[FLOAT] Urs Wilcke Conference Paper

Thermal-vacuum (TVAC) campaigns frequently require bespoke fixtures for mounting and aligning hardware under vacuum and temperature cycling. Metal fixtures are robust but slow and costly to procure, which hinders rapid iteration in early development phases. In the scope of a semester project at ETH Zürich conducted at NASA JPL, we evaluated fused-deposition modeling (FDM) with PETG as a fast, low-cost option for vacuum-exposed, non-load-critical fixtures. Our objective was to define a minimal process print strategy that (i) avoids trapped gas within printed structures, (ii) shows no observable outgassing or contamination at high vacuum, and (iii) maintains dimensional fidelity across representative TVAC cycles. We used clear PETG (Prusament) on a Prusa MK3S to minimize additive burden and potential volatile species from pigments. Dependent on geometry, parts were printed on their side with no bottom or no top and no bottom skins, triangular infill at 15%, and 3 perimeters—yielding a continuous, vented lattice whose internal channels are open to the exterior, thereby avoiding enclosed air volumes. (Hexagonal infill is expected to perform equivalently provided channel continuity is maintained.) Fixtures were exercised in a thermal-vacuum environment at pressures down to ~1.3×10e-3 Pa and temperatures from −40 to +30 degC, over 5 TVAC cycles. Post- processing was limited to simple deburring; no vacuum bake-out was performed. Across all runs we observed no visible outgassing, no deposits on nearby surfaces, and no blistering or delamination. Upon return to ambient conditions, parts retained sub- millimeter tolerances with no measurable mass change. The absence of visible contamination and the stable behavior under cycling provide practical evidence that this configuration is suitable for vacuum-exposed fixtures in early-stage testing. The approach materially reduced iteration time and cost relative to machined metal, enabling same-day design–print–test loops. From these results we distil actionable guidelines: (1) use open-lattice infill with zero top/bottom skins to guarantee vent paths; (2) print big parts on the side to align channels across part thickness; (3) set 3–5 perimeters for stiffness and handling; and (4) prefer clear PETG to reduce additive-driven volatiles compared to other polymers and colored equivalents. Known limitations include PETG’s temperature ceiling near its glass transition and potential long-term creep; accordingly, we recommend limiting use to non-load-critical fixtures and early development phases. Sharing this simple recipe aims to lower TVAC campaign costs and accelerate testbed development across laboratories.