I AD-A092 886 SANDIA LABS ALBUQUERQUE N MEX EXPERIMENTAL SYSTEMS DIV F/6 9/1SATELLITE 9441 20 WATT TBTA ANOMALY REPORT(U)APR 80 P H FOWLER F04701-80-C-002Z

UNCLASSIFIED TRW-36060-AR-021-R1 SD-TR-80-36 NL

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SECURIT YOSSIFICATION OF THIS PAGE (*%lin Vale Entered),__________________t ~ READ INSTRUCTIONSRPORT DOUMENTIM ON PAGEu BEFORE COMIPLETING FORM

2GOVT ACCESSION NO. 11. RECIPIENT'S CATALOG NUMBER

_VM M STR8-364. TITLE (and Subtitle) TYPE OF REPORT _! PERIOD COVERED

K Satell ite 9441 ZO0 Watt TWTA Anonidly Report. Final .Aepfft3 . /

t Jf~/ 36OW0-AR-021.7.-e ReYefr*wUMBRs

P. H./Fowler ( / E47901 CW2.9. PERFORMING ORGANIZATION NAME AND ADDRESS 10. PROGRAM ELEMENT. PROJECT. TASK

TRW Defense and Space Systems Group/ EAoITU ER

One Space ParkRedondo Beach, CA 90278

11. CONTRO LLIN'I ('cFICE NAME AND ADDRESS 12. REPOST-DATS -

Space DivisionDept. of the Air Force Headquarters 00 "toweF11PnESP. 0. Box 92960, Los Angeles, CA 90009 1

14. MONITORING AGENCY NAME & ADDRESS(it different from Controlllnd 0Office) 15. SECURITY CLASS. (of this report)

Unclassified1s. DECL ASSIIlCATION'DOWN GRADING

SCHEDULE

16. DISTRIBUTION STATEMENT (ofthis,1 Report)

Approved for public release; distribution unlimited.

17. DISTRIBUTION STATEMENT (of the abstract entered in Block 20, If different troin Report)

IS8 'UPPLEMENTARY NOTES

I' IS. KEY WORDS (Contnue on reverse aide it necessery and Identify by block numnber)

Travelling Wave Tube Amplifier, DSCS II, Satellite 9441

P 20. -A(3S;RACT (Continue, oni revere aidsItnecesary mid Idenifyby bonumber)iuain' scie h>Prsens te rsuls o aninvestigation of the cause of failure of a 20 watt

falr otepwrsppy(o h ue n suggests a probable cause.

DD 1 1473 EDITION Of I NOVB I5S1 OBSOLETE Unclassified ~1

///~ "~/SECURITY CLASSIFICATION OF THIS PAGE (Stion Date Entered)

SATELLITE 944120 WATT TWTA ANOMALY REPORT

Report No. 36060-AR-021-01CDRL No. 009A2F04701-80-C-002215 April 1980

Prepared by Approved byP. H. :owler F. R. Cartier

Commu ications SPM ManagerDSCS I Project DSCS II Project

Approved by4 2Q- /i Approved bynI. H-. AlbornA.PFa

Orbital Operations Satellite EngineeringManager APM

TRWBrwIN'cmva

CONTENTS

Page

1. INTRODUCTION 1

2. TELEMETRY INDICATIONS 1

3. BUILD AND TEST HISTORY 1

4. DIAGNOSIS 1

5. POSSIBLE FAILURE CAUSE 4

6. CONCLUSION 4

TABLE I 2

FIGURE 1 5

APPENDIX I 6

Accession For

NTIS GRA&I7DDTIC TAB

Urann ounced 0

Justification-

Distribution/

F v__._le t tY Codes'Avail and/or

Dit Special

-1

----------------------------

1.INTRODUCTION

At 0240 hours (Zulu) on January 25, 1980, narrow coverage highlevel amplifier "B" ceased operating. This is Model 1202 AmplifierSerial Number 24-27, containing TWT SN 527. The unit, per standard

contingency procedure, was commnanded "on", did not respond, and wascommnanded "off" and the "A" unit turned on.

2. TELEMETRY INDICATIONS

The last previous pass showed telemetry readings essentiallyidentical with the amplifier acceptance data. After conmmunication

was lost, the unit telernetries were as shown in Table I. Theindication is of a unit with no high voltages on, slightly low

filament voltage, and a corresponding low input power.

3. BUILD AND TEST HISTORY

There is no comparable failure recorded against this or anyother Model 1202 Amplifier, at Hughes (manufacturer of the amplifier),TRW, or in orbit.

Tube 527 had a single hi-pot trip at the cathode in manufac-

turing test. This is considered acceptable if two retests show

no repeat, which was the case.

There is one failure report recorded for this unit, V29938.This documents a failure to turn on ascribed to an open IN4148 diode.

The semiconductor module was replaced. Through the F12 build,compression bonded 1N4148's were used. Two modules were replaced

in 1200 (low level) amplifiers for similar problems and separatetest of the parts showed a tendency to open or partially open underthermal cycling. F13 and subsequent build uses metallurgically

bonded parts which are not subject to this failure mode.

4. DIAGNOSIS-1 The nature of the failure can be explored by first eliminatingcauses which could not produce the observed symptoms. Appendix I

shows relevant test results obtained by Hughes in support of this

report.

TABLE INORMAL VS FAILED DATA, TWTA S/N 24-27

RECORDED TLMTLM TRANSLATED

VOLTAGES VALUES NORMALFUNCTION (POST-FAILURE) (POST-FAILURE) VALUE

CATHODE .22 V 3446 V* 3805 VVOLTAGE

CATHODE .04 V .55 mA* 53 MACURRENT

FILAMENT 3.74 V 4.98 V 5.6 V

VOLTAGE

HELIX CURRENT .06 V .07 mA* .7 mA

INPUT CURRENT .3 V .36 A 3.2 A

PLATFORM N.A. 68.5 OF 92* FTEMPERATURE

Indication is characteristic of zero actual value.

2

a. Short circuits at the tube (or high voltage wiring)

produce excess input power or trip the input

overcurrent protect. By test, Table I-I and 1-11, the ampli-4 fier trips with 160 ko to ground at the collector, 400 ka

to ground at the cathode. Up to the trip point the

amplifier will operate, drawing excess input current.

Since the amplifier has not tripped (filament voltage

is still "on") and is not drawing excess current,

the problem is not a high voltage short.

b. The low filament voltage shows the unit is not in a

normal warm-up mode.

c. The combination of low filament voltage, lack of high

voltage, and low input current shows the unit does not

have a failure in the filament supply.

d. The existence of any filament voltage and the low

input power shows the unit does not have an excess

load on the 17 or 19 volt bus.

A reasonable possibility remaining may be seen by noting that

the only way to get a low filament voltage with the above limitations

is to assume the 19 volt bus has dropped to below 17 volts, e.g.,

to about 15 volts. Under this condition the high voltage section

will draw approximately 0.5 amp or less current, and all the symptoms

match. While analysis beyond this point must be speculative, Hughes

has developed a reasonable hypothesis which explains the failure in

terms of previous history as follows. Since a 1N4148 failure was a

likely possibility, tests were performed to show the effect at each

circuit location. Results are shown in Table I-III.

3

5. POSSIBLE FAILURE CAUSES

Table II contains a brief summary of possible failures with comments as

to the possibility and/or probability based on the symptoms gathered fromTable I.

Referring to schematic B200350-210 Sheet 2, a portion of which is

shown in Figure 1, it will be noted that the 19 volt bus voltage regulator

is controlled by the impedance of A4-CR3 (zone D12). CR3 is a 1N4148.

Ifit should fail to a high impedance (apoiael .k) the 19voltbus is controlled to a low voltage. The switching regulator transistor,

Q8 (2N3599) (zone CM4, then runs in a linear mode at high power and thus

fails. Hughes part specialists advise that the likely failure is to afixed relatively high impedance (approximately 9n). The 19 volt bus is

then permanently at a low (random) voltage and the observed symptoms are

observed.

The symptoms were duplicated by Hughes by setting up the above sequence

of events in the breadboard power supply. Table I-IV A, B and C show theresulting amplifier behavior.

6. CONCLUSION

The failure appears to be an isolated occurrence. The most likely cause

is a failure in a part not used in later builds. The current production40 watt amplifier has little in common with the 20 watt design. No furtheraction is recommended as far as the DSCS II high level amplifiers are concerned.

It was noted during this analysis that a small change in Orbital Operating

Procedure would provide extra diagnostic information in the event of anomalous

amplifier behavior.

To date, the practice has been to command an apparently failed amplifierlion" (without sending "off"), to check that the unit has not been inadvertnetly

shut down by the satellite. If this produces no result, the redundant unit is

commanded "on".

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It is proposed that the following sequence would provide more information:

While recording telemetries;

A. Command the "failed" unit "ON".

B. If unit fails to come "ON", send "OFF" command.

C. Transmit "ON" command timed to filament voltage

readout (20W TWTA's only), and after waiting between

30 to 60 seconds, transmit the "OFF" command.

D. Switch to the redundant unit.

7

APPENDIX I

Ref: TRW Report No. 36060-AR-021-01

As an assistance to TRW's investigation of an anomaly involving 1202HA

IWTA S/N 24-27 on DSCS IIR Spacecraft 9441, a series of tests and

analyses were performed at Hughes, EDD.

The tests performed were centered around:

a) Simulate a shorted collector-to-ground

b) Simulate a shorted cathode-to-ground

c) Simulate an "open" IN4148 diode

d) Special situation simulations

The tests were performed on the 1202H1A breadboard, wherein, the Helix

overcurrent trip had been disabled and the input current trip left

enabled (as per the units on 9441 and 9442), and using 265HC TWT

S/N 511 as the load.

Tests (a) and (b) were performed by placing a decade resistance box in

parallel with the particular element and reducing the resistance. The

results of these tests are shown in Tables I - I and I - II, respectively.

As can be seen from the data, the input current increased until the input

overcurrent protect circuit tripped.

Test (c) was performed by allowing the unit to "time-out" as normal,

then opening the particular diode. The results are shown on Tables

I - IliA and I - IIIB. Of particular note is the data on the first

line of Table I - IIB, A4-CR3. This data was near enough to the

telemetered data from Spacecraft 9441 that it was investigated further

to see if a particular failure mode could even more closely approximate

the Spacecraft data. The results are shown in Table I - IVA.

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Again using a decade resistance box, the series resistance of A4-CR3

was increased until a malfunction was observed. This occurred at

1.57 Kohm, but again the data did not exactly simulate the orbital

data. The main switching transistor, SC-Q8 was observed to begin

overheating and it was hypothesized that this could eventually damage

tile transistor, causing a "high" C-E resistance. (In a subsequent

test, the case temperature was actually caused to climb in excess of

230°C -466°F - and while the breadboard unit survived this tempera-

ture for several minutes, it is only a sample of one and is not

configured in the same manner as a flight unit.)

A value of 9 ohm was added in series with SC-Q8, with the results

shown in Table I - IVB. Previous test data observed by HEDD components

reliability personnel have shown that both the 1.57 Kohm and the 9 ohm

values are quite typical failure modes for these components. (SC-Q8

is a ?N3599 with a C-E resistance of 0.1 ohm maximum.)

Scveral other tests were performed on various components but none of

the results showed the interrelationship and resultant data nearly as

oll as the test described above. (These test data are available in

the anomaly log book for review.)

'utrther. since the information received from TRW indicates that this

anomalous state continued for "hours" versus "minutes", it is reasonable

to assume that SC-Q8 is now irreversibly damaged, even though A4-CR3 may

"heal" itself, and the TWTA cannot be successfully turned back on. This

is shown in Table I - IVC, wherein only the 9 ohm is left in series with

SC-Q8 and the unit was observed to continuously time-out and recycle to

zero.

9

rt

ABBREVIATIONS/NOMENCLATURE GLOSSARY

Designator Description

At Converter Board (B200365-XXX)

A3 Logic Board (B200364-XXX)

A4 Regulator Board (B200363-XXX)

SC Semiconductor Module (B200362-XXX)

EK Cathode Voltage

Eb Collector Voltage

Ehtr Heater (Filament) Voltage for TWT

E.S.R. Switching Regulator Voltage (Main Internal Bus)

L. BUS Linear Bus Voltage (for Heater Supply)

Iw Helix Current

A4-CR3 Diode NR. 3 (A 1N4148) on the A4 Board

SC-Q8 Transistor NR8 (A 2N3599) on the SC Chassis

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