ESA Science & Technology - #8: Successful integration of JUICE's 10.6-metre-long arm

Expanding JUICE's toolkit: integrating the magnetometer 'arm'. Credit: Airbus, Sener

In late February, JUICE hit a milestone when the boom for its J-MAG magnetometer and Radio and Plasma Wave Investigation (RPWI) instruments was successfully moved into place and installed at the Airbus satellite integration centre facilities in Friedrichshafen, Germany.

The boom will hold five magnetically sensitive sensors away from the main body of the spacecraft itself, in order to avoid any possible magnetic interference or disturbances as the instruments study the minute intricacies of Jupiter's magnetism. The boom is folded into three parts when stowed, weighs about 44 kilograms, and is made of non-magnetic materials – including carbon fibre, titanium and aluminium alloys, and bronze – that can withstand temperatures of -210 to +250 °C.

Artist's impression of the JUICE spacecraft. Credit: ESA/ATG medialab

Three J-MAG sensors (two fluxgate magnetometers and one scalar magnetometer) and two RPWI sensors will be mounted on the boom and will enable JUICE to characterise Jupiter's magnetic environment, explore the magnetism of Ganymede (the only Solar System moon with an intrinsic magnetic field), and probe the subsurface oceans of the icy Jovian moons. Between them, RPWI and J-MAG aim to study how Jupiter's magnetic field interacts with three of the planet's large icy moons (Europa, Callisto and Ganymede), and to reveal the plasma environment of the planetary system.

The boom was developed by SENER in Spain and tested at ESA's Test Centre in the Netherlands, undergoing simulated launch vibration on shaker tables before and after being test-deployed at the Test Centre with its weight borne by large helium balloons (to mimic the weightlessness the instrument will experience once in space). The boom has also completed extensive thermal testing to guarantee its performance during the extreme temperature and illumination variations it will experience during its mission lifetime (see JUICE Journal #2).

Spacecraft and instrument integration

The integration of JUICE's magnetometer boom is a major step in the overall integration process of the spacecraft's payload of advanced instruments. JUICE's main skeleton was delivered to the Arianegroup facility in Lampoldshausen, Germany on 2 September 2019, spent the next seven months undergoing intensive structural, thermal and chemical propulsion integration activities, and then moved to its current location at the Airbus facilities in Friedrichshafen in April 2020 (as detailed in JUICE Journal #6).

In the months since this move, many more instruments, units, antennas, communication systems and appendages have been tested and then integrated on JUICE, including the reaction wheels and star trackers needed for fine attitude control and extreme pointing accuracy, the optical bench needed to enable alignment between instruments and sensors and the steerable Medium Gain Antenna, which will allow communication and transfer of precious science data to Earth during JUICE's flybys of Venus (when the High Gain Antenna will work as sunshield) and Jupiter's icy moons.

Among the instruments, the 'Gravity & Geophysics of Jupiter and Galilean Moons', or 3GM, radio package was fully integrated in February following the arrival of the Ultra Stable Oscillator, which first underwent successful thermal, electromagnetic compatibility and performance testing at ESA's Test Centre and ESTEC TEC laboratories. This radio science experiment will study the gravity fields at Ganymede, Callisto and Europa, capture atmospheric and ionospheric profiles at Jupiter and its moons, and explore the extent of the moons' internal oceans.

Alongside 3GM, the Particle Environment Package (PEP-Lo), UV Imaging Spectrograph (UVS), Radio & Plasma Wave Investigation (RPWI) and Radar for Icy Moons Exploration (RIME) instruments have also been integrated.

PEP-Lo will investigate the space environments of Jupiter and of the icy moons, providing an unprecedented and comprehensive view of the huge areas of plasma and radiation that encircle Jupiter. UVS will characterise the atmospheres and aurorae of Jupiter and its icy moons, while RPWI will explore the radio and plasma environments of the Jovian system.

The ice-penetrating radar of RIME will see beneath the ice of Jupiter's moons down to a depth of nine kilometres, to explore the moons' subsurface structure and probe the potential habitability and geological activity of these alien environments. This instrument underwent the antenna testing via helicopter back in September 2017 in Heiligenberg, near Friedrichshafen, Germany, to test how the instrument's 16-metre-long antenna will interact with the spacecraft body and, in particular, with the massive solar arrays.

Furthermore, the in-line and the lateral panels of JUICE's solar array, the delivery and assembly of which was covered in detail in JUICE Journal #7, have also been test-deployed at Airbus Netherlands, in Leiden.

A lot of testing done – a lot of testing to do!

Earlier this year, the 2.5-metre High Gain Antenna (HGA) arrived at the Airbus cleanroom in Friedrichshafen, following extensive vibration testing by Thales Alenia Space in Italy (TAS-I) to ensure its readiness for launch.

The antenna was designed, produced and supplied by TAS-I and will provide a daily data downlink and communications connection of approximately 1.5 to 2 Gb (received by ESA ground stations in Australia, Spain and Argentina). It must be able to withstand extreme thermal fluctuations, ionising and ultraviolet radiation, and the conditions of launch. The composite materials and coatings used to build the HGA were subjected to an extensive testing qualification programme, with the antenna exposed to 32 000 equivalent Sun hours and temperatures of -214 to +214 °C.

Vibration testing mimics the forces and accelerations experienced during launch into space, to ensure that a given unit will not become damaged or fall apart. The HGA was mounted on hydraulic shaker tables and exposed to vibrations at different frequencies, beginning with low-frequency sine-wave vibrations and progressing to a sweep of waves at increasingly high frequencies. This makes the antenna move in both a controlled and random way subject to different vibrations (e.g. x and y sinusoidal variations that shake the instrument from side-to-side or up-and-down, or intermittent bursts of higher frequency that present more intense and randomised periods of stress).

Such testing is essential to confirm that the antenna is capable of enduring the intense conditions at launch and reliably delivering clear communications to Earth during the changeable conditions in space.

A suite of specialised and in-depth testing is required for all instruments and component of JUICE depending on form and function. All testing is performed in a cleanroom environment. JUICE was recently detached from its 'Multi-Purpose Trolley', lifted by crane, and moved from its typical positioning within the Friedrichshafen cleanroom to a special stand able to allow modifications and access to the bottom part of the spacecraft – namely, insulation and harnessing around its main engine. The next steps involve attaching multi-layer insulation to the spacecraft.

In the coming months the spacecraft will undergo major environmental and performance tests, including thermal vacuum, mechanical and electromagnetic compatibility tests, along with the end-to-end test of the ground segment. Furthermore, JUICE's numerous appendages will be test-deployed before preparing to pack up and ship to the launch site.

About JUICE

JUICE – JUpiter ICy moons Explorer – is the first large-class mission in ESA's Cosmic Vision 2015-2025 programme. It will complete a unique tour of the Jupiter system that will include in-depth studies of three potentially ocean-bearing satellites, Ganymede, Europa and Callisto.

The Jupiter tour includes several flybys of each planet-sized world, culminating with orbit insertion around Ganymede, the largest moon in the Solar System, followed by nine months of operations in its orbit.

JUICE will carry the most powerful scientific payload ever flown to the outer Solar System. It consists of 10 state-of-the-art instruments plus one experiment that uses the spacecraft telecommunication system with ground-based radio telescopes.

JUICE's instruments will enable scientists to compare each of these icy satellites and to investigate the potential for such bodies to harbour habitable environments such as subsurface oceans. They will also carry out observations of Jupiter, its atmosphere, magnetosphere, satellites and rings.