JUICE spacecraft gains momentum: Critical double flyby around the Moon and Earth TU Braunschweig involved in space project with measurement systems

On the 14th of April 2023 the satellite mission JUICE (Jupiter Icy Moons Explorer) of the European Space Agency ESA was launched from the spaceport Kourou in French Guiana. Technische Universität Braunschweig is participating in this mission with, among other things, a magnetometer from the Institute of Geophysics and Extraterrestrial Physics (IGEP). The aim of the mission is to explore the icy Galilean moons Europa, Ganymede and Callisto, which orbit the planet Jupiter. Researchers are particularly interested in whether life could exist beneath the surfaces of Europa and Ganymede, where oceans of liquid water are thought to exist. The measurements needed to answer this question will only be possible when the JUICE spacecraft arrives in the Jupiter system in 2031. The magnetometer will make an important contribution to the characterisation of the oceans.

In order for the spacecraft to make it to the Jupiter system at all, numerous flyby manoeuvres of Earth and Venus are required on the way there. The first and probably most spectacular of these manoeuvres will take place on the nights of 19 and 20 August 2024. First, JUICE will fly past Earth’s Moon, initiating an orbit correction manoeuvre that will take the spacecraft past Earth and back into the depths of interplanetary space towards Venus. Never before in the history of spaceflight has this critical double flyby manoeuvre been flown around the Moon and Earth.

Old acquaintances

As it passes through the threshold of gravity, the JUICE spacecraft will meet up with old friends: NASA’s five THEMIS satellites, which have been orbiting Earth since 2007. As part of the THEMIS mission, two of these spacecrafts were sent to the Moon, where they have been orbiting since 2010, under the new name ARTEMIS. Braunschweig technology is also being used on these spacecrafts: each THEMIS and ARTEMIS satellite is equipped with an additional IGEP magnetometer. The main aim of these missions is to study the dynamics of the Earth’s magnetosphere, which represents the influence of the Earth’s magnetic field in space.

Joint spacecraft exercise for the measurements in 2031

The Earth’s magnetosphere is strongly influenced by the solar wind, a stream of electrically charged particles that continuously flows from the Sun. The interaction with the solar wind causes the Earth’s magnetosphere to expand like a tail. At the time of the flyby, the Moon is located within this geomagnetic tail in the Earth’s magnetosphere. Together with the ARTEMIS spacecrafts, JUICE will be able to practice the precise characterisation of the magnetic fields here, which will be of great importance for the success of the entire JUICE mission in the Jupiter system. To do this, the ARTEMIS spacecrafts will be switched to a long-duration, high-resolution measurement mode.

Complex measurement situation expected in the Jupiter system

In the Jupiter system, JUICE will find a very similar measurement situation on the one hand, and a much more stringent one on the other. The Galilean moons always orbit Jupiter within its huge magnetosphere. However, Ganymede is the only moon known to generate its own magnetic field through an internal dynamo process. So there is a magnetosphere (of Ganymede) within a magnetosphere (of Jupiter) around Ganymede. In order to detect and characterise subsurface oceans in these moons, magnetic perturbations from these oceans must first be cleanly separated from complicated external magnetic structures.

Key to success: reliable interaction of all magnetometers

To achieve this without the need for other satellites, the IGEP magnetometer on board JUICE is part of the overall J-MAG instrument developed by a consortium of European universities and scientific institutes led by Professor Michele Dougherty (Imperial College London, ICL). In addition to ICL and IGEP, the Space Research Institute (IWF) in Graz is another key player in the consortium; the three institutes have each contributed a magnetometer to J-MAG. Only by working together will the three magnetometers be able to achieve the necessary measurement accuracy to allow a magnetic look beneath the surfaces of Europa, Ganymede and Callisto.