Parts of a satellite

Dr Allan McInnes describes the major components common to most satellites. He then explains how some of these function.

Point of interest:
Watch the video a second time and make tally marks or quick notes on the number and/or names of components common to most satellites.

Transcript

DR ALLAN MCINNES
All satellites have the same sort of major components. The one thing that tends to change from satellite to satellite is the payload, which is the sensors or the radios or whatever else that are actually involved in performing the mission of the satellite. The rest of the satellite consists of, well, a structure to hold everything, and that’s got to be something that can take the forces of a rocket launch and also keep the satellite together in space. Usually, there’ll be a radio maybe in addition to the other communication stuff to allow us to talk to the satellite, both to send it commands and also to get information back down from it about how it’s operating. Typically, we’ll have an onboard computer of some kind where commands get executed, and usually the computer’s monitoring what the satellite’s doing, making sure it’s pointing in the right direction, making sure that it’s doing what its intended mission is, and if there is anything that goes wrong, responding to that. If it’s a scientific satellite, it might also be storing the data on board for later transmission to the ground.

If you’re in space and you’re trying to talk to the Earth, you want to make sure you’re actually pointed at the Earth. So every satellite has what we call an attitude control system The attitude is the way you’re pointed, the attitude control system changes the direction you’re pointed in. That also means you need to have a way to sense which way you’re pointed so usually we have things like Sun sensors that tell us where the Sun is or magnetometers that are kind of like a highly complex compass, and we can use a combination of those things to figure out where we are pointed and then use things like thrusters to change the direction that we’re pointed in.

Thrusters – so that’s another part of a satellite. Usually we have a propulsion system of some kind. It might be thrusters to change the direction or to maintain the orbit. Attitude control isn’t always done with thrusters, sometimes it’s done with other things

Thermal control actually is an interesting one – again, a bit more of a problem in space than it is on the ground. If you think about your computer. Your computer has a fan in it because it’s got a power supply that gets hot and you need to cool it down, otherwise the computer’s going to stop working. Well in space, there’s no air, so fans aren’t going to work real well, but we still need a way of getting rid of heat, and so you have to have some kind of design for a thermal control system that essentially radiates heat out into space.

Spacecraft run on electricity, so they need a way to get power. The vast majority of them operate off solar arrays, so they’ll extend big solar arrays that are full of photovoltaic cells that take sunlight and convert it into electricity. Of course, you’re not always able to see the Sun especially if you’re in a low-Earth orbit – sometimes you’re behind the Earth relative to the Sun – so instead what we do is have a bunch of rechargeable batteries on board as well.

Acknowledgements:
Cryosat II footage courtesy of European Space Agency/ESA
NASA
MIT Satellite Team, Massachusetts Institute of Technology