Long term thinking is full of challenges and is also necessary, especially on topics related to systems that take time to change, such as society, cultural values and policies. The further we look into the horizon, the more unknown-unknowns we encounter and the harder it is to rely on existing knowledge, trends and extrapolation for envisioning the future. Expertise is limited when applied to long term futures. An 18-month design research project has been conducted to develop a methodology for participatory future studies with non-experts, given a complex and challenging context. A context of extreme unknowns: healthcare for future space missions. What does it mean to efficiently conduct productive futures studies in the face of unknowns with non-experts? The study does not reject expertise per se, however it does explore how to conduct futures studies with non-experts. Whilst the extreme context takes us out of the Earth, our methodology is discussed and evaluated in relation to existing futures thinking practices in healthcare settings. Our conclusions reflect on the findings from the project and contribute to improving non-expert participation in futures research through a platform embodying the Collective Imagination Framework for imagining new futures for healthcare in 2040 and beyond.