In Flight Research on Aerothermodynamics (Atd) and Thermal Protection Systems (Tps) for Space Transportation Systems

IN FLIGHT RESEARCH ON AEROTHERMODYNAMICS (ATD) AND THERMAL PROTECTION SYSTEMS (TPS) FOR SPACE TRANSPORTATION SYSTEMS

Jean Muylaert (1) , M. Ivanov (2) ,V. A. Danilkin (2), C. Park (3), H. Ritter (1), G. Ortega (1)

(1)ESA/ESTEC, Keplerlaan 1, 2200 AG Noordwijk, The Netherlands,

Email: [email protected], [email protected], [email protected] (2) ITAM Email : [email protected]

(4) KAIST Email:CPark216 @kaist.ac.kr

ABSTRACT

The paper addresses a strategy to perform in flight such as wake closure, capsule shoulder heating and TPS gap / step micro aero effects could be analysed. research on Aerothermodynamics (ATD) and Thermal Protection Systems (TPS) taking advantage of the low 4. Aero-assist Hopping being a General Study cost VOLNA and SHTIL class of launchers. Programme (GSP) internal activity to assess the A series of flight test beds will be addressed and their feasibility of a low cost flight gathering data on aero- relevance discussed as to the gathering of critical braking and aero-assist strategies. Aerothermodynamic and TPS related data for design It is concluded that these low cost class of in flight tool qualification and associated physical model research initiatives are “the” way forwards to improve validation. the tools to be used for design of future re-entry space transportation systems. The paper reviews 4 initiatives, all of them of the class flying test beds and launched by the VOLNA launcher: 1. BACKGROUND 1. The EXPERT (European Experimental re-entry Test bed) project where the objective is to acquire hypersonic The design of space transportation systems is always flight data for improved understanding of natural and driven by worst case scenario’s involving estimations of roughness induced boundary layer transition, catalysis uncertainties associated with critical phenomena. To and oxidation, real gas effects on shock wave boundary cope with those uncertainties, margins are defined layer interactions, base flows and real gas chemistry. providing robustness to the system. The flight is planned for early 2010. In this process it is crucial to understand the 2. Rad-flight, being a General Study Programme (GSP) uncertainties associated with the tools used for design feasibility study with the aim to acquire flight data on and more specifically the level of validation they were radiation and ablation coupling associated with re-entry subjected to. speeds of 11km/sec thereby simulating planetary exploration and lunar sample return environments; Validation of design tools involve: revisiting herewith the Fire II precursor Apollo flights • Validation of the physical models incorporated into performed more than 40 years ago. the CFD tools, 3. Polyspheres, being a corporate study to assess the • Experimental testing activities such as e.g. plasma feasibility of one flight where multiple small capsules wind tunnel testing simulating heat loads for TPS are being injected into a suborbital trajectory with the qualification, and objective to study the impact of various heat flux levels • Flight extrapolation and scaling, including the on TPS samples. In addition critical ATD measurements analysis of the uncertainties associated with the sensor integration and calibration . 2

3. JUSTIFICATION FOR IN-FLIGHT The primary objective of the present in flight research RESEARCH TEST BEDS initiatives is to reduce these uncertainties associated A brief summary of lessons learned of past flight with design. experimentation is given below justifying the present in flight research initiatives.

2. OVERALL IN-FLIGHT TESTING APPROACH

The Hermes and the follow up MSTP programme 1. FULL SCALE FLIGHT VEHICLES : provided the opportunity to test Orbiter shuttle e.g. - SHUTTLE, BOURANE, APOLLO, SHENZHOU, ARIANE 5, configurations in the European high enthalpy facilities - HUYGENS F4 and HEG. - HOPE, HERMES, OSP,CSTS - HERCULES, SOCRATES The need for enhanced facility free stream characterization, standard model testing as well as the 2. EXPERIMENTAL DEMONSTRATORS : need for testing flown configurations for improved e.g. - X23, X24, X38, AS201, AS202, APOLLO 4,6 ARD, - BOR4 for TPS ; BOR5 for GNC; understanding of extrapolation and scaling was one of the main recommendations of these programmes. - OREX, HYFLEX for TPS ; ALFEX for GNC - MAIA, PHOENIX 1 and 2 for GNC - FLPP IXV ( PRE-X ) – USV , BLAST The follow ARD project, highly successful on the system level addressed some deficiencies associated 3. IN FLIGHT RESEARCH - FLYING TESTBEDS with sensor integration and addressed the need for

e.g. - SHARP B1, B2 FLIGHTS, HYSHOT, X43, higher accuracy instrumentation when dealing with - IRDT, PAET, RAMC, FIRE local ATD phenomena and physical model validation. -MIRKA, EXPRESS, SHEFEX, SFYFE, PINCH, PIRAEUS . - EXPERT,RADFLIGHT,POLYSPHERES, AEROASSIST More recently but prior to Titan entry on 15 January 2006 a series of new experiments in shock tubes and Table 1: In-Flight experimentation classification plasmatrons were performed to verify whether the assumptions made during the design of the Huygens Table 1 presents a general in-flight experimentation heat shield were conservative enough. classification where in-flight testing can be grouped in 3 classes: full scale flight testing; experimental In doing so the task group came to the conclusion that demonstrators and in-flight research test-beds. radiation coupling is still not well enough understood and, in particular, that collisional radiative non- The present paper focuses on class-3 in-flight research – equilibrium data are still missing in part due to lack of flying test beds; this class addresses critical issues for well calibrated shock tubes and associated non intrusive design on the phenomenological level for instrumentation in conditions close to flight. Aerothermodynamimc and TPS gas surface interaction such as boundary layer transition, catalysis and It became clear that still al lot need to be achieved when oxidation, ablation, blackout, radiation, shock dealing with radiation coupling and its physical model interaction, real gas chemistry radiation, scram validation. combustion etc.. J.Moss summarised below in table 2 available numerical Class-2 deals with programme driven experimental computations performed for a point on the Fire II and demonstrations required for Class-1 full scale space Apollo 4 trajectory. transporatation system qualification. Class-2 deals with subsystem and system demonstrators required to qualify For Fire II the point was taken on the trajectory at the class-1 full scale flight. 1642.7 seconds corresponding to an altitude of 54km and a speed of 10.6 km/sec. Good examples for class-2 are the Bor 4, designed to match the local heat flux of the Bourane and the Bor 5, Note the large differences found for the convective heating: from 6 to 14 MW/m2 as well as for the radiative a 1/8 scaled Bourane configuration, for aero data basing 2 and guidance, navigation and control purposes. heating: from 3 to 6 MW/m confirming the need to understand even further thermo-chemical chemistry, non-equilibrium radiation coupling and absorption. 3

It is indeed now time, 40 years later after Fire II, to get injection, particle spallation; transition to turbulent flow new radiation flight data using advanced non-intrusive thereby enhancing ablation interaction. techniques in a way that the physical models associated with shock layer radiation / coupling and absorption can be improved. 4. PRIORITY ITEMS FOR IN FLIGHT Vehicle/Source max q max q max q c r t RESEARCH Fire II @1642.7 • Gupta2 6.8 (7.0) 3.2 10.0 total Based on the above lessons learned, a summary list of • Sutton (Inviscid)2a 6.8 (BL correlation) 3.8 10.6 total critical phenomena can be made to be studied by future in flight research initiatives: •Park3 6.6 6.5 13.1 total •Park3b Latest Result 14.3 3.8 18.1 total • Roughness induced Transition • Flight data 10.7 total • Micro aero • Real gas chemistry • Fay & Riddell 7.2 • TPS Catalysis and oxidation • TPS ablation Apollo 4 with ablation • Radiation / Ablation coupling •Park3 2.3 5.0 7.3 • Turbulence / Ablation •Park3b Latest results 3.6 1.7 5.3 • Base flows •D. B. Lee3a 1.1 Visible & IR 3.33a • Measurement sensors integration • Use of plasma facilities in design process • Fay & Riddell 2.3 In particular, managing uncertainties associated with Table 2: Heating Prediction and Measurements 2 Physical modelling: chemical modelling and (MW/m ) • radiation coupling • Flight measurement techniques: integration and calibration Anther interesting test bed was the US Re-entry F; it • Knowledge of free-stream conditions was a sharp-cone configuration designed to study • Wind tunnel to flight extrapolation (i.e. use of laminar/turbulence transition. Its base flow was ground based facilities) instrumented and revealed the non-existence in flight of are key ATD and TPS design drivers and need to be a disk shock. addressed . M. Wright pointed out that simulations of axi- symmetric bodies at high Mach number and zero angle of incidence frequently show a disk shock in the base of such configurations. This disk shock creates a large 5. VOLNA SUBORBIRAL PERFORMANCE increase in predicted base pressure combined with an CAPABILITIES increased heating.

The re-entry F flight data were not able to confirm the existence of this disk shock and sting mounted ground based facility experiments did not provide insight into this problem, leading to large uncertainties in the design of back cover thermal protection systems for planetary probes.

Ablation recession data measured during the Galileo entry phase indicated that: • Stagnation point recession was less than predicted

• Ablation at frustrum and shoulder was much higher than predicted Fig 1 : VOLNA with Volan shape for micro g flight Recent mathematical models have not been capable to testing fully explain the observed behavior. Possible reasons for this could be: enhanced turbulence due to mass

Fig.2: EXPERT testbed

EXPERT is a funded ESA undertaking scheduled to fly early 2010. (Ref 1).

Table 3: VOLNA Typical suborbital payload and Fig.3: EXPERT crossing high enthalpy performance trajectory capabilities (ref 3) envelops

The table 3 provides some typical VOLNA suborbital trajectories and corresponding available payload masses; it also provides Re-entry Vehicle (RV) entry velocities from 5km/sec to 7km/sec and minimum entry angles for different flight routes.

6. BRIEF DESCRIPTION OF THE 4 MISSION SCENARIO’S

6.1 EXPERT

Fig.4: EXPERT Mach Reynolds Envelop

The trajectory of EXPERT was selected to be the one corresponding to route 6 of table 2. The lower re-entry speed of 5km/sec was chosen enabling a detailed study of windtunnel to flight extrapolation and scaling. Indeed, figure 3 demonstrates that the EXPERT trajectory crosses the high enthalpy facility performance envelops of F4, HEG and TH2 in terms of the binary scaling simulating real gas dissociation reactions whereas figure 4 shows the high interest of the VKI Longshot for the study of transition and viscous interaction effects. 5

The following payloads are on board of the EXPERT vehicle : 3-rd stage Payload 1 – FADS Flush Air Data System

Payload 2 – PYREX Nose Heating Experiment

Payload 3 – Catalicity Experiment booster Payload 4 – Natural Transition Experiment

Payload 5 – Roughness Induced Transition Experiment RV

Payload 6 – SWBLI onto EXPERT Open Flaps Basic characteristics Payload 7 – SWBLI ahead of EXPERT Open Flaps Mass of fuelled booster РБ -963 kg; Payload 8 – IR Thermography Type of fuel – solid; Number of motors – 1; Motor thrust -3700 kgf; Payload 11 – Junction Experiment Specific thrust impulse of motor in vacuum – 275 s Time of operation – 60 s. Payload 10 – Re-entry Spectrometry (RESPECT) Payload 12 – Base Pressure and Heat Flux Sensors Fig. 5: SRM based booster

Payload 13 – Skin Friction Sensors

Payload 15 - Sharp Hot Structures

Payload 16 - Actively Cooled Sample

Payload 18 - Intermetallic Matrix Composite Tile

A large effort is being devoted to the qualification of the sensors integration and to the measurements of the free stream parameters through the use of an air data system and IMU’s ensuring the required accuracies needed to perform proper physical model validation activities.

6.2 RADFLIGHT

Fig. 5 and Fig. 6 show the results of a feasibility study RV separation demonstrating the capability of the Volna launcher to 3-rd stage with perform a re-entry flight at 11km/sec. The 3rd stage booster Booster separation carries a composite vehicle consisting of a booster providing the additional delta V as well as the instrumented capsule undergoing speeds up to Fig. 6: Flight Phases 11 km/sec and providing the proper environment for the study of radiation/ablation (Ref 2 ). Based on recommendations drawn from the lessons Fig. 7 shows a possible mission scenario using a solid learned from 2 planetary entries (Huygens, Galileo) and booster incorporated part of the 3rd stage. Its specific 2 Earth re-entry flights (Fire II, Re-entry F) the impulse of 275 seconds during 60 seconds provides the following flight data are required : required delta-V to reach the final speed up to 10.8 km/sec at 100 km altitude. The subsequent entry • spectral radiation data in the UV and visible angle is 22.7 degrees. bandwidths • data on radiation/ablation coupling • data on radiative and convective heating

• pressure and temperature evolutions at different locations on and inside the TPS • data on laminar to turbulent transition • data on turbulent / ablative heating especially in shoulder regions • data on base flows with attention to the existence of a supersonic wake closure • air data system • other spectroscopic measurements contributing to the understanding of radiation coupling

Again the final goal of Radflight is to manage improved uncertainties associated with:

• physical modelling: non equilibrium thermo chemistry , absorption and emission, ablation, spalation and pyrolyse Fig. 9: Dispenser with 4 small capsules • flight measurement techniques calibration and its integration into TPS • knowledge of free-stream conditions • wind tunnel to flight extrapolation (i.e. use of ground based facilities)

6.3 POLYSPHERES

The objectives of the polysphere initiative is to fly and recuperate multiple capsules ( 4 to 7 capsules ) with one suborbital flight at 7km/sec reentry speed using the Volna or the Shtil class of launcher.

The objectives is to get flight data on ablative TPS data for 4 , 7 , 9 and 11 MW/m2 on blunt cone configurations e.g. a capsule , blunt cone or using the flown VOLAN shape.

One of the capsules could even be used for advanced studies; e.g. driven by universities for the study of innovative boundary layer flow control methods such as Fig. 10: Dispenser with 4 small capsules MHD, energy addition, boundary layer bleed, cooled TPS using PCM or other techniques.

Fig 9. shows a sketch how potentially a 4-capsule Being able to get comparative flight data on one and the dispenser can be mounted onto the VOLNA 3rd stage. same TPS at different heat fluxes and in addition being By performing one mission different trajectories can be able to post-flight inspect the material and its flown as seen in figure 10. instrumentation will greatly advance ablative TPS characterization as well as improve methodologies as to the use of ground based facilities for design. 7

6.4 AERO ASSIST HOPPING The flight guidance strategy was simple (small number Figure 11 shows the bent biconic shape that was of roll reversals and simple angle of attack modulation) selected for an internal study assessing the potential for using CoG movement strategies. an aero assist flight, including recuperation at Kamchatka and complying with mass and volume Figures 12 shows initial aero assist hopping trajectories. requirements of the VOLNA launcher. Clearly this is only very premature but it demonstrates that with small vehicles one can get initial data for The mass was 400 kg, the flight path speed at entry understanding of new strategies such as skipping and (100kn altitude) was 6km/s and entry angle was: -5.2 aero assist manoeuvres. In addition air data systems degrees. could provide useful free stream data at those altitudes.

7. CONCLUSION

The paper, described 4 initiatives of the class of in flight research test beds: EXPERT, Radflight, Polyspheres and Aeroassist .

The objective of all are to gather data for “design tool” improvements encompassing: • validation of the physical models incorporated into the numerical tools, • experimental testing activities such as plasma wind tunnel testing simulating heat loads for TPS qualification and high enthalpy testing for ATD data basing and design and • flight extrapolation and scaling including the Fig. 11: Generic bent biconic configuration for aero analysis of the associated uncertainties. assist hopping research Finally it can be concluded that these test beds are affordable being flown on low cost launchers and that Altitude (km) Altitude (km) they are effective as they can be executed in a short 10 0 time. In addition they also provide a mechanism for education and training so as to maintain the expertise 80 and know how in this field.

8. REFERENCE 60 RD[1] 5th International Planetary Workshop IPPW5 1 paper “EXPERT Aerothermodynamic Flight 40 Instrumentation and Integration “, J. Muylaert , F. Ratti,, L.Walpot J. Gavira, M. Caporicci ; Bordeaux , June 20 2007.

RD[2] 5th European Workshop on Thermal protection 0 systems and hot structures , ESA proceedings SP 631 paper “proposal for in flight research on radiation/ablation coupling filling a 40 year gap after -20 0 20 0 4 00 600 80 0 10 0 0 1200 FIREII”, J. Muylaert , F. Mazoue, L. Marraffa, H. Time (s) Ritter, V. Danilkin , June 2006.RD[3]

RD[3] VOLNA Space–Rocket complex (VOLNA Fig. 12: Typical controlled aero assist hopping SpRC) User’s Guide Issue 1.0 January 2002 Space trajectory for 400kg bent biconic vehicle Rocket Centre , Miass, Russia

RD[4] Private communications with Chull Park.

Fig. 7: Rad flight mission trajectory

Fig. 8: Altitude Speed Diagramme for Radflight ( ref 4 )