The making of a satellite

12 May 2017

Graham Johnson, Senior Engineer, Spacecraft Platform and Operations, Inmarsat

  • maritime
  • enterprise
  • aviation
  • government

  • global-xpress

I’ve been passionate about space and space exploration for as long as I can remember. As a young child, I was lucky enough to be able to visit the Kennedy Space Center in Florida, and I still remember being completely amazed and in awe of the incredible machines on display and the idea of floating around in space.

Many hours watching Star Trek in the years that followed probably solidified my desire to work in the space industry, so there was really no doubt what kind of job I was going to apply for when I left university.

Fast forward and I’ve been working in the space industry for ten years now, the last three with Inmarsat. I still love going down to the cleanroom to see the spacecraft coming together and I can’t wait to watch the launch of our Inmarsat-5 Flight 4 (I-5 F4) satellite at SpaceX soon!

The satellite journey – from contract to launch pad

What many people may not realise is that getting a communications satellite to the launch pad is a process that typically starts at least four years before the rocket bursts into life.

To make sure we end up with a satellite that does the job, day-in, day-out, for 15 years or longer with no possibility of maintenance, we follow a strict design and development process. We conduct a series of reviews throughout the design phase, to check that the design is adequate and will comply to our requirements. Then during manufacture an Inmarsat representative will physically inspect virtually every single part on the spacecraft, right down to the level of nuts, bolts or individual solder joints!

The making of an Inmarsat satellite officially commences with the signing of a contract with one of the major satellite manufacturers, and in the case of I-5 F4, that manufacturer was Boeing, which has built all four of our advanced fifth generation satellites that make up the Global Xpress constellation.

The contract lays out all of our key requirements, explaining exactly what we want the satellite to do, the design rules to which it should be built, and a long list of the tests that it needs to pass before we will accept it.

The I-5 satellites are based on one of Boeing’s existing platforms so they had already defined all of the main parts that would be assembled into the spacecraft, for example the thrusters, the computers, the batteries and the fuel tanks.

Qualifying a satellite

The first big activity with any spacecraft is to then to check the ‘qualification’ status of every single part. ‘Qualification’ is a very important concept in the space industry. It’s how we decide whether a part is OK to be put on our spacecraft or not. To be ‘qualified’ it must have been put through a rigorous set of tests which simulate the space environment. This includes:

  • a fairly violent vibration test (to simulate the shaking that’s experienced during the launch)
  • a shock test (to simulate what happens when the different stages of the launch vehicle separate)
  • a radiation test (our spacecraft fly outside the Earth’s magnetic field, which means they are not protected from the Sun’s radiation like we are on the surface)
  • thermal vacuum testing (to make sure the spacecraft can survive the extreme temperatures of space).

A thermal vacuum test is carried out in a big cylindrical chamber which we seal and then pump out all of the air to make a vacuum, as in space.

We then run a cooling fluid around the walls of the chamber at any temperature we choose, to simulate the thermal environment that the unit will see inside the spacecraft. Later we also test the complete spacecraft in a chamber like this, and for that test we run liquid nitrogen (at -180°C) around the chamber walls to simulate the coldness of space. This test can last for several weeks, so you might see many tankers turning up throughout the test to deliver more liquid nitrogen!

Launch ready

If the part survives all of these tests, and still works just the way it did before the tests began, then we can say it’s ‘qualified’ for spaceflight.

While we like to use parts that we know have already passed these tests, Inmarsat is at the forefront of the satellite industry and therefore our spacecraft tend to be some of the most complex as we constantly push the manufacturers to develop more advanced and more capable technologies.

Finally, after testing, Inmarsat will review the results with the manufacturer and make sure that everything is working exactly in line with all those requirements that we put in the contract.

And if everything checks out, then we’re ready to head to the launch pad!

About the author

Graham bioGraham Johnson joined Inmarsat in 2014 and has been working as the Spacecraft Platform & Operations Engineer on the S-band satellite for Inmarsat’s European Aviation Network. After graduating from Cambridge University in 2006 with a Master’s degree in Engineering, Graham spent eight and a half years at Airbus Defence & Space where he worked primarily as a Thermal Engineer on BepiColombo, an ESA spacecraft due to launch in 2018 to explore Mercury: the innermost planet in our Solar System.