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2.3-6

Video Processing Equipment

The video control unit (VCU) is the central processor/controller for the CCTV system. The VCU consists of two line replaceable units (LRUs): the remote control unit (RCU) and the video switching unit (VSU). Both LRUs are located behind panels R17 and R18 in the aft flight deck. These units are forced air cooled by cabin fans, although neither LRU includes a temperature sensor. An extension of the VSU is the video processing unit (VPU), which allows for more video interfaces than the VSU can provide. It is located in panel R12. The latest addition to the Shuttle video processing equipment is the DTV system, which is located at L10L. Finally, one non-installed piece of equipment is the sequential still video (SSV) system that allows the shuttle to send sequential still video snapshots to MCC during Ku-band loss of signal (LOS) periods.

Remote Control Unit

The RCU receives all CCTV commands from both the crew and MCC. Ground command interface logic (GCIL) control switch located on panel A7U determines whether MCC can send commands to the CCTV system. When the TV POWER CONTROL switch is in the CMD position, MCC can uplink commands to the CCTV system, and the crew will be able to use all panel A7U TV switches except the TV POWER CONTR UNIT MN A / OFF / MN B switch. This TV POWER CONTR UNIT switch enables GCIL drivers to power up the VCU through either DC Main A or B via panel R14, thus this is the one true GCIL switch. The GCIL drivers prevent the crew and MCC from activating or deactivating the VCU simultaneously. When the GCIL TV POWER CONTROL switch is in PANEL, the crew can configure the TV POWER CONTR UNIT switch to provide VCU power or to turn the VCU off. All uplink commands to the CCTV system are inhibited when the GCIL switch is in PANEL.

TV POWER Controls on Panel A7U

Uplink commands to the RCU must pass through payload 2 mutiltiplexer/demultiplexer (PF2 MDM). The VCU power MN A / OFF / MN B commands to the GCIL drivers use PF1 or PF2 MDM like all other GCIL commands. However, if the GCIL Main C circuit power provided from panel R14 were to fail, the RCU will inhibit all uplink CCTV commands, except for the VCU power-on commands. The crew can send any uplink CCTV command by executing a real-time command (RTC) on SPEC1 of the Systems Management General Purpose Computer (SM GPC). The TV POWER CONTROL switch must be in the CMD position for crews to use this feature. Crews do not carry any CCTV specific RTCs in any Flight Data File (FDF) documents. This capability would only be used if MCC were unable to uplink commands or for functions not available from panel A7U. The RCU includes two independent video sync generators. The sync generators are tied to the power on logic and TV SYNC NORMAL/REVERSE switch on panel A7U.

When the TV SYNC switch is in NORMAL, sync generator A is powered by Main A with sync generator B on Main B. The bus that powers the VCU also applies power to the sync generator tied to that bus. When the TV SYNC switch is in REVERSE, sync generator A is tied to Main B and sync generator B is tied to Main A. This feature is provided to allow the crew to switch sync generators without power cycling the VCU in case of a sync generator failure. MCC can see the status of this switch, but cannot send a command to switch sync generators without switching main bus power sources.

In addition to generating master sync signals, the RCU also generates a full-field test signal,

better known as a test pattern. The test pattern is black and white. The test pattern can be selected as a video source from panel A7U or via an uplink command.

The sync signal is distributed to CCTV cameras and the VSU for synchronization purposes. Commands to the cameras are embedded in the sync signal. Each camera has a unique address. This address is sent out with the command in the sync signal. Therefore, only the correctly addressed camera will respond to the command. Uplinked commands are sent on a different sync (horizontal scanning) line than A7U commands. It is possible for the crew and MCC to send conflicting commands to a camera at the same time; coordination between crew and MCC is very important to prevent potential conflicts. Usually, the crew configures cameras and MCC selects cameras for downlink. Prior to launch, each crew should talk with the lead INCO for their flight to work out CCTV responsibilities during crew activity and sleep shifts.

The crew activates payload bay cameras using the TV CAMERA POWER switches located at the top of panel A7U. These switches are momentary in both the ON and OFF positions. The ON/OFF talkbacks are set by the RCU. The talkbacks indicate the status of a 28 V dc discrete signal that enables a remote power controller (RPC) to provide panel R14 circuit breaker power to a payload bay camera and PTU. The talkback status can be misleading because the talkback can indicate ON when the circuit breaker that provides power to the camera is out. Crews should always use these switches to power off the cameras prior to deactivating the VCU to ensure correct camera powerdown.

TV SYNC Switch on Panel A7U

CAMERA POWER Switches and Talkbacks on Panel A7U

TV DOWN LINK switch on Panel A7U

There are two RMS camera switches to note. In addition to the RMS TV CAMERA POWER switch, another RMS camera switch is located below the aft rotational hand controller (RHC) on panel A7U. The RMS CAMERA WRIST/ELBOW select switches toggle between the wrist (end effector) and elbow cameras. Only one RMS camera can be activated at a time. Cycling the switch powers off one camera and powers on the other. MCC cannot select between the wrist and elbow cameras nor can MCC identify the position of the switch using downlinked telemetry.

In addition to TV SYNC NORMAL/REVERSE and RMS CAMERA WRIST/ELBOW switches, MCC is unable to configure the TV DOWNLINK ENABLE/INHIBIT switch func- tion. This lever lock switch inhibits the VSU output to the analog downlink Ku-Band and S-Band FM communications systems. This switch can be used to ensure that no video is downlinked during "sensitive" mission operations. For the majority of mission operations, this switch should be in the ENABLE position. MCC receives telemetry that indicates the position of the TV DOWNLINK

2. SYSTEMS 2.3 CLOSED CIRCUIT TELEVISION (CCTV) 2.3-8

switch. For DTV, this enable/ inhibit function is performed by the MUX/ VTR/CC switch on the DTV MUX on panel L10L.

The RCU provides some telemetry to the pulse code modulation master unit (PCMMU) via OF4 MDM. This includes camera overtemp, downlink enable, VCU power source, sync normal/reverse, sync generator active, and "camera select." The camera select is the camera selected for downlink. This may be a different camera from the one the crew or MCC is commanding at the time. The crew and MCC can command different cameras at the same time. The ALC/Gamma status of the downlink camera will be included in the telemetry to the PCMMU.

Video Switching Unit (VSU)

The VSU can accommodate up to 13 video inputs and 7 outputs. However, panel A7U only provides for 10 inputs and 4 outputs. Adding pushbuttons to expand the VSU oper- ational capability has been determined by the SSP as being too expensive for the increase in capability and is planned for the advanced VPU.

The VSU is used to route video from a source to a destination. All commands to the VSU are processed by the RCU before being sent to the VSU. Note that the crew routes video by selecting a destination and then a source, whereas MCC selects a source and then a destination. When the crew selects a destination on panel A7U, that output PBI illuminates. Once an input is selected for that particular output, the input PBI will illuminate as well. If the input is a camera, the crew can select ALC/Gamma PBI settings and/or send PTU/lens commands to that camera and pan/tilt unit.

The VSU is synchronized to the RCU via the sync generators. This allows the VSU to change video sources for a destination at the end of a video field to prevent visible picture distortion when the video switches engage. The synchronization of the CCTV also allows the VSU to read CCTV camera telemetry. The VSU can read camera ID, temperature, and pan/tilt angles. If the VSU detects a camera exceeding 45° Celsius, an overtemp warning is sent to the RCU. The RCU sets a telemetry bit high so that

the SM GPC will annunciate a SM Alert and a S76 COMM CAM TEMP message. The temperature limit is set in the VSU and cannot be changed by a table maintenance block update (TMBU). A TMBU can be used to inhibit the SM alert and message.

The VSU is also capable of generating multiplex (mux) scenes that appear as a split screen of two CCTV cameras. The VSU takes the center portion of a camera scene and places it on the left or the right side of the mux picture. The VSU determines where to extract the center portion of the video source from the RCU’s sync signals. The VSU can only mux synchronous video sources. VTR playback and camcorders cannot be muxed by the VSU.

The VSU receives GMT from the orbiter timing buffer. The GMT is formatted and inserted in the vertical retrace interval by the VSU, using sync timing from the RCU as a reference. This GMT is inserted in all incoming video lines when the VSU is in the sync mode. Since both camcorders and VTRs are asynchronous devices (i.e., not in sync with the RCU), the VSU fails to insert the GMT timetag in the correct location of the asynchronous video. Crews and flight controllers will see this as a thin, flashing, segmented white line that scrolls across the screen of the color monitors and in the downlink video. The VSU interprets the GMT as an elevated camera temperature. This will produce a false SM S76 COMM CAM TEMP message. An asynchronous (async) mode command is available to inhibit GMT timetags and disable the VSU's temperature sensing circuits. The async mode affects camera mode sensing in the VSU. The ALC and Gamma pushbuttons on panel A7U may remain static and not reflect the true configuration of standard orbiter payload bay cameras. This async mode is usually enabled for VTR playback to downlink and for downlinking camcorder video. Otherwise, a white line will be visible in the scene. The asynchronous mode does not mean that the CCTV System is no longer synced together. CCTV cameras are still slaved to the RCU, as is the VSU. Since almost all payload customers require a GMT timetag in recorded and real-time video, crews and flight controllers must coordinate the use of async mode.