Arianit Preci

The In- Flight Sensor Systems PYREX, PHLUX and RESPECT for the Capsule EXPERT

*† ‡ § ** †† ‡‡ §§ Miniaturized flight experiments being developed at IRS for the European capsule program EXPERT are presented. PYREX, a pyrometric entry experiment, measures rear side temperatures and heat fluxes on ceramic TPS. It has already been flown (EXPRESS, MIRKA). PYREX-KAT38 is a fully qualified six-channel measurement system and was intended to be operated aboard the X-38. A similar design is being further developed for temperature and heat flux measurements in the nose structure of the EXPERT capsule. PHLUX (Sensor system for catalytic experiments) is a pyrometric catalysis based sensor system being developed for the EXPERT capsule. A breadboard with two sensors opposite each other has already been developed for ground tests by means of plasma wind tunnel experiments to qualify the sensor functionally and to investigate the plasma composition. The flight experiment aims to estimate the dissociation degree during the entry using measured heat fluxes on different catalytic surfaces. RESPECT is a spectrometer to be used to gain spectral data in the flow field around EXPERT during its entry. The main goal is to obtain more detailed information about the plasma state in the post shock regime by measuring the spectrally resolved radiation onto the surface. The data will be used for the comparison with results of numerical simulations to validate of aerothermodynamic models.

The Combined Sensor System COMPARE for SHEFEX II

The Institut fur Raumfahrtsysteme has developed the combined sensor system COMPARE for SHEFEX II. The goal of this system is to simultaneously measure the temperature of the thermal protection system, the radiative heat flux and the absolute pressure. The gained data will allow the reconstruction of important trajectory parameters. Furthermore, due to the fast response capabilities of the detectors used in the sensor system it is possible to determine the dynamic behavior of the vehicle during flight. With regard to upcoming re-entry missions with relative high entry velocities the application of COMPARE on SHEFEX II will allow to increase the Technology Readiness Level of this sensor system. In this paper, the design and layout of the sensor system are presented.

Sensitivity Analysis of Nonequilibrium Martian Entry Flow to Chemical and Thermal Modeling

Numerical simulations were performed for a reference Martian entry test case using the nonequilibrium code URANUS. The code was further developed to allow for various chemical and thermal modelings of the nonequilibrium Martian entry flow. The flowfield around the reference vehicle was calculated for several chemical and thermal models of a carbon dioxide/nitrogen gas inflow mixture and compared to results available in the literature. A sensitivity analysis of the gas radiation and radiative heat flux were performed by employing the ESA’s plasma radiation database and the radiation transport algorithm HERTA on the computational fluid dynamics results. It was found that the radiation of the carbon dioxide molecule must be taken into consideration due to the large contribution to the overall radiation.

Numerical Investigation of Variable Thermo-Chemistry Modeling for Nonequilibrium Flows

The development status of a code allowing for a variable thermo-chemical modeling of nonequilibrium flows is presented. A high enthalpy flow around a cylinder has been calculated using different modeling of the vibrational nonequilibrium. The effects due to different models on the temperature and the mol fraction of the species are shown. The results of the new code are compared to already verified codes.

COMPARE, a combined sensor system for re-entry missions

For the DLR mission SHEFEX II, the Institute of Space Systems (IRS) proposes a combined sensor system. This experiment combines both pyrometric and radiometric measurement during the re-entry phase. Additionally, total pressure can be measured via the optical path of the radiometer. The experiment will enable a separation of the radiative heat flux from the total heat flux and it will enable the specific enthalpy to be determined. By measuring at adequate wavelength ranges information on plasma composition can be gained.

Development Status of a Navier-Stokes Code for the Simulation of Entry Flows

The development status of a Navier-Stokes code allowing for a variable thermo-chemical modelling of nonequilibrium flows is presented. The system of the conservation equations is implemented allowing for the simulation of air flows as well as other flows, e.g. CO2 and CO2 N2. A high enthalpy flow in thermal equilibrium around a cylinder and a sphere has been calculated using different chemical models in order to verify the implementation.

Assembly, Integration and Test of the Sensor System COMPARE for SHEFEX II

The payload COMPARE is developed at the Institute of Space Systems for the German Aerospace Centre suborbital re-entry mission SHEFEX II, which had its successful roll-out in July 2010. The launch is scheduled for September 2011 in Andoya, Norway. The sensor system is a combination of a pyrometric measurement of the backside temperature of the thermal protection panels and a total pressure measurement using a miniaturized pressure sensor. Additionally, the pressure port is used as an optical access for a thermopile, employed as a broad-band radiometer, which measures the radiation from the surrounding. Furthermore, due to the relative high sampling rates, the radiometer enables a determination of the dynamic behavior of the vehicle. The combined measurement during the atmospheric entry allows for the determination of trajectory parameters during flight. The payload consisting of the sensor electronics and the sensor head has been fully developed, functionally tested and integrated for the mission SHEFEX II. I. Introduction HE German Aerospace Centre DLR is planning a mission within the flight test program Sharp Edge Flight Experiment (SHEFEX) to investigate the active aerodynamic control of re-entering space vehicles and the feasibility of facetted geometries for thermal protection systems. The suborbital mission SHEFEX II 1 will be launched in September 2011 in Andoya (Norway) on top of a Brazilian sounding rocket. The configuration is shown in Fig. 1. The maximum velocity of 3.5 km/s will be reached at an altitude of 35 km. The 350 kg heavy vehicle reaches the maximum Mach number of 12.6 at an altitude of 80 km. The Institute of Space Systems (IRS) has developed the combined sensor system COMPARE (Combined Pyrometric and Radiometric Trajectory Rebuilding Experiment) for SHEFEX II. The goal of this system is to simultaneously measure the temperature of the thermal protection system (TPS), the radiative heat flux and the absolute pressure. The gained data will allow the reconstruction of important trajectory parameters. Furthermore, due to the fast response capabilities of the detectors used in the sensor system it is possible to determine the dynamic behavior of the vehicle during flight. With regard to upcoming re-entry missions with relative high entry velocities the application of COMPARE on SHEFEX II will allow to increase the Technology Readiness Level (TRL) of this sensor system. In fact, further investigation with a sensor system for high speed atmospheric entries utilizing a similar approach of a combined measurement was successfully performed last year. Hereby, a breadboard was tested in relevant plasma environment. The temperature of the rear side of the SHEFEX II TPS panel will be measured during the flight by using a pyrometer. The measurement of the radiative heat flux will be performed with a thermopile, and since the radiometer needs an optical access to the surrounding plasma the pressure will be measured in the radiometer cavity

The flight of EXPERT: Assessment of Nonequilibrium Effects with IRS Payloads PYREX, PHLUX and RESPECT

An overview of the IRS payload development for ESA’s EXPERT mission is given. The final design and performance parameters of the payloads PYREX, PHLUX and RESPECT are described. PYREX is a sensor system measuring the TPS rear side temperature. PHLUX is a catalysis based experiment to determine the dissociation degree of the boundary layer. RESPECT applies optical emission spectroscopy to measure spectrally resolved the radiation onto a TPS surface. I. Introduction pace vehicles encounter high thermal loads during re-entry. The design and layout process of the TPS requires a detailed consideration of various high-temperature effects because the mass of the thermal protection system (TPS) has a considerable impact on the total mass of the vehicle. Furthermore, the portion of the costs for the development of a TPS is significant compared to the total development costs. The investigation of TPS and TPS typical materials is performed by ground based means, e.g. plasma wind tunnels or shock tubes, as well as numerical simulations. Numerical tools used for the calculation of the flow around a vehicle performing an atmospheric entry manoeuvre have to be robust, accurate and efficient and be applicable in a wide altitude and velocity range. The models used in these tools must consider many complex high-temperature effects, such as chemical reactions as dissociation, ionization and recombination and different energy exchange mechanisms as well as thermal nonequilibrium and transport phenomena. The plasma state of the post shock regime and the boundary layer during atmospheric entry are primarily defined by the inflow conditions and the vehicle geometry. In the past, various numerical codes have been developed to numerically simulate these complex conditions. Unfortunately, it is not possible to reproduce all relevant parameters in ground test facilities in order to verify and improve the existing codes. Therefore, experimental data has to be gathered with in-flight sensor systems. A dedicated mission to improve the knowledge of atmospheric entry phenomena is the ESA mission EXPERT 1 , represented by a 1.6 m x 1.2 m large ballistic capsule with a mass of m = 436 kg and a nose radius of r = 0.55 m. Besides the technology development and demonstration aspect of the mission, the second key objective is to build up a database containing various measured re-entry data. At IRS the in-flight sensor systems PYREX, PHLUX and RESPECT were development to serve this purpose. PYREX is a flight-qualified pyrometric entry experiment which measures the TPS rear side temperature distribution. Hence heat fluxes on ceramic TPS can be calculated by solving the inverse heat conduction problem. PHLUX is a catalysis based sensor system which measures rear side temperatures of closely placed material probes

Optical Design and Layout of the In-Flight Spectrometer System RESPECT on EXPERT

The paper reports the layout and verification of the measurement chain as developed for the EXPERT mission on basis of simulated spectrometer responses. To generate the spectrometer signals, flow field simulations of the EXPERT capsule for several trajectory points are conducted. The results, i.e. excitation temperatures and mole fractions of the plasma species, are presented in the paper. From the data, emission and absorption coefficients along the lines of sight of the RESPECT sensor heads are calculated. Furthermore, the calibration of the sensor system is described. In order to demonstrate the successful measurement chain design of the payload, expected spectrometer signals are presented. Nomenclature

Combined Analysis of Catalysis Influenced Heat Flux on PHLUX Sensor System Samples

The IRS sensor system PHLUX is based on catalysis effects. Two different material samples with different but known catalysis properties are placed close to each other, thus being exposed to the same plasma condition. In the course of choosing between suitable materials experimental investigations and numerical analysis has been performed. Catalysis models for SiO2, PM1000 and tungsten are implemented in the flow field solver URANUS in order to perform a numerical analysis of the material samples during the re-entry of the vehicle EXPERT. The recombination coefficients of oxygen and nitrogen on materials investigated here are based on recent measurements at the IRS and on data given in the literature.