Beyond Polarization: Scientific Ambivalence and Early-Stage Legitimacy in Planetary Sunshade Research

Planetary Sunshade research is advancing in a context where Solar Radiation Modification (SRM) has already experienced more than a decade of controversy and governance debate. While space-based approaches differ technically from atmospheric interventions, both propose planetary-scale action under deep uncertainty and climate emergency. This research presents empirical findings from a qualitative study and offers a socio-technical analysis of legitimacy, governance, and early-stage field stabilization in Planetary Sunshade research. Drawing on more than 26 semi-structured interviews with scientists involved in, supportive of, or critical of SRM research, it examines how expert communities construct credibility when working on high-stakes climate intervention technologies. Contrary to common portrayals of sharp polarization, the SRM field is structured by pervasive scientific ambivalence. This tension is managed through "boundary-work" by distinguishing modelling from deployment and exploration from endorsement. Precaution, reversibility, and epistemic modesty are mobilized to sustain research while limiting normative commitment. However, when these boundaries remain implicit, emergency framings and certain narratives can intensify politicization and destabilize field cohesion. Building on this analysis, the research shows that Planetary Sunshade development should be understood not only as an engineering challenge, but as a process of institutional co-production. Technical design choices actively shape legitimacy trajectories by clarifying scope, materializing research without committing to deployment, and stabilizing research–policy boundaries. Legitimacy is therefore not a by-product of feasibility; it is co-produced through the interaction between engineering architecture and governance framing. Moreover, from a technical standpoint, Planetary Sunshade architectures can be designed to support evidence-based public decision-making. A staged pathway of precursor missions, including optical performance validation, degradation monitoring, and solar-sail swarm formation tests, enables model verification without measurable radiative forcing. The resulting performance and risk allow integrated cost–benefit assessments that incorporate engineering feasibility, climate response uncertainty, and governance constraints, helping define decision thresholds while preserving reversibility and research–deployment boundaries.