Metis anomaly & rescue 

Space missions are very challenging by nature and have to deal with a lot of restrictions and limitations, before they can exploit the unique scientific opportunities. 

Among the more difficult moments in any mission is the realisation that a command sent to the spacecraft has not produced the expected result, for an unknown reason, and that there is no way to reach the spacecraft and fix the issue. 

Metis heatshield door anomaly

Unfortunately, that is exactly what happened to Solar Orbiter on Friday 27 February 2026, during one of its close perihelion passages at 0.29 au from the Sun. The payload was carrying out coordinated high-cadence and high-resolution observations. After an off-pointing manoeuvre towards a specific region of the Sun, the spacecraft returned to disk-centre pointing to allow observations with Metis. The coronagraph was due to open its protective heatshield door and resume observations of the solar corona. A pre-loaded onboard command initiated the door opening sequence … but it never reached its open state. The anomaly was detected during the next spacecraft contact on the following day. When a scheduled door closure was executed successfully (completing the closure, from the intermediate state) on Sunday, there was still hope that the event might have been an isolated glitch. 

That hope faded on Monday, when the next scheduled door opening again ended in an unknown state. An Anomaly Review Board, bringing together representatives from the Metis team, MOC, SOC, and industry, decided to place Metis in a safe state and to perform a manually commanded heatshield door opening test a few days later on 8 March, during ground-station visibility. The test was unsuccessful, unfortunately: the door consistently stopped at approximately 12 degrees into its motion, still fully covering the Metis aperture. 

What to do from now? Only a careful analysis will tell...

The situation was serious. Solar Orbiter was on the far side of the Sun, almost 200 million kilometres from Earth. The heatshield door, designed to protect the Metis aperture during non-observation periods, was stuck closed, depriving the coronagraph of the opportunity to observe the corona. Thankfully, the coronagraph itself appeared healthy.

Beyond the approximate angle at which the door had stopped, there was no clear indication of what was preventing the motion. Further attempts risked making the situation worse, so the priority shifted from action to analysis: understand the possible causes, assess the risks, and define a path forward. 

Over the following months, from February to May, the teams focused on analysing potential causes and evaluating the risks of any further opening attempts, including the possibility that the door might become stuck in an open position. A thermal analysis was also performed to verify Metis and the spacecraft can safely operate with the door always open, if this solution was to be decided upon. 

The investigation drew on a wide range of evidence: historical telemetry, detailed studies of the door mechanism and surrounding components, and straylight assessments in Metis imagery. Some early hypotheses were ruled out; others emerged. Although no definitive root cause could be established, the evidence increasingly pointed towards thermo-elastic effects as a likely contributor. 

On that basis, and after weighing the risks for both Metis and the spacecraft as a whole, the board decided to attempt a reopening at aphelion (0.9 au), when the thermal environment would be significantly colder than during the original incident. If successful, the plan was to keep the door open. 

A new test to be performed at aphelion

The test was scheduled for 26 May, during a long visibility period covered by 2 ground stations and prepared in much detail.  The door opening would be commanded in two phases: first a partial opening, then a complete opening, with all possible intermediate outcomes and decision points worked through in advance. 

Several members of the Metis team and the SOC system engineer travelled to ESOC for the critical test day, while others followed remotely. The operational constraints were demanding: at Solar Orbiter’s distance, the one-way light time was about 15 minutes, and the downlink rate for the required telemetry was very limited. The team therefore had carefully defined the minimum telemetry needed to assess the door status. SoloHI, the heliospheric imager on board Solar Orbiter, was also observing, ready to detect any particles that might be released during the door motion. 

Metis observes the Sun's corona again!

Soon after acquiring contact with the spacecraft, the heatshield door was commanded to open far enough to clear the telescope aperture and well beyond the position where it had previously stopped. After a tense 30-minute wait for the first housekeeping data, and another 15 minutes for the Metis imagery to come down, we all sighted in relief. The data acquired during the motion showed the scene changing with each motor step, together with hints of the faint coronal signal expected at 0.9 au from the Sun. The team then commanded the full opening and half an hour later, we saw the door status change to OPEN. Wow!! Is it open already? What a relief! 

The first Metis imagery received afterwards suggested that the instrument was in good health, although the low-quality data did not yet allow a full confirmation. With time still available during the pass, it was decided to take a deeper exposure to assess the instrument’s performance more thoroughly. 

While the Metis team prepared the additional instrument commanding, the Flight Control Team prepared updates to the onboard automatic reactions to prevent the door from being closed again. 

Another 30 minutes after uplink, the magnificent image below arrived. Metis was back! The coronagraph had not only surprised us with a beautiful coronal image far from the Sun but even caught a CME in full action! 

Champagne!! 

Metis will resume its science observations, in coordination with the rest of the payload, on 29 June 2026. 

Welcome back, Metis!  

Go, Solar Orbiter!