UK launches first dedicated Earth-imaging satellite

UK Space Command has launched its first dedicated Earth-imaging satellite. It is called TYCHE - named after the Greek goddess of fate and fortune - and the Ministry of Defence says it will help strengthen the UK’s intelligence, surveillance, and reconnaissance capabilities. So what should we know about it? I’ve been speaking with Phil Allen and Darren Jones at Surrey Satellite Technology Limited, which built the new satellite…

Darren - TYCHE is an intelligence surveillance and reconnaissance satellite. What that means in layman's terms really is using sensors to be able to image the Earth's surface and monitor what's going on. TYCHE is the first concept demonstrator that will be part of the future constellation that the MOD wants to launch into space. So it provides pictures and videos as well. And the aim over time is the MOD will build up a whole constellation of similar satellites, some with visible sensors, some with potentially infrared sensors, some with radar sensors.

Chris - I remember when I was little, Darren, my dad telling me about some spy satellites that the US military had put in space and saying, and I'm not sure if it was true, but this could read the headlines on a newspaper from space. What sort of quality of resolution will you be able to see with this?

Darren - TYCHE certainly doesn't have that level of capability, but tyke has a measure of resolution of around a metre. So it can pick out vehicles, determine what sort of type of vehicle, an aircraft they are, but certainly not down to the ability to read number plates off of cars. It's worth pointing out that this is the very first satellite that MOD is procuring and the aspiration is to deliver higher resolution spacecraft as well over the coming years.

Chris - Where did the MOD get its eyes in the sky before then, before you came along with this one? What were they using?

Darren - The UK Armed forces have ISR capability for many years, typically from aircraft manned or unmanned aircraft. So this really offers not necessarily replacing that capability, but complimentary capability. You can provide imagery from satellites over areas of the world that you wouldn't necessarily have access to.

Chris - Phil, you led the engineering on this. How big is it?

Phil - You may have seen that A lot of people have likened it to a washing machine size, which is not entirely unfair. It's about a metre by a metre by a metre

Chris - As satellites go. Am I forgiven for saying that's actually on the small side? Because a big GPS satellite, they're sort of bus sized, some of them, aren't they? So a washing machine sounds positively small in comparison.

Phil - I think you are dead on the money there. Surrey Satellite Technology was set up with the aim of making small satellites, seeing what we can do there and now we are the world leader in small satellites. TYCHE is smaller but also has a lot of capability behind it. Unfortunately what comes with large bus size satellites is a large bus size price tag and not always a huge amount more in capability.

Chris - What sort of orbit does it occupy? Because there is a range of ways of doing this isn't there? You can put them so they go over the poles and the planet turns inside the orbit. You get a big view of everything or you can stay in one position relative to the Earth's surface in a geostationary orbit. So where's this one gone?

Phil - This one is in a low Earth orbit. So it's in what's known as a polar sun synchronous orbit. As you quite rightly said, the world moves underneath and therefore you cover the globe in a number of days. Well what's special about a sun synchronous orbit is it means that your orbit plane relative to the sun is pretty much constant throughout a year. And that means that unlike some spacecraft that would have large tracking arrays, which are costly and very complicated, we can have arrays that are deployed to a fixed angle. They will always be facing the sun throughout the year.

Chris - These are your solar panels that presumably power it. Can I ask the question then that when you go behind the Earth, the satellite can't see the sun. So do you have to put some kind of provision in so that it can store enough energy when it can see the sun so it not just powers itself then but has got reserve for when it goes behind Earth and is in the shade?

Phil - That's correct. So the spacecraft has a large battery, a bit like in your mobile phone, but is much more carefully controlled. There's a lot of circuitry around to make sure that the battery is in good health. Anyone that's had a mobile phone or other rechargeable products will know that over time it doesn't perform as well as you'd like and can't hold its charge. We can't afford that for a spacecraft. Anytime that you go into a period of shadow or eclipse as it's known, then it's on battery power at that point. And once you come into sunlight, the solar cells start to charge that battery back up.

Chris - Did you have to solve any new or major problems in order to deliver this or is it very much a question of bringing together existing knowledge? Because Surrey Satellites has had form in this game for a long time. I mean you're one of the world's leaders in doing this kind of thing, so therefore was it a question of putting bits together you already knew or was there new science in this?

Phil - I would've loved to stick bits together already, but no, we had a number of key new components. The two that stick out to me more than any other one that is known as the ACP, the auxiliary computer peripheral, which provides onboard processing capability and the other is the ISL or inter satellite link, which allows us to communicate with the spacecraft when it's not in direct view of our ground station. Here in Guilford, both products themselves were new and getting an understanding of what the customer wants to use with these, how they work with existing systems, how they work with one another, were all big challenges to overcome on the project, but we are now seeing that they're working out as expected.

Chris - And can you move it around? Now you've put it there, can you change its position? Does it need a boost to put its altitude up periodically? How do you do that sort of thing?

Phil - So there's a couple of things. The orientation of the satellite itself. So the spacecraft is rotated around using reaction wheels. So these wheels spin up and have a mass on them and there's what you would conventionally think there'd be one per axis, but there's actually four in each, are in two axes. So that if any one of them were to fail, you could still rotate things around and a lot of spaces about working out if something goes wrong, how can you carry on? And this will allow you to track targets as you go over to take images with. It also allows you to track the ground station when you are downlinking your data. But in regards to orbit manoeuvre, the spacecraft has a water propulsion system and this allows us to raise or lower our orbit if we were to have to avoid space debris, for example. A spacecraft even as high as TYCHE is still subject to atmospheric drag, which will reduce its orbit height over time because it slows it down. And so we can use the propulsion system to raise the spacecraft's velocity and thus increase its orbit height. Again, back to its operational orbit.