Super-orbital re-entry in Australia - laboratory measurement, simulation and flight observation

There are large uncertainties in the aerothermodynamic modelling of super-orbital re-entry which impact the design of spacecraft thermal protection systems (TPS). Aspects of the thermal environment of super-orbital re-entry flows can be simulated in the laboratory using arc- and plasma jet facilities and these devices are regularly used for TPS certification work [5]. Another laboratory device which is capable of simulating certain critical features of both the aero and thermal environment of super-orbital re-entry is the expansion tube, and three such facilities have been operating at the University of Queensland in recent years[10]. Despite some success, wind tunnel tests do not achieve full simulation, however, a virtually complete physical simulation of particular re-entry conditions can be obtained from dedicated flight testing, and the Apollo era FIRE II flight experiment [2] is the premier example which still forms an important benchmark for modern simulations. Dedicated super-orbital flight testing is generally considered too expensive today, and there is a reluctance to incorporate substantial instrumentation for aerothermal diagnostics into existing missions since it may compromise primary mission objectives. An alternative approach to on-board flight measurements, with demonstrated success particularly in the ‘Stardust’ sample return mission, is remote observation of spectral emissions from the capsule and shock layer [8]. JAXA’s ‘Hayabusa’ sample return capsule provides a recent super-orbital reentry example through which we illustrate contributions in three areas: (1) physical simulation of super-orbital re-entry conditions in the laboratory; (2) computational simulation of such flows; and (3) remote acquisition of optical emissions from a super-orbital re entry event

Carrier transport in PbS nanocrystal conducting polymer composites

In this letter we report the carrier mobilities in an inorganic nanocrystal: conducting polymer composite. The composite material in question (lead sulphide nanocrystals in the conducting polymer poly [2-methoxy-5-(2(')-ethyl-hexyloxy)-p-phenylene vinylene] (MEH-PPV) was made using a single-pot, surfactant-free synthesis. Mobilties were measured using time of flight techniques. We have found that the inclusion of PbS nanocrystals in MEH-PPV both balances and markedly increases the hole and electron mobilities-the hole mobility is increased by a factor of similar to 10(5) and the electron mobility increased by similar to 10(7) under an applied bias of 5 kV cm(-1). These results explain why dramatic improvements in electrical conductivity and photovoltaic performance are seen in devices fabricated from these composites

Radiation-Ablation Coupling for Capsule Reentry Heating via Simulation and Expansion Tube Investigations

A capsule entering a planetary atmosphere at hypersonic speeds experiences high levels of radiative heating. Furthermore, coupling between the ablation products from the surface of the vehicle and the high temperature gas can have a major effect on the head load experienced by the vehicle. This paper discusses a collaborative project aimed at better characterising the flow processes involved. A ground-based expansion tube facility is described in which radiation-ablation coupling is achieved through the use of a pre-heated model placed in a high temperature flow. In parallel, simulation techniques are being developed to model the complex chemical processes occurring in the flow

Image-based visual servoing for the super-orbital re-entry of Hayabusa spacecraft

This paper presents an image-based visual servoing system that was used to track the atmospheric Earth re-entry of Hayabusa. The primary aim of this ground based tracking platform was to record the emission spectrum radiating from the superheated gas of the shock layer and the surface of the heat shield during re-entry. To the author's knowledge, this is the first time that a visual servoing system has successfully tracked a super-orbital re-entry of a spacecraft and recorded its pectral signature. Furthermore, we improved the system by including a simplified dynamic model for feed-forward control and demonstrate improved tracking performance on the International Space Station (ISS). We present comparisons between simulation and experimental results on different target trajectories including tracking results from Hayabusa and ISS. The required performance for tracking both spacecraft is demanding when combined with a narrow field of view (FOV). We also briefly discuss the preliminary results obtained from the spectroscopy of the Hayabusa's heat shield during re-entry

Expansion tunnel radiation experiments to support Hayabusa re-entry observations

The Hayabusa sample return capsule is scheduled for re-entry near Woomera, Australia in June 2010 and expansion tube experiments are being performed to support the planned re-entry observation campaign. Initial experiments using a 1/10th scale model of the Hayabusa forebody have been performed in the X2 expansion tunnel facility at The University of Queensland to simulate aerothermal elements of the anticipated re-entry. Experiments have been performed at an effective flight speed of around 9.8 km/s using steel models, and steel models coated with a layer of epoxy to simulate pyrolysis gases associated with heat shield ablation. Spectral emissions from the stagnation region of the capsule have been acquired using a spectrograph system. Two dimensional maps of the luminous emissions from the shock heated flow have also been acquired using a high speed camera. Deduction of flow conditions generated in the X2 expansion tunnel is achieved using quasione- dimensional simulations coupled to an axisymmetric simulation of the flow through the expansion tunnel nozzle. The effects of the ablative epoxy material are observed in the data from both the spectrograph system and the high speed camera. Both systems register strong emissions in the ablative layer, and the strength of the spectral peaks associated with CN emissions are shown to be enhanced by the presence of the epoxy. Further measurement and analysis is required to confidently define the flow conditions produced by the expansion tunnel, and to quantify results from the spectrograph and high speed camera measurements. Copyright © 2010 by Buttsworth, D'Souza, Potter, Eichmann, Mudford, McGilvray, McIntyre, Jacobs, and Morgan

Impulse facilities for the simulation of hypersonic radiating flows

At high flight speeds, radiation becomes an important component of aerodynamic heat transfer, and its coupling with the flow field can significantly change macroscopic features of the flow. As radiating flight conditions are typically encountered in reentry trajectories, the associated flight regimes range from rarefied to continuum, and may have many levels of thermal, chemical and electronic non-equilibrium

Shock standoff on hypersonic blunt bodies in multitemperature ionizing nonequilibrium gas flows

A new theory of hypersonic blunt body shock standoff is presented for ionizing nonequilibrium gas flow, based on a compressibility coordinate transformation for inviscid flow. The electron temperature depends on elastic and inelastic heavy particle collision rates and is treated separately to the heavy particle temperature. Specific application to binary monatomic gas mixtures is made in which the diluent gas is relatively inert up to high temperatures but acts as a collision partner for the electronic excitation of the ionizing gas. A generalised binary scaling property of the analysis is also demonstrated. Parametric results are presented for the density scaled shock standoff distance as a function of an ionization reaction blunt nose region Damkohler number and comparison with experimental results obtained in a superorbital expansion tube with a 15 Y hydrogen 85 Y neon gas mixture are given and discussed

Shock standoff on hypersonic blunt bodies in multitemperature ionizing nonequilibrium gas flows

A new theory of hypersonic blunt body shock standoff is presented for ionizing nonequilibrium gas flow, based on a compressibility coordinate transformation for inviscid flow. The electron temperature depends on elastic and inelastic heavy particle collision rates and is treated separately to the heavy particle temperature. Specific application to binary monatomic gas mixtures is made in which the diluent gas is relatively inert up to high temperatures but acts as a collision partner for the electronic excitation of the ionizing gas. A generalised binary scaling property of the analysis is also demonstrated. Parametric results are presented for the density scaled shock standoff distance as a function of an ionization reaction blunt nose region Damkohler number and comparison with experimental results obtained in a superorbital expansion tube with a 15 Y hydrogen 85 Y neon gas mixture are given and discussed

The generation and measurement of high temperature radiating flows in a high enthalpy pulsed facility

The experimental capabilities of the X2 hypersonic facility at the University of Queensland in Brisbane, Australia are described. The facility can be operated as an expansion tube and the radiation generated in a steady flow over a test model can be studied. Alternatively, the facility can be operated as a shock tube where conditions suitable for radiation studies are created behind a shock wave propagating through a test gas. The facility is instrumented with two intensified camera systems capable of recording spectral information about the flow as well as a high speed camera for time dependent studies and a holographic interferometry system that can measure the flow density and, where present, electron concentrations. The operating envelope of the facility is described and sample experimental results from expansion tube mode operation are presented