01 Jun 2006
-
Venus Express
Image courtesy of ESA
An ultra-precise radio system built by the ATC helped guide a spacecraft to a successful rendezvous with planet Venus on 11th April this year. The European Space Agency’s Venus Express probe used the technology to reach orbit around the mysterious world with pin-point accuracy so that it can conduct a survey of the planet. The system is based on revolutionary communications know-how developed by the ATC that is also being used for defence and security applications by BAE Systems.
Look up in the winter twilight and if you’re lucky you’ll catch a glimpse of what is widely described as the most beautiful object in the sky: the planet Venus.
Despite being called Earth’s twin sister because of their similar size and orbits, Venus remains an enigma. Its tranquil appearance disguises the terrifying conditions in its atmosphere and on its surface where clouds of sulphuric acid envelope a baking, pressure cooked landscape hot enough to melt lead. Scientists and environmentalists are keen to unravel the mystery of why our two worlds are so different and the Venus Express probe, navigated by the ATC software radio system will help to answer some of their questions.
At the heart of the radio system is a process developed jointly by the ATC and the University of Rome based on the ‘Delta DOR’ (Differential, One-way Range) concept. This produces highly accurate timing information (to better than 1 billionth of a second) by detecting radio signals from space at two deep space listening stations on opposite sides of the Earth: one near Madrid, the other near Perth in Australia.
Signals from the probe arrive at the receiving antennas at slightly different times, depending on the position of the spacecraft.
By performing a triangulation measurement, the probe’s position can be plotted rapidly to within 10 km from a distance of 120 million km. Equipped with the ATC’s version of Delta DOR, the mission planners can aim the spacecraft with the same accuracy needed to hit a ten pence coin in Sheffield from a shot fired in London.
“The main advantage of our simplified version of Delta DOR is that we can use this technique to get a very accurate check, very quickly to confirm the orbit of the probe. In the past, it would have taken up to two weeks to confirm orbit. With this system it can be done in 24 hours” says Nick James, radio systems expert at the ATC.
As the probe approached the planet, many factors could have conspired to knock it off course. Early confirmation that it had achieved the correct orbit was crucial to the success of that phase of the mission.
“Our system reduces the risk dramatically so even if something unusual happens in the approach to orbit, the mission controllers can respond quickly.” says Nick.
The communications experts at ATC have based their technique on a sophisticated radio technology that is already widely used by the European Space Agency and also by BAE Systems businesses for defence applications. These radios operate entirely by software rather than by the fixed electronic components found in conventional radios. For this reason they are extremely flexible and adaptable.
The Venus Express mission is expected to last two years and during its orbit the spacecraft will study in detail the atmosphere, plasma environment and surface of the planet and hopes to shed further light on the mechanisms of climate change on our own world.
