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The European Venus Explorer (EVE) mission was proposed to the European Space Agency in 2007, as an M-class mission under the Cosmic Vision Programme. Although it has not been chosen in the 2007 selection round for programmatic reasons, the EVE mission may serve as a useful reference point for future missions, so it is described here. It consists of one balloon platform floating at an altitude of 50-60 km, one descent probe provided by Russia, and an orbiter with a polar orbit which will relay data from the balloon and descent probe, and perform science observations. The balloon type preferred for scientific goals is one which oscillates in altitude through the cloud deck. To achieve this flight profile, the balloon envelope contains a phase change fluid, which results in a flight profile which oscillates in height. The nominal balloon lifetime is 7 days-enough for one full circumnavigation of the planet. The descent probe's fall through the atmosphere takes 60 min, followed by 30 min of operation on the surface. The key measurement objectives of EVE are: (1) in situ measurement from the balloon of noble gas abundances and stable isotope ratios, to study the record of the evolution of Venus; (2) in situ balloon-borne measurement of cloud particle and gas composition, and their spatial variation, to understand the complex cloud-level chemistry; (3) in situ measurements of environmental parameters and winds (from tracking of the balloon) for one rotation around the planet, to understand atmospheric dynamics and radiative balance in this crucial region. The portfolio of key measurements is complemented by the Russian descent probe, which enables the investigation of the deep atmosphere and surface.

Results of an investigation of the global aerodynamic coef cients and ow characterization around an Apollostyle capsule model at low speed are presented. Flow features were ascertained quantitatively with laser Doppler velocimetry, digital particle image velocimetry, and hot-wire measurements, as well as qualitatively by ow visualizations. The study revealed a meandering vortex ring around the capsule, well-organized streamwise vortices whose maximum vorticity increased in the recirculating wake before decaying farther downstream, as well as a complex array of ow separation and reattachment features. A number of particularities in the ow eld have been identi ed as potential candidates for triggering the onset of vehicle instability. Based on these ndings, a modeling approach is proposed. Nomenclature Cd= drag coef cient Cl = lift coef cient Cm cg = static moment coef cient about center of gravity D = capsule maximum heat-shield diameter, m f = oscillation frequency, Hz I = mass moment of inertia, kg-m 2 q 1 = freestream dynamic pressure, N/m 2 R = local radius, m S = projected heat-shield area, m 2 Sr = Strouhal number of the wake t = time, s U 1 = freestream velocity, m/s u; v; w = velocity components in Cartesian coordinates, m/s u 0 2 ; v 0 2 ; w 02 = turbulent normal stresses, (m/s) 2 u 0 v 0 ; u 0 w 0 = turbulent shear stresses, (m/s) 2 W = amplitude of the unsteady pitching moment relative to its mean X; Y; Z = Cartesian coordinates ® = angle of attack, deg @Cm cg =@® = static pitching moment coef cient slope, 1/rad ½ 1 = freestream density, kg/m 3 ! = angular frequency of wake oscillation, rad/s

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