Cooled rocket chamber wall

A rocket engine chamber (10) has a back structure (20) and a heat exchanger structure (18) located radially inwardly of the back structure (20). The heat exchanger structure (18) has a plurality of integrally formed cooling passageways with adjacent ones of the passageways (22) having a common sidewall structure (28). Each passageway (22) has a top section (30) which forms the wall (24) that contacts the hot gases. The top section (30) is formed by a wall structure having an inner and outer surface formed by an arc of a circle and a substantially constant wall thickness.