Tape recorders for nimbus satellite - electronic and magnetic systems, control of record & readou

Schneebaum, M. I.

Stampfl, R. A.

English

NASA Technical Reports Server

https://ntrs.nasa.gov/search.jsp?R=19630011395 2020-03-24T05:42:33+00:00Z
New electronic and magnetic systems 
have been developed to handle 
huge quantities of data during each Nimbus orbit 
Data storage lor meteorOlogiCal satellites 
BY M. I. SCHNEEBAUM and R. A. STAMPFL 
NASA Goddard Space Flight Center 
Huge quantities of data will be stored 
and readout from advanced weather 
satellites, such as Nimbus. Data stor-
age thus becomes a critical feature of 
design. This paper discusses some of 
the advanced research being conducted 
by the Goddard Space Flight Center 
(GSFC) in the field of electronic and 
magnetic data storage of video in-
formation in meteorological satellites. 
Electrostatic storage is the basis 
for two unique TV systems being de-
veloped by RCA for GSFC. Two basic 
processes characterize these systems: 
1. An optical image is converted to 
an electl'ical charge pattern that can 
be stored for relatively long periods of 
time (writing process). 
2. The transformation at will of 
this charge pattern into a video signal 
( read ing process) . 
The storage vidicon is the heart of 
the Automatic Picture Transm ission 
ystem (ArTS) which will be flown 
on Nimbus. This system provides 
wide-angle cloud-cover pictures from 
a satellite and transmits them in real 
time on a narrow-band channel to a 
local ground station for recording on 
facsim ile equipment. 
The storage vidicon resembles a con-
ventional vidicon except for the addi-
tion of a thin, high-resistance poly-
styrene storage layer on the photo-
conductive surface. A cutaway view 
of the front end of the vidicon is 
shown on page 4D. The tube is oper-
ated by holding the target potential 
constant and raising oj' lowering the 
M . I. SCHNEEBAUM 
mesh potential with respect to the 
target during the prepare, expose and 
readout sequences. The vidicon photo-
conductor is optically exposeu by 
means of a mechanical hutter, and is 
then electronically "developed," that 
is, the charge image is transferred 
from the photoconductol' layer to the 
polystyrene storage layer. The read-
out cycle follows for 200 sec, during 
which picture information is readout 
at the rate of 4 lines pel' sec. 
Experimental evi tlence indicates 
that the polystyrene surface suffers 
radiation damage under prolonged 
electron bombardment, resulting in 
I'educed lateral resistance and loss of 
storage capability. Research is being 
conducted to improve radiation resist-
ance of the polystyrene by increasing 
the purity of the materials. The addi-
tioll of a flood gun is being investi-
gated to reduce the electron bombard-
ment. In addition, other materials are 
being investigated. 
On readout, the video signal ampli-
tude modulates a 2400 cps subcalTier 
which in turn frequency modulates a 
5-w transmitter as indicated in the 
block diagram on page 49. The re-
quirement for the system to pass very 
low-frequency video signals was a 
difficult problem, solved by pulsing the 
cathode with a 4800 cps subcarrier. 
This subcarl'ier signal causes the 
readout electron beam to be chopped 
at the 4800 cps rate. The charge pat-
tern on the polystyrene storage layer 
amplitude modulates the subcarrier. 
heads the Systems Engineering 
Branch of Goddard's Aeronomy and 
Meteorology Div., responsible 
for development of the major 
subsystems for Nimbus . 
He previously headed the Physics Branch 
of NWP's Engineering Dept., where for 
13 years he was engaged in development of 
aircraft fire contro l, machine guns, 
Terrier GSE, and nonmagnetic too ls. 
t 
The video modulated subcarrier IS 
A.C. coupled to a bandpass amplifi er 
and detector. 
Video dala is continuously trans-
mitted during the daytime portion of 
the satellite orbit. The system has a 
linearity of 0.50/0 and a limiting reso-
lution of 700 TV lines. System linear-
ity was achieved through special 
yokes, vidicons, and digital sweep cir-
cuits. Highlight sensitivity is 0.7 foot-
candle sec. Signal-to-noise ratio is 26 
db, giving approximately 7 grey scales. 
A grey-scale calibration wedge, con-
sisting of 11 known levels, is located 
at the top of each picture, parallel 
with the horizontal scan. A flash tube 
illuminates the wedge each time the 
shutter is activated, giving a cali-
brated scale on each picture. The angu-
lar coverage is 108 deg, which, for a 
500-n. mi. altitude satellite, yields 
approximately 1150 by 1150 n. mi . 
ground coverage pel' picture. 
The storage vidicon thus permits 
slow scan readout, and a narrow band-
width permits use of simple ground-
station equipment. The APTS ground 
station can be assembled from inex-
pensive, off-the-shelf commercial com-
ponents. The ground station consists 
of a helix antenna and a preamplifier 
mounted on a pedestal, a narrow-band 
FyI I'eceiver, and a commercial fac -
simile recorder modified for automatic 
start and stop, employing the airborne 
subsystem control signals, and thus 
permitting any local weather station 
to obta in direct cloud-cover picture 
R. A. STAM P FL 
designed and specified the Nimbus 
spacecraft and its electronic systems, 
and was previously 
Project Ma nager for Tiros II. 
A native of Austria, he received his 
academic training there, earning 
a Ph .D. in communications from 
the Vienna Institute of Technology 
in 1953. He began professional work 
here with the Army Signal R&D Lab. 
Reprinted/rolll ASTRONAUTICS A N D AEHosr. \CE ENGINEERING, April ]963 
Copyright, 1963, by th e American lnstitute of Aeronautics and .\ stronautiC's ano reprinted by permission of the copyright oWllcr . 
-~ 
of the imm~diate atl'ea whenever the 
satellite is in view. 
With an investment for a ground 
station of approximately $30,000, 
meteorological groups throughout the 
world will receive local real-time cloud 
pictures at least once a day for im-
mediate use. 
A second television system under 
development for Nimbus which utilizes 
the electrostatic storage is the Di-
electric Tape Camera. The storage me-
dium is a thin flexible tape coated with 
suitable materials which permits stor-
age of an electric-charge pattern on 
an outer insulating layer. 
The writing process consists of ex-
posure of the tape to an optical image 
through a lens system in a manner 
s imilar to photography. However, in 
this process, the tape is also exposed 
to a uniform electron beam that de-
posits an electric charge on each ele-
mental area of the tape in proportion 
to the amount of light falling on that 
area. Optical and electrical exposures 
both occur from the insulating or di -
electric side of the tape. 
To convert this charge image to a 
video signal, the portion of tape on 
which the image is stored is moved to 
a location where it can be scanned by 
the electron beam that performs the 
readout process. In this process, the 
polystyrene surface is scanned by the 
read beam in much the same manner 
as an image orthicon target is scanned 
by the electron beam. The result is 
that in the scanning process, the re-
turn beam is modulated by the charge 
pattern on the insulation. 
The tape itself is 35 mm wide and 
consists of three layers on a base 
material, as shown at the right. The 
base material is optical quality nylon 
called "Cronar." These optical proper-
t ies were important in early develop-
ment, when the tape was exposed opti-
cally through the base material. Re-
search into the basic process indicates 
that it may be advantageous to make 
the base from an opaque material 
s ince optical exposure can be per-
formed directly on the dielectric mate-
r ial, rather than through the base. 
Three layers are superimposed on 
this base in sequence using vacuum 
deposition techniques. These layers are 
deposited on a continuous basis, with 
the tape moving at a constant rate of 
speed. Lengths as long as 50 ft have 
been processed on this laboratory tape 
machine. 
The first layer is a gold-and-copper 
combination approximately 0.01 mi-
crons thick which forms a transparent 
conducting coating that serves as the 
electrical connection to one side of 
the photoconductive layer. 
The photoconductive layer 
POLYSTYRENE STORAGE VIDICON 
r GLASS ENVELOPE 
~'- ---
GUN 
ARRANGEMENT 
WALL 
' TRANSPARENT CONDUCTIVE LAYER 
,. lH\C'I(N£SS GUAllY 
EXAGGERATED TO 
SHOW LO CATION 
APTS DIAGRAM FOR SATELLITE 
i-~::::. - - - ::.~~. - - ------ -.--- - ---': --= ~.~'~ -~"~; ----
DlflECIIOfil { 
CI RCUITII't' 
DIELECTRIC-TAPE CONSTRUCTION 
METALLIC 
CONDUCTING STRIP 
POLYSTYRENE - 0 .6 MICRON 
PHOTOCONDUCTOR - 2 MICRON 
DEfLECTION 
AMPllflEIIS 
SAWTOOTH TIMIHG _ l~~tfis 
GE NERAT OR r- CHA1HJ VIIRATOR 
lOCI!; 
PULS(S 
DAY 
ON·OFf 
poWEll 
CONTROL 
s':~:~H ~ 24 5'1 PRO&UfII 
CO fOUN D !'OWER COIIIM",.O 
ELECTRON BEAM 
.... 
POLYSTYRENE INSULATOR:::=t~~~==============j[==~ PHOTOCONDUCTOR S~S3 
TRANSPARENT THIN COPPER 
GOLD CONDUCTIVE LAYER 
TRANSPARENT BASE,CRONAR 
DIELECTRIC-TAPE CAMERA 
VACUUM PORT 
PREPARE GUN 
SCANN ING 
·MIRROR 
TENSION SPRING 
SUPPLY REEL .• 1 
CAPSTAN 
MOTOR 
READ GUN 
TAKE UP REel 
49 
r-------- -- --------
lai to "he photosensitive layer of com-
mercial vidicons, and the spectral re-
' l, onse of the system is determined by 
this layer. The material used at pres-
ent is arsenic trisulphide_ 
The final layer is an extremely thin 
uniform coating of polystyrene ap-
proximately 0_6 microns thick This 
is the insulating layel' that acts as a 
capacitor for holding the electric 
charges forming the charge pattern 
equivalent to the optical image. 
A laboratol'y camera has been de-
veloped which has demonstrated the 
feasibility of utilizing the dielectric 
Lape principles for observing the stOI'-
ing cloud-cover pictures from a satel-
lite. The tape camera performs the 
combined function of observation and 
s torag'e, replacing both the vidicon 
camera and the tape recorder. An ad-
vanced model is now under develop-
ment which will closely approximate 
the fli g ht configuration. This is shown 
on page 49. A number of problems re-
main to be solved, since the entire en-
closure must be evacuated for propel' 
operation. 
The electrostatic camera possesses 
the follow ing inherent capabilities: 
I, Higher packing density per pOLinu 
than the conventional camera l ta pe 
recorder co nfiguration. 
2. Limiting resolution comparable 
with the best image orthicons . 1200-
1500 TV lines is currently achievable, 
with a target of 2500 TV lines in the 
foreseeable future. 
~, Slit camera type operation, whi ch 
permits wide angular coverage with 
low distortion. 
4. Sensitivities comparable to cur-
rently avai lable airborne vidicons, and 
low light sensitivities of the order of 
0.01 ft-candle sec. 
5. Variable resolution readout ca-
pability. 
The present camera I configuration 
can store on tape two complete orbits 
with horizon-to-horizon coverage with 
0.2 mi. ground resolution. 
The present Tiros and initial Nim-
l>us spacecraft contain conventional 
vidicons with magnetic tape as the 
storage medium. The same is true of 
the infrared scanning system. 
Simple calculations indicate that 
10' infrared information bits and 5 
X IDS TV informations in 96 pictures 
must be stored per orbit. These data 
are presented in analog or binary 
coded form. Data storage without me-
chanical movement is, of course, at-
Lt'active . However, development of 
large memories with size, weight, and 
power comparable to magnetic tape 
recorders does not appear feasible 
w ithin the next few years. For this 
reason, the imrpovement of magnetic-
tape storage devices is constantly be-
ing investigated in-house at Goddard 
Space Flight Center. 
A medium capacity endless-loop 
tape recorder has been successfully 
developed for satellite applications. 
The recorder utilizes 120 ft of 1/ 4-in. 
tape. and records for 1 1/ 2 hr. Play-
back is at 30 times the record speed_ 
The recorder consumes 2 w of power 
on record and 10 w on playback. 
Recorder development has empha-
sized flexibility so as to serve as 
many applications as possible. Mo-
mentum compensation has also been of 
prime importance. Stabilized space-
craft are controlled by small torques 
so that even the small unbalanced mo-
mentum generated by the recordel's 
become major disturbances. Long-
life applications require a sealed pres-
surized container; the lower section of 
the container houses drive-amplifiers 
for 100-cps synchronous motors, a 
pressure transducer, and auxiliary 
Singl e Digital Record Ampl ifier 
is shown in this m icrophotogra ph, 
Small square is a field -effect 
transistor; larger silicon 
crystals contain other circuitry , 
electronics. Inherent ruggednesi> of 
these units Illakes dil'ect mounting on 
the container feasible with standard 
encapsulation employed. 
An analog version of the recorder 
has the endless-loop cartridge in the 
center of the container, partly covered 
by plugs, and the record and playback 
motors in the form of two cylinders 
to one side. A single capstan drives 
the tape across the head, held firm by 
a pressure pad . By single substitution, 
an eight-track digital head is mounted 
with the electronic record and play-
back amplifiers alongside. 
Since t he tape drive is a delicate 
mechanism, it must be mounted so a s 
to survive the large range of vibration 
environments encountered in different 
structures. In general, resonance of 
these structures occurs at low fre-
quencies, so th e mount itself can be 
designed for resonance at higher fre-
quencies. The tape drive is mounted 
between two plates tied to two shelves 
of the container by means of miniature 
dampers, and up to 20 g's rms of ran-
dom noise vibration can be applied, or 
an equivalent sinusoidal sweep, with -
O'lt failure. 
The record ami playback amplifiers 
for analog units are inherently more 
['el iable than the drive mechanism , 
, Conventional analog amplifiers are be-
ing used. Digital amplifiers, however, 
lend themselves more readily to de-
sign by integrated circuits. The high 
reliability of these circuits when sili-
con planar transistors are used, and 
their small size, makes it practical to 
include an eight record/playback am -
plifel' package in the recorder since it 
can be built with a volume equal t o 
that of the recorder head. Such cir-
cuits can be operated at power levels 
of one microwatt per stage so that 
thermal dissipation of an assembly is 
negligible. Thus, these circuits run at 
low temperatures and are extremely 
reliable. 
Each record amplifier consists of 
four transistors which can be mounted 
with its associated resistors in a 
standard transistor can, Conventional 
non-retUl'n-to-zero recording is used 
in which zeros and ones magnetize the 
tape in opposition. Separate erase is 
thus not needed. A microphotograph 
of the amplifier is shown at the left. 
The small square is a field-effect 
transistol' preamplifier; the next 
larger square a silicon crystal with 
load and coupling resistors etched on 
the surface which serves as the next 
transistor stage. The longest crystal 
contains two direct coupled transistors 
and associated circuitry. 
Similarly, playback amplifiers have 
been developed where the head output 
is amplified and the wave-shape re-
Astronautics and Aeros)lace Enoi1'leerill(J 
/ -- - -- ------
CAP AN~ TAPE 
DIRECTIO N 
,.,-- CAPSTAN 
APE SUPPORT 
pall ER 
(12) 
RQLER 
ASSEMBL Y 
(5) 
1200-F T TAPE 
PAC 
1200-lt- t a pe Endl ess-loop Reco r d er now looks as shown in the photo at top , 
a laboratory model. The drawing below shows details of its end less -loop cartridge. 
co nstructed by a multivibrator so that 
conventional or microminiature logic 
circuitry can process the pulse train. 
The power levels and small volume of 
these circuits permit selective re-
dundance at small cost in terms of 
weight and volume. 
Redundant logic circuitry can 
I'eadily be designed to achieve long-
life recorders. A contribution toward 
this end is the development of an ana-
log-to-digital converter sufficiently 
small and of sufficiently low power 
that digital recorder techniques be-
('ome comparable with analog. 
Analog-to-digital converters can 
also be built according to any of the 
standard techniques using integrated 
circuits for the logic. The speed re-
quired for the conversion often deter-
mines the techniques used. A com pro-
Apri/196S 
mise between complexity and speed 
in an analog-to-digital converter leads 
to a design where the input signal is 
compared sequentially to a number of 
binarily related voltages, setting ap-
propriate flip-flops. Readout can be 
serial or parallel as desired, since the 
flip-flops hold their positions until 
recycled. For most meteorological ap-
plications, seven bits or 128 levels is 
adequate. For infrared sensing, it is 
.·ufficient to operate this converter at 
a 40 microsec per bit rate, with total 
conversion requiring 280 microsec. 
Logic for such a converter has been 
microminiaturized and operates at less 
than 5 microwatts for this logic, with 
an additional 50 microwatts needed for 
the error amplifier and weighing net-
work. 
The requirement for large storage 
capat:ity led to the development of 
an endless-loop recorder having 1200 ft 
of 1/ 4-in. tape. Playback speed is 30 
ips, and record speed is either 30 cps 
0 1' 3 3/4 cps. The unit will record ana -
log video whose subcarrier is fre-
quency modulated. Initially, infrared 
scanner signals will be recorded. Later 
models will record TV frames when a 
rast start and stop is perfected. 
The advantages of endless-loop re-
corders over more conventional two-
reel types lie in their convenient read-
out capability. Since the tape moves 
in the same direction for record and 
playback, no I'ecycling time is lost and 
a complicated high-speed recycle 
mechanism is not needed. Readout can 
be commanded at arbitrary times and, 
since erase can be performed immedi -
ately prior to record, only the oldest 
information will be erased regardless 
of how many readouts are performed 
within a given time. 
A vi ew of a laboratory-model re-
corder and a cross-section of the tape 
cartridge al'e shown at the left. Loops 
of a few hundred feet or shorter call 
be pulled without additional guide. 
The differential velocity between tape 
layers demands good tape lubrication, 
particularly in view of wide tempera -
ture requirements and attendant ten -
sion changes. These side effects be-
came predominant when long loops 
"'ere designed. Regular mylar mag-
netic tape cannot be used in untreated 
form. Preshrinkage at high tempera-
tures creates good dimensional sta-
bility so that drive forces stay within 
tolerable limits. Tape lubrication ha -
a di rect infl uence on speed constancy. 
and the lubricant must be perfectly 
smooth. Low flutter and \\'ow can only 
be achieved in long loops when tape 
support rollers are used, thus helping 
to overcome the velocity differential 
between the inner and outer radius. 
Better performance has been 
achieved with long loops than with 
short ones, with flutter and wow of 
0.17 % rms up to 1000 cps and 0.102 % 
rms up to 300 cps measured on a lab-
oratory model. The general layout of 
the tape drive is an outgrowth of the 
short loops. Around the spoked wheel, 
retained by l'ollers, is the tape loop 
which is driven by two capstans from 
the innermost portion of the tape to 
the outer. As in other recorders, Mylar 
belts are used for speed reductions 
and a clutch engages the capstans to 
the record or pla~'ha ck drive chain. 
respectively . 
The same drive principle can be ap-
plied to multiple track 1/4- and 1 / 2-in. 
tapes and to dig-ital recorders, thereby 
generating a family of equipment for 
a variety of meteorological satellite 
requirement. •• 
6} 


DATA STORAGE FOR METEOROLOGICAL SATELLITES

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