T HE UN IV ER SIT Y OF MICHIGAN COLT.EGE OF ENGINEERING Department of Electrical Engineering Space Physics Research Laboratory and Electronic Defense Group Final Report Period Covering October 3, 1958, to November 30, 1959 A TWO-FREQUENCY BEACON FOR HIGH-ALTITUDE IONOSPHERE ROCKET RESEARCH L. W. Orr P. G. Cath B. R. Darnall UMRI Project 2816-3 under contract with: DEPARTMENT OF THE ARMY BALLISTIC RESEARCH LABORATORY PROJECT NO. DA-5B03-06-Oll-ORD (TB 3-0538) CONTRACT NO. DA-20-018-509-ORD-103 ABERDEEN PROVING GROUND, MARYLAND administered by: THE UNIVERSITY OF MICHIGAN RESEARCH INSTITUTE ANN ARBOR December 1959

TABLE OF CONTENTS Page LIST OF ILLUSTRATIONS v ABSTRACT vii 1. INTRODUCTION 1 2. REQUIRED TRANSMITTER POWER 3 2.1. Power Required at 37 Mc for D = 1000 Miles 3 2.2. Power Required at 148 Mc for D = 1000 Miles 5 3. NOSE-CONE ANTENNA DESIGN 7 4. DESIGN OF BEACON TRANSMITTER 19 4.1. Block Diagram 19 4.2. Oscillator 21 4.3o Design of Class C Output Stages 29 4.4. 37 Mc Power Amplifier 31 4.5. Frequency Doublers and 148 Mc Amplifier 33 4.6. Telemeter Generator 35 4.7. Battery Pack 35 4.8. Constructional Details 39 5. THERMAL CONSIDERATIONS 45 5.1. Thermal Design of Beacon Package 45 5.2. Heat Exchange and Thermal Constants 47 5o3. Heat Exchange During Flight 49 5.4. Preflight Thermal Preparation 51 5. 5. Temperature Measurement and Control 53 6. RESULTS OF NOVEMBER 10 FIRING 55 6.1. Nose-Cone Temperature History 55 6.2. Beacon-Case Temperature History 55 6.3. Signal Droop at 37 Mc 55 7. CONCLUSIONS 57 8. ACKNOWLEDGMENT 59 9. PERSONNEL 61 DISTRIBUTION LIST 63 111

LIST OF ILLUSTRATIONS Table Page I Preflight Preparation of Beacon Transmitter Package 50 Figure 1 Beacon with antenna completely assembled. viii 2 Tracking bandwidth vs. Doppler step acceleration. 4 3 Antenna dimensions. 8 4 Antenna feed methods. 9 5 Feed loop 37 Mc antenna. 10 6 Feed loop 148 Mc antenna. 10 7 Impedance vs. frequency 37 Mc antenna. 12 8 Impedance vs. frequency 148 Mc antenna. 13 9 Tuning platform 37 Mc antenna. 14 10 Tuning platform 148 Mc antenna. 15 ll Experimetal setup for heat run. 16 12 Temperature stability 37 Mc antenna. 17 13 Beacon block diagram. 20 14 Control cable and junction box. 22 15 Control panels. 23 16 Oscillator with case. 24 17 Oscillator circuit. 25 18 Oscillator vector diagram. 25 19 Frequency shift due to bias changes. 26 20 Frequency shift due to temperature changes. 27 21 Crystal temperature coefficient vs. temperature. 28 22 Class C output stage. 30 23 Maximum efficiency vs. load. 30 24 37 Mc power amplifier. 32 25 148 Mc amplifier and telemeter generator. 34 26 Temperature fuse. 36 27 Telemeter pulse rate vso nose-cone temperature. 37 28 Package assembly drawing. 38 29 View of 37 Mc amplifier. 40 30 View of 148 Mc amplifier and telemeter generator. 41 31 Beacon assembly completed with foam. 42 32 Outside view of beacon assembly. 44 33 Heat exchange in nose-cone assembly. 46 34 Cumulative oscillator heat during flight. 48 35 Typical correction curve for temperature circuit. 52 36 Nose-cone temperature history. 54 37 Estimated beacon-case temperature history. 56 v

ABSTRACT The design of a two-frequency beacon is described. The fully transistorized beacon transmits at frequencies of 37 and 148 megacycles, with powers of 100 and 20 milliwatt respectively. Loop antennas are used at both frequencies and telemetry is provided on the 148 Me signal for measuring the nose-cone temperature. The crystal oscillator is temperature stabilized by the heat of fusion method and has a frequency stability of better than one part in 108 during flight. Also discussed are the transmitter powers required at the two frequencies and thermal design considerations of the beacon. A short summary is given of the results of the firing on November 10, 1959. vii

Fig. 1 Beacon With Antenna Completely Assembleci viii

1. INTRODUCTION A vertical profile of electron density in the ionosphere was measured by the two-frequency method to a height of roughly 1100 miles on 10 November 1959. This required a five-stage rocket vehicle, a two-frequency beacon transmitter in the nose of the fifth stage, and a ground station for receiving the beacon signals. The ground station was furnished and staffed bythe Ballistic Research Laboratory, Aberdeen Proving Ground, Maryland. The rocket vehicle and beacon transmitter were developed and operated by The University of Michigan under contract with the Ballistic Research Laboratory. The development and operation of the beacon is the subject of this report. Figure 1 shows the complete two-frequency beacon package, together with its antenna system. Because weight in the nose was needed for flight stability, no particular attention was given to lightening the payload and, in fact, an antenna 1000 grams heavier than the one first designed was required. As seen in the figure, the beacon package weighs 1800 grams while the antenna assembly (heavy model) weighs 1760 grams. The primary purposes of this five-stage rocket experiment were: a. Measurement of the electron density profile to a height of roughly 1000 miles. b. Proving in the vehicle. Secondary purposes of the experiment were: a. Examination of the frequency stability achievable in the rocket environment. b. Measurement of nose cone-temperature. c. Measurement of the package temperature. The minimum requirements specified by the Ballistic Research Laboratory for the two-frequency beacon are as follows: 1. A 100-milliwatttransmitter at 37 Mc. 2. A 20-milliwatt transmitter at exactly 4 times the first frequency and phase locked to it. 3. A frequency stability* of one part in 106. *A single frequency probe was contemplated at the beginning of the project with a frequency stability requirement of better than one part in 107. Since the method had been developed to satisfy this, it was decided to continue with the high stability beacon design. The frequency stability actually achieved in the flying models was one part in 108 or better. 1

A highly successful firing took place at 0700 hours from Wallops Island, Virginia, on 10 November 1959. Signals were received continuously on both frequencies for 1500 seconds of flight at the Wallops ground station, and for 1515 seconds at the Aberdeen Proving Ground station. The telemeter record obtained at Wallops Island gave measurements of the nose cone temperature and gave one point in the temperature rise of the package during flight (Section 6).

2. REQUIRED TRANSMITTER POWER The transmitter power required for the two-frequency nose-cone beacon depends on a number of factors including space attenuation, cosmic noise, antenna gains and efficiency, effective bandwidth of the ground receiver, and minimum signal-to-noise ratio required for phase lock of the tracking filter. A review of the various factors is presented here, and the margin of safety (gain margin) is calculated for the nominal values of power chosen for the beacon. For free space propagation, the power received from the rocket-borne transmitter is given by PtGtAr PtGtGrc2 4jtDZ - (4ctDF)2 where: Pt is the transmitted power, Gt and Gr are the antenna power gains, Ar is the effective area of the receiver antenna Ar = GrX2/4t = Grc2/4TF2 D is the transmission path length, F and x are the frequency and wavelength of the transmission, and c is the velocity of light. A convenient formula for the space attenuation in decibels when using dipole antennas (Gt = Gr = 1.6 power gain) can be derived from (1): Space atten. = 32.6 + 20 (log D + log F) decibels, (2) where D and F are expressed in miles and megacycles. 2.1. POWER REQUIRED AT 37 MC FOR D = 1000 MILES At this frequency the cosmic noise level is so high that the noise figure of the receiver need not be considered. Because of the small size of the nose

From: Victor W. Richard, Operation And Application Of The Ballistic Research Laboratories' Tracking Filter. 13th Annual Conference Of The Instrument Society of America; Sept. 1958 10 a110 I ____I_ I I_ I z_1T_ 05 0.1 I 10 102 103 DOPPLER STEP ACCELERATION IN CYCLES PER SECOND2 Fig. 2 Tracking Bandwidth vs. Doppler Step Acceleration

cone, a full-size loop antenna cannot be used, and the inefficiency of the 37 Mc antenna must be considered. The receiving system in the ground station contains a tracking filter which tracks with marginal locking with a phase jitter of 300 rms, and this requires a signal-to-noise ratio of 6 db. The Doppler acceleration in cycles per sec2 is given by the expression b = Ag (3) 30.6 where F is the frequency of the radio wave in megacycles per second and Ag is the radial acceleration in g's. This expression gives the maximum Doppler acceleration* at 80 g's for the 57 megacycle transmission as 96.7 cycles per sec2. The required tracking filter bandwidth is obtained from Fig. 2. A Doppler acceleration of 96.7 cycles per sec2 requires a bandwidth of 19 cps. The next larger bandwidth has to be used for the filter which is B = 25 cps. The space attenuation is first found from Eq. (2) Space atten. = 32.6 + 20 (log 1000 + log 37) = 124.0 db Loss due to antenna inefficiency = 16 db Total signal attenuation = 140.0 db Mean cosmic noise temperature** at 37 Mc = Tn = 2 x 104 OK Minimum tracking filter bandwidth = B = 25 cps Boltzmann's constant = k = 1.38 x 10-23 joules/~K Equivalent input noise power to receiver = kTnB = 6.9 x 10-18 watt Signal power required for marginal locking of tracking filter (6 db above noise) = 4kTnB = 2.8 x 10-17 watt Transmitter power required is 140 db above 2.8 x 10-17 watt or Pt = 2.8 x 10-3 watt. (4) A nominal power of 100 milliwatts was suggested for the 37-Mc output. This gives a gain margin of 15 db. If the gain of the helical receiving antenna is now considered (approximately 8 db above dipole), a gain margin of 23 db is obtained. 2.2. POWER REQUIRED AT 148 MC FOR D = 1000 MILES At this frequency the cosmic background noise is much lower, and contribu*The largest step in acceleration occurs at stage 4 burnout, and this does not exceed 80 g's. **F. T. Haddock, private communication.

tions due to internal receiver noise must be considered. A noise figure F = 2 (or 3 db) will be assumed. Equation (3) gives a value of 387 cycles per sec2 for the maximum Doppler acceleration. Using Fig. 2 we find that a tracking filter bandwidth of 50 cps is needed, this being the next larger bandwidth above 38 cps. Space atten. [Eq. (2)] = 32.6 + 20 (log 1000 + log 148) = 136 db Loss due to inefficiency of rocket-borne high-frequency loop antenna = 3 db Total 139 db Minimum tracking filter bandwidty at 148 Mc, B = 50 cps Receiver reference temperature Tr = 300~K Equivalent noise power at receiver input due to internal receiver noise = (F-l)kTrB = 300kB Mean cosmic noise temperature* at 148 Mc, Tn = 7000K Cosmic noise power = kTnB = 700kB Equivalent receiver input noise power = 1000kB = 6.9 x 10-19 watt Signal power for 30~ jitter (S/N = 6 db) = 2.8 x 10-18 watt Transmitter power required 139 db above 2.8 x 10-18 watt or Pt = 2.2 x 10-4 watt (5) A nominal transmitter power of 20 milliwatts was suggested for the highfrequency unit. This would give a gain margin of approximately 19 db. Allowing for the added gain of the ground receiving antenna, the gain margin increases to at least 27 db. *F. T. Haddock, private Communication 6

3. NOSE-CONE ANTENNA DESIGN Physically the nose-cone antennas for both frequencies are trapezoidal loops, constructed of brass with fiberglass spacers. The complete antenna mounted on the beacon package is shown in Fig. 1. The antenna loops are mutually perpendicular. With this arrangement it is found that the radiation pattern of either is essentially unaffected by the presence of the other. The dimensions of the 37 Me antenna are governed by the inside dimensions of the nose cone and are shown in Fig. 3. Round fiberglass spacers are inserted at heights of 7, 14, and 20 inches and are held in place by brass brackets. -The legs of the 37 Mc antenna loop are constructed from 3/16 in. solid brass rather than the lighter 1/32 in. channel, to obtain a proper overall center of gravity for the complete final stage of the missile. The maximum allowable dimensions of the 148 Mc antenna are determined primarily by the shape of the resultant radiation pattern. It turns out that a multilobed radiation pattern results if the circumference of the antenna loop exceeds 0.3 wavelengths'*. Another size limitation arises from the fact that the size of the tuning capacitor decreases to a point of impracticability as the loop is enlarged. Final dimensions for the 148 Mc antenna are shown in Fig. 3. Radiation patterns were obtained through the cooperation of the research staff at Ballistic Research Laboratories. The departure from a circular radiation pattern was less than one db for the 37 Mc antenna, and less than 3 db for the 148 Me antenna, when plotted in the plane of either antenna. Electrical features of the antennas include current feed loops and temperature compensation in the tuning capacitors. Current feed loops (Fig. 4b) are used in preference to voltage feed (Fig. 4a) for three reasons; (a) it simplifies the construction and eliminates extra components and transmission cables; (b) current feed loops were found experimentally to be as efficient as the voltage feed; (c) impedance matching is simpler and is independent of tuning in a current-fed antenna. The loop sizes are adjusted so that the antenna input impedance becomes 50 +j:O a at resonance, which is the proper load impedance for the transmitters. Final current feed loop dimensions are illustrated in Figs. 5 and 6. A Hewlett Packard VHF Signal Generator (608-D), Bridge (803-A) and Detector (417-A) were used to measure the antenna impedances as functions of frequency. The results of these measure*Mr. Victor W. Richard, private communication. 7

FOR DETAIL OF TUNING PLATFORMS SEE FIG. 9 8 FIG. 10 FOR DETAIL OF FEED LOOPS SEE FIG. 5 a FIG.6 ALL DIMENSIONS EXTERNAL 2.98"'- 37 MC ANTENNA IS 3/16 x 7/8 SOLID BRASS 148 MC ANTENNA IS 6" 1/32 BRASS CHANNEL {SEE FIG.6 26.5" 3.71" 7" [ 4 I t4.57 4. 57'".50 86.50 86.50 86.50 I f I —, t, 5.375"- - 5.375" 37 MC ANTENNA 148 MC ANTENNA Fig. 3 Antenna Dimensions

CM CT CT= TUNING CAPACITOR CT CM = MATCHING CAPACITOR COAXIALI ifo CABLE FEED LOOP a. VOLTAGE FEED b. CURRENT FEED Fig. 4 Antenna Feed Methods

7 3 i616~ 8 F~//'i l16I SEC. A-A A A LI j A A 3 —~~ SEC. A-A 5 I,, B4 Li~~~~~~3 3 16 I" F-~~~' 86.50 _~3 0 1'SEC. B-B 86.50,/. 3-~ 16 3' I~~~~~~~~~~~~~~~~ — I a6 3~~~~~~~~~~~~~1 8 - 8 8"8 Fig. 5 Feed L —-o 5 3 ~~~~~~~~~~~~~~~~~~~~~~~~~~5,,.. 8 " - Fig, 5 Feed Loop 37MC Antenna 8~~~~~~~~~~~Fg 6 Feed_ L o o 14CAnen

ments are shown in Figs. 7 and 8. These, by the way, are the impedances measured at the input of the transmission line connecting the antenna to the bridge. The antenna input impedance at the feed point, when plotted on the Z-9 chart, will approximate a circle with the points 0 and 50 Q lying on a diameter. Tuning of each antenna is accomplished by means of a ceramic trimmer with associated padding capacitors determined by operating frequency and desired tuning range. The capacitor values were determined with the antenna placed inside the nose cone. The nose cone lowers the resonant frequency of the 37 Mc antenna by about 300 kilocycles. Figures 9 and 10 illustrate the arrangement of components on each tuning platform and a diagram of the circuit used. To facilitate tuning of the 148 Mc antenna while enclosed by the nose cone, the 37 Me tuning capacitor (C-2 in Fig. 9) is offset to allow insertion of a tuning wand to the trimmer of the 148 Me antenna. Additional care was necessary in choosing capacitors to insure adequate frequency stability of the antennas over the anticipated range of flight temperatures. To determine the correct temperature compensation a heat run was made using the experimental set-up shown in Fig. 11. The experiment determines first the resonant frequency of the 37 Me antenna as a function of temperature. The resonant frequency is the frequency at which the antenna input impedance has an imaginary part equal to zero. In our case the input impedance at resonance is 50 + jO Q, providing the ideal match to the 37 Mc transmitter. Secondly the variation in phase angle was measured for the 37 Me antenna as a function of temperature. This is the phase angle of the antenna input impedance at a fixed frequency. It is a measure of the mismatch between the antenna and the transmitter, that occurs due to temperature changes. The results of both these experiments, performed on a temperature compensated antenna, are plotted in Fig. 12. The change in phase angle of the 37 Me antenna impedance is a direct result of the high Q of this antenna structure. The Q was measured to be 160. A combination of capacitors with different temperature coefficients (Fig. 9) was chosen to minimize both the variation in phase angle and in resonant frequency. The 148 Me antenna did not require special compensation since its phase angle at constant frequency input, did not vary noticeably in any of the temperature runs. Final antenna characteristics were as follows: 11

.37 so 31 I F If I 14~~~69 36-90 ~ ~ ~ a/ XK I I 7~f~~ / /737.027 36-87~~~~~~~~s 36.81II "369 o IS 20 25 SO 300 u~~~zo 50d ~ ~6~i~~ c ~ ~CILII~rtP' 3.9211 r-r r77 CHART.99 g 7~~X(Yv~~f r-II ~3-u~1Fig. 7r rI Impedance vs. FrequencY 37 MC Antenna~~YV~XT~1 L

.371.3.22~~~~~ I1 3 40O \ i~~ I I -T10 150~o IU 148.00~~~~~6 ~t~T~~i~X1'5Cr' lt4 i rf-tS-~t~i_(49.0 ~ JYKXzj 5onY pb~XXK~u~` l 7yc~C I t LfHM-L2d IIYP TT~7- Z \\ \C CHARTlY-~ VY~/m Z, ~~~~~~~~~~~~~~~-taII ("A).nq

C, ERIE CERAMICON TUBULAR C2 C, NPO ~120P/M 4.4/upfd ~251pfd C2 ERIE CERAMIC TRIMMER NPO 1.5-7/1y fd o0 C3 t — ~ C3 POSITIVE TEMPERATURE COEE VITRAMON +115P/M/~C 181ufd 500 VDCW ~ 5% C4 NEGATIVE TEMPERATURE COEF. IC4,CENTRALAB TCN 3.3 N750 600 VDCW ~2% 3.3~pfd CAPACITOR SCREW 1/4" OFF CENTER ~~~2. ~18"~TOP BRACKET C-4 TOP BOTTOM Fig. 9 Tuning Platform 37 MC Antenna

2 ERIE CERAMICON TUBULAR NPO +120 P/M I/,/fd C2 ERIE CERAMIC TRIMMER NPO 1.5-7 7,ffd C3 ERIE CERAMICON TUBULAR NPO +120 P/M 2/z/qfd C3 4.57" CAPACITOR SCREW CENTERED /\ ~ __/ ANTENNA TOP BRACKET orP 80/ A Fig. 10 Tuning Platform 148 MC Antenna

HOT AIR HAIR DRIER CALIBRATED THERM ISTORS ANTENNA UNDER TEST SIGNAL GENERATOR BRIDGE DETECTOR l CARDBOARD H. P.' \ \M AND PAPER 608-D H.P H. P. I | \ LNSULATING 803-A 417-A I 17. I 1 >L SHEATH OHMMETERS Fig. 11 Experimental Set-Up For Heat Run

RESONANT FREQUENCY vs TEMPERATURE 37.040'-"< ---- 12 37.035 t 07 l lPHASE ANGLE vs TEMPERATURE 37.035 1 1 I I 37.030 -X f MC 4 37.025 2 00 37.020 I 111 1 20 30 40 50 60 70 80 90 100 110 T ~C -* Fig. 12 Temperature Stability 37 MC Antenna

Frequency "Q" Tuning Range Efficiency Input Impedance 37 Mc 160 36.2 —-37.4 Me 16 db below dipole* 50 + jO Q 148 Me 50 135 —— 160 Mc 2 db below dipole 50 + jO Q In conclusion, the final antennas were made to conform to the imposed size limitations and flight expectations of the missile and at the same time meet their primary purposes electrically. The design and choice of components have proven adequate in the recent flight. *The efficiency of the 37 Me antenna in the flying model was never actually measured, but this figure is within one or two decibels of the true value based on accurate measurements on Antenna No. 4A. The 37 Me unit of model No. 4A had a Q and physical dimensions almost identical with the flying models, and it showed a radiation efficiency of 15 db below dipole as reported by Mr. Victor Richard on October 8, 1959. 18

4, DESIGN OF BEACON TRANSMITTER 4.1. BLOCK DIAGRAM A block diagram of the two-frequency beacon is shown in Fig. 13. It consists of the following parts: (a) A 37 Mc crystal oscillator, powered by a separate battery. (b) A three stage 37 Mc amplifier. The amplifier is driven by the oscillator and delivers approximately 120 mW to the antenna. (c) Two frequency doublers and a final amplifier delivering nominally 20 mW to the 148 Mc antenna.'he first frequency doubler is driven by the second stage of the 37 Mc amplifier. (d) A telemeter generator, amplitude modulating the 148 Mc signal. The telemeter generator is a multivibrator producing a 10 msec pulse. Its repetition rate is determined by a thermistor. (e) A Ledex stepping switch is furnished to disconnect battery power from the transmitters or to connect them to an external battery. The four positions of the Ledex correspond to the following functions: Position 1: transmitters off. Position 2: 37 Mc transmitter connected to the external battery. Position 3: both transmitters connected to the external battery. Position 4: beacon on internal battery for flight. With this arrangement it is possible to measure the currents drawn by the two transmitters separately, as a final check before flight. (f) A 16 volt mercury battery. (g) Two thermistors (VECO type 32A84) are mounted in the beacon to measure the package temperature and the oscillator temperature prior to takeoff. (h) An oscillator heater (12 watts) is used to bring the oscillator case to operating temperature (47~C) and to melt part of the alloy that is used for temperature stabilization of the oscillator. This will be discussed further in Section 5.1 19

PACKAGE NEM 37 MC/I 148 M6 \V TTHERMAL BLANKET 20mW OSC. TEMP 2 > ~~~~~~~~~DOUBLERS I TELENEE OSCILLATOR ~' 37MC AMP -- 148 MC AMP MOD GENERATOR 3> COMMONI +16 V I + 16 V +- 1.34V I 0 IOSCILLATOR~ BATTEE:RY -2.6 8 V OSCILLATOR 50~2 to HEATER 0 A -I. - _ I V Vs VO L6 LEDEX POSITION 6 27K 8200 4700 12K 12 3 4 LEDEX CONTROL + EXTE RNAL BATTERYV COMMON II,f HEATER 62 NOTE: THERE IS MO ELECTRICAL 9 CONNECTION BETWEEN ANY PARTr OF THIS CIRCUIT AND __________________ THE 5Th' STA GE ROCKET CASE Fig. 13 Beacon Block Diagram

(i) A package heater (100 watts) is necessary to keep the package temperature above 5~C. Below this temperature the mercury batteries are not considered reliable. The package is connected to two control panels via a 100-ft umbilical cable, a junction box on the launching pad, and a 1500-ft control cable (Fig. 14). The control panels were mounted in the BRL ground station. Figure 15 shows a diagram of the control panels. The heater control panel consists of two thermometer circuits to measure package and oscillator temperatures (see Section 5.5). The variacs on this panel furnish power to the two heaters inside the beacon. The transmitter control panel contains a power supply to operate the Ledex switch, an indicator for the position of the Ledex switch and a variable external power supply. 4.2. OSC ILLATOR The oscillator assembly is shown in Fig. 16. The mechanical and thermal design of this assembly will be discussed in Sections 4.8 and 5B1. The oscillator circuit is shown in Fig. 17. This circuit is an improved version of a circuit originally developed by the Ballistic Research Laboratories.* The operation of this circuit can best be explained using the vector diagram shown in Fig. 18. Assuming that the phase shift in the transistor does not differ appreciably from 1800, the condition for oscillation is that the voltage OD is 1800 out of phase with voltage OC, while at the same time the voltage gain in the transistor is larger than OC/OD. The phase condition will be fulfilled at a frequency wo, which is the series resonant frequency of the crystal. At a slightly different frequency the voltage to the base changes both in magnitude and in phase as indicated in Fig. 18 by the point D'. The faster the phase of the voltage OD changes with frequency, the more stable will be the frequency of the oscillator. It is apparent that this fast rate of change can be achieved by designing the oscillator so that the point D is as close to point 0 as possible. Of course the voltage gain in the transistor must always be larger than OC/OD, which is the reason that OD cannot be made arbitrarily small. Figure 19 shows the change in frequency due to changes in the transistor bias. This is typical for the oscillator of Fig. 17. Figure 20 shows the change in frequency due to temperature changes. The solid line indicates the frequency shift when all components of the oscillator, including the crystal, are placed in the oven. The broken line shows the frequency shift when only the crystal is heated, while the other components remain at room temperature. The slope of this latter curve represents the temperature *Orr, L. W. and Cath, P. G., Instrumentation and Tracking of Ionosphere Probes, UMRI Report No. 2816: 3-1-P, Ann Arbor, February i959. 21

#22 GAGE 244 _ 2> #22I24~~ 2 OSPACK TEMP #22 24 3 O 2 #22 24~2 -. 2 OSO. TEMP # 22 24 IT 3 > IIP 8 COMMONIE *22 245 4 >- 80- — p 4 OSC. HEATER 0.5 I 224.0 I AMP.002 IOL f 4 AMP I 22 24 ~ 5 > —------— ~ 5 LESDEX POSITIO 6 0 6 LEDEX CONTFJI #242 2 4S 71> 7 EXTERNAL BA # 22 24S 8 ft CABLE JUNCTIO 8 COMMON L C ELEs lo84 9 > 0 —---—,> —-—'1 9 PACKAGE HEATE 0. 5 110: 24 V.002- loIL fL 4AMP #14 D CB 10 > > —--------— i 1 C C a Junct 10 COMMON Ii o 14 4 ~ II > —-------------------- ~ > 00 —-- I I SPARE 1500 ft CABLE JUNCTION BOX AT LAUNCHER I -9 VINYL COVERED PLASTIC INSULATED CABLE STRANDED BELDEN-# 844-9 10-11 # 14 DUPLEX CABLE Fig;. 14 Control Cable and Junction Box

1500 1500 j 21P, + —-— _ 2 J 12 vJ22 j 13 I V J23 2 680 68013~4~1 i~ 1 5~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 0 0 R - 0 10D I S I S 1 2 0 + 0 -100 + 22 -5 1.34V 11.34V 0R21 150 R 1RT000 150021 ~10 PACKAGE TEMP 1000 OSCILLP v OQ50 DC 0 IA 0 7 IN92 LTSC. O VARIAC PACK I OR LINE 0 0- 150 AC OSCILLA ATOR 11V i O HATR 3A 0AAC 3A IA ~~~~VARI AC VARIAC ~~~~PACKAGE HEATER HEATER CONTROL PANVEL A_ B_ C__ _ _ E___ TRANSM/ITTER CONTROL PANEL IAVARIAC IN1084 I 000 f 6800 LEDEXY'000g 6800 CONTROL LEDEX IOOV VOLT ADJUST 1N92 LEDEX __ M POSIT/ON 0-I I IV 12 V 150/47LT 2500 IA VARIAC ioin 1/8 A PILOT 0 - 100 DC IPIOVIAC OTv+ I000Lf + + 5 K I IOV C 110 25V -. 41 0-50. REGULATED 92 50V N5 0 BAFi. 1 Fig. 15 Control Panels

';? ~!iirii? ~:?: i:":':implicitly: ~i!!!!ii?~:i~ ~ ~ ~ ~~ ~~~,iiiiiil;~si,.:i!:::,:~:~: ~ ~.............:iii'~iii~i~iii~~iiii~...... i::iiii/iiiii:iii-:':,i:ii:n;~:ii~i. rii:::I:: i;~i':",::.~~i~ii~iiiiii,;iii~i~:ii:/~:!i~:"i I:;~iir~!~i.l";~1:ii:~',ii:~i;i:;iii~ii~:.si::i:~ii~i~.~i;.!... ~~~~~~~~~~~~~~~~~~..............':i?'~.!~:, i~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~.,,~:..~................,:~;;!;i::,,:i;"'',~i?:?~: ~71;;~:~,i~;,i:~;/: i~:~~~~~~~~~~~~~~~~~~i~x................. ir~~iB~~d, Ijl 0 I 2 ~~~~~~INCHES Fig. 16 Oscillator With Case

3.5 p h - TO 37MC AMPLIFIER 27p f.0021if C 36.94 MC - D 2N384.002tzf 560Q 0 + 1.34V Coil data: collector winding 7 turns feedback winding 2 turns c.t. output winding 1 turn outside diameter 5/16"; # 28 enamel wire. Fig. 17 Oscillator Circuit W)o - AD, \A B'C Dv 0 D\ O / \ 7 Fig. 18 Oscillator Vector Diagram 25

30 100 V:6.OV 20 r- 50 VC 4.5V 1n - 1 z a v=:3.ov 0 --- 36.9 M C 1V =t 15V -10 I I I I 50 1 2 3 4 5 6 Ie IN mA 0 Fig. 19 Frequency Shift Due To Bias Changes

36.9 MC 0 0 -50 0 2X \ I S 1 1 itcn~~~~~~~ /~CRYSTAL ONLY 0 ~ 1-100 / I -30 / COMPLETE OSCILLATOR -40 -150 20 30 40 50 60 70 TEMPERATURE IN C - Fig. 20 Frequency Shift Due To Temperature Changes 27

+10 TEMPERATURE COEFFICIENT +5 0 cr_ w a. Go~~~~~~~~~~~~~~~~ 0~~~~~~~~~~~~~~~~~~~~ z 0f Ir 10 TURNING TEMPERATURE Q. -5 TEMPERATURE -10 45 50 55 OC Fig. 21 Crystal Temperature Coefficient vs. Temperature

coefficient of the crystal. Figure 21 shows how the temperature coefficient varies with temperature for the crystal of Fig. 20. The crystal that was flown on November 10 had a turning temperature of 45'C and a temperature coefficient of 2.2 cycles per second per ~C (or 6 parts in 108 per ~C) at 470C, the operating temperature. The point at which the temperature coefficient is zero is determined by the individual crystal. It depends upon the orientation of the crystal surfaces with respect to the crystal axes. The third-harmonic crystals that are used in the oscillator are so thin, that it becomes virtually impossible to orient the crystal accurately enough during grinding, to be able still to control the temperature at which the temperature coefficient is zero. This turning temperature is therefore different for each individual unit. Fifth-harmonic crystals are much better in this respect because their larger thickness makes it easier to control the turning temperature. The disadvantage of these crystals is their larger size and higher series resistance. The more convenient third-harmonic crystals were finally used because they provided adequate frequency stability. The crystals were supplied on special order by McCoy Electronics Corporation. 4.3. DESIGN OF CLASS C OUTPUT STAGES The main problem in the design of the 37 Me amplifier is the output stage. In this section we shall briefly review the theoretical and practical limitations that are encountered. The maximum power output and the efficiency of the final stage are primarily determined by the collector load. The size of this load is limited by the collector to base breakdown voltage (BVcbo), the saturation voltageand the collector dissipation. Consider the circuit shown in Fig. 22. The peak voltage across RL can never exceed Vb. Therefore the power delivered to RL at the resonant frequency of the tank, can be at most Vb2 WL max = 2RL WL cannot be increased arbitrarily by increasing Vb, because of the collectorto-base breakdown voltage (BVcbo). The supply voltage Vb should not exceed approximately 1/2 BVcbo. Neither can WL be arbitrarily increased by decreasing the value of RL. When RL is made smaller, the collector efficiency decreases and quite soon the collector dissipation becomes a limiting factor. The cause of the drop in efficiency with a decrease of RL lies in the saturation voltage of the transistor. To be able to draw a certain value of peak current Icp, a minimum collector voltage Vcmin is needed. The d-c admittance of the transistor under this condition can be called a = Icp/Vcmin. 29

Vb Fig. 22 Class C Output Stage 100 50 Z o 0 - 0.I 10 100 Fiig. "~'~ Maximum Efficiency vs. Load 30

It can be shown that the product aRL determines the maximum efficiency that can be obtained in class C operation.* This relationship is shown in Fig. 23. Obviously a compromise between power output and efficiency must be made when choosing a value for RL. Another transistor parameter that must be considered is the emitter to base reverse breakdown voltage (BVebo). This voltage is inherently low for a diffused base transistor because of the high impurity level in the base at the emitter junction. A typical value for BVebo is 0.5 - 1.0 volt. When an attempt is made to increase the output power WL by decreasing RL, the driving voltage to the emitter has to be increased also'. This means that, during the nonconducting part of the cycle, the emitter voltage may exceed BVebo. Fortunately this breakdown is not very sharp, and it has been reported that the transistors suffer no damage when BVebo is exceeded, provided that the total emitter dissipation stays within bounds. 4.4. 37 MC POWER AMPLIFIER Only a small amount of power is available from the oscillator for two reasons. To prevent heating of the crystal the oscillator is operated at a low power level, thus facilitating crystal temperature control. Only a small portion of this power is fed into the 37 Me amplifier to prevent frequency pulling due to possible changes in the amplifier. The amplifier has a power gain of approximately 500 (= 27 db) and delivers 120 mW to the 50 1 antenna load with an overall efficiency of 35%. The circuit diagram is shown in Fig. 24. In the first two stages 2N384 transistors are used. These are RCA drift transistors (p-n-p, alloy). A Texas Instrument 2N1143 transistor (diffused base) is used in the output stage. It is in the design of this last stage,that the considerations mentioned above have to be taken into account, to obtain the desired power output at a reasonable efficiency. The tap on the output coil is adjusted so that the 50 S2 load is transformed to a load RL =1000 Q2 at the collector. With a supply voltage of Vb = 16 volts, this stage delivers 120 mW with a collector efficiency of q = 50%. This is in good agreement with Fig. 23. The values of inductance and capacitance in the output tank are chosen to give a loaded Q of about 20. The value of Q is not critical but it should not be too high because drift in component values might otherwise detune the stage. Too low a Q gives insufficient rejection of higher harmonics. The collector of the 2N1143 is connected to the transistor case. The tran.sistor is therefore mounted in a small brass heat sink which is electrically insulated from the package mounting plate (Fig. 28, item 15) by a thin layer of *Heyboer, J. P., Transmitting Valves, Philips Technical Library, Book VII, 1953. 31

| HEAT SI NK 2N384 2N384 45 2N 1143 INPUT _ _ 70 m V 45 50 45 50 45 75 ANTENNA Li LLLOAD 22K 150K IK 2000 TO FREQUENCY - DOUBLERS 2000 2000 2000 16V.22 /h.22,ih All.Cupacitor Values in Elf L1 primary 8 turns; secondary 2 turns interlaced with primary. 1/4" coil form; j20 enamel wire. L2 identical with L1; third winding 5 turns #26 enamel wire. L 4 turns #12 bare copper wire; tap 1 turn from end. inside diameter 1/2". Fig. 24 37 MC Power Amplifier

teflon. Heat generated in the transistor is conducted through the teflon to the package mounting plate which also acts as a large heat sink. Teflon was chosen because it combines a reasonably good heat conductivity with a very low dielectric constant. For the dimensions used in the amplifier, the heat conductivity through the teflon layer is 76 mW/OC and the capacity added to the tank circuit by the heat sink is 8.5 Off. The small heat sinks around the transistors are at the same time support and spacers for the amplifier mounting boards (see Fig. 28, item 2, and also Section 4.8). 4.5. FREQUENCY DOUBLERS AND 148 MC AMPLIFIER A circuit diagram for the frequency doublers, the 148 Mc amplifier, and the telemeter generator is shown in Fig. 25. A 37 Me input signal to the first doubler is taken from the second stage of the 37 Mc amplifier. The frequency doubler consists of a grounded base transistor (2N1143). A diode is connected in series with the emitter to increase the second harmonic output at the collector side. Insertion of the diode decreases the portion of the RF cycle during which the transistor conducts. We believe that this accounts for the larger harmonic output at the collector. The collector tank is tuned to 74 Mc. The second frequency doubler is identical to the first. Its output tank is tuned to 148 Mc, and drives the 148 Me amplifier. The considerations of Section 4.3 apply of course to the collector load of the final 148 Mc stage. Because only 20 mW is required at this frequency, the tap on the output coil is adjusted so that the 50 S antenna load transforms into a 2000,2 collector load to improve the efficiency. Under certain conditions, determined by individual differences in transistor parameters, the 148 Mc transmitter oscillates. To eliminate the oscillations, damping resistors are added to the circuit as shown in Fig. 25. Amplitude modulation of the 148 Me signal is obtained by modulating the supply voltage to the second frequency doubler. This modulates the driving voltage to the final stage. Changing the supply voltage to the second transistor will also change the collector capacitance, which will produce some phase modulation on the 148 Mc signal. The collector capacitance however is small (1.5 Off) compared to the fixed capacitance (approx. 10 iff) in the tank. The amount of phase modulation is therefore small and was found not to affect the tracking filters in the ground station. The 10-msec pulses from the telemeter generator reduce the amplitude of the 148 Mc signal by 6 db. 33

-'r' -l- -'1 I HEAT SINKS I -r1-, 74 MC | 148 MC 148 MC 37 MC L I I E R T2000 0~2 6.22p h.221ih Capacitcr tTolues in.fi, _ __ 390 11 3* 3J Q Damping Resistors Only When Needed 3300E AT 470 I 150K 6.8 K I T FUSE L primary 6 turns; secondary L 1 turn interlaced with primary. 2N214 1500 1/4" coil form; 20 enamel wire. 2 1500 L2 primary 6 turns; secondary 1 turn interlaced. 180K 1/4" coil form; #20 ernamel wire. L3 3 turns #14 bare copper wire. C tap 1/2 turn from end. inside diameter 3/8". THERMISTOR Fig. 25 148 MC Amplifier and Telemeter Generator

4.6. TELEMETER GENERATOR At the request of the aeronautical designers, telemetry was added to the beacon for measuring the temperature at the interface of the fiberglass and teflon on the nose cone. This is probably the first measurement of its kind ever madeo The temperature of the beacon assembly itself is also of considerable interest because it determines the transistor environment.* The assembly is expected to heat up during flight, due chiefly to aerodynamic heating through the nose cone and the hot rocket case of the Scale Sergeant after burn-out. The beacon package is thermally insulated from the rocket for this reason. The third source of heat, the dissipation in the transistor circuits (about 750 milliwatt), is negligible compared to the two just mentioned. One point on the temperature rise curve of the package was obtained using a temperature fuse. An assembly drawing of this fuse is shown in Fig. 26. The bottom stud of the fuse is screwed into the package heat sink (Figo 28, item 15). When the package temperature reaches 470C, the solder melts and releases the spring. This disables the telemeter generator. The telemeter generator is a free running multivibrator. The circuit is shown in Fig. 25. N-P-N transistors are used in the multivibrator to obtain the proper polarity of output pulse for modulating the second frequency doubler by direct coupling. The pulses on the collector of the 2N214 transistors have an amplitude of 15 volts. A voltage divider (390 and 47DP ) is used to produce the 6 volt pulses (duration 10 msec) needed to modulate the second frequency doubler. The pulse repetition rate is determined by the resistance of the thermistor (VECO type 61A7) bonded to the nose cone. Fig. 27 shows the pulse rate as a function of nose-cone temperature. The S-shape of this curve is obtained by resistances in series and in parallel with the thermistor. The series resistance consists of the 6800 and 1500 2 resistors in the multivibrator and the parallel resistance is 180 k2. 4.7. BATTERY PACK Mercury batteries were chosen for the beacon because of their constant terminal voltage throughout the useful life of the cells. The oscillator battery consists of one I-volt battery (Mallory type: TR133RT2). The capacity of this battery is 1000 mah, which is sufficient to *The beacon for the second firing on November 18, was instrumented to measure the package temperature by mounting the telemeter thermistor on the package instead of the nose cone and omitting the temperature fuse. No results were obtained. 35

CONNECTED TO TELEMETER GENERATOR BRASS NUT 6-32 STUD SPRING (.004" PIANO WIRE) LINEN-BASE PHENOLIC INSULATOR SOLDERED WITH CERROLOW 117 ALLOY _ 6-32 STUD I a I O INCH 1/4 1/2 Fig. 26 Temperature Fuse 36

250 INTERFACE NOSE- CONE TEMPERATURE, Ti vs PULSE RATE 200 Ti IC 150 100 50 1.5 2 3 4 5 7 10 20 30 40 60 RATE IN PULSES PER SEC Fig. 27 Telemeter Pulse Rate vs. Nose-Cone Temperature 37

I D,, I I,,,| -, ) 60 INCH 27 1. Tuning Capacitor 12. Thermal Isolation Blanket 2. Amplifier Mounting Board 13. Bottom of 37 MC Antenna 3. RF Coil 14. Antenna Base Plate 4. Multivibrator Mounting Board 15. Mounting Plate and Heat Sink 5- Package Bolt (4) 16. Aluminum Cylinder and Support 6. Bottom of 148 MC Antenna 17. Battery Pack 7. Antenna Mounting Bolt (4) 18. Mounting Bolt (8) 8. Oscillator Cavity 19. Glass-Fibre Ring (G-5) 1////3 X, v8 1. si cia tor Housing120. Tefl Psolateo Bla 6. Boto of18 CAnen BteyPc 7. Anen onigBl 4 8 onigBl 8 8. Oscillator Cvity 19. Glass-ibre Ring (G-5 9. Oscillto Houin 20. Teflo Plt 10. Crystal Well 21. Amounting Shoulder of Scale SergeantI 6.Botm f14 M ntna 7~Bttr 8c

power the oscillator for 500 hours. The oscillator can therefore be connected 10 days or more before the firing. The 16-volt battery which powers the transmitter circuits, is made up of four 4-volt mercury batteries (Mallory type: TR133RT2). Its capacity is sufficient for at least 16 hours of continuous operation. These five batteries are assembled to form one battery pack. This pack is mounted on the package mounting plate (Fig. 28, item 15) with three bolts. This facilitates replacement by fresh batteries prior to flight. 4.8. CONSTRUCTIONAL DETAILS The most important mechanical features of the beacon assembly are shown in Fig. 28. The chief member of the assembly is the package mounting plate and heat sink (item 15). All components, oscillators, amplifiers, batteries,etc., are mounted on the bottom of this plate. The antenna is mounted on top. The mounting plate is supported by a cylindrical aluminum shell (item 16) and mounted on a glass-fibre ring (item 19) with bolts (item 5). The glass-fibre ring and the teflon plate (item 20) provide the thermal insulation between the package and the rocket case (item 21). The oscillator case contains two cavities. The oscillator circuit is mounted in the upper one (item 8) with the crystal fitting in the crystal well (item 10) (compare Fig. 16). The other cavity (item 11) is filled with Cerrolow 117, which is the alloy used for temperature control of the oscillator (see Section 5.1). The oscillator case is surrounded by an insulating plastic foam blanket* (item 12). The other components of the beacon are placed around the oscillator (Figs. 29, 30, and 31). Figure 29 shows a close-up of the 37 Mc amplifier. This whole amplifier section can easily be removed by removing the four mounting screws, two of which can be seen. Next to the last mounting screw the small heat sink is visible, that fits over the transistor case. This heat sink is electrically insulated from the package mounting plate by a square piece of teflon. The heat sink acts as support and spacer for the 37 Mc amplifier mounting board. The tuning capacitors (Figo 28, item 1) are mounted on this board and can be tuned through holes in the package mounting plate. Figure 30 shows a close-up of the 148 Me transmitter and the telemeter generator. The same construction is used for this section, with the transistor heat sinks acting as spacers and supports for the mounting board. To withstand flight conditions the amplifier components are surrounded by plastic foam*. A foamed-in package ready for flight is shown in Fig. 31. Notice also the package heater mounted on the aluminum shell, consisting of several *E-P-Fome with 270 catalyst. Electronic Plastics Corporation, New York. 39

"i.~~~~~~~~~~l | | | | | |. ~~~~~~~~~~~ ~ ~ ~~~~~ ~~~..:.......; itg::;; yg i:;..: l''....................W~~~~~~~~~a~~~~~~.i~~~~~~~~,~~~~~~~.aE v,~~~~~~~~~~~~~...... ~~~~~~~P~~~PX~~~~PI ~~~~~~pl~~~~.^8~~~~~ 4-X ii. L3~~~...... - W - ] - - ~i s:iii8:a M:ir | i s E E:i EERE.S S k E: | | | | l l | i:E i: -- 2EryTEEEziC iLERE:EES - f\. 00.... s;9'->%f? — i-..... - --- R...................................... 9? i:':U. 6. -'. i~~............. ".......?d irii k~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~r(~~~~ii ~~~~~~~~~~~~~~~~~~~ig~~ -.,.?'RtB1I,' 2-.. 4s tR iig~~ Ifv???-.................:..:..-?g|??i?,............... 5SR'? g i i..................,' ": i::i E ~:: — W,:~:.-' ~ v:......................................::.:. -i2 -'?...... A F.....................:. 9................-...:...........& L.....Sl_ Ri.9 | R...i j:i E c.......-.-. j.....i.......:.......... 9~~I 0i ~-Ei`I I::?d___......................I._i ~~~~~~~~~~__:_j:: 5...........................................................29 - -_ _rii> -9i1 i. _ |C I.......:::::::::::'...':......?, iC-:% ~- - -:99:ltI8'- I L),sB~~8~~r............~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~Ezj99.....iE.-gi~t-E2-i jgE i66Z-0?&0>>0Eg ifi~~~~~~~~~~~llll ~ ~ ~ igiicne e~~~~-~~~qs~~~~e. ~~~~~ 8~~~aaa~~~~~~Pl~~~~,~~~r~~~:~;~~~~~:??j&Ri9-~:-:ij:i~: ~.: —-. B88B 86I~g IBB&BEli:~lj~~ ji g-.i9 &,&?g9,i2:-:4ig - 9 | -—: H —?t-EE:- iBi.. E:Ei::. E E i:?9 9t16?>::g9?j? - -g _ Eii: -_-ii 9i il0IQ _~~~~~~~~~~~~~~~~~~~~~~~~~~~~ _ s _ i? 4 I 40~~~~~~~~~~.~~~~~~~~~~~~~~~~..... q_......'-..?. ~~ ~~~~~~~ ~~~~~~~~~_..................?i:_8..i. _ ~~~~~_ — _........:i....lr& Z_............. ~ ~ ~ ~ ~ ~ i........;o.... ~~~~~~~~~~~~~~~~~~~~:~ 0 —................................................................8s|................t...........< _.................................... ~~~~~~~~~' ii................................................in IL ~~~~~.............''; F........_..a. _- "| -X ~~~ _......... f~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~....g_ _.-......-98.........,stii9[j -.....SCi'R........... 9?' _., -gfg~ — -S_?i9 fs ___i9'-i iA i.................................................................................................i.

...........W poll:Militia: ki.................................. Z.1: p F:;activists...................................!F-7.00.......... 0 2 INCHES Fig. 30 View of 148 MC Amplifier and Telemeter Generator

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~...... H r%4 -4-) r4-.,i...... XIL.~~~I~ i?!?!?'i I............... PI); I nn,,,,,, AD ~~~~~~~~,i:,,, iIti~~i; alkali!~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~iiiii~iii~iiii 42 * * -,: -'-,','.B <-:. c-'l...........................::::' -i:: B B B:'', g:::' -:t''a'BBB —'.................. 4 l d vW <~~~~~~~~~~~ gk,,r HN g do~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~y~~~~~~~~c; fg >~~~~~~~~~~~~~~~~~~~~0 <,:liv -"E B o l; g i,-iiz', g<.~z.i~: i, R; Bg: g, -;gH:,,-B,, B~t,,, #. B f -.............. Bi t- B.............-, E S i -— E:, —:, B' & "B"' 1 7 l'':::' 0.'~ i;'" —: i,,,..g, E. f~............ ~; <,,i:;g::':g "'''gg;:;'''*,. B.'B-.42- g.-':,' -

turns of resistance wire taped to the outer surface. to make contact with the nose-cone thermistor.

-id ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~........ I I I i r. J........:.. Fig:32Outsi Vew oBeacon:A:ssml 44.. I..INCHES

5. THERMAL CONSIDERATIONS 5.-1. THEIRMAL DESIGN OF BEACON PACKAGE The two major problems in the thermal design of the beacon were (a) to produce an environment having temperature limits within which the mercury batteries, transistors, and other components can operate dependably, and (b) to produce a closely controlled temperature environment for the crystal oscillator so that a high degree of frequency stability is achieved. Satisfactory component operation requires that the temperature remain between 5 and 750C. This environment is furnished by the large thermal capacity of the beacon top plate., shell.,and antenna (items 135, 14., 15., and 16 in Fig. 28). In addition., heat flow from the hot., burned-out rocket bottle is minimized by the fiber~glass,-ring (item 19) and teflon plate (item 20). Because teflon is transparent to a large portion of the infra-red spectrum., radiation shields (item 22) of one mil aluminum foil are added to stop radiant heat from entering the package from below. To produce a closely controlled temperature environment for the crystal oscillator, the heat of fusion principle was used. If the liquid and solid phases of a pure material,, such as water, are present in thermal equilibrium., the temperature remains at the melting point. If heat is added or withdrawn from the container., its temperature will depart only slightly from the melting point., and by an amount sufficient to establish the required gradient between the container and the melting or freezing interfaces of the two phases. Since water gave an unsuitably low operating point., the material used was a- eutectic alloy,* Cerrolow 117. The properties of this alloy are as follows: Melting point = 470C (1170F) Heat of fusion = 5.55 calories per gramn Density= 8.85 grams per cm3 Specific heat = 0.035 calorie per 0C per gram The alloy chamber (item 11, Fig. 28) is filled with approximately 500 gramns of alloy,, allowing a small air space for expansion on melting. Thus approximately 1000 calories of heat can be absorbed by the oscillator case without any ap

Ka =OD Kc Ko Gca Goc ACA CASE OSC. NOSE CONE Gcb Gob IIBANTENNA ROCKET BOTTLE INSULATOR Fig. 33 Heat Exchange in Nose-Cone Assembly

preciable chaoig in temperature. The crystal is located, in the crystal well (item 10, Fig. 28) so that it is almost completely surrounded with alloy. The entire case is surrounded by a blanket of plastic foam (item 12) acting as an efficient thermal insulator, while being strong and rigid for mechanical support. With this construction., and the heat exchange rates anticipated during flight, the crystal temperature is maintained within approximately ~ 0.10C of the melting point. 5.2. HEAT EXCHANGE AND THERMAL CONSTANTS Heat exchange in the nose-cone assembly may be understood with reference to Fig. 55. Various items to be considered are diagrammed on the left while the important thermal masses and conductances are symbolized on the right. Subscripts a, b, c, and o refer respectively to the ambient air, the empty rocket bottle, case and antenna assembly of the beacon, and the oscillator unit. For a systematic treatment, the following symbols are used: Symbol Quantity Units K Thermal capacity small calories/OC A Heat flow calories/mmn Q Temperature 0 Time derivative of OC/min temperature G.. Thermal conductance calories/min per'C between i and j temperature difference between i and j Wx External electrical* watts heat input, The basic equation for heat flowing into a body, i, is as follows: Ai Ki~i GiZ j (Qj - oi) + 14.5 Wx*(6

200 - _ __ ___ __ 0 z (D ~~~~~CUMULATIVE HEAT H* w 0 ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~.0 w F- 200~~~~~~~~~~~~~~~ 100 0 -40 -too 0 5 1 0 1 5 2 0 2 5 MINUTES FROM LIFT OFF-* Fig. 34 Cumulative Oscillator Heat During Flight

Using experimental data taken both in the laboratory and on the launcher, and a suitable form of Eq. 6, the following values for the thermal constants were found: Gob =0.151 calorie/min-0C Go 0.575 calorie/min-oC O'C ~~~~~~~~(Note 1) Gcb 0.82 calorie/mrin-0C Gc 8.7T ~ 1.0 calories/mrin-0C K0 52.5 calories/OC (Note 2) Kc 250 calories/OC (Note 3) K 0 a Kb 550 calories/OC (estimated) Note 1. Values of conductances are for sea level. For vacuum flight, these values will be somewhat smaller. Note 2. This value holds both above and below 1f70C. However at 4-70C, K. is essentially infinite so long as the alloy is present in both solid and liquid phases. In this case approximately 1000 calories of heat may be added to the oscillator case with essentially no temperature change as previously explained. Note 5. This checks closely with the computed value for the case and 1760 gram brass antenna. Thermal capacity of the case without the antenna assembly is 94i calories/OC. 5.5. HEAT EXCHANGE DURING FLIGHT Probably the most important thermal aspect of the flight is oscillator temperature control. This section will therefore be concerned with heat exchange between the oscillator and its immediate environment. At the time of take-off it will be assumed that the oscillator is at its operating temperature,, and that sufficient of the alloy is melted to take care of any heat loss in the early part of the flight. It will be further assumed

TABLE I PREFLIGHT PREPARATION OF BEACON TRANSMITTER PACKAGE Step Time Operation Comments No. "T" minus 1 --- Full power applied to case and. oscil- Safety and circuit lator heaters and transmitter for 15 check. seconds. 2 --- Residual case heat applied to main- Beacon batteries not tamn case temp. at 10 to 12'C. dependable below 50C. 5 2 hr Case temp. raised to 355C. To store reserve heat. 4 --- All heaters off during arming of Safety measure. rocket. After arming completed, case temp. noted and residual case heat applied as necessary to maintain case temp. at 10 to 120C. 5 40 mmn 8 watts asc. heat applied. Osc. Checks indicated melttemp. noted until alloy begins to ing temp. on control melt at 470C. Heat on for further panel. 15 seconds then removed. 6 50 mmn Osc. temp. noted; when it drops to Temp. now close enough 450C, osc. heat finely adjusted to for frequency check. maintain this temp. Power noted. (1.7 watts for Nov. 10) 7 8 mmn Full osc. heat (17.5 watts) applied Net heat added for until 9o= 470C (alloy begins melting) melting alloy = 570 and for an additional 100 seconds. calories. 8 6 mmn After step 7, osc. heat dropped to Sufficient to furnish 1.8 watts and held at this level. osc. heat loss at 470. 9 3-1/2 mmn All circuits disconnected from nose- Osc. begins losing cone assembly. heat at 26 cal/mmn. 10 3 mmn Pull nose-cone umbilicus.

Heat flow into the oscillator is given by Eq. 6., i.e.., H0 G0c (Gc - GO) + Gob (9b- GO calories per minute (7) = 0.575 (G - 47) + 0.131 (G-b -47) calories per minute (7a) The cumulative oscillator heat 0* from take-off to +t minutes is obtained by integrat ion: * ~t. H0(t Hof dt (8) 0 Figure 34 also shows a plot of cumulative heat H0 found from Eqs. 7 and 8. It is seen that during the first minute of flight., 26 calories of heat are extracted from the oscillator. Thereafter, although some heat is lost to the case (for the first 8 minutes)., more heat is acquired from the hot rocket,, giving a net gain in heat for the remainder of the flight. At the end of 25 minutes (approximate time of splash), 530 calories of total heat have accumulated. Since this is well within the caloric capacity of the melting alloy, i.e.,, 1000 calories, the temperature of the oscillator remains constant at 470C throughout the flight. 5.4. PREFLIGHT THERMAL PREPARATION The paramount feature of preflight thermal preparation is the insurance that at take-off, sufficient alloy in the oscillator is melted to furnish heat losses for the first minute of flight., while leaving a sufficient reserve of solid material for the remainder. Since the umbilicus is removed at T-3 minutes, and a safety margin of 10 minutes is desirable in the event of a hold in countdown after removing the umbilicus., sufficient alloy was melted to sustain the oscillator temperature at 470C for about 14 minutes. Details of the thermal preparation are itemized in Table I. The table indicates a thermal reserve of 280 calories at firing time., which allows for a possible hold in coumtdown., a reserve for the first minute of flight., and any possible errors in computation. Referring to the previous section, the oscillator accumulates 530 calories from firing until splash. With the above preparationwe have 280 + 530 = 810 calories, which leaves a flight margin of 190 calories before the 1000 calories of fusion heat are consumed. A seco,,nd fe-Ature of,, -prefigh thermal - k I contro l, whc appl-IesonyAurn

~ 5 ~4 THERMISTOR #15 VECO TYPE 32A84 o -13 R8 -I.55 KAT 30 C (D ~~~~COE F. -3.90 PER'C z +t2 I — z 0 0 0 -2 -3 -4__ _ _ _ __ _ _ _ 0 20 40 60 80 INDICATED TEMPERATURE 0C Fig. 35 Typical Correction Curve For Temperature Circuit

In the case of f iring in sunny, hot weather., nose -cone temperature control would be required to keep the package temperature within reason. For conditions of little or no wind, and ambient temperatures below 355C (950F), a light-weight radiation shield of metal foil could be used. This could be pulled off with the umbilicus. 5.5. TEM~PERATU7RE MEASUR~EMENT AND CONTROL To indicate package (case) and oscillator temperatures of the beacon while on the launcher., temperature circuits were used in the ground station heater control panel. The circuit diagram of this is shown in Fig. 15. At the upper left, the package temperature circuit is seen to be a bridge circuit., the Type 32A84 VECO thermistor in the beacon package being connected to terminals 1 and 3 via the umbilicus and 1500-foot ground cable. The temperature is read directly with an accuracy of ~ 10 between 15 and 750C. For more accurate readings', a correction curve., Fig. 355, may be used. Calibration of the circuit is performed by connecting two preset*.. res~istance boxes to jacks J12 and J13., and adjusting RI, and RB2 until correct readings are obtained at 20 and 40'C in switch positions 15 and 4. Two variacs on the heater control panel, Fig. 15., gave continuous control of heater power to the oscillator and package heaters. The indicating amnmeters were calibrated in terms of the actual load currents flowing in the package., so that the wattage input to either heater was accurately known at all times.

50O ~~500 r_______COMPUTED INNER SURFACE TEMPERATURE NEAR NOSE TIP (DOUGLAS AIRCRAFT CURVE DATED 25 AUG. 59) 250 LU z ua 400 400- 200 wJ L I (.9~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~( uJ 300 ~ 18 o C 1 o(iAT5D SCNS( CAERECE Lt z o ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~z QP OBSERVED TEFLON -PFIBERGLASS TELEMETER R I INTERFACE TEMPERATURE 28.80 INCHES ~O uJ 200' u5 POINT OF TELEMETER RECOVERY PLANNED TELEMETER CUTOFF OCCURRE u AT 500.8 SECONDS. (PACKAGE REACHED F- ~~~~~~~~~~~~~~~~~~~~~~~~47 O~C )n A SECONiDS FROM LIFT- OFF Fig. 36 Nose-Cone Temperature History I~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~00 36~F AT LIFT- OFF-0 0 0~~~~I0 2_00 300 400 500 SECONDS FROM LIFT-OFF Fig. 36 Nose-Cone Temperature History

6. RESULTS OF THE NOVEMBER 10 FIRING The firing of 10 November 1959 gave so much data that results on electron density profile are not available at this writing. However the telemeter record has been completely reduced, which gave the following results. 6.1. NOSE -CONE TEMPERATURE HISTORY Figure 56 indicates the nose-cone temperature for the first 500 seconds of flight. The temperature was measured at the interface between the teflon coating and the fiberglass at a point 28.80 in. from the nose tip. The telemeter record indicates an open thermistor circuit for the first 76 seconds,* but at 77 seconds from lift-off., the circuit recovered and valid data were- received. The temperature reached a maximum of 1580C (5160F) at about 100 seconds from lift-off. 6.2. BEACON-CASE TEMPERATURE HISTORY Although only two points on the curve were obtained, a rough estimate of the temperature may be made as shown in Fig. 57. The point at 500 seconds was obtained by the planned telemeter cutoff which occurred when the beacon case reached 470C (see Section 4.6). 6.3. SIGNAL DRO.OP AT 57 MC Starting at about 57 seconds and ending at about 47 seconds, a droop of about 6 decibels was noted in the signal level as received by the Aberdeen and Wallops ground stations. During this period the inside pressure of the nose' cone is changing from about 0.4 mm Hg to about 0.004 mm. This is a pressure range in which electric breakdown at rf is likely to occur if the voltage is sufficiently high. The rf voltage at the upper gap of the 57 Mc antenna with an input of 0.1 watt is 52.5 volts., and this is adequate to initiate a glow discharge. The signal droop is therefore attributed to rf breakdown of the air within the nose cone.

I00 80k - - - - - - x SPLASH 1515 SEC w60 -.~ 0 200 400 600 800 1000 1200 1400 1600 SECONDS FROM LIFT-OFF Fig. 37 Estimated Beacon Case Temperature i DATA/,G w 40!KON~. zo A 0 200 400C 600 800 I 000 1200 14(0100 SECONDS FROM LIFT-OFF Fig. 37 Estimated Beacon Case Temperature Histo.ry

7. CONCLUSI ONS The beacon package described above is considered a highly satisfactory design for high thrust rocket experiments. Although the design is quite conservative., both mechanically and electrically, no great reductions in weight., except for the antenna., could be made without sacrificing some aspect of performance or dependability. Germanium transistors performed satisfactorily over the temperature range 0 to 80'C. For extended temperature ranges and more power (up to 1 watt at 57 Mc), silicon transistors could be used. However no suitable silicon transistors were available for the 148 Mc amplifier at the time of its design. A high degree of frequency stability is obtainable in the adverse rocket environment by the use of a properly cut crystal, and the heat-of-fusion method of temperature control. In the November 10 flight, the crystal temperature was maintained within ~ O.10C, giving a frequency stability better than one part in 108.

8. ACKNOWLEDGMENT The success of this project was in no small measure due to the cooperation and assistance received from various members of the staff of the Ballistic Research Laboratories, The University of Michigan, and the Wallops Island Station of the National Aeronautics and Space Administration. In particular we wish to thank Messrs. W. W. Berning, V. W. Richard, and C. L. Wilson of the Ballistic Research Laboratories, and Messrs. N. W. Spencer, W. H. Hansen, and F. F. Fischbach of The University of Michigan.

9. PERSONNEL Nelson W. Spencer Project Director Lyman W. Orr Task Engineer Pieter G. Cath Research Associate Bruce R. Darnall Technician Ancil S. Zeitak Technician 61

DISTRIBUTION LIST Ballistic Research Laboratory 25 Aberdeen Proving Ground, Maryland Attn: Mr. Warren Berning Detroit Ordnance District 2 574 East Woodbridge Detroit 31, Michigan Attn: Mr. Skeffington The University of Michigan Ann Arbor, Michigan Nelson W. Spencer 2 Lyman W. Orr 2 Pieter G. Cath 2 Electronic Defense Group file 2 Engineering Library 1 Research Institute file 1

UNIVERSITY OF MICHIGAN l!l3 901lll 0369l 55!84II