The Kinetic-kill-vehicle Hardware-in-the-Loop Simulation Facility (KHILS), located at Eglin AFB FL, has been involved in the development and ground testing of Ballistic Missile Defense Organization hit-to-kill interceptor concepts for 10 years. Work is ongoing to characterize the implement hardware-in-the-loop models for missile `environment' effects that are associated with high speed flight in general and endo-atmospheric flight in particular. Two critical areas of interest in endo-atmospheric simulation are: (1) effects on the line-of-sight due to divert thruster firings and the resulting structural vibration, and (2) the line-of-sight aero-optical environment which can be influenced by heated missile flowfields, coolant layers, and thruster fringes. The structural and aero-optical effects manifest themselves as image jitter, blurring, boresight shifts, and increased background radiance. At the KHILS facility, real-time closed-loop simulation techniques are being developed for structural and aero-optical effects presentation. These techniques include both software and hardware solutions. This paper describe the status of activities by describing the issues and the present KHILS solutions. The paper includes discussion of model interfaces with hardware-in-the-loop simulations, timing issues, and data transmittal bandwidth requirements. Image show the effects of structural and aero-optical disturbances on seeker focal plane energy distributions.