NASA Office of Logic Design

NASA Office of Logic Design

A scientific study of the problems of digital engineering for space flight systems,
with a view to their practical solution.

NASA SP-504: Space Shuttle Avionics System

Section 4  System Mechanization/Operation

Display and Control

The display and control (D&C) subsystem includes the crew interface devices located at the commander and pilot forward stations and the mission and payload specialist stations in the aft part of the flight deck. Figures 4-21 and 4-22 are photographs of the forward and aft flight decks, respectively, showing the locations of the various devices. Figure 4-23 contains a simplified block diagram of the D&C system. (See also the avionics system block diagram [A, I] through [D,7].) Included are the multifunctional CRT display system (MCDS), the dedicated flight control displays driven by the display driver units, the heads-up displays, the various pilot input devices, and dedicated, hardwired subsystem displays and controls. All, except for the dedicated, hardwired devices, receive data from, and execute commands through, the central computer complex.

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Figure 4-21. - Forward flight deck.

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Figure 4-22. - Aft flight deck.

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Figure 4-23. - Display and control block diagram.

Four MCDS's are normally installed in the vehicle, three on the forward flight deck and one in the mission specialist station. Provisions are included for a fifth unit if required. Each MCDS is made up of a display electronics unit, a display unit (DU), which includes a CRT, and a keyboard unit (KBU). Switches associated with each CRT allow crew selection of GNC, SM, or PL major functions. In the case of the three systems located at the forward station, two keyboards are shared by three DEU's. Redundant contacts on each key on the shared keyboards provide keystroke inputs simultaneously to the left and center or the right and center DEU's, respectively. Keystrokes are displayed on a message line at the bottom of the CRT for crew assessment and approval before execution. When a message is designated for action, the DEU performs a validity assessment and calculates a checksum; then, when polled, the DEU transmits the checksum to the GPC complex. Each display bus is connected to all five GPC's; therefore, all DEU messages can be received by all computers if appropriate. All computers listening to the bus will act on the message and, depending on the major function selected, the message content, and the operation in progress, will send appropriate format information and dynamic data to the DEU for display.

Three display driver units service dedicated flight control displays for the commander, pilot, and aft stations, respectively. The data which drive these displays originate in the computer complex, are transmitted over four flight-critical data buses, and are converted and conditioned as required in the DDU. Each DDU has four data bus inputs, with a manual switch for selection of the active data source. The aft unit services only an attitude direction indicator.

The flight control input devices include the rotational hand controller, the translational hand controller (THC), the speed brake thrust controller (SBTC), and the rudder pedal transducer assembly (RPTA). One RHC and one THC are located in the aft station, and one THC is located in the commander's station. Duplicate sets of the rest of the devices are located in the commander and pilot stations. All of the controllers use triply redundant outputs, which are distributed among the four flight forward MDM's for transmission to the computer complex. Electrical power is supplied by the DDU's.

Heads-up displays are located in front of the commander and the pilot for use primarily during approach and landing. These units provide a display of flight control data superimposed on the out-the-windshield view of each station. Each HUD interfaces with two of the flight-critical buses. Manual switches provide for selection of the driving data source.

Flight-critical switches, such as those which establish the flight control system mode, use triply redundant contacts routed through separate flight-critical MDM's and buses to the computer complex. Signal selection is performed in software in the GPC's using a majority vote technique. The action requested is then commanded by the computer complex.

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