Consideration is given to the experimental investigation of the original method of providing radio communications with a reentry vehicle along the trajectory section when a vehicle is surrounded by plasma of the ionized shock layer. The method suggests placing of the antennas in special small containers. The containers are located at about zero angle of attack on a pylon ahead of the bow shock wave generated near a vehicle. Because of the small container bluntness low level of ionization near the antennas could be provided. But many problems connected with heating and thermal protection of the container and pylon arise in this case. Therefore along with the measurements of ionization near the container, heating and thermal protection of the container and pylon and their in uence on the vehicle aerodynamics were investigated. The experiments were performed in four hypersonic wind tunnels of different types in Mach-number range from 6.5 to 20.5. Various measurement methods were used. The investigation shows that the remote antenna assembly can provide uninterrupted radio communication with the reentry vehicle. NomenclatureC i = rolling-moment coef cient C L = lifting coef cient C m = pitching-moment coef cient C n = yawing-moment coef cient d = diameter of remote antenna assembly container, 0.08 m F = model planform area G = total mass-ow rate of injected gas H = ight altitude i = gas enthalpy K = correlation parameter for nonequilibrium ionization L = model length M = Mach number m = local mass-ow rate of injected gas, ½ w v w n = concentration of particles P = pressure q = heat ux R = nose bluntness radius Re 0 = Reynolds number for stagnation temperature viscosity, ½ 1 V 1 R=¹ 0 Re 1 L = Reynolds number for undisturbed ow viscosity, ½ 1 V 1 L=¹ 1 S = distance from stagnation point along surface T = temperature t = time V = ow velocity, ight velocity v w = injection velocity X cg , Y cg = center-of-mass position coordinate y = shock-layer coordinate normal to the surface ® = angle of attack = sideslip angle 3 = nonequilibrium ionization parameter ½ = density 9 = dihedral angle of wing 19 = angle of wing de ection ! = radio signal frequency ! p = plasma frequency Subscripts e = electron eq = equilibrium i = ionization, ions j = injected gas max = maximum t = total w = wall conditions 0 = stagnation point 1 = for unit Reynolds number 1 = freestream Superscripts L/D = lift/drag R/L = right/left

Abstract. HF sounding of the mesosphere was ®rst carried out at SURA in summer 1994 at frequencies in the range 8±9 MHz using one of the sub-arrays of the SURA heating facility. The observations had a range resolution of 3 km. Almost all measurements indicated the presence of strong radar returns from altitudes between 83 and 90 km with features very similar to VHF measurements of mesopause summer echoes at midlatitudes and polar mesopause summer echoes. In contrast to VHF observations, HF mesopause echoes are almost always present.

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