4MOST Milestone: Commissioning Success and OpR4 beginnings
by Lisa Kelsey and Harry Addison on 2026-01-28
As we entered the new year, we also entered a new phase of 4MOST. System Verification and Commissioning were completed on schedule on January 1st thanks to the amazing efforts of the System Verification and Commissioning teams, with heroic efforts all through the Christmas and New Year period (special thanks to Jen-Kristian Krogoger, Hugo Méndez-Hernández, Jacco Terwel, Marica Valentini, Harry Addison, and of course Genoveva Micheva). Overall commissioning was very successful with results showing that all critical requirements were met, several by a significant margin. On January 20th, the results of commissioning were presented to ESO as part of the Operations Readiness Review 2. We successfully passed the review allowing us to move to the next phase: Operations Rehearsal 4 (OpR4).
OpR4 is an exciting milestone as the project moves closer to routine survey operations. In simple terms, OpR4 is a month-long “dress rehearsal” for how 4MOST will run night after night in the coming years. It brings together the instrument, software, people and procedures needed to take observations efficiently and reliably, and to turn those observations into high-quality scientific data.
Jakob Walcher (4MOST Operations Manager) explains:
"The start of OpR4 is a very significant milestone for the Operations Development Group. While our colleagues working on the hardware and instrument software have developed and commissioned an excellent instrument, we have been working on the preparations for the software needed to produce an excellent survey with that instrument. The biggest challenge here has always been the need for automation of nearly everything we are planning to do - there is no other way to run a survey the size and length of 4MOST. Seeing on the first night of OpR4 how one OB gets executed, producing data, while the next one already appears by magic in the execution sequence has been hugely satisfying for everyone involved."
OpR4 is also about preparing for long-term operations at Paranal. During the run, project staff will work closely with ESO colleagues, helping train the teams who will run the instrument and refining practical details to keep observations smooth. The focus is on building experience, testing the system and procedures under real conditions, and making improvements as needed. As Jakob puts it: "We now have an intensive month ahead of us to iron out all issues that will inevitably appear".
With OpR4 now underway, we wish the teams involved the very best for a successful run!