The fatigue life of metallic materials is significantly influenced by a combination of intrinsic and extrinsic factors, among which environmental conditions and loading characteristics play a critical role. While the effects of stress amplitude, microstructure, and surface finish have been extensively documented, the specific influence of loading frequency (particularly under varying environmental conditions) remains insufficiently explored. This study presents an experimental investigation into the fatigue behavior of Aluminum Alloy 1100 under both atmospheric and partial vacuum environments, focusing on the influence of loading frequency. Fatigue tests were conducted across a range of frequencies, intentionally selected to avoid resonance effects, thereby ensuring that the observed responses reflect the inherent influence of frequency rather than dynamic amplification. The results reveal a clear divergence in fatigue life between atmospheric and partial vacuum conditions, highlighting the substantial impact of environmental interaction. A predictive relationship was developed to estimate fatigue life as a function of loading frequency, offering a practical tool for design and life assessment. These findings contribute to a deeper understanding of frequency-dependent fatigue mechanisms and provide valuable insights for structural components subjected to cyclic loading in aerospace-relevant environments. Given the increasing utilization of aluminum alloys in orbital platforms, satellite structures, and high-altitude systems, the proposed framework assists in optimizing fatigue performance and extending service life under the reduced-pressure or partial vacuum conditions typical of aerospace applications.