Of the 35 TV cameras sent into space, some use slow-scan, some use digital techniques, ad one uses a unique line-by-line scan room 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, (types of TV Cameras) 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.
At 5:10 p.m. PST on July 14, 1965, after a flight of some 30 million miles taking about 71/2 months, the 575-pound Mariner Mars spacecraft (Fig. 1) took 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.
The spacecraft is designed to make eight scientific investigations. Six of theses are intended to measure radiation, magnetic fields, and micrometeorites in interplanetary space and near Mars. The seventh is an occultation experiment designed to determine characteristics of the Martian atmosphere. The eighth experiment, the taking and transmission of photographs of the Marian surface, will be covered here.
The resolution of the TV pictures of Mars and the are 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 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 41/2-pound honeycomb dih 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 omni directional 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 dating 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 Lunar Orbiter differs room 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.
The high-resolution film negatives are placed in from 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 continuously rotating metal drum. The scan period is 1250 microseconds and the scan line is about 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, the exposed density existing at each point modulates it. Collecting optics then pass this light to a photomultiplier. The video is then combined with necessary sync pulses, telemetry signals, and a reference pilot tone, and 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. filmstrip.
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 applications 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 4.5 pound cameras have a bandwidth of 500 kc. with a frame rate of 10 per second wit 320 lines per frame. Consuming 6 ć 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., f 1:9 lenses and a 20- to 80-mm., f 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 isle, and e 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, and 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 station.
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.
DATED 1965, Leslie Solomon
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.