JUICE: A Journey to the Icy Moons of Jupiter

Will we find life on Jupiter's moons?

Issue 52 Subscribers 1,825.

With the launch of ESA’s JUICE mission just days away, I thought I’d take a closer look at the mission and what makes it so special. I am trying to spend a little time with my family this long weekend, so there won’t be any news section in today’s issue. 

To my 28 new subscribers, enjoy your first issue and, as always, if you have any comments, suggestions, or tips, you can reply to this email.

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JUICE: A Journey to the Icy Moons of Jupiter

Jupiter Icy Moons Explorer (JUICE) is a European Space Agency (ESA) interplanetary mission that will be tasked with studying Jupiter and its icy moons. The mission is, in so many ways, a world-beater showing the excellence of European institutions and industry alike. 

JUICE will be the first spacecraft to perform a lunar-Earth gravity assist, the first to change orbit from another planet to one of its moons (Jupiter to Ganymede), and the first to orbit a moon other than our own. It will also be one of the largest interplanetary spacecraft ever launched with the USSR’s Phobos 1 and 2 missions, both of which were launched in 1988, likely being the only spacecraft larger. Closer to home, it will be noteworthy as the first of ESA’s L-class (Large Class) science missions which are expected to launch at a cadence of approximately one per decade. Athena and LISA have already been selected to be the second and third L-class missions with Athena expected to be launched in 2035. These missions are to be some of the most ambitious ESA has ever pursued.

Background

The origins of JUICE date back as far as 2004 when ESA began consulting the wider scientific community to set Europe’s goals for space exploration in the coming decade. The actual call for proposals for the first set of ESA L-class missions, however, did not occur until 2007 and was part of the agency's new Cosmic Vision 2015-2025 initiative.

Originally, ESA had counted on partnerships with other international agencies to take on some of the financial and technical burdens of the L-class missions. By 2011, however, it became clear that NASA was the most likely candidate to take on an equal role and the agency's recent budget outlook had shown that joining ESA in developing these missions was not a priority for NASA. As a result, ESA leadership decided in April 2011 that it would, for at least the first L-class mission, take on the responsibility of funding and developing the mission itself.

The next major milestone in the development of JUICE was its actual selection. The selection occurred in May 2012 with JUICE getting the nod over NGO, the New Gravitational wave Observatory, and ATHENA, the Advanced Telescope for High-Energy Astrophysics. At the time, JUICE was scheduled to be launched from French Guiana in 2022. Considering the project was started over ten years ago, it's pretty astonishing that it’s going to miss its proposed launch date by less than one year. It’s an absolutely stunning testament to the amazing work that has been done by ESA and Airbus in the planning and delivery of JUICE from concept to launchpad. If nothing else about this mission was noteworthy this alone would be reason enough to celebrate the launch of JUICE.

In February 2013, a total of 11 scientific experiments were selected to fly aboard JUICE. Interestingly, that’s one more than are currently aboard the spacecraft atop the Ariane 5 launch vehicle. The reason for this is that the eleventh does not include any spacecraft hardware. The Planetary Radio Interferometer and Doppler Experiment (PRIDE) will exploit the spacecraft’s communications system and Very Large Base Interferometry. You can find out more about PRIDE and the rest of the experiments further down.

Airbus Defence & Space in France was selected to be the mission’s prime industrial contractor in July 2015. The company received a €350.8 million contract to design, develop, integrate, and test the spacecraft in addition to activities surrounding the launch campaign, and its in-space commissioning. It did, however, not include the cost of the Ariane 5 launch. 

Ariane 5 was not the only vehicle considered for the launch of JUICE. In June 2019, ESA selected Arianespace to launch the spacecraft. The announcement from ESA indicates that both parties were examining launching JUICE from either an Ariane 5 or an Ariane 64. However, a launch aboard the latter of those two vehicles was precluded after its maiden flight slipped several years with ESA and ArianeGroup currently targeting late 2023 for the vehicle’s maiden flight. Instead of being one of the first to be launched aboard Araine 6, JUICE will be the last ESA science mission launched aboard Ariane 5.

Assembly of the flight model began in September 2019. The qualification and acceptance review was completed on 18 January 2023 and the spacecraft was shipped to Kourou a month later. JUICE was encased in the Ariane 5 fairing on 5 April ahead of the launch of JUICE on 13 April.

The mission

JUICE has a number of scientific mission objectives but one key burning question: is life possible elsewhere in our Solar System or is Earth unique? To answer this question, the spacecraft will explore habitable zones, which are characterised in this context by oceans, icy shells, compositions, and environments on Ganymede, Europa, and Callisto. It will also explore the wide Jupiter system with the aim of characterising Jupiter's atmosphere, magnetic environment, ring system, and other moons, including Io. 

Key mission milestones:

• April 2023: Launch 

• August 2024: Earth flyby #1

• August 2025: Venus flyby

• September 2026: Earth flyby #2

• January 2029: Earth flyby #3

• July 2031: Jupiter orbit insertion

• July 2031- June 2032: Energy reduction phase

• July 2031 to November 2034 35 icy moon flybys 

• December 2034: Ganymede orbit insertion

• September 2035: End of mission

Europa will get two flybys with a closest approach of 400 kilometres. The primary objective of these flybys is to search for biosignatures and pockets of water and explore geology, and surface and subsurface activity. Callisto will get 21 flybys with a closest approach of 200 kilometres. The primary objective of these flybys is to glimpse the environment around early Jupiter. Ganymede will get 12 flybys before JUICE begins to orbit the moon. The closest approach during these flybys will be 400 kilometres. The primary goal when observing Ganymede will be to explore its magnetic field, hidden ocean, complex core, ice content, its interaction with Jupiter, past and present activity, and its habitability. Io will also get at least one flyby with the aim to understand the surface of Io, examine how the moon's intense volcanic activity shapes Jupiter's plasma environment, and why there is such a stable relationship between the orbits of Ganymede, Europa, and Io.

The spacecraft

The creation of JUICE has been a titanic effort. Its development, construction, and launch will have included 18 institutions, 83 companies, 116 industry contracts, and over 2,000 people across 23 countries. In total, the cost of JUICE has been estimated by ESA at around €1.6 billion.

When stowed in the fairing of its Ariane 5 launch vehicle, JUICE comes in a compact form measuring 4,09 x 2.86 x 4.35 metres. However, once the spacecraft's solar wings and various booms are deployed, it measures 16.8 x 27.1 x 13.7 metres. 

The spacecraft has a total launch mass of around 6.2 tonnes. This total mass has expanded over the years. In April 2016, the launch mass of JUICE was estimated to be 5,264 kilograms with 2,857 kilograms of propellant and a 219-kilogram payload mass. In April 2020, an Airbus press release stated that JUICE was still at that 5.2-tonne mark. However, by April 2021 this had changed to 6.2 tons, which is 5.6 tonnes if the authors of the Airbus press release had the correct spelling. The most recent stated mass of the spacecraft is approximately 6.2 tonnes. The spacecraft's dry mass (including the payload adaptor) accounts for 2,420 kilograms, the propellant 3,650 kilograms, and the instrument payload 280 kilograms.

To survive the dramatic changes in temperature that JUICE will experience (lows of -230 °C and highs of 250 °C), the spacecraft is wrapped in 500 protective thermal insulation blankets, a system known as Multi-Layer Insulation. The overall mass of the spacecraft's thermal insulation is 100 kilograms.

The large propellant capacity of the spacecraft is required to perform the large number of gravity assists and flybys that JUICE will need to undertake during its mission. The propulsion system is made of one 425-newton bi-propellant main engine that will be used for the larger orbital manoeuvres, eight 22-newton thrusters for smaller manoeuvres and as a backup system, and twelve 10-newton thrusters for attitude control.

The spacecraft’s solar wings have a total area of close to 85 square metres, which is the largest ever fitted to an interplanetary spacecraft. The wings are divided into ten panels each measuring 2.5 metres by 3.5 metres that contain a combined 23,560 solar cells. Solar wings of this massive size are necessary as sunlight collected at the distance Jupiter is from the sun is around 25 times weaker than what can be collected when orbiting Earth. The wings will generate around 850 watts and five onboard battery modules will allow the spacecraft to survive eclipses of around five hours. The spacecraft’s solar wings were initially going to be even larger. In April 2016, ESA was reporting that the solar wings would measure 97 square metres. Interestingly, despite the wings being larger the expected power generation was still 850 watts, suggesting an advancement in the solar cell technology utilised for the spacecraft.

Sending commands and receiving data to and from Juice will be no small feat. The distances involved mean that a signal sent from Earth to the spacecraft in the region of Jupiter and back again will take approximately 106 minutes. As a result, the spacecraft is equipped with a large high gain antenna (HGA) measuring approximately 2.5 metres in diameter to provide at least 1.4 Gb daily downlink. The spacecraft also has a steerable medium gain antenna which will be used to return data to Earth during Venus flybys and some manoeuvres at Jupiter when the HGA will serve as a sunshield to protect the spacecraft's instruments. 1.25 terabytes of onboard storage, which is sufficient for several days of science data, will ensure that no data is lost during periods when transmission to Earth is not possible.

In order to ensure that the 106-minute signal roundtrip does not negatively affect the spacecraft’s mission objectives, JUICE is equipped with EAGLE, an autonomous navigation technology that uses the spacecraft's optical cameras to independently refine the viewing angle of its instruments.

The spacecraft is also equipped with a 10.6-metre-long boom dubbed the Magboom. The purpose of the boom is to keep the spacecraft's most sensitive sensors away from the probe and any electromagnetic interferences it may generate. Magboom is constructed from non-magnetic materials, such as carbon fiber, various titanium and aluminum alloys, and bronze, and weighs 44 kilograms including the sensors. A total of five instrument sensors are equipped to the boom as part of the J-Mag and RPWI experiments. 

The Experiments

I went back and forth about how detailed to make my descriptions of the different experiments. I settled on a basic overview of what each experiment will do, who the principal investigators are, and where the funding for each experiment is coming from. For a more detailed look at each one, you can view this page.

JANUS - Camera system - An optical camera that will take a closer look at Jupiter's Galilean moons and will also map the clouds of Jupiter. The principal investigators are from the Università degli Studi di Napoli in Italy and the Institut für Planetenforschung in Germany. Lead funding for the experiment is supplied by ASI.

MAJIS - Moons and Jupiter Imaging Spectrometer - A hyper-spectral imaging spectrometer that will be used to examine tropospheric (one of the innermost layers of Jupiter's atmosphere) cloud features and for the characterisation of ice and minerals on the surfaces of the icy moons. The principal investigators are from the Institut d'Astrophysique Spatiale in France and INAF/IAPS in Italy. Lead funding for the experiment is supplied by CNES.

UVS - UV imaging Spectrograph - A UV spectrometer that will be used to examine the composition and nature of the exospheres (in this context, a thin atmosphere-like volume surrounding a planet’s natural satellite) of the icy moons, to study Jupiter’s aurorae, and to investigate the planet’s upper atmosphere. The principal investigator is from the Southwest Research Institute in the US. Lead funding for the experiment is supplied by NASA.  

SWI - Sub-millimeter Wave Instrument - A sub-millimeter wave instrument to investigate the temperature structure, composition, and dynamics of Jupiter's troposphere and stratosphere (two of some of the innermost layers of Jupiter's atmosphere), and the exospheres (the uppermost layer of Jupiter’s atmosphere) and surfaces of the icy moons. The principal investigator is from the Max-Planck-Institut für Sonnensystemforschung in Germany. Lead funding for the experiment is supplied by DLR.

GALA - GAnymede Laser Altimeter - A laser altimeter for studying the tidal deformation of Ganymede and the morphology and topography of the surfaces of the icy moons. The principal investigator is from the Institut für Planetenforschung in Germany. Lead funding for the experiment is supplied by DLR.

RIME - Radar for Icy Moons Exploration - An ice-penetrating radar to study the subsurface structure of the icy moons down to 9 km depth. The principal investigators are from the Università degli Studi di Trento in Italy and JPL in the US. Lead funding for the experiment is supplied by ASI.

J-MAG - A magnetometer for JUICE - A magnetometer to characterise the magnetic field of Jupiter, its interaction with the internal magnetic field of Ganymede, and to study subsurface oceans of the icy moons. The principal investigator is from the Imperial College of London. Lead funding for the experiment is supplied by the UK Space Agency.

PEP - Particle Environment Package - A plasma package with sensors to characterise the plasma environment in the Jovian system. The principal investigators are from the Swedish Institute of Space Physics, the Universität Bern in Switzerland, and the Johns Hopkins University Applied Physics Laboratory in the US. Lead funding for the experiment is supplied by the Swedish National Space Agency

RPWI - Radio & Plasma Wave Investigation - A radio plasma wave instrument to characterise the radio emission and plasma environment of Jupiter and its icy moons. The principal investigators are from the Swedish Institute of Space Physics, LESIA-Observatoire de Paris in France, Space Research Centre of the Polish Academy of Sciences, the Imperial College in the United Kingdom, Tohoku University in Japan, and the Institute of Atmospheric Physic in the Czech Republic. Lead funding for the experiment is supplied by the Swedish National Space Agency.

3GM - Gravity & Geophysics of Jupiter and Galilean Moons - A radio science package comprising a Ka transponder and an ultrastable oscillator. 3GM will be used to study the gravity field of Ganymede and the extent of internal oceans on the icy moons, and to investigate the structure of the neutral atmospheres and ionospheres of Jupiter and its moons. The principal investigators are from the Università di Roma in Italy, Weizmann Institute of Science in Israel, and the California Institute of Technology in the USA. Lead funding for the experiment is supplied by ASI and the Israel Space Agency.

PRIDE - Planetary Radio Interferometer & Doppler Experiment (does not include any equipment on the JUICE spacecraft itself) - PRIDE will use the standard telecommunication system of the JUICE spacecraft and Very Long Baseline Interferometry to perform precise measurements of the spacecraft position and velocity to investigate the gravity fields of Jupiter and the icy moons. The principal investigator is from the Joint Institute for VLBI in Europe in The Netherlands. Lead funding for the experiment is supplied by the Dutch Research Council and the Netherlands Space Office.

Conclusion

I have, over the last few weeks, advocated for ESA to develop crewed launch capabilities. It is a goal that, I think, will instill a sense of pride in the agency for many European citizens that may otherwise have very little interest in space. In advocating for these bold goals, however, I do often lose sight of the many astonishing missions that ESA has and is preparing to launch. Although JUICE will likely get far less coverage and far less attention from the average European citizen than a crewed launch capability, it is something that we can be no less proud of. 

ESA is undoubtedly setting ambitious standards with JUICE with the spacecraft set to perform an extremely complex journey to Jupiter and its moons to answer questions that no other mission has before. It is a world first in a number of areas and will transmit back to Earth invaluable data that will assist humanity in our never-ending quest to understand our place in the universe. I cannot wait to receive the first images of Jupiter and its moons and report on all the exciting discoveries that are sure to follow.