Because quartz–cyanate ester (QCE) composites are employed to fabricate missile and aircraft radomes, retaining their structural and electromagnetic (EM) integrity after prolonged exposure to environmental stresses is essential for long-term deployment as radar protectors. Therefore, in this study, QCE composite samples were subjected to environmental conditioning tests, namely, transient temperature (transition from −67 to 145 °C), high-temperature storage (cycling between 35 and 85 °C), thermal shock (cycling between −55 and 100 °C), fluid contamination (immersion in mineral and turbine oils), and humidity cycles (conditioning at 30 °C and 85% RH), to observe the effect of conditioning on the physical, morphological, thermal, mechanical, and dielectric properties of composites. Interfacial damage was observed in all the conditioned samples. Samples after fluid immersion test were found to have the highest deviation in properties compared to unconditioned ones. Fluid diffusion led to higher surface crack width, lower impact damaged area, and higher EM energy dissipation (higher dielectric loss tangent). High-temperature storage tested samples had the highest surface crack intensity, while humidity cycles caused matrix plasticization, resulting in lower density and thermal conductivity values. A high degree of postcuring in thermally shocked samples resulted in brittleness of cyanate ester, leading to an increase in density and impact damaged area. Although a slight degree of damage is reported, the change in QCE composite properties postconditioning is not significant enough to prevent its application as uncoated radome materials, except for rain erosion at 150 m/s.

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