Thursday, April 13, the space probe Juice will take off from Kourou aboard an Ariane 5. The journey to Jupiter and its system will last eight years. Arnaud Boutonnet, flight dynamics expert at the European Space Agency (ESA), explains the flight plan to us. The JuiceJuice (Jupiter Icy Moons Explorer) probe aims to explore Jupiter and its system, in particular the icy Galilean moons Europa, GanymedeGanymede and Callisto, in order to characterize whether they are habitable. The flight plan is as follows: April 13, 2023: takeoff from the CSG (guiana space centerguiana space centre); August 2024: flyby flyby the Moon and the Earth (gravitational assistance); August 2025: flyby of VenusVenus (gravitational assistance); September 2026: flyby of the Earth (gravitational assistance); January 2029: flyby of the Earth (gravitational assistance); July 2031: arrival in the Jovianjovian system (start of the scientific mission six months before, during the approach); Juice performs 35 flybys of Europa, Ganymede and Callisto; December 2034: orbit orbit around Ganymede. Live with us on April 13 the event launch of the Juice mission to Jupiter Follow live with Futura the launch of the Juice Mission: the Europe’s space challenge! Juice is an ambitious mission that aims to study the mysteries of Jupiter, this giant planet, and its icy moons, by exploring their composition, their structure and their potential for life. © Futura Arnaud Boutonnet, flight dynamics expert at the European Space Agency (ESA), answers our questions. Futura: Why does Juice’s journey last eight years? Arnaud Boutonnet: The answer lies in one word: the launcher. When we have a very powerful launcher, we do what is called in technical jargon a Hohmann transfer, that is to say a half-ellipse from Earth to JupiterJupiter. It takes two and a half years. It’s very fast, but you need a very powerful launcher, like the SLS (Space Launch System). Ariane 5 is not powerful enough, so we create “gravitational assistance”. After several flybys of the Earth, the Moon and Venus, the last flyby of the Earth will allow us to leave for Jupiter with the same conditions that the SLS would have given us. Arnaud Boutonnet: Difficult to use the gravitational assistances of the Earth and Mars as with RosettaRosetta because the problem of Mars is that the massmass is quite low. Mars is also farther from Venus compared to the SunSun, and therefore revolves more slowly around it, so that we have to wait to be able to “phase” with it. [Rappel : un voyage court Terre-Mars n’est possible que tous les 26 mois, Ndlr]. Flight plan of ESA’s Juice mission to Jupiter and its moons. © ESA Futura: This is the first time that we are going to use the Moon and the Earth as gravitational aids, what is the contribution of the Moon?Arnaud Boutonnet: When we fly over the Earth, the trajectory follows a geometric shape called a hyperbola. We have a certain speedspeed on arrival and the flyover changes direction while keeping the same speed relative to the Earth. But when afterwards we look at the speed relative to the Sun, we see that we have accelerated. This is the principle of normal gravitational assistance with the Earth. Now, if you have the Moon in the way, you will gain speed relative to the Earth, and therefore we accelerate even more relative to the Sun. This saves us from asking the launcher for this, for example. Futura: With the overflights and a few trajectory correction maneuvers, what proportion of the probe’s 3,500 kilos of fuel is devoted to interplanetary travel? Arnaud Boutonnet: A few hundred kilos. Arnaud Boutonnet: In fact, we will have about 30 overflights. This is to meet the scientific pillars of the mission: fly over Europa, study Jupiter’s magnetospheremagnetosphere from a 23° inclined orbit, and enter orbit around Ganymede. One could adjust the speed to accomplish each of these objectives, but that would require an immeasurable amount of propellant. So, same principle as for interplanetary travel: to arrive in orbit around Ganymede for example, you have to reduce the size of the maneuver. For this, gravitational assistance is used with Ganymede and Callisto. It therefore takes a more or less fixed number of overflights to reach Ganymede in the right conditions: between 6 and 8. To end up at 23° inclination, you need between 10 and 15 overflights. To fly over Europe in the right conditions, you need 6. We therefore total about 30 overflights, more or less five. Futura: Can we hope to fly over other moons of Jupiter, like Io, or other smaller ones? Arnaud Boutonnet: We’re not going to see IoIo because of the radiation. It’s already costing us a lot to go and see Europe. Almost all of the other moons are very distant. The only chance to see them is during our arrival at Jupiter. We have very little freedom on this part of the journey, we looked if by chance we would have the chance to cross one, and this is not the case. Arnaud Boutonnet: It’s in two stages. The first is called global search. It’s a bit like wondering which is the highest peak in the Pyrenees. You will initially preselect those which seem to you the highest. Then you make a huge zoom on each of them, taking into account a precise relief to have an exact measurement of their height. We do the same. First, we have global search tools to give us the best [plans de vol] candidates, with modelingdynamic modeling that simplifies, for example with a limited number of manoeuvres. Then, we move on to fine optimization where we use completely different tools which, from a starting point, give us a local minimum, by authorizing maneuvers in many places with very precise modeling. For the first stage, the calculations that are launched in parallel on serversservers will last several days. Then, when we take the candidates to optimize them locally, it takes a few tens of minutes. Futura: What is the legacy of ESA’s latest interplanetary missions (Rosetta, Bepicolombo, Solar Orbiter) in Juice’s flight plan? Arnaud Boutonnet: We use methods and tools that allow us to optimize overall. The innovative part with Juice, where we started from scratch 15 years ago, is around Jupiter. There, it was almost research. We have published a lot. This was Juice’s big challenge. Futura: What freedom will allow us a “perfect” flight of Ariane 5, like the one that doubled the life expectancy of the James-Webb?Arnaud Boutonnet: The margin that we have planned does not isn’t really that big. On the other hand, where we will have a lot to gain is on the shooting window. Juice’s starts on April 13 and ends on the 30th. The most optimized flight plan was to have us leave on April 11 initially. The further we go from this date, the more the propellant cost will increase, and very quickly. There is a huge difference in fuel budget between a launch that takes place on the 13th and one on the 30th. If we launch the 13th, we can make a change of orbit around Ganymede. Futura: Why can’t the take-off time suffer any delay? Arnaud Boutonnet: The optimized interplanetary trajectory should send us off in a very precise direction, to the nearest second. If we leave 10 seconds later, we’ll eat fuel to correct that.