As part of an internal program to develop laser radar guidance systems for advanced cruise missiles, we developed a low cost, thermal control unit (TCU) for captive flight testing. Because lasers dissipate high heat fluxes and require stable operating temperatures to minimize optical misalignment and frequency drift, they require active thermal control. Our guidance systems are mounted in a missile-shaped, pod located under a subsonic test aircraft. Aircraft environmental control was not available, and the pod does not have the thermal control systems normally available on cruise missiles. Also, off-the-shelf refrigerators and existing pod environmental control units were not feasible because of their volume, weight, and/or cost. We, therefore, developed an active, closed-loop, liquid TCU that uses ram air as the heat sink or source. Thermoelectric devices pump heat from the liquid coolant to the ram air to cool the laser on hot days, or from the air to the liquid for heating on cold days. This low cost thermal control unit uses off-the-shelf components, is weight and volume efficient, and was found to be reliable and maintenance free in flight testing.