On a quiet stretch of the German Aerospace Center (DLR) campus in Cologne, six volunteers recently stepped through an airlock door and heard it seal behind them. They won’t step back out for 100 days. Their home until late summer is a windowless habitat inside DLR’s :envihab research facility, where the European Space Agency is running what it calls SOLIS100, one of the longest isolation experiments ever conducted on European soil.
The study began in late April 2026, according to ESA’s institutional announcements. The goal is deceptively simple: find out what happens to the human mind and body when a small group is cut off from sunlight, fresh air, and normal social life for roughly the same stretch of time a crew might spend on the lunar surface or in the early leg of a Mars transit. As of May 2026, no space agency has sent astronauts beyond low Earth orbit for more than a few weeks. Before they do, they need data that only experiments like this one can provide.
Inside the sealed habitat
The :envihab facility was purpose-built for human spaceflight research. Its modules allow scientists to control nearly every environmental variable a crew encounters: lighting color and intensity, air composition, noise levels, and the timing of work-rest cycles. For SOLIS100, the six volunteers live and work inside a sealed section of the complex, following a tightly structured daily schedule of tasks, physical exercise, meals, and monitored rest periods.
Researchers can tweak conditions on the fly. They might shift the light spectrum to mimic a Martian sol, compress or extend the sleep window, or introduce unexpected schedule changes to see how the crew adapts. Every interaction, from a shared dinner to a disagreement over task priorities, is recorded and analyzed. Sleep quality, reaction times, stress hormones, and social dynamics are all tracked in near-real time.
“We want to understand not just whether people can survive long confinement, but whether they can still perform at the level a real mission would demand,” an ESA spokesperson said in the agency’s announcement of the study. The study name itself offers a further clue to its priorities. SOLIS points toward sleep, circadian rhythm regulation, and the social cohesion challenges that surface when a small group cannot escape one another’s company. These are problems that standard astronaut training addresses only partially, because the effects compound over weeks and months in ways short-duration missions on the International Space Station rarely reveal.
Why 100 days matters
Most people adjust to a new confined environment within two to three weeks. After that initial settling-in period, a different set of pressures takes hold. Mood regulation becomes harder. Cognitive sharpness dips. Small interpersonal frictions that were easy to shrug off in week one can calcify into genuine conflict by week eight. Researchers studying Antarctic winter-over crews and submarine deployments have documented these patterns for decades, but the data from those settings don’t translate neatly to spaceflight, where the crew is smaller, the environment more artificial, and the psychological stakes higher.
One hundred days pushes well past that adjustment window. It also lands in a range that is operationally relevant. NASA’s Artemis program envisions lunar surface stays that could eventually last a month or longer. A one-way trip to Mars, depending on orbital mechanics, takes roughly six to nine months. SOLIS100 doesn’t replicate either scenario exactly, but it occupies the critical middle ground where isolation effects shift from manageable nuisance to genuine mission risk.
“The first weeks are about adaptation. What interests us most is what happens after that, when the novelty has worn off and the monotony sets in,” a DLR scientist involved in the study’s design noted in the German-language briefing. A German-language ESA announcement confirms the same core details: six crew members, 100 days, the Cologne facility, and the division of responsibilities between ESA and DLR. The study falls under ESA’s broader exploration science program, which funds research on astronaut health, radiation exposure, and long-duration operational resilience.
What we don’t know yet
ESA’s official announcements leave significant gaps. The agency has not published the volunteers’ names, professional backgrounds, ages, or the criteria used to select them. The exact dimensions of the living quarters, the air recycling setup, and whether the crew has any form of delayed communication with the outside world have not been detailed in primary source material. Some news outlets have cited a 120-square-meter module, but that figure does not appear in ESA’s own releases.
No direct quotes from the volunteers themselves have surfaced in institutional channels. Public statements so far have come from ESA spokespeople and program-level descriptions, not from the people actually sealed inside. Baseline health data, the starting-point measurements against which researchers will gauge any cognitive or physiological changes, have not been published either. Without those baselines, outside observers have no way to evaluate interim claims about crew performance.
The link between SOLIS100 and specific mission timelines is also looser than some coverage suggests. While the study clearly feeds into planning for lunar and Mars missions, no ESA or DLR statement ties its results directly to crew selection, training protocols, or a named mission. The connection is logical, but it remains informal.
How SOLIS100 fits the bigger picture
Europe is not working in isolation on isolation. NASA’s CHAPEA program has been running its own long-duration confinement studies at Johnson Space Center in Houston. The first CHAPEA crew completed 378 days inside a simulated Mars habitat in July 2024, and a second crew began its own year-long stint in spring 2025. Russia’s SIRIUS project, conducted at the Institute of Biomedical Problems in Moscow, has tested crews in confinement periods ranging from weeks to months. China has run similar closed-environment experiments at its Lunar Palace facility in Beijing.
Each program operates under different rules, with different crew sizes, cultural contexts, and scientific instruments. That variety is both a strength and a limitation. Comparing results across programs could eventually reveal which countermeasures, whether adaptive lighting, structured social rituals, modified work schedules, or something else entirely, do the most to protect crew well-being. But that comparison depends on agencies publishing their methods and data in compatible formats, something that has historically been uneven.
SOLIS100 adds a distinctly European, medically instrumented data point to this growing body of research. The :envihab facility’s ability to fine-tune environmental variables gives it a level of experimental control that field analogs like Antarctic stations cannot match. If ESA and DLR share their findings openly, the study could help fill gaps that no single national program can address alone.
What to watch for when the airlock reopens
The volunteers are expected to emerge sometime in August 2026. When they do, the immediate question will be straightforward: how did they hold up? But the longer-term value of SOLIS100 will depend on what ESA publishes afterward. Detailed methods, raw data, and honest discussion of limitations will matter far more than headline-friendly claims about “cracking the code” of deep-space psychology.
For now, the verified picture is narrow but significant. Six people are living in a sealed, heavily monitored habitat in Cologne as part of a European-led effort to understand how prolonged confinement reshapes human behavior and performance. The questions they are helping to answer, how do you keep a small crew sharp, cooperative, and mentally healthy when there is no door to walk through, sit at the center of every serious plan to send humans beyond Earth orbit. The data from those 100 days could shape how those missions are designed, staffed, and sustained.
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*This article was researched with the help of AI, with human editors creating the final content.
