Solving the RIME deployment mystery on ESA’s Juice mission

When the RIME antenna on ESA’s Juice mission did not deploy a couple of days after launch, the engineering groups confronted the mighty problem of understanding the fault and rectifying it. At stake was an opportunity to see inside Jupiter’s mysterious icy moons.

The stakes have been already excessive earlier than the spacecraft ever left the bottom. ESA’s Jupiter Icy Moons Explorer (Juice) was designed by Airbus to conduct an unprecedented investigation of the Jupiter system and its household of icy moons.

A key to that investigation is the Radar for Icy Moon Exploration (RIME) antenna, which is a part of Juice’s complete suite of ten science devices. As soon as within the Jupiter system, RIME will likely be used to remotely probe the subsurface of Jupiter’s icy moons. Its radar alerts will penetrate the moons to a depth of 9 km, and reveal particulars of between 50 and 140 m throughout. It will give perception into their geology and supply distinctive knowledge to know the habitability of those distant, icy moons.

However to achieve accumulating this knowledge, scientists needed to first get the spacecraft and its devices into space—and that meant folding up a number of the {hardware}.

At 16 m in size, the RIME antenna was too lengthy to suit contained in the nostril cone of the Ariane 5 rocket that launched Juice into space. It was due to this fact constructed in two booms of 4 segments every. Of these eight segments, three would deploy on one facet of the spacecraft, three on the opposite facet, and two would stay fastened on the spacecraft. For launch, the three deployable segments have been folded again onto the fastened section and held in place by two brackets.

As soon as in space, units referred to as non-explosive actuators (NEAs) could be remotely activated one after the opposite from the European Area Operations Centre (ESOC), Darmstadt, Germany. Every NEA would take away a holding pin from its bracket, permitting that part to spring into place.

And that is the place the issues started.

Ronan Le Letty, Senior Mechanisms Engineer for ESA and a part of the Juice group, was at ESOC through the RIME deployment, advising the flight management group who have been receiving telemetry from the spacecraft’s numerous onboard sensors and sending Juice instructions.

The process started on 17 April 2023, three days after the launch and with all the pieces having proceeded easily up till that time.

Persevering with this pattern, step one went with no hitch. Two monitoring cameras, mounted onboard the spacecraft, have been used to comply with the RIME deployment. From the downloads, the antenna section was seen on one picture, after which not on the subsequent. In between the pictures, the NEA had fired, the pin had launched and the antenna section had snapped into place. A test of the exterior digital camera’s picture confirmed the section in place, and the telemetry knowledge additionally confirmed this. It confirmed that the spacecraft was oscillating as anticipated from the sudden deployment of the growth, and that the Angle and Orbit Management System (AOCS) was correcting for the final of those actions.

Happy, the group moved on to the second section.

The command was given to fireplace the actuator. The telemetry arrived earlier than the pictures, however one thing was improper. The anticipated oscillation was not exhibiting. A number of seconds later, the digital camera picture got here again. The growth section was nonetheless clearly seen in its stowed configuration. The deployment had failed.

“You expertise a state of disbelief,” says Ronan, “Probably the most undesirable state of affairs is going on. We checked the image two, three, 4 instances. We tried once more to activate the actuator, however nothing occurred.”

Additionally watching in a state {of professional} disbelief have been the group at Airbus Defence and Area, Toulouse, France. Chosen because the spacecraft’s prime contractor in 2015, they have been answerable for main the design, building and testing of the spacecraft and bringing in different firms to produce elements, methods and devices as wanted.

“We knew that we needed to rapidly attempt to perceive what had occurred, after which attempt to discover a workaround,” says Frédéric Faye, Airbus’s chief engineer for Juice.

The very subsequent morning, with the disbelief banished from their minds, the groups gathered on-line for a teleconference to share their insights and talk about the anomaly. On one hand, they knew they needed to discover some strategy to free the caught section, however on the opposite they knew that they may not do something that will compromise the deployment of the opposite segments, or certainly the remainder of the spacecraft.

The primary thought that occurred to the groups was that maybe some ice had shaped on the pin holding the section in place. Each time a spacecraft leaves Earth, it finds itself in a chilly, airless surroundings. This sudden and dramatic lack of air stress implies that a small quantity of water vapor will immediately escape from the fabric used to make the craft. This will then freeze onto the extremely chilly surfaces of the spacecraft.

Since there aren’t any heaters on the spacecraft close to RIME, eradicating the ice would imply rotating the spacecraft in order that the antenna confronted the Solar. However, the floor of the spacecraft holding RIME was designed to be a ‘chilly face’, which means that it was by no means meant to be uncovered to the direct daylight simply after launch. Nor have been the elements, devices and methods that have been connected to it.

After a number of days of research, the group started regularly slewing the spacecraft in order that the floor was illuminated. “We did eight slews over two weeks to light up the RIME bracket,” says Angela Dietz, Spacecraft Operations Supervisor at ESOC. Every time they uncovered the floor for longer, rigorously watching the telemetry from the onboard sensors to know the boundaries of this operation. At first, the maneuver lasted simply 25 minutes. By the tip, they felt snug exposing the floor for 73 minutes at a time.

Concurrently, different attainable restoration eventualities have been being contemplated.

If it weren’t ice holding RIME shut, and the pin had merely caught, then maybe shaking the spacecraft would jog it free—though the phrase ‘shaking’ is simply too excessive to explain the precise movement.

The spacecraft weighs six tons and the thrusters onboard can solely rock it backwards and forwards very gently. Nonetheless, the groups felt it was value attempting. The caught pin most likely solely wanted shifting by a millimeter or two, however the groups needed to be cautious. They may not danger harming the rest with a violent jolt of the spacecraft. So, because the group had completed with the heating, they started testing this maneuver cautiously.

“We did a number of thruster firings and used the primary engine, typically linked with the heating up slews. The thrusters have been even fired in a sure sequence to attempt to shake off the stacked growth, however we solely noticed small actions throughout the bracket,” says Angela.

And so the group moved on to different concepts.

The producer of the antenna, German firm SpaceTech, additionally proposed a restoration plan. Successfully, it was to proceed deploying the opposite 4 sections of the antenna as if nothing had occurred. They knew that as every NEA fired, it might produce a small mechanical shock in the remainder of the antenna that would dislodge the caught pin.

Then, the producer made a breakthrough. The engineers at SpaceTech managed to breed the anomaly with a mannequin of the antenna that had been used for testing and confirmed that the firing of the closest NEA normally managed to dislodge the caught pin. It was additionally recognized that to extend the probabilities of a profitable end result, the antenna needs to be heated by publicity to daylight.

This was as a result of though the engineering mannequin had been absolutely examined on the chilly temperatures of space, the precise flight mannequin had not. The group concluded that the extraordinarily chilly situations encountered through the failed NEA launch may need been a contributing issue, and so the antenna needs to be warmed by the Solar earlier than all future actuations to get it as near ‘room temperature’ as attainable, the place they knew it labored.

Armed with a number of concepts for recuperate the instrument, the groups determined to satisfy in individual to determine the way in which ahead. At a technical workshop held at SpaceTech, the groups determined to attempt the heating first. If that didn’t work, they’d proceed with firing the opposite NEAs, having warmed them first with daylight. “This train to place down a plan and get all of the groups working in the direction of it was actually helpful,” says Ronan.

It was now a number of weeks because the anomaly had occurred and stress was mounting. The mission had a timetable to maintain and as necessary as RIME is, it was just one instrument on the spacecraft. “To me this was probably the most difficult factor through the restoration,” says Guillaume Chambon of Airbus’s Technical Authority Group. Guillaume was positioned in command of managing the Airbus facet of the restoration. “You need to be quick sufficient to behave as a result of everyone seems to be anticipating you to make progress, however you’ll want to take sufficient time to contemplate all of the uncomfortable side effects of what you’re proposing,” he says.

One afternoon, whereas considering the rescue try, Guillaume did certainly notice a possible downside. In the event that they went forward with the nominal deployment sequence, there was an opportunity that two segments of the antenna might collide.

Recall that the RIME antenna consists of six deploying segments, three on both sides of the spacecraft. Within the nominal deployment situation, an NEA could be fired first on one facet of the antenna after which on the opposite. Nonetheless, in the event that they did this now, and the caught part got here free, then the 2 sides of the antenna could be deploying collectively in reverse instructions and will collide.

So, the groups agreed to reorder the deployment sequence, and the restoration makes an attempt started. First, the spacecraft was heated to drive off any ice, however the antenna remained fastened.

And so it turned apparent that the one risk to recuperate the antenna was to warmth the antenna once more, after which proceed with the deployment within the hopes that the shocks from the opposite NEAs would unjam the pin. Their evaluation had proven them that this is able to give the very best likelihood of success however every NEA might solely be fired as soon as. In different phrases, it was all or nothing.

It was round 2 pm on 12 Might that the groups gathered at their respective consoles and started this remaining try. The command was despatched and the groups watched the telemetry for any trace of an oscillation that will point out success. There it was: motion on the spacecraft. However was it the proper motion? Had they dislodged the caught section?

When the digital camera downloaded, the picture confirmed them all the pieces they wanted to know.

Complete success. The three segments of the antenna that needs to be deployed, have been deployed. “Within the operations group we turned quietly assured,” says Angela.

However the job was not over but. They have been solely midway by way of the complete deployment process. One different NEA nonetheless wanted to be fired to deploy the second growth earlier than RIME might assume its remaining working configuration. And if something, the stress felt by some on the group was even higher than earlier than as a result of now the group knew that it was attainable for the pins to jam. And now that only one pin remained, it was probably the most essential of all.

If any of the earlier ones had jammed, the group might have fired the subsequent in sequence and hoped that the shock would end the job—because it had on the unique caught section. However now, there have been no extra NEAs to fireplace. Proper on the end line, they may nonetheless be defeated if the pin jammed.

It was at this level that Cyril Cavel, the Juice challenge supervisor for Airbus discovered himself interested by the scientists who have been relying on them. Some had even been engaged on the antenna for many years. “RIME was an industrial supply to those individuals. With out this antenna, the radar experiment could be both very decreased and even useless. It could be excess of only a disgrace,” he says.

Certainly, the possibility to actually be taught what was beneath the icy surfaces of these enchanting moons might have been considerably diminished and even misplaced for the present technology of planetary scientists.

“We knew that, although the RIME was one instrument out of ten, a failure to completely open the antenna would have degraded the scientific efficiency of the mission and compromised the—till that second—glorious picture of Juice and ESA to the exterior world,” says Giuseppe Sarri, ESA’s Juice Mission Supervisor.

Because of this, the group took one remaining precaution. By now, the ultimate bracket had been in daylight for its most permitted time that day of 73 minutes. Because of this, its temperature was larger than the ambient temperature at which it had been examined within the labs in Germany. To breed the situations of that lab as intently as attainable, the group took the choice to rotate the spacecraft, shifting the antenna away from the Solar, and wait for 3 to 4 hours for its temperature to drop.

“These three to 4 hours have been very lengthy,” says Frédéric.

On the finish of the wait, when the situations have been proper, the command was despatched.

The NEA activated, the telemetry confirmed Juice oscillating as the ultimate section deployed, the AOCS lower in and stabilized the spacecraft. Lastly, the cameras confirmed the groups’ victory, RIME was now in its absolutely deployed configuration.

For Ronan, the aid at seeing the deployment was tinged with a well-recognized sense of disbelief. “It was a bit like the primary day of the incident. There was a sense of disbelief as a result of 4 weeks of an infinite quantity of stress was simply immediately gone. I could not fairly imagine it, regardless of seeing the photographs,” he says.

“When RIME was finally launched I might nearly see tears within the eyes of my colleagues,” says Giuseppe, earlier than including, “However we have been optimistic from the start and the Champagne was already within the fridge…”

As soon as the bubbly was drunk and the group suitably rested, the flight controllers at ESOC moved on to the opposite deployments needed on the spacecraft, all of which have now been accomplished efficiently. And the RIME anomaly groups at ESA, Airbus and SpaceTech, are simply wrapping up their understanding of the unique trigger in order that it may be averted in future on comparable methods.

And the Juice mission itself is as soon as once more on a path to finish success.