Solid state timing apparatus to disconnect solar cells from batteries after two year perio

Clem, T. D.

English

NASA Technical Reports Server

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TMX-55019 
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,THE EPE-D TWO YEAR TIMER 
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N 6 4  2 7 2 5 3  
1 
APRIL 1964 
, I  - GODDARD SPACE FLIGHT CENTER 
GREENBELT, MARYLAND 
OTS PRICE I 
, 
XEROX $ f LO n h h  I 
i MICROFILM $ 
https://ntrs.nasa.gov/search.jsp?R=19640017339 2020-03-24T06:29:08+00:00Z
. THE EPE-D 
T W O  YEAR TIMER 
Prepared by: 
T. D. Clem 
Programmers  Section 
Flight R-F  Systems Branch 
Approved by: 
H. J. Peake 
Branch Head 
TABLE OF CONTENTS 
.. FOREWORD . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  11 
S U M M A R Y . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  iii 
GENERAL FUNCTION AND DESCRIPTION . . . . . . . . . . . .  1 
BASIC TIMING CIRCUIT OPERATION . . . . . . . . . . . . . . .  1 
. . . . . . . . . . . . . . .  TELEMETRY MONITOR OPERATION 3 
SPEED U P  AND CABLE DRIVING OPERATION . . . . . . . . .  10 
DATA INTERPRETATION . . . . . . . . . . . . . . . . . . . . .  10 
POWER REQUIREMENT . . . . . . . . . . . . . . . . . . . . . .  12 
ACCURACY AND STABILITY . . . .  . . . . . . .  . . . . . . . .  12 
COMPONENT RELIABILITY CONTROL 
ANDUNIT TESTING . . . . . . . . . . . . . . . . . . . . . . .  13 
PRELAUNCH TESTS AND MONITORING . . . . . . . . . . . . .  13 
4 
i 
FOREWORD 
. 
This document i s  intended for general  descriptive pur-  
poses only. It i s  a guide for those who needor  wish to  know 
the general  c i rcui t ry  and the specific functional operation 
of the Two Year Timer in relation to the spacecraf t  during 
testing and flight. No attempt has  been made to present  
detailed theoretical  o r  circuit  analysis. 
I 
4 
.. 
11 
. SUMMARY 
A solid s ta te  timing system used to disconnect the solar  
cells f r o m  the batteries after an intervalof two yea r s  is de-  
scribed. The basic timing principle is discussed,  as well  
as  the circui ts  used to provide te lemetry monitoring of the 
timing system performance. The c i rcu i t ry  for  providing 
blockhouse testing and monitoring of the sys tem i s  shown, 
along with an explanation of the precautions taken to isolate 
the tes t  c i rcui t ry  f r o m  the actual timing sys tem after tes t -  
ing. Examples and the interpretation of the information 
received during testing a r e  given. Finally, expected te lem-  
e t ry  monitor readout during the complete two year  period 
is tabulated. 
. 
iii 
GENERAL FUNCTION AND DESCRIPTION 
The miss ion  of the EPE-D Two Year Timer  is to disable the pay- 
load so that t ransmiss ions  will cease af ter  a period of approximately 
2 yea r s  f r o m  launch. 
magnetic la tch-relay contacts which connect the so l a r  ce l l  panel and 
the battery.  
cui ts  which independently operate two latch relays.  Connections a r e  
made to the re lays  such that both re lays  a r e  requi red  to operate  before 
the solar  cel ls  a r e  disconnected f rom the battery. 
This is accomplished by opening normally-closed 
The t imer  consis ts  of two identical, para l le l ,  timing c i r -  
F R E E  
VOLTAGE RUNNING PULSE 
UNIJUNCTION AMPLIFIER -b 
OSCl L L A T O R  IN 
BASIC TIMING CIRCUIT OPERATION 
c 
INCREMENTAL SCR 
M AGN ET1 C POWER L A T C H  
CORE DIVIDER -b PULSE RELAY 
e20 x 106 FORMER 
A block diagram of the basic timing c i rcu i t ry  is shown in  F igu re  1. 
The power for  the c i rcu i t ry  i s  obtained through a voltage regulator 
operating direct ly  f rom the spacecraft  t19.6 volts bat tery line. The 
t iming pulses a r e  derived f r o m  a unijunction t rans is tor  acting as a 
relaxation oscil lator.  
before entering the magnetic core divider. 
The pulse output of the unijunction i s  amplified 
An output f r o m  the divider 
occur s  af ter  20 x l o 6  inputs. This output pulse then f i r e s  a silicon 
controlled rec t i f ie r ,  used as a power pulse- former ,  which in turn  ener - 
gizes a magnetic latch relay.  Figure 2 shows this basic timing c i rcu i t ry  
in a schematic diagram. 
I 
Figure 1-Block Diagram of Basic Timing Circui t  EPE-D 
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Figure 3 shows two basic timing circui ts  connected to fo rm the 
Two Year Timer.  
except a t  the battery power input. 
The two timing circuits a r e  completely independent 
I 
TELEMETRY MONITOR 
Figure 4 is a block diagram showing the operation of the te lemetry 
monitor incorporated into the t imer units a s  well a s  the re lay  wiring. 
The monitor is a flip-flop which operates f rom cer ta in  intermediate 
outputs of the core  dividers and which acts  to provide a shunt to ground 
to a section of a voltage divider network in the encoder. 
network then furnishes voltage to a voltage controlled oscil lator whose 
frequency is sampled and transmitted in the te lemetry information. 
This divider 
b 
Figure 5 depicts the operation of the te lemetry monitor flip-flop 
upon the voltage divider network in the encoder. 
pulses f rom t imer  A o r  the 39 day pulses f rom Timer  B will operate 
the flip-flop of Q7 and 0 9 .  Q8 of this flip-flop in turn  causes  Q l O  to be 
on o r  off and hence short  the 10K encoder r e s i s to r  to ground or  leave 
it open. 
actuated and the res i s tor  RA is connected in s e r i e s  with the 10K encoder 
r e s i s to r .  
other  contact of Relay A, acting as  one of the paral le l  Solar Cell-Battery 
Connect switches, i s  also opened a t  this time. 
Either the 36 day 
This operation pers i s t s  for 720 days. At this t ime,  Relay A is 
The operation of QlO and the flip-flop remain the same.  The 
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pp8 1 B )-zF\ 5.6 K ENCORDER 
F R O M  TIMER"B" 
AT 720 DAYS A T  780 DAYS 
3 9  DAY 
PULSES FROM 
TIMER "B' 
36 DAY PULSES 
FROM TIMER l l ~ * '  
Figure 5-Two Year Timer Switching Sequence EPE-D 
4 
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Resistance Switching 
Figure 5 
Open to 10K 
Open to 10K + R A  
5.6K (10K t RA) 
5.6K t l O K  t RA 
5.6K to 
At T=780 days, Relay B is actuated. With this,  the 5.6K encoder 
r e s i s to r  is connected to ground through one se t  of the re lay  contacts. 
The other set  opens the remaining Solar Cell-Battery Connect switch 
and completes the disconnect of the Solar Cells and Battery.  When 
this occurs ,  the life of the spacecraft depends solely upon the remaining 
capacity of the battery. 
Voltage Level Switching Relay Relay 
Figure 6 "A" "B" 
1 to 3 Closed Closed 
1 to 2 Open Closed 
4 to 5 Closed Closed 
Table I summarizes  the switching sequence of the Timer.  The 
column labeled Resistance Switching is mere ly  a l is t  of the switching 
sequence of the r e s i s to r s  in the encoder voltage level network. 
column labeled Voltage Level Switching r e f e r s  to the curves shown in 
F igure  6. The re ference  voltage of the divider network in the encoder 
is derived f r o m  the -17.8 volt bus. 
parameter  8 of the encoder sequence and comparing it to a calibration 
curve will give information concerning the -17.8 volt has  a s  well a s  
the condition and operation of the Two Year Timer Unit. 
The 
Therefore ,  monitoring performance 
Time 
T = 0 to T = 720 days 
T = 720 days to  T = 780 days 
T = 780 days to batt. death 
(z 2 - 3 hours) 
7 
T = O  T O  I\ 
T-720 DAYS T O  I '  
T=780 DAW 
F I G U R E  6 
-\ 
PP8,  INPUT VOLTAGE - VDC 
Figure 6-Encoder Divider Resistance 
8 
SPEED-UP AND CABLE DRIVER OPERATION 
~~~ ~ 
Figure  7 i s  a block diagram of the auxiliary speed-up and cable 
dr iver  c i rcui t ry  provided for testing. 
f rom the timing circui t  by diodes and r e s i s t o r s  and uses  separa te  power 
f rom the blockhouse. 
any possible failures due to the auxiliary circuitry.  
is a pulse s t re tcher  and amplifier for monitoring the normal  r a t e  of 
the oscil lator and the functioning of the pulseformer section of the 
This auxiliary c i rcu i t ry  is isolated 
Therefore the timing c i rcu i t ry  is protected f rom 
The cable dr iver  
magnetic core  divider. 
both timing circui ts  a r e  diode coupled and fed through the Normal Rate 
line to the blockhouse. 
a separate  oscil lator whose output is coupled into the pulse amplifier 
preceding the divider. Upon completion of the timing cycle a t  speed-up 
r a t e ,  the output of the SCR operating the relay f i r e s  a SCR which shunts 
the speed-up oscil lator power to ground. 
until the speed-up power is  released. 
t imer  does not pass  theTo position of the timing cycle a t  the accelerated 
rate .  
The pulse outputs f rom the cable dr iver  f r o m  
The speed up ra te  for the t imer  is derived f r o m  
The shunt SCR will stay on 
This operation insures  that the 
DATA INTERPRETATION 
Figure 8 shows the telemetry indication of the operation of the 
t imer  for the full  two year interval. The indications a r e  based on ideal-  
ized timing oscil lator function, that i s ,  no e r r o r  in accuracy or  stability. 
F igure  8 also assumes  that the te lemetry monitor flip-flop i s  in such a 
position that the te lemetry indication i s  at  Level 1 a t  t ime To. (See 
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Figure 6) However, since the speed-up osci l la tors  of the t imer  a r e  not 
synchronized with the normal  r a t e  osci l la tors  the te lemetry indication 
may  be at  either Line 1 or  line 3 a t  t ime To. 
oscil lator r a t e  that may be expected f r o m  normal  variations in temper-  
a ture ,  stability, and accuracy will be measured  and estimated for  each 
flight unit. This data will then be available to aid in te lemetry data 
interpretation. 
Variations in normal  
POWER REQUIREMENTS 
~~ 
The two year  t imer  will operate normally with bat tery voltage input 
range from t l O . O  volts to t 2 5  volts. At the normal  spacecraft  voltage 
of t19 .6  volts, the unit draws 8 to  10 mil l iamperes .  
ACCURACY AND STABILITY 
The maximum components of e r r o r  in the total accuracy of the 
Two Year Timer over the flight lifetime of two yea r s  a r e  tabularized 
below: 
Maximum Percentage of the 
Component Timing E r r o r  
Accuracy in initial oscillator r a t e  *170 
Stability a t  a given temperature  
Stability over the temperature  
range of -2OOC to t7O'C 
3~370 
*670 
Battery voltage variations <*170 
Therefore,  the total e r r o r  of the two year  interval will  be *lo70 o r  
less .  
12 
COMPONENT RELIABILITY CONTROL AND UNIT TESTING 
The basic c i rcui t ry  is relatively simple and has been flown success-  
fully in severa l  spacecraft. 
analysis has not been necessary.  However, considerable effort has been 
Therefore, extensive additional c i rcui t  
extended toward ensuring maximum component reliability. F i l te r  and 
timing capacitors a r e  high reliability solid tantalum types. Coupling 
capaci tors  a r e  low temperature  coefficient mylar .  The capacitors a r e  
individually checked electrically and given burn-in tes t s  in the lab before 
use. The unijunction t rans is tors  a re  selected and lab tested,  p r imar i ly  
to ascer ta in  low and stable peak point emit ter  current .  
controlled rect i f iers  a r e  selected and given extensive t e s t s  for  holding 
and firing cur ren t  variations. 
bility versions which have passed 200 hour burn-in tes t s .  
The silicon 
The remaining t rans is tors  a r e  high re l ia -  
The fabricated flight units will be given operating temperature  
t e s t s  in the lab to ensure overall  stability. 
minimum of 20 temperature  cycles between -3OOC and +75OC in addition 
to a minimum of 100 hours of operation a t  t75OC. 
These t e s t s  will include a 
PRELAUNCH TESTS AND MONITOR 
Since the timing cycle of the Two Year Timer i s  continuous, it is 
important that the prelaunch tests and monitoring of the unit be pe r -  
formed with ca re  and thought to ensure that the t imer  is a t  the beginning 
of its two-year cycle. 
ient t ime pr ior  t~ launch. 
through its cycle twice at the speed up rate.  
These tests should be performed at any conven- 
The tes ts  will consist  of running the t imer  
13 
The tests will include the following: 
1. 
2 .  
3. 
4. 
5. 
6 .  
7.  
8.  
9 .  
Timing of the interval length at speed-up rate .  
Recording the flip flop monitor output and observing the number 
and interval of the c r o s s  over points (See Figure 8). 
Noting speed up power line cur ren t  to ensure that the speed-up 
oscil lators a r e  turned off at the end of the timing cycle. 
Ensuring operation of both relays in the t imer  a t  the end of the 
timing cycle. 
Correlating the above information with decommutated te lemetry 
readout. 
Ensuring that the lines between the bat ter ies  and the solar cel ls  
a r e  reconnected after the speed-up cycle. 
Checking the normal  oscil lator ra tes .  
Ensuring that speed-up cur ren t  is not inadvertently applied 
before launch. 
Recording position of te lemetry monitor through te lemetry 
r eadout . 
All of this information will be available with proper monitoring of 
the Blockhouse lines f rom the Timer in the spacecraft .  The complete 
tes t  sequence and performance monitoring will be performed with the 
tes t  panel provided with the Timer.  
c i rcui t ry  for the P rogram Switch and the Despin t imer .  
This panel will a lso include t e s t  
The schematic 
of the tes t  circuitry is shown in Figure 9. 
performed by P rogrammers  Section personnel. 
The prelaunch t e s t s  will be 
The t ime required to 
perform the tests will be 2 hours o r  less .  
14 
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The schematic of the complete Two Y e a r  T imer  with Monitor is 
shown i n  F igure  10. 
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The epe-d two year timer

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