When a missile is launched from a canister, the impingement of the exhaust Bases on the plenum chamber creates a complex, viscous/shock interaction flow field. In order to study the rocket plume heat transfer effects on the closed and open plenum chambers, static rocket motor firings are carried out. Static tests are conducted in a small-scale rocket motor loaded with a typical nitramine propellant to produce a nozzle exit Mach number of 3. This supersonic jet is made to interact with the plenum chamber having closed and open sides. The distance between the nozzle exit and the plenum chamber back plate is varied from 6.3 to 9.6 times the nozzle exit diameter for the closed plenum chamber and 5.9 to 9.4 times the nozzle exit diameter for the open plenum chamber. In the plenum chamber, the heat flux has been measured using slug type heat flux gauges mounted at different locations. The temperature - time data are analyzed to obtain an insight into the flow field in the plenum chamber. Thirteen static tests are carried out to obtain the effect of axial distance between the nozzle exit and the plenum chamber back plate, and stagnation pressure in the rocket motor on the local heat transfer, characterized by Nusselt number in the closed and open plenum chambers.