How Does A Satellite Stay Up In Space?


Let’s start with the background before we dive in and answer the questions ‘how does a satellite stay up in space?’ and ‘where does a satellite go after it dies?’.

For starters, a satellite is anything that orbits something larger than itself. So, all of us Earth-dwellers (which will be most of you reading this) are sitting, standing or even body-popping on a satellite of the Sun, with the Earth also having its very own natural satellite: the Moon.

All that’s well and good, but we’re talking here about the satellites that the boffins build and then throw into orbit.

Throw That Satellite Real Good

Now, I’m using that phrase ‘throw into orbit’, because that’s pretty much how it works with satellites. Grab a stone and I’ll show you how a satellite stays up in space.

So, drop that stone that you have and it falls to the ground. Yup, that’ll be gravity (which doesn’t actually exist, but that’s another story for another time). Now, throw that same stone with a bit of force and it’ll trace an arc away from you before it hits the ground. Throw it a bit harder, with a bit more power behind it and that arc gets a bit longer before it falls to the ground.

your-stone-throw

OK, now give it your best shot and really throw that stone as hard as you can. Give it all you’ve got. But be careful, it may hit you on the back of the head if you’ve done it properly. Or if you’re really unlucky, you might be paying out for your neighbour a new pane of glass for his or her greenhouse. Don’t go dropping that bill on me, it’s your stone, so make sure you take responsibility for it.

my-stone-throw

Why’s that stone maybe going to hit you on the back of your noggin?

All Rounded Out

Well, a few of you reading this may have noticed that the Earth is spherical. Not because somebody told you so, but because you can see for yourself. Just look out to the horizon and there’s the curve. Right there. A few of you may be flat-Earthers, so just stop reading now and maybe go indulge in some pointless homeopathy.

For the rest of us, the fact that the Earth is spherical means that if you throw something hard enough, it will fall at the same rate as the Earth is curving away from it.

meme1

That’s all a satellite does to stay up in space. It falls to the Earth as the Earth curves away. Just stick your satellite into or onto a rocket, get it outside the atmosphere and then throw it.

Simple.

Kinda.

Superfast And Deadly

The thing is, those boffins have to work out some other stuff too. The rocket must fly between 100,000m to 200,000m above the earth to get outside the atmosphere. To make things a bit easier, the rocket is launched in the same direction that the Earth is spinning, which gives it a little extra boost. A bit like an acrobat swinging off a trapeze when it’s moving forward. Once the space rocket hits a pre-determined orbit elevation, it could be heading sideways at 15,000 miles per hour or more. I once modded up a car so it could reach those sort of speeds, but the speedo was knackered, so I never did get a true reading.

Anyways, the rocket switches off and drops the satellite, which is now in the same orbit, belting along at those same speeds.

At those heights, the atmosphere is just thin enough to prevent the satellite from burning up from the air friction, but it might need an energy source to give it some propulsion and stop the air acting as a brake and tilting it towards the Earth. If that happens and it drops lower, the thicker air is probably going to burn up that sucker and light it up like a firework.

However, get a satellite up high. Way high. 600,000m high, where the International Space Station orbits and there’s no air friction. Here that stone will just keep on squirting around the Earth for a mighty long time.

And at this height they are travelling fast. Even faster than that old car of mine. We’re talking 5 miles every second, so in a minute that’s 300 miles that they’ve covered. Dang, suddenly space doesn’t look that empty anymore. That’s going to be one busy street to cross.

So really, a satellite’s ability to maintain its orbit is all about its velocity (the speed at which it would travel in a straight line) and the gravitational pull between the satellite and the planet it orbits. The higher the orbit, the less velocity is required. The nearer the orbit, the faster it must move to ensure that it does not fall back to Earth. Job done.

This Is The End, Beautiful Friend

But these hi-tech falling stones ain’t going to last forever. Like all of us – except maybe Mick Jagger or Keith Richards (if you don’t know about them, Google is your friend) – they’re all going to grow old, wear out and die, just like that old smart phone that you dropped in the toilet. You know the one, fool.

So what happens when a satellite’s time comes? Well, we got two choices: some boffin could use up the last bit of fuel to slow it down, allowing it to fall out of orbit and burn up in the atmosphere.

nasa

Source: NASA

It’s better to burn out than fade away. Google that too, some real crazy legend once sang that a long, long time ago.

The second choice is to send the satellite even further away from Earth. Great if you have a satellite in a high orbit. You’re going to need just a little bit of juice to blast it way into space rather than sending it back to Earth.

Now, those satellites that we nudge back towards Earth don’t always burn up completely on re-entry. If they’re big badass lumps of junk then they could reach the ground. And that’s going to hurt you more than your stone hitting you on the back of the bonce.

Going To The Graveyard

So, those boffins have a plan. It’s called the Spacecraft Cemetery. And that’s one of the few horror-sounding things that Stephen King didn’t use as a title for a book. The Spacecraft Cemetery is in the Pacific Ocean and it’s pretty much the farthest place from any human civilization you can find. That’s where they point those hunks of space junk. It’s home to the defunct Russian Mir space station, resupply spacecraft for the International Space Station and the European Space Agency’s Automated Transfer Vehicle. In all, there have been nearly 300 spacecraft disposed of in the Spacecraft Cemetery since 1971.

spacecraft-graveyard

So, that’s a bit more knowledge shoved into your noggin. Now go out there and drop all that shnizzle into a conversation. Dork or rock star, your audience will be the judge. It’s all in your delivery. Don’t crash and burn on me now.

Hopefully cramming this tasty bit of information into your head hasn’t pushed out another vital piece of knowledge. I don’t know, maybe like controlling your bladder or perhaps how to walk and breathe at the same time.

That would be a bit bad.

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