Science Interviews


Tue, 29th Mar 2016

Prospero: Britain's pride and joy

Doug Millard, Deputy Keeper, Technologies and Engineering at the Science Museum in London

Listen Now    Download as mp3 from the show Adventures in Satspotting

It's been over 50 years since Prospero launched and its long-since been Prospero satellitedecommisioned but what happens when a satellite 'dies?' Graihagh Jackson went to the Science Museum to meet Doug Millard...

Doug - When you launch a satellite or a crew into space, you canít just use one vehicle because as you burn up the fuel (the propellants), you get an increasing amount of dead weight, if you think about it, which is why we have these rockets in stages.  In a way, you have a sequence of rockets each firing one after the other.  So the first stage of Black Arrow, that uses a Gamma rocket engine.  If you look at the back of it you can see that each rocket chamber is arranged in pairs and they can swivel and that helps steer the rocket.  So, it gets it off the ground, starts to steer it and the second stage here, that takes over and that takes it a little bit higher still.  And then finally the third stage, which is the Waxwing rocket just above our heads, that has the satellite attached to it and that gives it the final kick into orbit and... mission accomplished.

Graihagh - I heard it was a bit of bumpy ride on the way up there - it wasnít all plain sailing?

Doug - It was yes.  The launch was successful but we can see one of the upper stage rockets called Waxwing and that was a little bit too enthusiastic.  Once it has put Prospero into orbit, it carried on firing and bashed into it and knocked one of Prosperoís radio aerials off.  Fortunately, it didnít disrupt the mission but it didnít shut down quite as quickly as it should have done.

Graihagh - And just if we look at Prospero, it does look like a little puck almost with - is it solar panels all the way round the outside?

Doug - Yes it is.  Itís covered in fillets they call them of different surfaces.  Most of them are, as you say, solar panels so theyíre generating electricity to help power the satellite.  But youíve also got some experimental surfaces - you can just see a white one there, and theyíre looking at different types of material and how they behave in space (in the vacuum of space) where thereís radiation.  Thereís also a little detector called a micrometeoroid detector, which just registers all the little bits of dust that were impacting the spacecraft.  So itís telling us as much as possible about how satellites could be launched and survive and also about the space environment.

Graihagh - It basically set out to find out as much as it could about what life for a satellite would be like, out in space. Up against the radiation, vacuums, the cold, the heat, itís not a particularly friendly place to be! Prospero engineers hoped that once we knew exactly what they were up against, they could build other satellites that would last many, many years...

Doug - So it was a test satellite.  It was telling us the rudiments of how to make a satellite that will last many years.

Graihagh - And indeed it has because itís still up there in space now.

Dough - Itís still up there.  Itís orbiting almost over the poles (we call it a polar orbit) and it takes about 100 minutes to go round the Earth but itís still up there.  We were communicating with it for many years after itís launch.

Graihagh - Indeed, a BBC TV series called Coasts Ďtalkedí to it back in 2004, but theyíre not alone, many people have listened out for itís tail-tail roar, like Greg Roberts.


Heís what you might call a radio ham - this is where hobbyists like Greg point their radio antennas at the sky and record these Ďweirdí signals from satellites and then do some detective work to find out which metal lump they had come from.


But sadly, it appears that Prospero is no moreÖ

Doug - Presumably the systems have finally succumbed to what is a pretty harsh environment (lots of radiation and temperature extremes) and, as far as I know, it no longer talks to us.

Graihagh - But people did try from UCL, I believe, a could of years ago to see if they could communicate with it?

Doug - Yes, for many years we tried to communicate with it every year on its anniversary and then in 2011, as you say, the UCL Physics Department tried to see if there was any life there but Iím afraid there was no indication that it was still Ďalive and kickingí.

Graihagh - Is that a fairly typical story of a satellite then that itís still orbiting forever, presumably?

Doug - Well you can launch a satellite into a variety of orbits depending on what sort of mission you want to carry out.  So, for example, let's think of the television satellites, the satellites that beam television direct to our dishes on the side of our houses.  They are a long way out - they are 36,000 kilometers out into space and theyíre going to stay up there for a long time, you know thousands of yearsÖ

Graihagh - Thousands of years!

Doug - Thousands of years.

Graihagh - How can they withstand the freezing cold, thereís solarwinds, thereís radiation - thereís so much to contend with?

Doug - Well, once youíre moving in space, unless you have something to obstruct your movement, youíll carry on moving almost forever.  When youíre that far out, there is really no vestiges of the Earthís atmosphere to slow you down.  The lower the orbit, for example Prospero, is only a few hundred kilometers above the Earth, so toward the end of this century itís orbit will start to decay quite rapidly and eventually it will burn up in the atmosphere - a fiery end.

Graihagh - It will burn up?  I just presumed weíd start seeing it raining satellites at some point.

Doug - Well Prosperoís quite small and none of it will survive - it will just be one brief fireball.  Satellites are really astonishing.  We tend to either take them for granted or not really think about them at all even though weíre using sat-navs and DBS broadcasting and so on, but they are made to survive in space without needing a fix.  You canít send round and engineer or a technician to fix a satellite thatís gone wrong.  You might be able to beam up some new software to remedy a fault but thatís not always the case.  So when youíve invested millions and millions of pounds in a satellite and itís launch, you want to make sure it works so they really are remarkable technologies.  The problem we face is because they are so successful and because most of them stay up there a long time, space is getting rather crowded and there is a risk of satellite collision.

Graihagh - What would happen in an incident like that?  Iím assuming that all these orbits are tracked so that hopefully they donít collide but, obviously, accidents happen?

Doug -   Accidents do happen. There is an unwritten protocol that the orbit is chosen so that no collision can occur but, occasionally, these things do happen.  There was a collision between a Russian satellite and another one not so many years ago causing a tremendous amount of debris and that is tracked.  You can keep an eye on something about the size no smaller than a grapefruit.  Fortunately with that particular collision most of the junk is now coming back down to Earth and it will burn up in the atmosphere.


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