Unsurprisingly then, by all accounts the internet on the International Space Station is pretty slow. Astronauts rate it “worse than dial-up” but it’s at least there, and lets them write emails, post pictures on twitter, and call home to their families.

Interestingly, Twitter only became a part of ISS life in 2010! Before 2010, the access to the internet was pretty limited, so if an astronaut wanted to put something up online they would have to email it to the ground team via their radio connection, and the ground team could log into their account on their behalf and post it for them. Considering that the ISS has been going since 1998, this is a relatively recent upgrade.

There is another potential upgrade to the internet in space being tested. The machinery for it was delivered by one of the SpaceX capsules in April, 2014, called OPALS. Opals stands for Optical PAyload for Lasercomm Science, and it’s successfully gotten data down from the ISS to a listening station in California. OPALS is cool because it uses lasers, which means we’re switching from an analogue radio signal to an optical one. As anyone who happens to have fiber optic cables for their internet can tell you, optical data rates are way better than the alternative.

Artist’s illustration of OPALS instrument firing a laser. Image credit: NASA/JPL

Artist’s illustration of OPALS instrument firing a laser. Image credit: NASA/JPL

If we get the ISS switched over to OPALS completely, the internet for the astronauts will speed up by a considerable amount – the OPALS team estimates it’ll be somewhere between 10 and 1,000 times faster than what they have now. Unfortunately the tech is still in the testing phase, so the internet won’t have a speed bump just yet. In order to really scale this up, you’d need to have listening stations all over the planet, and the laser itself will have to very accurately point itself at the listening station. When you’re moving as fast as the ISS is, pointing in the right direction is no mean feat. In fact, the ISS is moving so fast, there’s only about a minute and forty seconds of communication between the ISS and the current listening station before the space station goes over the horizon again.

If this optical technology can be fully implemented, the ISS will enjoy the internet at significantly higher speeds through the wonders of laser beams!  In the meantime, the ISS, along with a number of other uncrewed spacecraft, will continue to talk, video, send data, and tweet with the earth via radio signals, beamed down to us through a constellation of satellites.

 

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How loud would a cell phone on the moon be?

We certainly wouldn’t be able to hear it ring - the lack of air in space would keep the sound waves from making it to us, but a cell phone does produce radio waves, and radio waves don’t need air to make it from the moon to the earth.

Let’s say a cell phone produces a radio signal of 1 Watt at a frequency of 1.8 GHz. Your average light bulb produces 60 Watts of energy at a much higher frequency (hence why we can see the energy produced as light!) 1.8 GHz is a radio wavelength, so we’re not going to notice this radio wave coming from our phone. 1 watt is not very much energy, and the moon is pretty far away - but we can work out what the energy would be when it arrives at earth.

We know that as light (or any other wave) radiates away from a point source, the further from the source you are, the weaker the light appears. You can quantify how much weaker it is if you know the distance - power decreases with the distance squared - if you’re twice as far away, the light is four times weaker.

Now, since we know the distance to the moon, the strength of the signal when it starts, we can figure out how much weaker it is when it arrives at the earth.

Radio astronomers use a super intuitive unit of radio power: the Jansky. A Jansky is defined as 10^-26 Watts per square metre per Hertz, which is a super tiny amount of power. So to figure out how many Janskys of power would be arriving at the earth from this single cell phone on the moon, all we have to do is to divide the power produced by the phone by the square of distance to the moon in metres, and then divide by the frequency of the power we’re looking at.

In our case, the power is 1 Watt, the distance to the moon is 384,400 km (3.844 x 10^8 metres), and our frequency is 1.8 GHz, or 1.8 x 10^9 Hz. This gives an equation of:

=1/((3.844 x 10^8)^2) / (1.8x10^9)

=1.45 Janskys

Now, nearly 1.5 Janskys of power arriving at the earth is a pretty small amount of power. Can you even detect this little amount of power?

It turns out that you can! Radio telescopes regularly use calibration sources that are about the same brightness as our moon cell phone! And these are relatively bright sources - you want to calibrate to something that is bright enough to see relatively easily. A science target, which is usually much fainter than a calibrator, can be a hundred times fainter than this! Imagine trying to look at a very faint object in the sky, and having a cell phone signal come in from the moon and overwhelm your science target by being 100 times brighter than your target.

So a cell phone on the moon is definitely loud enough to be heard by current radio telescopes, even if there’s no way the sound of the ring would make it to earth.

Have your own question? Feel free to ask!