QotW: Are there space traffic controllers?

Listener Matt wrote to us at the Naked Scientists to solve his cosmic conumdrumn, so we found Dr Chris Bridges from the University of Surrey and had Katie King interview him for the answer.

Matt - Early commercial flights were scheduled and had air traffic control, but pilots were allowed a fair amount of latitude in the early days, which resulted in some mid-air collisions. I was wondering, with three space missions currently converging on Mars, how do the nations involved avoid orbital collisions? Do this year of data? Do they have transponders or space traffic control? Thank you.

Katie - I spoke with Chris Bridges, academic at Surrey Space Centre in the University of Surrey to find out more about your question. Let's see if you were right. Do they share data? Do they have transponders or perhaps even space traffic control? Let's find out more.

Chris Bridges - So fortunately there are not many missions out on Mars. Only about eight or so missions are currently orbiting the planet. If we compare that with the 34,000 objects around earth, Mars orbits are practically empty. Each mission does indeed share data on position and speed and we call those the state vectors of the given satellite. This data is shared between all major agencies like NASA, ISA plus our own UK space agency.

Katie - You were bang on the money Matt. Congratulations. Nations do share data. But how is this data obtained?

Chris Bridges - For almost all missions we use something called 'The Deep Space Network', and that uses a transponder to take highly accurate radio measurements, to determine what we call the range and velocity.

Katie - Right again Matt. They do also use transponders much like aircraft send that position to air traffic control. Before answering your final question, though, I want to know how do we determine the position and speed of a spacecraft when it's so far away?

Chris Bridges - The actual thing that we're measuring is signal lag and the 'Doppler shift', which gives us a change in frequency. We use these to determine the distance and the speed around a spacecraft on Mars.

Katie - Much like when sirens whizz past you on the street and they start to sound different due to the 'Doppler effect', we can use the frequency of the radio signals to determine how fast these spacecraft are going. Okay Matt, the final question, can you get the hat trick? Is there a dedicated space traffic control?

Chris Bridges - We don't have big space networks. We rely on a combination of special messages and critically the operators actually share the information like GPS data. So we have to work together so that our spacecraft aren't on track for any collisions. Especially in low earth orbit, we use thrusters to maneuver away if we need to. We often budget for this and our missions.

Katie - So Matt, I'm afraid you didn't quite get the hat trick as that isn't yet the dedicated space traffic control team. But as the use of space is growing so rapidly, maybe it won't be long before one exists. Thank you to Chris Bridges for your answers and next week we will be answering Sarah's question of...

Sarah - Why do ant bites hurt so much?