The paper is motivated by a need for describing high-altitude gas releases from rockets or the Space Shuttle In the tenuous upper atmosphere, the injected gases expand from a collisionless to a collision-dominated state The analysis presented extends the efforts of Baum (1973-1974) to include the effects of a nonuniform background atmosphere and a velocity-dependent collision frequency The unsteady expansion of gas releases is analyzed using gas kinetic theory The Boltzmann equation with the Krook collision integral is solved numerically At late times (after many collisions with the background atmosphere) the solution is identical to the one given by diffusion in a nonuniform atmosphere (Bernhardt, 1979) The theoretical model predicts elongation and heating of the vapor trails due to collisions

High-altitude gas releases: transition from collisionless flow to diffusive flow in a nonuniform atmosphere

Ultra-wideband (UWB), short-pulse (SP) electromagnetics are now being used for an increasingly wide variety of applications, including collision avoidance radar, concealed object detection, and communications. Notable progress in UWB and SP technologies has been achieved by investigations of their theoretical bases and improvements in solid-state manufacturing, computers, and digitizers. UWB radar systems are also being used for mine clearing, oil pipeline inspections, archeology, geology, and electronic effects testing. Ultra-wideband Short-Pulse Electromagnetics 7 presents selected papers of deep technical content and high scientific quality from the UWB-SP7 Conference, including wide-ranging contributions on electromagnetic theory, scattering, UWB antennas, UWB systems, ground penetrating radar (GPR), UWB communications, pulsed-power generation, time-domain computational electromagnetics, UWB compatibility, target detection and discrimination, propagation through dispersive media, and wavelet and multi-resolution techniques. This book serves as an essential for scientists and engineers working in these applications areas.

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Ultra-Wideband, Short-Pulse Electromagnetics 7

Observations of acoustic-gravity waves in the thermosphere following Space Shuttle ascents

In this paper, a multiphysics numerical approach for predicting the ionization level in solid rocket engine plumes is presented. Ionization takes place in the rocket combustion chamber and in the exhaust plume. A low-temperature, high-density plasma is created, with small Debye length in most of the plume region. Ambipolar diffusion is therefore assumed for ions and electrons in the plume, and a set of conservation equations is derived to be solved by the numerical model. A number of numerical strategies to resolve this system is derived, as well as a novel scheme that enforces charge neutrality. This approach is integrated into a complex code for compressible, multispecies, turbulent flow simulations. The model is then coupled with a Maxwell’s equations solver in order to simulate the radar cross section of rocket plumes. Finally, computations of ionization levels and radar cross section of a Black Brant rocket plume are presented.

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Numerical Simulation of Ionized Rocket Plumes

Space transportation systems are exposed to high thermal
and mechanical loads during the ascend in the transonic
flow regime. By now, there are still many uncertainties,
which can not be solved with state of the art computational
fluid dynamic models or experiments with cold jet
flows. A test facility with a high degree of similarity to
flight with respect to the influence of the hot nozzle flow
can contribute to improve the understanding of interaction
effects between the hot nozzle flow and the ambient
flow by providing reliable data for validation. The objective
of the paper at hand is to present the work progress
on such a facility. Issues and challenges concerning the
base flows are discussed and potential research areas for
investigations are considered. Relevant conditions during
the ascend of Ariane 5 are used as baseline and appropriate
scaling laws are discussed to conclude requirements
for the operational conditions for the existing wind tunnel
Vertical Test Section Cologne (VMK). These operational
conditions are used to develop a concept. After a proof of
concept is given by CFD calculations, details to the supply
system including the operational range are described
and opposed to existing test benches without interaction
capabilities.

Design of a Hot Plume Interaction Facility at DLR Cologne

Rocket Plumes in the Thermosphere

An approximate analysis of radar backscattering from the underdense turbulent rocket exhaust plume at high altitudes is offered. The tail aspect radar backscatter spectral content is analyzed using an exhaust mean flow model that has been shown accurate for engineering analyses and upon which a gaussian velocity turbulence perturbation is superimposed. The turbulence intensity is directly related to combustion chamber temperature-fluctuations for small perturbations. The radar wave is assumed scattered from an elemental volume in the exhaust flow in which the turbulence is assumed quasi-isotropic and for which the flow properties vary negligibly over a radar wavelength. The resulting expressions yield the total and spectral radar cross section of the underdense plume backscattering in terms of engine combustion chamber temperature, temperature fluctuations, electron density, area ratio, throat diameter, exhaust gas ratio of specific heats, vehicle velocity and radar wavelength. Comparisons with data are made; however, little data is available and many aspects of the approximate theory offered cannot be confirmed at present.

Analysis of radar return from turbulent high- altitude rocket exhaust plumes

Detachment of the outer shock from underexpanded rocket plumes.

: The gasdynamic structure of high altitude rocket plumes is investigated. A simple analytical model for the expansion of a gas into a vacuum is constructed and is shown to represent the expansion of exhaust gases from rocket motors into the region bounded by the inner shock wave and Mach disc. A comparison of the exhaust expansion model with solutions obtained with the method of characteristics is made and shows good agreement. Contours of constant density, electron density, and collision frequency in the exhaust plume of a typical rocket engine are determined. The blast wave theory of Hill et al is extended to allow the calculation of the size and shape of rocket plumes of solid propellant missiles. A method is derived which determines the plume drag of solid propellant motors. The method accounts for the fact that solid propellant rocket plume flow is a two phase flow of gas and solids and that the solids present in the exhaust take part in determining the mass flow but not the pressure or the expansion of the exhaust gases upon exit from the rocket nozzle. The plume expansion and resulting plume size is shown to depend on the thrust and the engine exit plane conditions of the gas phase of the two phase flow.

James Stark Draper

Papers

Rocket Plumes in the Thermosphere

Analysis of radar return from turbulent high- altitude rocket exhaust plumes

Detachment of the outer shock from underexpanded rocket plumes.

High altitude rocket plumes

Rarefaction in underexpanded flows.