A Base Pressure Experiment for Determining the Atmospheric Pressure Profile of Planets

Abstract

An experiment is described which consists of monitoring the base pressure of an entry probe and deriving the freestream pressure profile of a planet through correlation curves which directly relate base pressure to freestream pressure for the varying trajectory conditions. The experiment/technique is applicable for Mars, Venus, and Jupiter entry probes. The base pressure experiment offers distinct advantages to an entry probe mission such as a positive indication of where M x = 1 occurs in the entry trajectory, a positive indication of boundary-layer transition onset, and a freestream pressure boundary condition at the A/ x = 1.2 trajectory point independent of any other onboard or offboard measurements. The results of a recent slender cone R/V flight test have demonstrated the feasibility of the experiment by deriving the atmospheric pressure profile of Earth from base pressure measurements. Available flight and ground test base pressure data have been reviewed and an assessment made of which parameters are important to the base flow phenomena, which are well known and which require more investigaton to calibrate the experiment by obtaining additional data. Nomenclature A = base area D B -base diameter M L = local Mach number preceding the base MOO = freestream Mach number m= mass addition rate m/pAV -mass addition parameter P b = base pressure P b /P n -base pressure ratio P L = local cone pressure preceding the base P^ = freestream pressure Re D = freestream Reynolds number based on diameter R/V = re-entry vehicle rJR = radius ratio on base r/R = nose to base radius bluntness ratio V = velocity X/L = axial station a = angle of attack 0 = offset angle on base 6 C = cone angle 7 = ratio of specific heats p = freestream density