CONSIDERABLE work has been done on solid rocket ^->< propellants using various fuels (often polymers) and oxidizers. Recently Rastogi and Ouseph have studied the combustion of phenol-f ormaldehy de/NH 4C10 4 system . They observed that the rate of burning decreases as the amount of cross-linking increases in the polymer. An attempt was made to correlate the burning rate with degree of cross-linking of the binder, but no simple relationship could be derived because the nature and the extent of cross-linking in the phenolformaldehyde polymer was not clearly known. Accordingly, it was thought to study polyester/NH4Cr04 system, since in this case cross-linking can be controlled by the addition of cross-linking agents such as styrene, methyl-methacrylate, etc. The selection of polyester was also made due to ease in its preparation, handling, curing, and good mechanical properties.