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Closed-Circuit Television System

The closed-circuit television system is used primarily to support on-orbit activities that require visual feedback to the crew. The CCTV system also provides the capability to document on-orbit activities and vehicle configurations for permanent record or for real-time transmission to the ground. The CCTV system can be controlled by both onboard and remote uplink commands. The CCTV system is a standard monochrome (black and white) system with an optional color capability by means of interchangeable camera lenses. Color scenes are not available on the onboard monitors because of hardware restrictions; however, color scenes are available on recorded and downlinked video.

Video inputs to the CCTV system are available from cameras mounted at several locations in the payload bay and on the remote manipulator system arm, which is mission dependent.

Cameras are also used in the middeck and the flight deck of the crew compartment. The video signals from these cameras can be viewed by the crew on one of two monitors in the flight deck, then sent to a video tape recorder for later viewing or to the ground on the S-band FM or Ku-band systems.

The video control unit controls power and input/output configuration, including camera control of pan, tilt, zoom, focus, iris operations and synchronization for the CCTV system. It processes video and data inputs from cameras and video tape recorder channels and routes them to monitors, the VTR or the ground by downlink.

Typical uses of the CCTV system for monitoring and recording mission activities include payload bay door operations, remote manipulator system operations, experiment operations, rendezvous and stationkeeping operations, and onboard crew activities.

The CCTV system consists of the video control unit, television cameras, VTR and onboard television monitors 1 and 2.

Audio from orbiter intercom channels A and B can be interleaved with the video output, along with Greenwich Mean Time data from the orbiter master timing unit. The VCU also generates a standard test pattern for use in adjusting the monitors and verifying downlink and provides multiplex capability for two split-screen outputs.

All television cameras are identical with the exception of accessory hardware. Any camera can be equipped with three types of interchangeable lens assemblies, depending on mission requirements. Both monochrome and color lenses are available with normal field of view. Color lenses are also available with a wide-angle field of view. In addition to focus control for sharp images, several special lens control functions are available. All functions can be controlled by both onboard and ground uplink commands.

An automatic light control is available for each camera. Its modes compensate for scene brightness by eliminating a fraction of the brightness. It then adjusts the light level of the scene by controlling (1) the silicone intensified target tube high voltage, (2) lens aperture (iris) and (3) automatic gain control. As a result, more detail and contrast are available in the brighter areas of a scene. Light or dark areas of a camera scene can be enhanced or subdued by means of gamma commands. More contrast can be obtained within light or dark areas. Zoom capability magnifies or reduces the size of objects in a camera's field of view by adjusting the focal length of the lens. The minimum focus for standard lenses is 3 feet, the maximum is infinity.

Although five payload camera bay inputs can be used per mission, more than five camera locations are available. If a mission requires a keel camera, only one camera can be positioned at one of four locations along the keel. If a camera is connected to the keel/EVA position, then TV camera views are not available while the EVA camera is in use. Each remote manipulator system can accommodate two cameras, mounted at the wrist and elbow locations; however, scenes are only available from either the wrist or the elbow, selectable by means of panel A7 switches.

With the exception of the RMS wrist camera and keel camera, all exterior cameras are mounted on motor-driven pan-tilt units. Camera azimuth (left and right) position and elevation (up and down) from a reference can be controlled on board by the flight crew or by ground uplink. The front tilt unit can accommodate up to plus or minus 170 degrees of pan and plus or minus 170 degrees of tilt from center. In tilt, the cameras cannot look straight down; in pan, the cameras cannot look straight down or straight back, which accounts for the range of 340 degrees instead of 360 degrees. The pan and tilt units move at two speeds: the high rate allows 12-degree-per-second rotation, and the low rate allows 1.2-degree-per-second rotation. Each pan and tilt unit contains a thermostatically controlled heater to maintain proper temperature.

Up to three cameras can originate from payload sources. These inputs can come from pallet-mounted cameras or from the Spacelab module during a Spacelab mission. If the payload cameras are part of the orbiter flight hardware, the video control unit can command the camera in focus and zoom. However, Spacelab provides the electrical interface camera outlets that are available inside the orbiter crew compartment for portable cameras. The flight crew would deploy, set up and stow the portable TV system.

All interior cameras are equipped with a color lens. Monitors 1 and 2 and the TV viewfinder monitor provide a monochrome output regardless of the lens assembly utilized, allowing the crew to adjust and view the video scenes. The flicker that appears in the interior camera scenes is caused by the rotating color wheel used to generate the field-sequential color signal that allows color outputs on the ground. The color-conversion process on the ground eliminates the flicker before the color signal is distributed.

The basic monochrome camera converts light images into a composite video signal (picture plus sync) and can produce either a black-and-white or color image, depending on the lens assembly used. The lens provided with the TV system is an f/1.4 color zoom lens equipped with a six-segment, three-color rotating filter wheel that produces sequential red, green and blue color fields. Motorized lens control functions that vary the zoom, iris and focus are controlled manually by lens switches remotely from panel A7 or by ground command. The small portable monochrome viewfinder monitor (8 by 4.25 by 3.6 inches, weighing 4 pounds) enables the crew to view camera video output for picture quality and scene verification when monitors 1 and 2 are not accessible or available. The TV cable connects the camera and the two TV system input stations located in the crew cabin at panels O19 and M058F. The cable provides the camera with 28-volt dc power; camera and lens commands along with the sync signal; and video, including camera and lens data, to the control unit for distribution. The viewfinder monitor cable, which is 9 feet long, provides an interface between the camera and the monitor.

Interior camera mounts restrain the camera assembly where it is used. Fixed-location quick-shoe mounts interface with any smooth, flat crew compartment surface. Clamp adapters can be used to affix the camera to panel switch guards or handholds. In addition, a special baseplate can be attached to either of two mounting locations on the sills of overhead windows 9 and 10.

The two black-and-white TV console monitors in the aft flight deck crew station on panel A3 are identical and are arranged one over the other. The top one is monitor 1 and the bottom is monitor 2. The monitors are used to view video on board. Camera scenes from any exterior, interior or payload camera can be viewed on either monitor. The video being downlinked can also be observed on either monitor. In addition, the monitors can be used to view the video being recorded or played back on the VTR. They can also display cabin TV output when it is more convenient than using the viewfinder monitor.

Each monitor accommodates a split-screen image from any two cameras. This feature is generated by the control unit and selected by panel A7 commands. Alphanumeric displays of camera location, pan and tilt angles, and temperatures of any cameras in an overtemperature condition can be superimposed on the monitor scene. A cross hair is also available at the center of the screen as an aid in remote manipulator system and proximity operations. The monitors are equipped with displays and controls for direct control of most monitor operations; however, the assignment of an input source to the monitor is controlled by panel A7. Each monitor is 12.5 by 10 by 7 inches and weighs 21 pounds.

The video tape recorder is a cassette recorder with the capability to record both video data and voice annotation. Video from any camera source can be recorded on board and in color if the selected camera has color capability using off-the-shelf cassettes of 20 and 30 minutes. Voice annotation can be input directly to the VTR through a headset interface unit. The HIU interfaces only with the VTR, not with the vehicle communications system. A tone may also be recorded to identify a particular location for subsequent playback operations. Voice annotation can be added during playback and records over any previously recorded audio.

All actual VTR operations must be performed by the crew-everything from tape changeout to VTR activation. The VTR is configured to receive its video input from monitor 2 (to record video on the VTR, the desired camera output must be displayed on monitor 2, which is connected directly to the recorder). For onboard playback, the recorded video can be reviewed on monitor 2 by positioning its source switch to direct and initiating a playback mode. For downlink purposes, the VTR is connected to the payload 1 input, which is a panel A7 video input selection. The switch panel located above the VTR includes a circuit breaker for the recorder. The recorder is equipped with a no video light that is illuminated when no video source is present at the recorder. When recording, the operator should verify that the no video light is off. An end of tape light indicates when the cassette is out of tape, and the VTR automatically stops. Tape changeout is simply a matter of ejecting the cassette from the recorder.

The extravehicular mobility unit TV is a fully portable remote television unit. It transmits black-and-white television pictures to the orbiter CCTV system from virtually any location outside the orbiter. Orbiter reception is through either of the S-band FM hemispherical antennas. The TV assembly fits over the EMU helmet and light assembly. It is battery powered (28 volts dc) and transmits video at 1,775.7 MHz to a video receiver/processing unit installed in the orbiter's middeck. When the receiver is connected to the TV input station at panel M058F by a standard 20-foot TV power cable, crew members can view real-time EVA video on either monitor by selecting the middeck camera input on panel A7. EVA video can also be selected for return link or taping.

Auxiliary lighting to improve scene quality is available for both exterior and interior cameras. In the payload bay, floodlights are mounted on the forward bulkhead and at various locations along the lower payload bay interior. A spotlight is also connected to the RMS wrist. These lights are controlled from panel A7.

Video signals can be downlinked by means of onboard or uplink commands. If a scene assignment for downlink is commanded through S-band or Ku-band uplink, the appropriate camera command is received through the network signal processor by the orbiter general-purpose computer. The GPC then transmits the command to the control unit on payload MDM PF2. The control unit selects the desired camera video and combines it with intercom A or B (if desired) and then sends a composite signal to the FM signal processor.

The FM signal processor transfers the TV signal to the FM transmitter, which modulates the signal and transmits it to a ground station with TV capability. Video data consisting of one of four signals (including real-time TV, main engine data, recorder dumps and payload data) can be individually assigned for downlink to the single S-band FM wide-band channel. Thus, if one of the other sources is being downlinked, video cannot be transmitted to the ground simultaneously.

The ground station receives, processes and records the downlinked TV signal. Real-time TV can be transmitted directly from the ground station to the Mission Control Center through a relay satellite. Sites with TV capability are Merritt Island, Goldstone and Hawaii.

The orbiter Ku-band system can downlink TV signals through the TDRSS directly to the Houston Mission Control Center. Since the TDRSS is not restricted to specific tracking stations, more continuous TV capability is available. However, only one Ku-band FM channel is used to downlink real-time TV, main engine data, recorder dumps and payload data. Therefore, video cannot be transmitted if one of the other sources is being downlinked.

Curator: Kim Dismukes | Responsible NASA Official: John Ira Petty | Updated: 04/07/2002
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