The U.S. Army Aviation and Missile Command, Aviation and Missile Research, Engineering, and Development Center (AMRDEC) is currently developing the Compact Kinetic Energy Missile (CKEM) which achieves hypersonic velocities at sea level. The system incorporates guidance to the target and requires active guidance technology. CKEM's kinetic energy warhead requires an accurate guidance sub-system in order to achieve high probability of kills at long range. Due to the severity of the aerothermal environments, minimized reaction time for small time to target conditions, and the communication degrading effects of the missile's energetic boost motor, a state of the art guidance technique is being developed by the AMRDEC Missile Guidance Directorate called Side-Scatter Laser Beam Rider. This technology incorporates a 1.06 micron laser to receive an off-axis laser guidance link to communicate guidance information from the launch site to the missile. This concept requires the use of optical windows on board the missile for the missile-borne laser energy signal receivers. The current concept utilizes four rectangular windows at 90° increments around the missile. The peak velocity during flight can reach approximately 6300 ft/sec inducing severe aerothermal heating and highly transient thermal gradients. The Propulsion and Structures Directorate was tasked to design and experimentally validate the laser window. Additionally, flight tests were conducted to demonstrate the laser guidance technology. This paper will present the laser window design development process as well as aerothermal testing to induce flight like environments and assess worst case thermostructural conditions.