August 1965 Electronics World
Wax nostalgic about and learn from the history of early electronics. See articles
Electronics World, published May 1959
- December 1971. All copyrights hereby acknowledged.
A mere five years elapsed from the time
Echo, a gas-filled metallized plastic sphere that passively
reflected radio signals back to Earth, was launched and the
time that 35 television cameras had been launched into space.
The Space Race was at a fever pitch. Although the Ruskies beat
us in being the first to launch both an active satellite (Sputnik)
and a man (Yuri
Gagarin) into space, America's deep pool of intellectual
resources, consisting of both native scientists and many of
the world's top scientists who chose to flourish in freedom
here rather than oppression behind the Iron Curtain, fostered
the advantage that in short order established the United States
as the leading super power both in space and on terra firma.
TIROS satellites began providing real-time visual data on
the Earth's weather in 1960. Not only were cameras transmitting
images of the Earth, but a month before this issue of Electronics
World went to press the Mariner spacecraft sent close-up
images of the planet Mercury's surface. A year before this article
Syncom 3 became the first communications satellite in geostationary
Earth orbit. A year after this article
Lunar Orbiter beamed back photos of the moon's surface in
preparation for the Apollo missions that would transport the
first humans to and from the moon. We are now nearly at the
point where amateur rockets are powerful enough for anyone with
enough technical savvy to launch a small payload into low Earth
orbit - something the world's militaries are not looking forward
Television in Space
Of the 35 TV cameras sent into space, some use slow-scan,
some use digital techniques, and one uses a unique line-by-line
scan from processed photographs. The Mariner Mars, Ranger, lunar
Orbiter, and Apollo spacecraft are covered.
The first use of a TV camera in space took place on April
1, 1960 aboard the Tiros I weather satellite. This spacecraft
carried two TV cameras into a 400 mile high orbit to photograph
weather conditions around the world. Since then, thirty-three
more TV cameras have been successfully launched into space on
eight more Tiros vehicles, Nimbus I, the Ranger lunar spacecraft,
and the Mariner Mars, now approaching the red planet.
There are many variations in the type of TV system used in
these spacecraft, and this article will cover the digital system
in the Mariner Mars, the slow scan in the Ranger program, and
the one-line scan in the Lunar Orbiter. Some of the other programs
will be briefly covered.
Three Ranger spacecraft, each using six television
cameras operating in the slow-scan mode, have successfully taken
the first close-up pictures of the lunar surface. These shots
will be followed by Lunar Orbiter, Surveyor, and then manned
landing by two astronauts from the Project Apollo spacecraft.
At 5:10 p.m. PST on July 14, 1965, after a flight of some
350 million miles taking about 7 1/2 months, the 575-pound Mariner
Mars spacecraft (Fig. 1) will take about 20 photographs of the
red planet and, after passing by at slightly above 11,000 mph
relative to Mars, will radio those photos back to earth.
Fig. 1a - Top view of the Mariner Mars spacecraft
now headed past Mars and expected to take and transmit photographs.
Fig. 1b - Bottom view of the Mariner Mars
spacecraft now headed past Mars and expected to take and transmit
The spacecraft is designed to make eight scientific investigations.
Six of these are intended to measure radiation, magnetic fields,
and micrometeorites in interplanetary space and near Mars. The
seventh is an occultation experiment designed to determine the
characteristics of the Martian atmosphere. The eighth experiment,
the taking and transmission of photographs of the Martian surface,
will be covered here.
The resolution of the TV pictures of Mars and the area of
the planet they will cover are difficult to predict because
these factors will depend on the fly-by distance from the planet.
However, if planned trajectories are achieved, these pictures
should be comparable in detail to photographs of the moon taken
by the best earth-based cameras.
If the desired accuracies are obtained, the spacecraft will
pass within 5600 miles of the Martian surface; if it is on the
desired trajectory, the spacecraft will pass Mars between the
Martian equator and the South Pole on the trailing edge of the
planet as viewed from earth. It will then pass behind Mars for
approximately one hour and subsequently re-appear to earth trackers
for completion of the program.
A high-gain antenna is attached to the spacecraft atop the
main octagonal body. Its 4 1/2-pound honeycomb dish reflector
is an ellipse, 46 by 21 inches, parabolic in cross-section.
This antenna is pointed towards the earth during planet encounter
and post-encounter phases, and it is painted green to keep it
at operating temperature during planet encounter but within
its upper thermal limit earlier in the mission.
A low-gain omnidirectional antenna is mounted at the end
of a circular aluminum tube 3.88 inches in diameter and extending
88 inches from the top of the octagonal structure. The tube
acts as a waveguide for the low-gain antenna.
Primary power is from 28,224 solar cells mounted on four
panels facing the sun. A rechargeable silver-zinc battery provides
spacecraft power during launch, mid-course maneuver, and whenever
the solar paddles are turned away from the sun. Nominal power
from the panels is 640 watts near the earth, decreasing to about
310 watts during Mars post-encounter. Total power demands during
the mission range from about 140 watts during post-encounter
playback of the TV data to 255 watts for a mid-course maneuver.
Primary power to the spacecraft TV system is 2400 cps, 50 v.r.m.s.
Two-way communication with the Mariner is by a dual 10-watt
transmitter and a single receiver aboard the spacecraft. All
communication is in digital form with the spacecraft capable
of accepting 29 direct commands (from the earth-based 10-kw.
transmitters) and one stored command.
The 100-channel telemetry subsystem is capable of sampling
the 90 engineering and science measurements being made. All
engineering and science data except the TV pictures will be
transmitted in real time. The science data at Mars encounter
will also be recorded, along with the tape-recorded pictures,
for retransmission with the photos.
The television system is divided into two portions: the slow-scan
camera head and a small segment of the electronics mounted on
a scan platform; and the remainder of the electronic equipment,
including the tape recorder is placed in a compartment within
the spacecraft frame. The basic TV system is shown in Fig. 2.
Fig. 2. Basic TV system as used in the Mariner
Mars spacecraft. The analog video information is converted into
The heart of the camera is an electrostatic vidicon with
a specially developed target surface having 200 scanned lines
with 200 picture elements per line and capable of storing the
image for 24 seconds.
A picture is formed on the vidicon target in 1/5 of a second
every 48 seconds. The scanning, or readout, of the 200-line
picture requires 24 seconds while image erasure and preparation
for the next picture takes 24 seconds.
Working in conjunction with this vidicon is a solenoid-operated
shutter disc containing four openings for alternating optical
filters. Two filters will be orange-red with the other two blue-green.
These filters will provide high contrast in the black-and-white
photographs received on earth and will emphasize the difference
in Martian coloration as seen from earth.
The optical system for the camera consists of an ƒ:8
Cassegranian telescope system of 12-inch equivalent focal length.
Its beryllium primary mirror has a diameter of 1.62 inches and
an ƒ ratio of 2.47, while a beryllium secondary mirror
provides an amplification of 3.0.
The over-all camera system will be capable of resolving objects
about three miles across at the fly-by altitude.
Approximately six hours before the fly-by, internal commands
(or earth-based signals) will turn the camera system on. However,
pictures will not be recorded until a narrow-angle planet-acquisition
gate having a 1.5° field of view generates a signal indicating
that Mars is within camera range. As a backstop, when the vidicon
senses the increase in light due to solar reflection from the
Martian surface, this gate also signals for tape-recorder start.
It is anticipated that the camera system will sweep through
a large illumination range on Mars that will include the shadow
line or terminator; therefore, the system is equipped to decrease
or increase its internal amplification with either an increase
or decrease in the amount of available light.
Some 20 resultant photographs will be taken during the fly-by.
The signals for these images will be recorded and stored in
digital form on magnetic tape until the earth station requests
transmission after the spacecraft has appeared from behind Mars
and is in view of the earth antennas. These photographs will
be taken in groups of two with a small time gap between each
pair. Depending on camera distance from the surface, each pair
will cover overlapping areas of the Martian surface. The number
of pictures recorded will be determined by the time required
at encounter to synchronize the tape recorder and camera for
the first picture and by the lighting conditions on the Martian
surface. The tape recorder will be turned off after recording
each picture and turned on again to record the next. The magnetic
tape is a continuous loop 330 ft. long and the data will be
recorded on two tracks.
Besides the sweep voltages, the electronics associated with
the vidicon also includes a 1l0-kc. oscillator that modulates
the vidicon beam, thus giving rise to an r.f. carrier signal
output modulated by the target information between d.c. and
7 kc. This AM signal is processed to produce a six-bit digital
word for each picture element some 200 times per scanned horizontal
line, and it takes 24 seconds to read out each frame. The resulting
10,000-bits-per-second information is recorded on the magnetic
Upon completion of a vidicon readout, a 12-second erase and
prime mode is started, and the target is fully cleansed of the
stored image and prepared for the next shot.
Once the spacecraft has passed by Mars (about 13 to 15 hours
after the last picture is taken) and the spacecraft is in the
clear for the earth stations, a tape-recorder transmit signal
is sent. Because of the lengthy transmission path involved and
the relatively low transmitter power available on the spacecraft,
the electronic system reduces the 10,000-bits-per-second recorded
video data to a slow 8.33-bits-per-second rate. With this slow
transmission rate, it will take about 8 1/3 hours to play back
the quarter of a million bits comprising each picture. About
1 1/2 hours of engineering data will be transmitted between
each picture. All data from the other scientific instruments
will be recorded with the pictures as a back-up for the real-time
transmission of science data. Pictures are not erased after
If the communication distance has not been exceeded after
one playback of all pictures, each frame will be transmitted
again to provide a comparison for the detection of errors that
may crop up during transmission.
There has been a great deal of speculation about the texture
of the surface of the moon but little scientific proof because
astronomical observations are limited to details about one mile
in size. With such restricted knowledge about the moon's surface,
it is virtually impossible to design a manned spaceship to land
on the moon. It is for this reason that the Ranger-type vehicle
(lead photo) came into existence.
The picture-taking sequence begins at a minimum of 13 minutes
and 40 seconds before impact at an altitude of about 1200 miles
and continues uninterrupted until the vehicle crashes into the
moon at a speed of approximately 6000 mph.
The initial pictures from this altitude cover a wide area
of the lunar surface at resolution comparable to that obtained
by earth-based telescopes. As the Ranger falls toward the surface
of the moon, area coverage is traded for increasing resolution,
until resolutions of 0.5 meter or better per optical line pair
are achieved in the final picture sequence just prior to impact.
The six TV cameras (Fig. 5) are designated F (for full scan)
and P (for partial scan). One of the two F cameras has a 25-mm.
(wide-angle) ƒ:1 lens with a field of view of 25°,
while the other has a 75-mm. (narrow-angle) ƒ:2 lens with
a field of 8.4°. Shutter speed of the F cameras is 1/200
Fig. 5. The RCA six-camera configuration
used in the Ranger craft.
Cameras P1 and P2 have 75-mm., ƒ:2 lenses with a 2.1°
field of view, while P3 and P4 have 25-mm., ƒ:1 lenses
with a 6.3° field of view. Shutter speed for these cameras
is 1/500 second. Video bandwidth is 200 kc. for each channel.
The basic timing signals for the cameras are provided by
a camera-control assembly, Camera P1 is also provided with a
"free-running" capability by the incorporation of secondary
synchronization and sequencing circuits within the P1 camera
electronics. These circuits enable independent operation of
the P1 camera in the event that the P-channel sequencer fails.
In the P cameras, the central 282 resolution lines of the
1125-resolution-line camera raster are scanned for readout in
0.2 second. An additional 0.6 second is required for preparation
of the camera for its next exposure. Thus, the exposure of the
cameras in the P channel is sequenced at 0.8-second intervals
to provide for the continuous transmission of video data.
The 0.2-second readout time of the P cameras enables the
TV system to achieve extremely high resolution in the final
sequence of four pictures taken from an altitude of less than
7000 feet above the moon's surface. These final pictures are
exposed and transmitted to the earth in the last 0.8 second
of flight prior to impact.
The cameras used in the F channel are essentially the same
those used in the P channel except that in the former cameras
the entire 1125-resolution-line raster is scanned for readout
in 2.5 seconds. As a result, the area covered by a picture from
an 800-line camera is approximately 16 times that of a 200-line
camera from an equivalent altitude. In this manner, the two
F cameras provide the desired wide-area coverage.
Both types of cameras are used to provide area-coverage and
high-resolution data during the final few minutes before impact.
Both channels (F and P) are capable of independent or simultaneous
operation. The power distribution network and signal paths for
the two channels are completely independent, with the exception
of the r.f. combining network.
Metallic focal-plane shutters are used on all camera lenses.
This shutter is not cocked as in conventional cameras but is
a solenoid-operated, sliding-aperture type that moves from one
side of the lens to the other each time a picture is taken.
One reason for having several cameras with different lens
apertures is that the lighting conditions on the moon cannot
be precisely determined from the earth. The different lenses
provide greater exposure latitude. The range of lunar lighting
conditions covered by the lenses and the dynamic range of the
vidicons is about 30 to 2600 footlamberts, corresponding roughly
to about high noon till dusk of an average earth day.
The camera control sends three types of instructions to the
cameras: (1) snap shutter, (2) read vidicon faceplate, and (3)
erase faceplate and prepare for the next picture. The vidicon
faceplates are erased by special lights built around the vidicons
which are flashed to saturate the faceplate. The plate is then
scanned twice by the electron beam to remove all traces of the
previous image. The vidicon is then prepared to receive the
The camera output signals are processed, amplified, and sent
to a video combiner that enables sequential transmission of
the cameras in each channel. The video combiner provides gating
circuitry that blocks the erase-video signal from the vidicons
while they are being prepared for their next picture.
The output of the video combiner is converted into an FM
signal and sent to the two 60-watt transmitters where telemetry
information is added as a subcarrier, and the resultant signal
is transmitted to earth over the high-gain, four-foot parabolic
antenna on the spacecraft.
The Lunar Orbiter (Fig. 3) is one of the three NASA programs
for the unmanned exploration of the moon in advance of Project
Apollo manned landing mission. The Ranger program has given
us our first close views of the lunar surface, and it now remains
for the Surveyor and Lunar Orbiter programs working as a team
to provide specific types of information about selected areas
of the moon's surface in order to make a safe manned lunar landing
Fig. 3. Configuration of the proposed Lunar
Surveyor will make a soft landing so that its instruments
can measure important surface properties while eye-level TV
cameras provide visual information.
It will be the job of the Lunar Orbiter to make the initial
examination so that Surveyor data can be extrapolated over a
full-sized landing site. Since protuberances only half a meter
high are significant, and the area to be covered is over 8000
square kilometers per mission, heavy demands are made on the
Lunar Orbiter's data-gathering capacity.
The Lunar Orbiter differs from other video satellites in
that it mounts two photographic cameras and a roll of 260 feet
of 70-mm film. Once the vehicle has been placed in the desired
lunar orbit, its cameras proceed to take the necessary pictures.
Using the Eastman Kodak "Bimat" process, the films are fully
developed within the spacecraft, and the negatives are stored
pending electronic readout with the system shown in Fig. 4.
Fig. 4. Line-by-line photographic readout
The high-resolution film negatives are placed in front of
a special flying-spot CRT whose electron beam traces one scanning
line only. At the beam intensities required, the phosphor would
burn up if it did not keep moving. In this tube, the phosphor
is coated on the outer surface of a continuously rotating metal
drum. The scan period is 1250 microseconds and the scan line
is about 2 1/2 inches long at the phosphor. The emitted light
is focused on the film negative through a scanning lens that
reduces the line width to 1/10 of an inch. Mechanical motion
of the scanning lens moves the now-tiny bright line across the
film. It takes about 17,000 horizontal scans of the original
electron beam to cover the 57-mm. width of the film negative.
This process requires about 20 seconds. The film negative is
then mechanically advanced 1/10 of an inch and the scanning
lens then scans the next segment in the reverse direction. It
takes 40 minutes to read out the 11.6 inches of film negative
corresponding to a single exposure.
After the bright spot has passed through the film negative,
it is modulated by the exposed density existing at each point.
Collecting optics then pass this light to a photomultiplier.
The video is then combined with the necessary sync pulses, telemetry
signals, and a reference pilot tone; then the composite signal
is conditioned for radio transmission to the earth.
At the earth station, the r.f. carrier is demodulated and
the telemetry signals diverted to equipment and stored on magnetic
tape, while the picture information is passed on to the picture-reconstruction
system for further processing and magnetic-tape storage. The
video data is displayed line by line on a kinescope face with
the image being recorded on a continuously moving 35-mm. film
Within the capsule of this first three-men-to-the-moon flight
will be a hand-held TV camera head that will be used to provide
real-time TV pictures of crew activities for public information
(TV as required, newsreels, and newspaper use) and documentation.
The on-board camera has the unique capability of providing
dynamic scenes of activities aboard and outside the spacecraft
without the necessity of vehicle recovery. Secondary application
such as monitoring propellant tanks, launch escape tower, recovery
chute development, etc., are probable as the project progresses.
These are secondary, however, and the TV camera has been optimized
around the public-information requirement.
The 4 1/2-pound camera has a bandwidth of 500 kc. with a
frame rate of 10 per second with 320 lines per frame. Consuming
6 3/4 watts, the camera has a .1 footcandle highlight-illumination
sensitivity minimum and a resolution of 227 lines. It uses a
one-inch vidicon and is provided with a 9-mm., ƒ 1:9 lens
and a 20- to 80-mm., ƒ 2:5 zoom lens.
The camera will be mounted in one of two positions within
the spacecraft. One of these positions is near the bottom of
the instrument panel and slightly to the right of the center
astronaut so as to view the crew during the launch phase. After
powered flight, the center astronaut will stow the center seat
so as to make an aisle, and he will mount the camera in the
second position where it can monitor activities of the crew
in this center aisle.
Alternate applications of the TV camera are provided for
portable operation. The camera may be hand held and moved throughout
the control module as desired. A second zoom lens is available
for external viewing through the module windows to obtain TV
pictures of the earth or moon.
The Apollo TV camera feeds into a premodulator where it will
be frequency multiplexed with both voice and telemetry data.
The composite signal is fed to an S-band transponder, then power
amplified and passed through either the S-band omni antenna
for near-earth transmissions or the high-gain S-band antenna
for transmission from deep space.
Once the Apollo command module has been placed in lunar orbit,
one astronaut remains in the command module while the other
two are soft landed on the moon by the Lunar Excursion Module
(LEM). The same TV camera as used on the mission will accompany
them. Pictures will then be transmitted directly between the
LEM and the earth stations.
Typical of the Tiros class of weather satellites is the Tiros
I, now circling the earth in a polar orbit.
The two-camera TV system used in these observations has a
ground resolution of about two miles at the picture center.
The two cameras are mounted on the sides of the spacecraft so
that they view the earth once every revolution (every six seconds).
An on-board timer programs the cameras to take pictures only
when they are looking directly at the earth.
The camera tube is a 500-scan-line vidicon with a persistence
that permits a two-second scan with less than 20% degradation
in picture quality. Each wide-angle camera, using 104-degree
lenses, nominally takes 16 pictures per orbit at 128-second
intervals, providing nearly full dawn-to-dusk coverage. Each
picture will cover a 550,000 square mile area. The interval
can be reduced to 64 or 32 seconds for overlap pictures if desired.
The video data is stored on one of two tape recorders for
readout when the satellite passes within 1500 miles of a ground
Transmission time for a full orbit of pictures takes about
three minutes from receipt of the ground radio command. Sufficient
tape is provided in each of the two recorders for storing 48
picture frames at a speed of 50 ips. The tapes are erased immediately
after playback and again just before recording.
Editor's Note: According to the latest report we have received
from NASA on Mariner Mars (Mariner 4), the spacecraft is still
holding steady on its course and is continuing to transmit scientific
and engineering data from interplanetary space. Although two
of the radiation experiments have evidently failed, the other
experiments are still operating. It is expected that up to 21
photographs of Mars will be taken when the craft gets as close
as 5600 miles of the planet on July 14. On June 16, Mariner
4 was over 109 million miles from Earth traveling at a velocity
of about 57,000 mph.
Posted May 3, 2015