After months practicing with a ‘fake’ Juice spacecraft, teams at ESA’s mission control centre in Darmstadt, Germany, today got in touch with the real thing. For the first time, mission engineers connected to the Ariane 5 rocket and inside its fairing the Juice spacecraft, for a dress rehearsal of the all-important “network countdown”. 

The dress rehearsal is the moment that ESA’s mission control brings together the various partners and elements of the mission for a final fully integrated test before launch. Today, Juice’s signals streamed into ESA’s Space Operations Centre via an umbilical connection that will be disconnected in the moments before liftoff, joined by mission partners Airbus and Arianespace. 

It is during the network countdown that the Flight Operations Director Andrea Accomazzo performs the well-known ‘final Rollcall’, as he contacts various teams and positions around the globe who each declare – when things are going well – they are “GO” for launch. 

The dress rehearsal is a live re-enactment of this countdown and every step has to go right to declare launch readiness, from setting up the connection to Juice on the launch pad to establishing ground station links across the globe and ensuring all mission control software and systems are up and running. 

This rehearsal comes after months of simulations in the Main Control Room, in which teams fly a spacecraft simulator controlled by devious Simulations Officers in the room below. Their job is to think up all the ways that something can go wrong. 

In this period the teams focussed predominantly on the critical moments after liftoff – the Launch and Early Orbit Phase. Among hundreds of errors, large and small, Juice’s 85 square metre solar arrays failed to deploy, the spacecraft was lost to Earth’s antennas on dozens of occasions and it entered emergency Safe Mode five times. 

Now that simulations are complete and dozens of worrying scenarios have been worked through, it’s time to focus on a nominal launch.  

“For the last time we have practiced critical operations for the complex Juice mission – and everything went perfectly to plan. Next time, we’ll be doing this for real”, explains Andrea Accomazzo, Flight Operations Director for the mission. 

“After speaking to Juice for the first time, we’re ready and couldn’t be more excited for the decade-long conversation about to take place across deep space”.   

Juice has now been installed in its Ariane 5 rocket, fuelled, and final checks are underway before it is rolled out to the launch pad at Europe’s Spaceport in Kourou, French Guiana, for a scheduled launch on 13 April at 13:15 BST (14:15 CEST). 

The mission, ESA’s Jupiter Icy Moons Explorer, will make detailed observations of the giant gas planet and its three large ocean-bearing moons – Ganymede, Callisto and Europa – with a suite of remote sensing, geophysical and in situ instruments. 

Juice will characterise these moons as both planetary objects and possible habitats, explore Jupiter’s complex environment in depth, and study the wider Jupiter system as an archetype for gas giants across the Universe. 

To make all this possible, teams at ESA’s mission control centre in Germany will perform back-to-back critical operations including four planetary flybys to get to Jupiter and 35 flybys of its icy moons. 

Follow @esaoperations, @esascience and @esa_juice for live updates of Juice’s launch, its long eight-year journey and ultimately the fascinating science it will uncover.