This lecture discusses the design principles and strategies for mechanical systems operating in challenging environments, such as radiative and dusty conditions. It begins by addressing the constraints posed by radiative environments, emphasizing the importance of radiation hardening, redundancy, shielding, and effective thermal management. The instructor highlights the necessity of minimizing complexity in design to reduce potential failures. The lecture then transitions to dusty environments, identifying various dust sources and the implications for system design. Key mitigation strategies are presented, including the use of sealed enclosures and effective filtration systems. The discussion extends to cleanrooms, detailing their significance in maintaining contaminant-free conditions for sensitive operations. The lecture concludes with an exploration of sterile environments, particularly in surgical device design, emphasizing biocompatibility and sterilization methods. Overall, the lecture provides a comprehensive overview of the critical considerations for designing mechanical systems that can withstand extreme environmental challenges.