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A series of reusable external insulation (REI) materials are being developed by the Re-Entry and Environmental Systems Division of the General Electric Company (RESD) for application to the Space Shuttle. These materials are bonded to a substrate in the form of panels resulting in numerous panel-to-panel joints. A plasmaarc ground-test facility has been used to evaluate the effects of the local heat transfer in these interface areas. Models with transverse, axial, and "tee" joints, both filled and open, have been tested. The major results of the test program are that the unfilled gaps run hotter than comparable undisturbed areas, and that for transverse and axial gaps a trend of decreasing temperatures with decreasing gap width is evident. The major conclusion is that unfilled butt joints are acceptable for the Orbiter if H/L > 17, but a conservative design approach would be to partially fill all gaps. NomenclatureH = depth of gap, enthalpy L -width of gap M = Mach number q = heat flux Qs = total energy flux crossing the shear layer dividing streamline over an Area A l Q A = total energy flux to the wall over the gap projected area A 1 if attached flow existed S* = dimensionless parameter, L/X 1 X 1 = wetted length e = emittance Subscripts A = projected area c = convection e = local m = model o = orbiter R = radiation RR = reradiation S = shear layer W =wall

Tests were conducted in the Arnold Engineering Development Center (AEDC) C Tunnel at a Mach number of 10 on a sharp slender cone and on the frustum, with three alternate spherical bluntness noses to determine the size of spherical roughness required to effectively trip to a turbulent boundary layer. The spherical roughnesses were placed on the surface of the sharp cone and at several flow-inclination angles on the spherical noses. Data are correlated in terms of k/d* and a trip-diameter Reynolds number that accounts for changes of local Reynolds number profile over the trip height. A definite effect of tripping effectiveness was noted as wall temperature changed. Laminar and turbulent heat-transfer results were in good agreement with the Eckert reference enthalpy method. Angle of attack affected transition by causing it to occur earlier on the leeward side for a smooth cone, but where transition was induced by roughness, it occurred earlier on the windward side. The results of the investigation may be utilized to determine allowable size of ablation roughness or spacing and position of roughness required for artificially inducing turbulence on cones and sphere cones for turbulent heating experiments in wind tunnels and flight. NomenclatureCp = specific heat at constant pressure, Btu/lb °R Cv = specific heat at constant volume, Btu/lb °R g = 32.2 ft/sec 2 = gravitational const h = enthalpy, Btu/lb H = q/T Q -T w = heat-transfer coeff, Btu/ft 2 sec°R J = 778 ft-lb/Btu = Joule's const k = trip diam, ft K = thermal conductivity, Btu/ft sec°R L = characteristic length, ft M = Mach number p = pressure, psf p r = (C P /K}n = Prandtl number q = heating rate, Btu/ft 2 sec RN = nose radius, in. RB = base radius, in. Rek = pkUkk/nk = trip Reynolds number Re x = peVeX/Ve = Reynolds number based on length Red* = peHeS*/v e = Reynolds number based on displacement thickness Rexk = In I P~^ V x = Reynolds number based on integrated J 0 \ fJLe / flow and length to the trip condition

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