Cassini - A 20 year mission to Saturn

The Cassini space probe is due to end its 20 year mission to study Saturn, by crashing in to the planet on Friday 15 September.

Michele Dougherty, The Royal Society, Research Professor, is Professor of Space Physics at Imperial College London and a principal investigator for the Cassini mission.

Q. What is the Cassini mission and who is involved?

"The Cassini Huygens mission is an international mission between the European space agency and the US space agency, which has been orbiting around Saturn since July 2004.

"Nasa is responsible for the Cassini part of the spacecraft; ESA is responsible for the Huygens probe, which travelled down through the atmosphere of Titan."

Q. When did the mission first start and when did you get involved?

"It’s a very long-term mission; these kinds of missions take a long time to get there. People first started thinking about them in the early 80s. We were launched in 1997.

"I first became involved just after launch, when the principle investigator of the magnetometer instrument went to the ESA as director of science, so I took over from him."

Q. Why has the mission been going on for so long?

"The original plan was the mission would last for four years, but all the instruments in the spacecraft were doing really well and the science we were getting back was great, and so it was extended and extended again.

"But we will not extend again...because we have essentially run out of fuel; even if we changed our minds, there’s nothing we can do about it."

Q. How will the Cassini mission end?

"The end of the mission takes place on 15 September...I’m going to go to Caltech where most of the teams are, because I want to be with my team at the end of the mission. And what we will do is stand and watch a screen and there will be a signal coming back and then it will stop, and then we will know it’s the end.

"We don’t know how long – we think it’s going to end at about 5am – but the atmosphere might be denser than we think, it might be less dense than we think.

"As the density of the atmosphere becomes stronger, we will then lose control of the spacecraft – we won’t be able to orientate the spacecraft – once we lose that signal then that’s the end of mission.

"It might take a bit of time to take the spacecraft to burn up, but we won’t know that because we will have lost the signal."

Q. What will you do after the mission ends?

"The first three days of the following week I’m planning to get together with my team. We’re going to continue to analyse the data, plan who’s going to work on what data set.

"So, that’s when the really exciting stuff starts, because the end of the mission – that last half an hour or so – we’re never going to get closer to Saturn than that, and so that’s going to be crucial to try and understand what’s going on."

Watch the full interview