Re-Entry Analysis Of Research Rockets Payloads

Abstract

The atmospheric re-entry of sounding rocket payloads is an important phase of ballistic flight, especially if instruments and experiments are to be recovered for future flights or interpretation of experimental data. Understanding the dynamic behaviour of cylindrical and cone-cylindrical payloads during the re-entry is a prerequisite for ensuring successful deployment of the parachute system1 2. This includes not only knowledge of the payload vehicle attitude and rate data but also the “global view" of deceleration, descent time and terminal recovery velocity. The paper describes the analysis work that has been conducted at the German Aerospace Center’s Mobile Rocket Base on the flight data of several TEXUS (Technologische EXperimente Unter Schwerelosigkeit) and MAXUS payloads that have been reviewed and compared. Vehicles, in which the centre of gravity coincides with the longitudinal aerodynamic centre, as is the case with TEXUS, MAXUS and MASER payloads, are usually spunup about the longitudinal axis before entry into the atmosphere to eliminate concentration of surface aerodynamic heating and enhance the condition for a flat-spin. Analyses of flight data have shown that the payload pinning stops when dynamic pressure starts to build and it is stabilised to one lateral position depending on devices like Telecommando- or GPS-Antennae before the payload reaches the flight time with maximum deceleration. The differences in the flow separation, forces the cylindrical payload into a rotational motion about the axis of highest inertial moment when it reaches subsonic velocity. During the analysis work that has been conducted at the Mobile Rocket Base, flight data from several TEXUS and MAXUS payloads have been reviewed and compared. The availability of accurate GPS and sensor data support the analysis of the acceleration of the payload from a altitude of 120 km during descent. With the use of gravitation models the acceleration is reduced to its aerodynamic component only. The density of the atmosphere is taken from atmospheric models to calculate the drag coefficient which is dependent on payload attitude, Reynolds-Number and Mach-Number. Up to now estimations for drag coefficients have been based on theoretical data and measurements of a cylinder in a flow field of a certain Reynolds-Number. Modelling the re-entry has also been performed by simulating the payload motion during its flight through the atmosphere, as well as the change of the drag. This paper describes the similar behaviour of the drag coefficient for sounding rocket payloads regarding the dependence on geometry, Reynolds-Number and Mach-Number.