JUICE will launch on 13 April and for eight years, the craft will travel towards Jupiter. Three moons orbiting the giant planet have caught the eye of researchers back on earth. They are covered in ice and by combining a number of experiments researchers will be able to deduce if there is water under the ice. One of the experiments will utilize four electric probes mounted on JUICE, spherical, 0.5 mm thin shells of titanium that are slightly larger than tennis balls. These probes are coated with a 380 nanometer thin layer of a special titanium-aluminium-nitrogen alloy specifically designed to make them highly sensitive to electrically charged particles, namely ions and electrons.
“It is the same particles that create auroras here on Earth, but much, much less particles. We developed this coating and how to apply it with ultra high precision and uniformity. Basically it is a coating that is hypersensitive to ions in vacuum. The auroras around Jupiter's icy moons have specific attributes depending on what's inside them and together with the other experiments on board the JUICE spacecraft, it will be possible to see if it is liquid water or ice - or maybe something else”, says Jens Birch, professor at the thin film physics division at LiU.
The measuring probes have to perform at a very high and specific level. Not only did they need a coating that could perform the task at hand, but also to be able to survive the journey. No small feat, considering that JUICE will get very close to the sun while using it for a slingshot maneuver.
“It can survive up to 400 degrees celsius.”
Uppsala University created a similar probe to be used to research the planet Mercury in a previous mission. Due to the extremely thin atmosphere in the vicinity of Jupiter, these probes are much larger than anything that has been coated before with such extreme demands. This time they didn't have the necessary tools for the job and asked the researchers at LiU if they could do it.
The team that took on the challenge consisted of Prof. Jens Birch, Dr. Babak Bakhit, Prof. Grzegorz Greczynski with technical assistance of research engineer Harri Savimäki. The probe is a sphere of titan, half a millimeter thick, like an egg shell. They had to create a way to make the coating equally thick all over, which was very difficult. Also, in the creating process, the coating's sensitivity to ions became an unexpected problem.
“We had to find a way to neutralize the electrical charge during the coating process. We also had to find a way to manipulate the probe inside the chamber”, says Jens Birch.
Using a carousel-like construct with two rails, the researchers could make the probe roll around and get an exactly even coating of 380 nm thickness.
Spacetravel comes with extreme demands
Sending something out in space that has to perform after years of travel has other specific challenges.
“The quality control was extremely rigorous and we were lucky to have a clean room that is clean enough for space applications and a large enough chamber for the coating process”
If the results show that there is water under the ice of the moons of Jupiter, researchers think it is highly likely that life exists in many more planetary systems than previously thought.
“Discovering new things nobody has known about before is why I'm a scientist in the first place, so contributing to a discovery like that would feel good”, says Jens Birch.