Why space matters: Imaging satellite operations, part 10–short bus schooling

Labor Day took its toll, but I’m back to write more (hopefully) interesting articles for you.

What a space operator should know about satellite systems and space operations fills several volumes of books, folders and checklists.  But, in essence, a space operator and space operations crew worries about three things:  the satellite ground system, the satellite bus, and the satellite payload (which typically receives a lot of a space operator’s attention).  There is additionally, the mission, but this depends very much on the payload(s).

We’ve already talked about the ground system in this lesson and this lesson.  But now we’re going to get into the satellite itself.  Starting with the satellite bus.

Satellite bus
Satellite bus

The satellite bus, depending on who you are, can be the least interesting or most interesting aspect of the satellite.  Whatever it is to you, be aware that the satellite bus is the foundation, the satellite’s infrastructure, and is what enables the satellite payload to work and talk with the space operations center in the ground system (so it’s not the picture above–although you could have a bus shaped like a bus).  The bus is an integration of a whole lot of sub-systems:  Power (solar panels, batteries), data (satellite telemetry and tracking information, antennas), thermal (radiators—active/passive/both), pointing (control moment gyroscopes, thrusters, reaction wheels), and fuel (for the thrusters).  Plus there are places on it for the payload.

And typically, if the builders and owners of these satellites are trying to buy down the risk of something going wrong, there are duplicates and backups of these sub-systems.  Just take a look at this GOES databook’s illustration on page 103.  Note the redundancies:  command receiver A/command receiver B, DSN Transmitter A/DSN Transmitter B, etc.  And that’s just one sub-system.

Remember, with some very small exceptions (Hubble), there isn’t a way to physically repair satellites once they are in orbit.   And a satellite that’s broken at the very beginning of its mission is just a very expensive and fast moving star in the sky (sometimes it’s a falling star).  In some ways, it’s quite amazing it all works, every—single—day.

What controls all of these sub-systems, is (I bet you know the answer to this one):  another sub-system.  Since we haven’t had the good fortune of raising a sentient race of space monkeys just yet, the space program has had to develop computer systems which are specifically designed to control the other sub-systems.  These computer systems are also known as control sub-systems and are the brains and the nervous system of the satellite.

There’s no mystery to these systems, as they work just like the computer you’re reading this lesson on (but they might be slower, with older hardware).  If you feel the need to learn more about computers generally, then please head over to the TWIT or Revision3 networks and get your learning on.

Since this control sub-system is the satellite’s brain and nervous system, I bet you are thinking:  “Gosh, it must be the most important sub-system on the satellite; therefore, it probably has a backup, too, maybe two.”

And you’d be right in thinking that–congratulations!  So, now you know what a basic (not short) bus is:  control, power, data, thermal, pointing, and fuel.  Maybe one day we’ll get into detail about those sub-systems, but not today—we’re trying to get you from the bus-driving space operator level, to the payload space operator level (which is more interesting to me personally, anyway).

But you do need those bus-drivers to help keep the whole thing a success…

Until the next lesson!

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