Visual flame characteristics, burning rates, and final flame temperatures for propellants based on ammonium dinitramide (ADN) and hydroxyl-terminated polybutadiene (HTPB) at different HTPB concentrations (3-20%) have been studied at pressures of 0.05 to 0.6 MPa. The flame structure was studied by probing molecular-beam mass-spectrometry, thin thermocouples, and video recording. The burning-zone width at 0.1 MPa was similar to 1.5 mm. Thermocouples revealed temperature fluctuations of about +/- 400 K at 0.1 Wa in the flame zone within 1.5 to 4 mm from the burning surface. Along with temperature fluctuations, fluctuations also occurred in the intensities of the mass peaks of mass spectra of samples withdrawn from the flame. These are a consequence of the nonhomogeneous and nonstationary combustion of the propellant. Video recordings revealed the existence of several brightly luminous flame jets (torches) of about 1 ram in diameter at the burning surface, disappearing from one site and re-appearing at another. Combustion products were found remote from the burning surface and in it, immediate vicinity by using molecular-beam mass spectrometry. The reactions in the condensed phase (mainly the ADN decomposition reaction) control ADN/HTPB propellant combustion. The oxidation of HTPB decomposition products in the gas phase increases the heat release there and accelerates reactions in the first and second zones of the ADN flame.