Chamber Valve Characteristic

Appendix A Chamber Valve Characteristic

The position of a valve can be read by the MCC system from end switches; they indicate the full open or close status (Fig. A.1). In a valve switch test characteristic time delays can be identiﬁed.

Open

Close 250 256 371 248

Appears Appears

Disappears Disappears

Open

Closed

Open

Closing Command

Closed

Fig. A.1 Time delay in Opening Command milliseconds for the manoeuvring of a valve

Feed Back Back Feed

(chamber valve hydrogen of a Back Feed

Feed Back Back Feed

Vulcain engine) (Photo: DLR) Back Feed

W. Kitsche, Operation of a Cryogenic Rocket Engine, Springer Aerospace Technology, 95 DOI 10.1007/978-3-642-10565-4, C Springer-Verlag Berlin Heidelberg 2011

Appendix B Chamber Igniter Characteristic

The chamber igniter is itself ignited by a pill of powder at its tip. A wire in a short- circuit conducting a current of 6 A for 50 ms ignites the pill. Thus the main powder charge is ignited and the internal pressure (Fig. B.1) of the pyrotechnical element increases. At a pressure of about 120 bar, three membranes which had sealed the element burst. Via three openings at an angle of 120◦ to each other the hot smoke is injected into the combustion chamber and ignites the fuel/oxidiser mixture. The time taken to reach 80% of the maximum pressure inside the igniter in this context is called the ignition delay (Fig. B.1). Figure B.2 is a series of photos showing the ignition of the fuel/oxidiser mixture and the ﬂame evolution in the combustion chamber. The photos were taken with a high speed camera (2000 frames per second) via a mirror below the engine.

140 120 100 80 60

Pressure [bar] Pressure 40 20 0 0 100 200 300 400 500 600 700 Time [ms] Fig. B.1 Ignition delay of a chamber igniter (Photo: DLR)

Fig. B.2 Ignition of a Vulcain-combustion chamber (Photo: DLR)

Appendix C Measurement and Correction of the Ovality of a Vulcain Nozzle

The measurement and correction of the ovality of the Vulcain nozzle has been per- formed regularly since 1993. The protocol (Fig. C.1) documents such a procedure. The diameter was measured at different circumferential positions (before and after) and with a special clamping device the nozzle exit was reformed into a shape close to the circle.

Fig. C.1 Inspection sheet (Inspection sheet: VOLVO)

Appendix D Compare of Flow Schemes Vulcain/Vulcain 2

Fig. D.1 Compare of Flow Schemes Vulcain/Vulcain 2 (Photo: SNECMA)

101

Appendix E Flow Scheme of the Ariane 5 Main Stage

Fig. E.1 Flow scheme of the Ariane 5 main stage (Photo: SNECMA/EADS (formerly SEP/ Aerospatiale))

103

Appendix F Flow Scheme of Vulcain 2

Ce document est la propriété de SNECMA . Il ne peut être reproduit ou communiqué sans son autorisation préalable et écrite LEFP1 F H 1 P R Matériels Volume conditionné Conditionnement Huile GAM FBSH FEFP (évacuation huile GAM) CBJTH CBJPH TP LH2 PPH (Pressurisation RLH2) BMH (balayage hydrogène) CBH EVVGO EVVCO EVVCH (VCH+VMRH) EVVGH Gaz chaud + GHe Hélium gazeux GOX+GHe Hélium liquide LAH (alim.LH2) VMRH LCH1 BEVC LEH CEVC VCH Gaz chaud Hydrogène liquide Hydrogène gazeux Oxygène liquide LAH (conditionnement GHe) CBCER SFAVCH FPHE TPCH (purge LH2) F C E R CTPCH (chasse ergols) CBCH LTH FPHM LMRH H SFAVGH G V A C FCE LCH2 LEFP2 VPH CBGH GG L G H V G H AG V G O AC L G O ECCH (conditionnement GHe) ETAGE V U L C A I N DM CBGO1 CP CBCO1 VPO O G V A SFAVGO C VCO FEC

CBGO2 CBCO2 SFAVCO F P O M FPOE PGD (GHe commande) LTO TPCO (purge LOX) BEVB EVSCP (purge SCP) (Photo: SNECMA/EADS (formerly SEP/Aerospatiale)) EPC A5E LEO MOTEUR VGC EVVP TP LOX EVBO EVVGC L F P O

(VPO + VPH)

(BCO + BGO) pour information, en Diffusion provisoire du document officiel LCO attente d'une édition

l Vulcain 2

LAO (alim.LOX) é r

h u

c é R 01 1199 CBPTM2 CBJTO VCBPTM LPRO CBPTM1 CBOR CBJTOS Schéma fonctionnel fluides présenté en phase propulsée F H L Mise à jour : F P R O PPO (pressu. RLOX) Flow scheme of LEP 1 F E P EVAE (alimentation LHe) S O F B BMO (balayage TPO) SYNOPTIQUE VULCAIN 2 LAO + EVSCP (conditionnement GHe) Fig. F.1

105

Appendix G Flow Scheme of Vinci (Photo: SNECMA) Vinci Flow scheme of Fig. G.1

107

Appendix H Mixtures of Oxygen and Nitrogen Close to Their Boiling Points

The main component of an oxygen (O2) supply to a rocket engine is the run tank with liquid O2. If the tank is pressurised with nitrogen (N2) the condensation of N2 at the surface of the liquid O2 has to be considered. The equilibrium of both ﬂuids close to their boiling point is shown in the phase diagram (Fig. H.1). For the calculation of the dewpoint and boilingpoint curve (H.1) and (H.2), [16] were used; the vapour pressure Pi (T ) was calculated according to [21]. − ( ) = P P2 T Boiling curve X1 (H.1) P1(T ) − P2(T ) − ( ) ( ) ( ) = P1 T P2 T 1 + P1 T Dew curve X1 (H.2) P1(T ) − P2(T ) P P1(T ) − P2(T )

The symbols are:

T temperature of the mixture (here the temperature of the liquid O2), P pressure of the mixture (here the pressure in the vessel), P1(T ) vapour pressure of the ﬁrst component (here N2), P2(T ) vapour pressure of the second component (here O2), X liquid mole fraction of N2, 1 X1 gaseous mole fraction of N2.

Pressure = 1 bar Pressure = 2 bar Pressure = 6 bar Temperature of the Mixture [ K] Temperature of the Mixture[ K] Temperature of the Mixture [ K] 100 100 120 Mixture of Gas Mixture of Gas 95 Mixture of Gas 95 115 Gas/Liquid Mixture 110 90 K Line 90 K Linie 90 90 105 Gas/Liquid Mixture Gas/Liquid Mixture 85 85 100 95 80 80 Mixture of Liquids 90 Mixture of Liquids Mixture of Liquids 90 K Line 75 75 85 0 0,2 0,4 0,6 0,8 1 0 0,2 0,4 0,6 0,8 1 0 0,2 0,4 0,6 0,8 1 Nitrogen Fraction of the Mixture Nitrogen Fraction of the Mixture Nitrogen Fraction of the Mixture

Fig. H.1 Phase diagram of O2/N2 mixtures at 1, 2 and 6 bar (Photo: DLR)

109 110 Appendix H Mixtures of Oxygen and Nitrogen Close to Their Boiling Points

In fact the mixture is not homogeneous in time and space and is not at equilibrium. The pressure is deﬁned by the pressurisation system; above the liquid it is constant, below the surface it increases with depth. The temperature around the surface is dominated by the temperature of the liquid oxygen, normally close to 90 K. If the tank pressure is held at 1 bar for a long time only very small fractions of N2 can be found in the liquid. When the pressurisation is started the condensation at the surface begins and the N2 fraction increases. We can assume that the condensed N2 remains mainly in the upper layers of the liquid (see below). After test, particularly when the pressure is reduced to 1 bar, the N2 as the more volatile component evaporates again. The typical evaporation rate of a vacuum insulated tank is 0.1% of the inner volume per day. For the oxygen tank (200 m3) on the facility P5 that means 200 L per day. Hence it takes 7 days to re-evaporate the N2. But in the normal test cycle the tank is reﬁlled the day after the test. Due to this dilution the concentration of N2 decreases to a tenth part, which is a far more drastic decrease than that due to the evaporation. Nevertheless, for the engine test the N2 fraction in the oxygen means pollution. A sample taken during a normal test period had a fraction of 0.36% of N2 in O2.

Diffusion of Liquid N2 in Liquid O2

In order to check whether a fast diffusion can distribute the N2 fraction all over the tank, we have to look for the solution of the diffusion equation (H.3)atthe applicable conditions. We also need the coefficient of N2 diffusion in liquid O2. The diffusion equation has the same mathematical structure as the heat conduction equation (H.5) for which we find the general solution (H.6)in[16] and transfer it to the diffusion equation. For the diffusion coefficient D no measured value could be found in the literature or on the internet; therefore the Stokes-Einstein-equation (H.4) was applied.

∂ c ∂2c Diffusion equation = D (H.3) ∂ t ∂ xi ∂ x j where c is the concentration, t the time, and xi the position vector (or, more cor- rectly, the coefﬁcients of the components of the position vector). The Stokes-Einstein equation gives us

K T − D = B = 97.6 × 10 9 Ns/m2 (H.4) 6 πμR0

−23 where K B = 1.38 × 10 as the Boltzmann number, T = 90 K as temperature, −6 2 μ = 6.5 × 10 Ns/m as the dynamic viscosity (of O2 at 90 K, 6 bar) and R0 = −11 10.4 × 10 m as particle radius (of N2). We obtain the general solution for the concentration c(x, t) in the one dimen- sional case: Appendix H Mixtures of Oxygen and Nitrogen Close to Their Boiling Points 111 ( , ) = + + − 2 ( ( ) + ( )) c x t c0 c1x exp Dant An cos an x Bn sin an x (H.5) n with the constants c0, c1, an, An, Bn. The importance of N2 diffusion in the O2 tank is checked in an example. Assume at time t = 0 a pure layer of liquid N2 is situated above a pure layer of liquid O2. Both layers have the same thickness, together d = 100 mm. (this complies with the N2 mass which normally condensates in our tank): c nπ 2 1 nπ c(x, t) = max − 2 c exp −D t sin x (H.6) 2 max d nπ d n>0 odd

The statements at (H.5) and (H.6) are transferred from the solution of a heat conduction problem, here the adiabatic bar [16]. We can see (Fig. H.2) that the relative concentration c/cmax after 2 h of diffusion is still far from the homogeneous (50% of cmax at each point) state. Hence we can conclude that the process of diffusion cannot really distribute the N2 in the tank within the relevant small period of time. Pressurisation, depressurisation and ﬁlling provide a much stronger mixing process of the two components.

4 For t = infinite 3 2 1 0 –1 For t = 2 hours

–2 For t = 0 –3 –4 –5 Height above the point of contact [cm] 00,20,40,60,81 Relative concentration of oxygen after two hours

Fig. H.2 Diffusion in a layer of N2 and O2 (Photo: DLR)

Appendix I Jet Pump

A fluid flow engine which increases the total pressure of a fluid is called a pump (for a liquid) or a compressor (for a gas) (Fig. I.1). A very simple engine of this category is the jet pump. It has a nozzle to create a jet (gas or liquid) of high velocity but low pressure. Due to the low pressure the jet is able to suck in fluids from a somewhat higher pressure level. This fluid is carried along and energy is transferred from the jet to the fluid. Behind a mixing passage the flow is guided in such a manner that the kinetic energy is transformed into pressure energy, this pressure being higher than the original pressure of the fluid. Hence we rightly state that the fluid carried along is compressed or pumped. The jet pump has no moving or rotating parts, it can provide high power despite small dimensions and it is very suitable to suck off fluids from low pressure regions. For short term operation (e.g. 1 h) on a test facility the jet pump is preferred in comparison to other pumps (e.g. rotary vane pump) due to lower investment and maintenance costs.

Exit Pressure Supply Jet Nozzle

Cavity Mixing Passage Suction Flange Fig. I.1 Gas jet pump on the facility P5 (Photo: DLR)

The convergent/divergent jet nozzle is driven at high pressure (e.g. 40 bar) and provides a supersonic jet of low static pressure. The jet increases in diameter and impinges the inner wall of the mixing passage. Up to that point it sucks in gas from the cavity and creates here a pressure decrease. At the impingement point (respec- tively circle) a sonic shock or a series of shock patterns occurs. Via the suction ﬂange further gas is sucked in. Behind the mixing passage the jet is further compressed and leaves the jet pump as a subsonic jet. For the design of a jet pump and for the computation of the operational parameters the equations of balance for energy and mass are applied, as well as functions of gas dynamics and empirical coefﬁcients.

113 114 Appendix I Jet Pump

One operational mode of a jet pump is the zero-suction-mode. This mode means an operation at closed suction valves; the cavity is evacuated and no suction ﬂow is possible. We study a full supplied jet pump (reference point) in this mode. As normal the jet impinges the inner wall, the Mach number MA in this point depending on the diameter of the jet at that point. The sonic shock causes a strong loss of total pressure. The ratio of total pressure behind the shock to the ambient pressure is equivalent to the pressure ratio (static/total) at the exit. For computation purpose we make a variation of MA, compute the pressure loss across the shock and compute the pressure ratio at the exit (Fig. I.2). In the solution MA has to match the correct static pressure at the exit which adapts to the ambient pressure. The area and the static pressure of the jet at the impingement point can be computed as well from MA and hence follows the suction pressure in zero-suction-mode. For the supply of the jet pump with 14 kg/s N2 at 288 K the computation of the zero-suction-mode is summarized in Table I.1. Even without knowledge of the loss coefﬁcients in the supersonic jet and in the mixing passage, we have good agreement of the computation with the measurement during operation.

Fig. I.2 Computation sections of the jet pump (Photo: DLR)

In the normal operation the suction flow has to be considered. The lower the suction pressure of the pump the higher the performance. Flow and pressure can be shown as a characteristic of the jet pump. On the other hand the flow also depends on the leak ratio of the connected device (e.g. a vacuum chamber) and on the pressure loss in the line between. The behaviour of this device is also given as a characteristic. The intersection of both characteristics is the reference point of the jet pump (Fig. I.3). To calculate the properties of the mixture of jet and suction flow (Table I.2)we apply the balance of mass and energy and assume that the entropy of the mixture is

Table I.1 Gas dynamic parameters in zero-suction-mode Static pressure Total pressure Area Mach number Section [bar] [bar] [m2] E 0 Supply 40 40 E 1 Nozzle throat 21.13 40 0.0015 1 E 2 Nozzle exit 0.1924 40 0.0201 4.24 E 3 Directly before the shock 0.02 40 0.0935 6.232 E 4 Directly before the shock 0.9052 1.012 0.0935 0.4023 E 5 Directly behind the shock 1 1.012 0.283 0.13 E 6 Suction ﬂange 0.02 Appendix I Jet Pump 115

Characteristic of a Jet Pump 40 35 30 25 20 15 10 5

Suction Pressure [mbar] 0 012345678 Suction Flow [kg / m3]

Fig. I.3 Characteristic of a jet pump (Photo: DLR)

Table I.2 Gas dynamic parameters at 3 kg/s suction flow Static Total Mass pressure pressure Area Mach flow Section [bar] [bar] [m2] number [kg/s] E 0 Supply 40 40 14 E 1 Nozzle throat 21.13 40 0.0015 1 14 E 2 Nozzle exit 0.1924 40 0.0201 4.24 14 E 3 Directly before the shock 0.0287 20.9 0.1083 5.28 17 E 4 Directly before the shock 0.93 1.04 0.1083 0.403 17 E 5 Directly behind the shock 1 1.04 0.283 0.2375 17 E 6 Suction flange 1.04 3 E 7 Surface of the jet 1.04 equal to the sum of entropy of both flows. Indeed, we know the impulse of the mass flow but not the forces on the inner surface and therefore we do not use the balance of impulse.

˙ + ˙ = ˙ mcp TG Jet mcp TG Suction Flow mcp TG Mixture (I.1)

m˙ Jet +˙mSuction Flow =˙mMixture (I.2)

˙ + ˙ = ˙ (ms)Jet (ms)Suction Flow (ms)Mixture (I.3)

= ( / ) − ( / ) s cP ln Ttotal Treference RN2 ln Ptotal Preference (I.4)

The specific heat cP of both components (N2 and air) is considered as equal, m˙ is the mass flow and Ttotal and Ptotal are total temperature and pressure of the gas. Total in contrast to static is used her in the sense of gas dynamics (see Remark I.1). = = The specific entropy s refers to Treference 288 K and Preference 1 bar. RN2 is the specific gas constant of nitrogen. 116 Appendix I Jet Pump

Remark I.1 The technicians on the test facility also use the term static for a pneumatic system when no consumer load is active (no consumption). The system is, e.g. adjusted to 20 bar before the consumer is activated, the pressure may drop then, e.g. by 2 bar when the consumers are active. This use of the term must not be confused with the context of gas dynamics. In general all pressure values in the Ariane program (another context of terms) are given as absolute values relative to the vacuum pressure of 0 bar. Because jet and suction ﬂow have both Ttotal =288 K and Ptotal suction ﬂow =1 bar we can conclude by (I.3) and (I.4): P P m˙ ln total = m˙ ln total (I.5) Preference jet Preference mixture

From (I.5) we can compute the total pressure before the shock and with the total temperature and mass flow we continue our computation analogue to the zero- suction-case. The calculated suction pressure was 28.7 mbar, and 115 mbar was measured. The difference is only 86 mbar (8.6% relative to 1 bar ambient pressure) but, on the other hand, the result of this nominal case is just in the order of the measured values. However, the system was designed for a pressure of 200 mbar in the casing, and the measurement was taken at 300 mbar. For isentropic compression of 3 kg/s from 29 mbar to 1 bar a power of 1512 kW is required. The supply of the jet pump (40 bar, 14 kg/s) is 7536 kW which means an efficiency of η = 1512/7536 = 0, 2. This efficiency is much less than for any other hydraulic/mechanic pump, the reason for the low efficiency being the high entropy production across the sonic shock. The characteristics of the jet pump were measured in pre-tests in which the end of the suction line was closed except for a combination of orifices. The casing was not connected to the jet pump. The mass flow during operation depends on the leakage of the casing. As soon as the casing pressure is below 0.52 bar a critical pressure ratio is reached at the points of leakage and the leak flow does not increase further more (except if the leak area increases). The desired pressure in the casing can be adjusted by the regulation valves which quasi-create a desired pressure loss in the line. Hence we have

Pcasing = Psuction + Pline + Pvalve (I.6)

The pressure loss at a sonic/subsonic transfer is not avoidable. The highest loss can be assumed across a normal shock (perpendicular to the flow), planar oblique shocks (wedge like) having less pressure loss and the oblique shock at the tip of a cone again having less pressure loss. The loss across shocks at the inner wall of a tube (as we have it in a jet pump) is a bit less than at a normal shock but still significantly higher than in a wedge like flow. In particular in a jet pump of high power (e.g. for the vacuum chamber of an upper stage engine) it is desirable to Appendix I Jet Pump 117 reduce the pressure losses across the sonic shocks. For that purpose an rotationally symmetric centre body is integrated behind the mixing passage. The sharp cone has the perfect gas dynamic performance; it causes a slight deviation of the flow and decelerates the flow to a low Mach number. But the tip would have to bear a very high thermal load and therefore the centre body normally has a blunt nose which creates a detached shock in front of it.

Appendix J Fluids of the Test Process

For the operation of a test facility it is of essential importance to consider carefully the properties of the fluids used within the operation (test). We use the term fluids because some substances are used in liquid as well as in gaseous form. Further on the possibility of freezing of the fluids must also be checked. The most important fluids on a test facility for a cryogenic rocket engine are listed in Table J.1. At ambient condition (15 ◦C, 1 bar) the hydrogen and helium is much lighter than air the gas climbs up and may accumulate at the ceiling of a closed room. Remark J.1 In the design of the test cell of the facility P5 the roof is lower on the side of the tower of the building and higher the on the outward side. Due to this design the ascending hydrogen is deflected from the building. On the other hand, unfortunately, rain water on the roof is directed towards the building. Any holes in the test cell roof directly cause problems because the penetrating water is collected in the thrust cone like in a giant funnel and than directed to the engine where it can cause failures on electrical and electronic components. Even in the liquid state (20 K, 1 bar) hydrogen is relative light, its specific density equals the density of rock wool. The specific density of liquid oxygen is of the order of water. Remark J.2 On the facility P5 in November 1991 severe damage occurred due to a broken water line. The chute for the hydrogen tank filled up temporarily almost to the top. The tank was at that moment not far from floating. The empty steel tank of 200 tons and its hydrogen filling of approximately 30 tons were much less than its displacement of more than 600 tons of water. Thanks to the fact that the tank was not totally covered by water and that the connections to the facility did not break, no greater damage to the test facility occurred. Remark J.3 The routing of the oxygen feed line is vertical for several metres and is equipped with flow turbines. To fill the line from the top is harmful for the turbines, and therefore an alternative filling procedure was developed. In order to avoid a water hammer in the oxygen feed the closing times for the valves in this line have to be defined with extra care.

119 120 Appendix J Fluids of the Test Process

Table J.1 Fluids in the test process of a cryogenic test facility Hydrogen Helium Oxygen Nitrogen Specific density at kg/m3 0.0841 0.167 1.337 1.17 15 ◦Cand1bar Ratio of the specific 1.41 1.66 1.4 1.4 heat Cp/Cv = κ Specific density at the kg/m3 70 125 1140 810 boiling point Molecular weight M kg/kmol 2.016 4.003 32 28.01 Specific gas constant J/(kg K) 4124.16 2077.02 259.82 296.83 RS Triple point bar 0.072 – 0.0015 0.125 kg/m3 80 or 0.13 – 1306 or 0.01 867 or 0.68 K 13.95 – 54.4 63.15 Critical point bar 13.16 2.3 50.9 33.98 kg/m3 31.57 70 405.8 281 K 33.2 5.2 154.8 126.3 Evaporation heat r at kJ/kg 460 20.59 238.7 198.2 1bar Melting point at 1 bar K 14 1 54.8 63.3 Tm Boiling point at 1 bar K 20.4 4.2 90.2 77.3 Tb Specific heat at kJ/(kg K) 14.32 5.23 0.917 1.038 constant pressure cp Air Propane Water hydraulic oil Specific density at kg/m3 1.21 1.88 1000 869 15 ◦Cand1bar Ratio of the specific 1.4 1.14 1.33 heat Cp/Cv = κ Specific density at the kg/m3 581 1000 boiling point Molecular weight M kg/kmol 44.1 18 Specific gas constant J/(kg K) 287.00 188.53 461.91 RS Triple point bar 0.0061 kg/m3 1000 or 0.005 K 273 Critical point bar 42.42 221 kg/m3 K 370 647 Evaporation heat r at kJ/kg 426.5 2258 1bar Melting point at 1 bar K 86.5 273.15 (213) Boiling point at 1 bar K 231 373.15 Specific heat at kJ/(kg K) 1.005 1.595 1860 constant pressure Appendix J Fluids of the Test Process 121

When heat is introduced into a cryogenic fluid, and this is mostly the case because there is no perfect insulation, evaporation and a pressure increase occurs. Therefore any segment for a cryogenic fluid has to be equipped with safety components (burst disc, safety valve) and the process has to be conducted in such a manner that the fluid is never locked. In cases of direct contact of different fluids the reactivity (e.g. detonating gas) has to be considered. In cases of extreme temperature differences condensation and icing has to be expected. These effects can also occur on the outer surface of tubes and engine components. Remark J.4 During the first start up of a sub-system involving liquid helium, at some tubes a lot of air was liquefied. Besides water, liquid N2 in fact also rained down from the tubes. Remark J.5 In a combustion chamber for research purpose running on liquid hydrogen/oxygen, an annular icing around the injection elements was detected. Fuel and oxidiser are ducted through the injection plate and thus keep it at a very low temperature despite the combustion downstream. In the recirculation zone directly below the injection plate (face plate) there is of course water as the product of the combustion. This water, cooled down, deposits as ice at the face plate. If a gas gets in contact with a cryogenic fluid, condensation and mixing can occur (see Appendix H). Due to the contact a pressurisation gas normally cools down, increases in density and decreases in pressure. Sometimes the term collapse factor is used to describe this effect but this is no mysterious phenomenon and it is not necessary to measure the factor empirically; it can be explained and calculated within thermodynamics. Another term used for an effect in the context of cryogenic fluids is cryo- pumping. Remark 5.4 describes impressively what happens when a gas comes into contact with a surface whose temperature is lower than the saturation temperature of the fluid. The gas increases in density, condenses to liquid and the pressure decreases if this occurs in a closed cavity, or further gas is sucked in if the cavity is open. The most meaningful diagram concerning the thermodynamic state of a fluid is the enthalpy-entropy-diagram (h-s-diagram, Fig. J.1). In particular, a status or process close to the two-phase area (liquid/gaseous) can be visualised properly in the h-s diagram. At normal condition (1 bar, 0 ◦C) hydrogen, oxygen and nitrogen are far from their two-phase area. But the processes in a cryogenic rocket engine are running close to that area or traverse the two-phase area. Extremely high temperatures (e.g. the H2 fraction in the exhaust of the rocket) are not included in Fig. J.1. The properties of hydrogen in this state are given in Table J.2. At extremely high pressures (e.g. in a bottle at 250 bar, 0 ◦C) the gas has no ideal behaviour any more. In the given example the compressibility factor z = pv/(RS T ) is 1.13. 122 Appendix J Fluids of the Test Process

300 bar Enthalpy [kJ/kg] 5000 1 bar 4500 4000 Ambient Condition High Pressure Bottle 0°C 3500 3000 2500 115 bar Combustion Chamber Inlet 2000 140 K 1500 1000 Saturation Line 20,4 K 500 0 0 10 20 30 40 50 60 Area of Entropy [kJ/(kg K)] Turbo Pump Process

Enthalpy [kJ/kg] 500 158 bar 115 bar 33 K 400

300

200 Pumping 100 Process

0 0 2 4 6 8 10 Entropy [kJ/(kg K)] Fig. J.1 Enthalpy-entropy diagram of hydrogen (Photo: DLR)

Table J.2 Hydrogen at normal conditions and at high temperature [5] Pressure bar 1 100 Temperature K 273.15 3000 Density kg/m3 0.0887 08117 × 10−3 spec. Enthalpy kJ/kg 3573 48460 spec. Entropy kJ/(kg k) 52 81.67 Cp kJ/(kg K) 14 18.49 Cv kJ/(kg K) 10 14.35 Speed of sound m / s 1261 4026 κ = Cp/Cv 1.41 1.29 Appendix K Pressure Transducer

In the typical pressure transducer on the test facility and on the rocket engine, strain gauges are widely used to transform pressure (as the physical parameter) into voltage (as an electrical parameter). The strain gauge is a ﬂexible membrane with thin wires glued to the surface. The strain gauges are arranged in the manner of a Wheatstone bridge. The membrane is deformed according to the pressure and the deformation changes the resistance of the strain gauges (Figs. K.2–K.4) and hence a measurement voltage is available on the Wheatstone bridge. As an example, in Fig. K.1 the strain gauges (resistors) R1, R4 are expanded and R2, R3 are compressed if the membrane is deformed.

R1 R3

Sensed Voltage

Supply Voltage R2 R4

Measured Voltage Fig. K.1 Strain gauge in a Wheatstone bridge measurement element (complementary resistances for temperature compensation are not shown) (Photo: DLR)

The measured voltage is proportional to the supply voltage. On test facilities the supply is normally far from the sensor and a loss in the cable must be considered. Therefore the effective supply voltage is also measured on the sensor by means of a so-called sense line. That means there are six wires (plus screen) in one sensor cable (Table K.1). A higher resistance of the sensor would reduce or avoid a voltage loss but it has the disadvantage that dynamic pressures cannot be measured because the capacity of the cable combined with a high resistance of the sensor causes a considerable damping in the measurement chain.

123 124 Appendix K Pressure Transducer

Fig. K.2 Strain gauge in a pressure transducer (Photo: DLR)

Fig. K.3 Disassembled pressure transducer (Photo: DLR)

Fig. K.4 Sensor with cut casing (Photo: DLR)

Table K.1 Typical parameters of a pressure transducer Supply voltage 12 V Cable voltage loss 2 V Sensed voltage 10 V Resistance of the cable 60 Ohm Resistance of the sensor 300 Ohm Measured voltage at full signal 20 mV Appendix L Measurement Chain

The design of a measurement chain depends on the parameter to be measured (temperature, pressure, vibration etc.) and on the measurement mode (range, acquisition rate, precision etc.). Normally the chain from the sensor into the computer has several plugged and ﬁxed cable connections and has at least one unit for ampliﬁcation and signal adjustment. Normally the analogue signal is converted at the entrance of the computer. Inside the computer the signal is treated again for different purposes (archiving, regulation, display, monitoring).

Sensor Plug

Cable tree Plugged connection Amplifier rack Filter Rigid connection

Arrangement array

A/D converter

Computer

Fig. L.1 Typical measurement chain between a pressure transducer and the computer system (Photo: DLR)

125

Appendix M Valve Control Circuit

Most the valves on the facility as well as on the rocket engine are opened/closed by means of a pneumatic actuator. The activation of the actuator is again controlled by a pilot valve, an electrically driven open/close valve which switches the in/outlet of the actuator to a pressure gas source or to a venting line (atmosphere). The electrical actuation of the pilot valve is realised by a chain of electrical components between the valve and the control computer.

Venting Line Pneumatic Actuator

Pressure Line Pilot Valve Fluid Valve

Electical Power Junction Box

Battery

Relay Rack MCC System

Back Up System System Signal Sources Selection Manual System

Fig. M.1 Typical valve control circuit for an open/close valve (Photo: DLR)

The outer tube of the vacuum sections (Fig. M.3) is a rigid, welded or well sealed tube of stainless steal. The outside of the conventional insulation (Fig. M.4) looks almost the same, but here we have a thin aluminium cover which protects the hard foam insulation.

127 128 Appendix M Valve Control Circuit

Pneumatic lines

Pilot valves

Buffertank

Fig. M.2 Rack of pilot valves (Photo: DLR)

Fig. M.3 Automatic valves for cryogenic lines (integrated in a vacuum box) (Photo: DLR) Appendix M Valve Control Circuit 129

Fig. M.4 Automatic valves for venting lines (integrated in “conventional” insulation) (Photo: DLR)

Appendix N Oxygen Detector

Design

The measuring cell consists of a plastic casing which houses two electrodes emerged into an electrolyte. The cathode is a gold plated grid, the anode is a cylinder made of sintered lead. The tightness of the component is good but gas tightness is guaranteed by a thin Teﬂon diaphragm.

Fig. N.1 Gas analyser rack with oxygen detectors (blue casing) (Photo: DLR)

131 132 Appendix N Oxygen Detector

Measurement Principle

When the anode comes into contact with oxygen a reduction – oxidation reaction is initiated. Due to the reaction a potential difference (voltage) is created between the electrodes. The voltage is proportional to the partial pressure of the oxygen. Because the cell is inﬂuenced by temperature an adjustment by means of a thermistor is necessary. The voltage at the contacts is ampliﬁed and displayed. References

1. S.A Durteste, Transient model of the VINCI cryogenic upper stage rocket engine, AIAA Joint Propulsion Conference, Cincinnati, 2007 2. J. Gastal, J.R.L. Barton, VULCAIN: A cryogenic engine for ARIANE 5, lecture series 1993- 01 von Karman Institute for Fluid Dynamics 3. A. Haberzettl et al., VULCAIN 2 flight load simulation device, EUCASS European Conference for Aerospace Sciences, Moscow, 2005 4. D.T. Harrje, F.H. Reardon, Liquid propellant rocket combustion instability, NASA SP-194 National Aerospace and Space Administration, U.S.A, 1972 5. R.C. Hendricks et al., NASA TN D-7808 Cleveland, OH, 1975 6. C. Hujeux, W. Kitsche, Evolution of the rocket engine testing process, AAAF Association Aeronautique et Astronautique de France, Versailles, 2002 7. INERIS Retour d’expérience issu de la mise en ouvre d’un réservoir d’hydrogène liquide haut pression, Journée technique, 07.10.2003 8. Exploitation of various internet websites 9. P. James,Technological readiness of the vinci expander engine, IAC International Astronauti- cal Congress, Glasgow, 2008 10. W.H. Kitsche, Simulation of flight conditions on a test facility for rocket engines, EUCASS European Conference for Aerospace Sciences, Brussels, 2007 11. W.H. Kitsche, Pollution control on a test facility for a cryogenic rocket engine, EUCASS Euro- pean Conference for Aerospace Sciences, Versailles, 2009 12. K. Koch, Analysis of signals from an unique ground-truth infrasound source observed at IMS station IS26 in southern germany, Pure Applied Geophysics, 167, 401–412, Basel, 2010 13. C.R. Koppel et al., A platform satellite modelling with ecosimpro: simulation results, AIAA Joint Propulsion Conference, Denver, 2009, AIAA 2009, 5418 14. P. Magnant, B. Juery, and N. Chazal, PF52 test facility for cryogenic engines and subsystems, SpaceOps Conference, Huntsville Alabama 2010, AIAA 2010-2253 15. R.E. Martin, Atlas II and IIA analyses and environments validation, Acta Astronautica 35(12), 1995 16. I. Müller, Grundzüge der Thermodynamik mit historischen Anmerkungen,3.Auflage (Springer, Berlin, 2001) 17. G. Ordonneau, F. Lévy, Low frequency oscillation phenomena during VULCAIN shutdown transient, AIAA Joint Propulsion Conference, Salt Lake City, 2001 18. Holy Spirit, Bible (Christian Church, Worldwide) 19. G.P. Sutton, Rocket Propulsion Elements (Wiley, New York, NY, 1986) 20. M. Williamson, Dictionary of Space Technology (Adam Hilger, New York, NY, 1990) 21. W. Wagner, Multifluid Package (Ruhruniversität Bochum, 2003)

133

Index

A Boroscopic inspections, 16 Acceleration, 63 Boundary layer effects, 60 Acceptance, 11–12, 81, 87 Bubble counter, 18 Acoustic chamber, 68 Buffeting, 69 Acoustic load, 67–72 Buffeting effect, 69 Acoustic panel, 68 Bunker, 7, 39, 47, 49, 54, 84–85 Actuator, 11, 53, 55, 64, 127 Burner system, 73 Adjustment instruction, 88 Burn time, 7 Air, 120 Burst disc, 19, 70, 84, 121 Altitude conditions, 7, 61, 69 C facilities, 69 Cabling plan, 16, 88 facility, 7, 37, 39, 60–62 Campaign, 10–16, 70 simulation, 60–61 Carbon dioxide, 42 Ampliﬁcation, 54, 125 Cavitation, 27, 65 Ampliﬁers, 16 Centre body, 117 Analogue gauge, 47 Challenger, 17 Analogue signal, 50, 125 Chamber ignition, 11, 30 Anemometer, 18 Chamber valve, 27–30, 95 Anomaly, 25, 75, 77–78 Characteristic of the load, 35 Ariane 5, 9–12, 103 Chemical propulsion system, 1, 27 Ariane 5 ECA, 72, 78 Chemical reaction, 60 Ariane program, 6, 11 Chill down, 4, 27–28, 42–43 Arianespace, 9–10 criteria, 28, 42 ARTA (Ariane Research and Technology phase, 4, 24, 27 Accompaniment), 12 Chromatograph, 23 Attitude control system (SCA), 12 Chronology, 88–89 Automation, 48 Chugging, 33–34 Cleaning procedure, 19–20, 23–24 B Cleanliness Balance of impulse, 115 check, 16, 19 Battle ship tank, 64 criteria, 23–24 Bearing, 21, 27–28 level, 20 Bench access, 85 requirements, 24 Bipropellant, 28 Closed loop, 30–31 Boiling point, 4, 109–111, 120 Collapse factor, 121 Boltzmann number, 110 Combustion, 30, 33, 36, 60, 121 Booster(s), 63, 65–67 chamber, 19, 35, 46, 60, 97 shut down, 65–66 pressure, 29, 34–35

135 136 Index

Commissioning, 79, 81–82 E Component level test, 7 Efficiency, 1, 77, 115 Compressibility factor, 121 Ejector, 7, 56–57, 61–62, 70–71 Concentration, 24, 55, 110–111 jet, 56–57, 60 Condensation, 21, 45, 109–110, 121 Electromagnetic valve, 53 Condenser, 60 Emergency shut down, 85, 88 Conditioning procedure, 23 Engine Configuration management, 80–82 characteristic, 30 Control control, 30, 53 building, 40, 49, 75 cycle, 4, 25 bunker, 39, 49, 54 exhaust, 60 desk, 7 regulation, 11 element, 31, 53 test, 2–3, 7, 9, 23, 25–38, 110 parameter, 16, 30 Engine level test, 7 room, 7, 47–50, 55, 78, 92 Entropy, 114–115, 121–122 technique, 48 Entropy-enthalpy-diagram, 121 Convergent/divergent nozzle, 19 Entropy production, 115 Cooling system, 58–59, 70, 73 Erection, 24, 39–40, 79, 83, 87 Cooling water, 56, 58 ESA (European Space Agency), 9–10, 46, 92 Corrosion, 20 Evaporation heat, 120 Crack detection, 16 Evaporation rate, 110 Critical point, 120 Evaporator, 74 Critical pressure, 33, 116 Exhaust ratio, 116 cooling, 59, 73 Cryo circuit, 27 guide tube, 73 Cryogenic engine, 4, 24, 57 guiding, 56, 57–59 Cryogenic fluid, 4, 27–28, 74, 84 jet, 3, 12, 57, 58–60 Cryo pumping, 121 Expander cycle, 4–5, 33, 37–38 Explosion proof, 83

D F Data acquisition, 16, 53–54 Facility operation, 83 Data base, 14, 16, 25 Facility operator, 83, 88–89 Data exploitation, 89 Facility system, 15, 75, 89–90 Demineralised water, 23 Failure Design phase, 27 case, 74, 83 Design point, 9, 35–36 test, 11 Detonator, 70 Feed back, 50, 53, 89, 95 Development, 9–12, 46–47 Feed line, 44–46, 63–64, 66–67 Development test, 9, 10–11, 31 Feed system, 4, 43–46 Diffuser, 60 Fibreglass, 71 Diffusion, 105, 110–111 Film cooling, 11 Dismounting, 89 Filter, 20–21, 23, 125 Diverse redundancy, 85 Fire Documentation, 13–14, 77–78, 87–90 brigade, 84–85 Double failure, 85 detection, 85 Double-walled tank, 42 ﬁghting, 74, 85–86 Dry run, 15, 26–27, 77, 89, 92 Flare stack, 74 Durability, 11 Flight Dynamic forces, 71 acceptance, 9 Dynamic seal, 16–17 conditions, 6, 63–72 Dynamic viscosity, 110 line, 45, 66 Index 137

Flow scheme, 101, 103, 105, 107 Injector plate, 21–22 Fluid circuit, 20, 23–24 Inlet pressure, 29, 38, 63–65, 67 Fluids, 4, 42, 84, 109, 119–121 Inspection, 13–24, 42, 58, 85 Flushing, 27, 33 Inspection request, 88 FMECA, 80, 83 Instruction manual, 89–90 Fog, 75 Insulation, 42–43, 127, 129 Foreign gas, 20–21, 23 Integration, 13, 15, 89 Fuel Interface, 13, 26, 46, 53, 63 oxidiser combination, 19 Internal leak, 18, 24, 55 storage, 39 Interventions, 88–89 tank, 3, 39 Isentropic compression, 115 transfer, 15 Functional aspects, 21 J Functional test, 16–17 Jet pump, 60, 113–117 G L Gas Launch table, 57 analyser, 24, 55, 131 Launcher, 1–4, 9–10, 12, 63–64, 66, 69–70 detector, 17, 55 Launch pad, 3–4, 11, 75 dynamics, 60, 113, 115 Launch procedure, 28 generator, 4–5, 22, 28–31, 33 Lead item, 81 cycle, 4–5 Leak Gaseous oxygen, 21 detector, 17 Gauges, 16, 47, 123 flow, 18, 71, 116 Gimbal, 12, 89 measurement, 16–18 H rate, 71 Hazard area, 75, 83–84 ratio, 71–72, 114 Heat Leakage, 16–18, 55, 116 conduction, 43, 110 Life time, 42, 59, 78 jacket, 38 Lift off, 63 transfer, 74 Lighting arrester, 75 transition, 61 Lightning, 75, 77 Helium, 16–17, 23–24, 119–121 Light pen, 48 Hermes, 10 Limitations and constraints, 77 Homogeneous redundancy, 85 Limits of operation, 35 Hot run, 4, 13–16, 18–19, 24, 26–34, 40–41, Liquefied, 60, 121 43, 47, 52, 56, 59, 65, 67–68, Liquid oxygen, 4, 21, 22, 64, 66, 110, 119 71–72, 84, 88–89 Load simulation device (LSD), 69–72 Hot run sequence, 52 Logbook, 13–14, 25 Humidity, 20–21, 23–24, 42, 74 Hydraulic actuator, 12, 64 M Hydraulic dummy, 45 Mach number, 60, 114, 117 Hydraulic oil, 26, 120 Maiden flight, 6 Hydrogen, 4, 43, 46, 56, 119–122 Main engine, 41 Main frame computer, 49, 50 I Main stage, 103 Igniter, 29, 53, 90, 97 Majority logic, 32 Ignition Malfunction, 9, 11, 17, 31, 85 delay, 97 Management process, 15 system, 37, 57, 74 Manual, 13, 47, 51, 88–90 Industrial return, 9 Mass flow, 7, 30, 33–35 Inert gas, 17, 27, 55 MCC (measurement, control and command Injection element, 21–22, 35, 121 system), 12, 15, 28–32, 46–55 138 Index

Measurement Pilot valve, 22, 53, 127–128 chain, 16, 45, 53, 123, 125 Piping diagram, 88 device, 75 Pneumatic actuator, 24, 53, 64, 127 request, 15–16, 88 Pneumatic system, 115 Melting point, 120 Pogo oscillation, 66–67 Men rated, 10 Pollution, 4, 19–24, 110 Microscopic examination, 23 Post test check, 89 Mixture ratio, 29–30, 34–35, 37, 47 Powder charge, 97 Modifications, 79, 81 Power consumption, 40 Molecular weight, 120 Pressure Monitored parameter, 31–32 gauge, 47, 74 Monitoring, 3, 31–32, 40, 54–55 loss, 63, 114, 116–117 pressurisation system, 3, 21, 43, 63, 110 N profile, 26, 28, 63–65 NCR (non-conformance reports), 15, 78–79 ratio, 114, 116 Net positive suction head (NPSH), 43 transducer, 123–124 Nitrogen, 23–24, 109–111, 120–121 Procedure, 2–3, 12–15, 23, 25–28, 77–82 Non conformance, 15, 78–79 Progress meeting, 81–82 Normal shock, 116 Propagation of the sound, 76 Nozzle extension, 19, 69, 72 Propane, 73, 120 Numeration system, 87 Propane tank, 73 Propellant, 1, 3–4, 28, 30, 76 O Propulsion cycle, 4, 28 Objective, 3, 10–11, 77, 79, 89 Propulsion system, 1, 3–4, 34, 37, 46 Oblique shock, 116 Punctual check, 32 Open loop, 30 Purge lines, 39 Operational Purity, 19, 23 aspects, 3–8, 19, 37, 39, 87 Pyrotechnical element, 20, 25, 29, 53, 97 behaviour, 34, 65 cycle, 3–4, 6, 10–11, 28 Q limit, 35–36 Quality, 77–78 mode, 77, 114 Quality assurance, 9, 14, 25, 81 point, 3, 9, 11–12, 30–31, 33, 35–37 Operator, 12, 46, 88–89, 92 R Oscillation, 31, 33–34, 45, 65–67 RAMS, 83 Output specification, 88 Ratio of the specific heat, 120 Ovality, 99 Raw value, 54 Overpressure, 23 Real time, 31 Oxidiser, 7, 27, 41–46, 121 Reception, 71 Oxygen, 21–24, 28–30, 32–34, 64–66, Red button, 52 109–111, 119–121, 131–132 Redline, 31–32, 77 Oxygen pump, 11, 16, 28, 32, 36 margins, 77 Reference point, 35, 114 P Regulation, 11–12, 15, 30–31, 35, 37, 47, 50, Particles, 20–21, 23–24 53–55 Passenger Test Request, 89 algorithm, 31, 55 Passive insulation, 42 cycle, 31 Performance, 15, 34–37 valves, 47, 53, 70, 116 map, 11, 29, 31, 34–37 Reignitability, 37 Periphery, 46, 50, 53 Reliability, 6, 10–11, 19, 21–22, 40 Periscope, 47 Relief valve, 64 Phase diagram, 109 Re-liquidation, 73 Physical data, 16 Remote control, 48–49, 84 Pilot burner, 11, 56 Reproducibility, 77 Index 139

Rest position, 83–84 SPF, 83 Review board, 78 Standards, 92 Reviews, 15, 77, 81 Start up transient, 29–30 Risk Steady state, 34 analyse, 15, 79–80 Steam generator, 7, 39, 60 management, 79–80, 83 Stoichiometric point, 29 Rock wool, 119 Stokes-Einstein-equation, 110 Roll torque, 12 Storable propellant, 76 Rotary vane pump, 44, 61, 113 Storage device, 46 Rules, 14, 31, 91–93 Strain gauges, 123–124 Run tank, 7, 41–43, 45–46 Subsonic, 33, 69, 113, 116 Suction flow, 114–116 S Suction line, 71, 116 Safe state, 52 Suction system, 57, 60, 70–71 Safety Supersonic, 33, 69, 113–114 component, 121 Surge effect, 45 engineer, 75 Switch board, 48–49 inspection, 85 officer, 85 T principle, 84 Tank, 39, 41–43, 45–46, 63–64, 109–111 radii, 83 runs, 63 status, 83 Test system, 7, 83, 85 abort, 31–32, 47, 77 valve, 84, 121 analysis, 15 Satellite, 3, 9 area, 75 Saturation temperature, 121 campaign, 11–16, 70 Sealing, 16, 21 cell, 39, 56–58, 60–61, 119 Sense line, 54, 123 conduction, 75, 91 Sensor configuration, 25–27, 80, 88–89 failure, 31 execution, 9, 12, 14, 89 signal, 41, 50, 54 facility, 3–8, 39–43, 46–48 Sequence, 14, 29–33, 49, 50–52 green light, 78–80 Service pressure, 83 leader, 13–16, 52 Shaft speed, 32, 35–36, 54 objective, 3, 79, 88–89 Shock pattern, 113 period, 9–24, 78 Shock wave, 69 phase, 85 Shut down, 3–4, 37–38, 52–53, 65–67 plan, 77, 93 sequence, 11, 29, 31–33 position, 56 Shuttle, 6, 10, 17, 57 process, 79–80, 85, 119–122 Signal conditioning system, 53–54 readiness, 15, 27, 77–78, 80 Single-point failure, 85 meeting, 15, 77–78, 80 Sonic shock, 69, 113–115, 117 report, 15, 88–89 Sound level, 68 request, 14–15, 25–28, 87–89 Sound measurement, 68–69, 76 requirer, 14–15, 25, 77–78, 81 Space shuttle, 6, 17, 57 Thermal behaviour, 70 Space shuttle main engine, 6, 57 Thermal load, 25, 42, 57, 117 Specification of the campaign, 88 Throttle, 11, 30, 63–64 Specific Thrust density, 119–120 frame, 56 gas constant, 115, 120 vector, 53, 59 heat, 115, 120 control, 53, 59 impulse, 4, 21 Tightness, 17, 24, 70, 74, 91, 131 Specimen, 7, 12–16, 25 TNT equivalent, 83 140 Index

Torque meter, 12 Valve control, 127–129 Total pressure, 113–115 Vapour pressure, 66, 73, 109 Total temperature, 115 Venting line, 127, 129 Traceability, 77 Venting point, 27, 33 Training matrix, 91 Video monitor, 55 Transport, 1, 10, 13, 40, 89 Vinci, 5, 37, 61, 107 Triple point, 120 Viscosity, 110 Turbine, 16–17, 29–30, 37–38 Visual inspection, 16, 18–19 Turbo pump, 29–30, 32, 35, 63, 65 Voltage loss, 123–124 starter, 29 Vulcain, 4–5, 7–11, 13–14, 21–24, 101, 105 Turbulence, 60 Two-phase area, 121 W Watch dog, 40, 80 U Water Ultrasonic bath, 23 hammer, 33, 65, 119 Uninterrupted power supply, 40 tower, 39, 58 Upgrades, 78 Weather conditions, 73–76 Upper stage engine, 37, 60, 116 Wheatstone bridge, 123 V Wind, 76–77 Vacuum Work instruction, 12–15, 90 chamber, 7, 37, 60, 114, 116 Work plan, 88 insulated, 7, 42, 66, 110 section, 42–43, 127 Z test cell, 69 Zero-suction-case, 115 Validation process, 14, 54 Zero-suction-mode, 114 About the Author

Wolfgang Kitsche works as a senior test leader at the test centre for rocket engines of the German Aerospace Center (DLR), Institute of Space Propulsion, Lampolds- hausen, Germany. Impressed by the manned space ﬂights of NASA in the 1960s he decided as a young boy to become an aircraft engineer. He studied aerospace engineering at the Technical University of Berlin and focussed on propulsion and thermodynamics. Several internships in the ﬁeld of physics of propulsion at VFW- Fokker, Bremen and some years work on turbo machinery at Borsig, Berlin extended his theoretical knowledge before he entered his current position, which he once called in an interview a present from heaven (see Job 1.21).

141 142 About the Author