APPENDIX F

DC-8 DATA DISTRIBUTION SYSTEM (DADS) CHARACTERISTICS

DC-8 Data Acquisition and Distribution System (DADS)

Characteristics and Output Products

DC-8 DADS Data Products

A. In-Flight Data Products

During each flight there are several DADS displays, viewable on monitors throughout the cabin. The DADS Parameter Display (see table F1) shows a subset of DADS data in table format. The Track Plot Display shows the aircraft flight track superimposed on a reference map. The Real-Time Plot shows several parameters as a color graph, generally in a time-series strip chart format. All of these are configurable as required and are continuously updated. In addition, the Weather Satellite APT Receiver displays real-time satellite images from the NOAA polar orbiters whenever available. It is also be possible to graphically examine all DADS parameters from any portion of the flight at the DADS station computer if necessary.

The DC-8 DADS serial transfer of housekeeping data is available in-flight to allow easy access to aircraft data by experimenter computers. The data is in ASCII format, in engineering units Data is sent at one second intervals with transmission rates of 1200, 9600, and 19.2K baud. Format and hardware interface requirements are described in another section below.

B. Post-Flight Data Products

After each flight several hardcopy DADS data products will be available. The DC-8 Mission Director Log will contain time/data stamped commentary on the flight. A set of Track Plots will show the DC-8 flight track, including flight-level winds. A set of Time-Series Plots will show a selection of DADS parameters. The Parameter Printout will contain 10-second picks of representative parameters. Other graphical products may be produced by request of the Mission Director. All of these products will be given to the GTE Project Office after each flight, in both hardcopy and electronic format. The DADS ASCII-formatted data set will also be submitted.

DADS Serial Outputs to Experiments

The DADS ASCII-formatted data is available in real time in-flight through a serial interface, and post-flight as a computer file (9600/19.2K baud format only). This section describes the formats and hardware interface requirements used to access this data.

A. 1200 Baud Data Format

Data is transferred once per second at 1200 baud in two 56-character blocks which each begin with a unique character identifier and end with an ASCII carriage return and line feed. The total number of characters every second is 112. Parameter fields within each block are not separated by a space, but there may be one or more blanks at the end of a block (before the carriage return and line feed) to pad the length to 56 characters. Table F2 shows the configuration, and Table F3 shows an example.

B. 9600/19.2K Baud Data Format

Data is transferred once per second at 9600 and 19.2K baud in seven 56-character blocks which each begin with a unique character identifier and end with an ASCII carriage return and line feed. The total number of characters available every second is 392. Parameter fields within each block (including the start-of-block character) are separated by at least one space, and there may be one or more blanks at the end of a block (before the carriage return and line feed) to pad the length to 56 characters. The contents of the first five blocks (identifiers C through G) are fixed. The contents of the last two blocks (identifiers H and I) are at the discretion of the Mission Manager and will be configured for PEM Tropics. Table F4 shows the configuration, and Table F5 shows an example.

C. General DADS Serial Output Format Information

All data parameters are in engineering units. For integer formats, the number of digits in a field may vary from one to the number shown above. For other formats, the placement of the decimal point and number of digits to the right of it are guaranteed to be as shown. However, the number of digits to the left of the decimal point may vary from one to the number shown in the field format. Unused leading digits are padded with blanks or zeroes.

Individual parameter fields will be filled with special characters for the following reasons:

Additionally, invalid or unavailable data may be replaced by question marks (?), however, the absence of question marks in a parameter field does not guarantee the validity of the data.

D. Hardware Interface Information

The DADS data distribution subsystem provides a well-defined data transfer mechanism between the DADS and onboard experiments. It broadcasts aircraft houskeeping data in ASCII-formatted engineering units via RS-232-C serial connections to experiment stations at one second intervals. Experimenters who want to receive DADS serial data in-flight will have a DADS data box on or near their experimenter station. Each box outputs the data via three RS-232-C female DB-25 connectors, corresponding to the three baud rates, which may be used in any combination. Each DB-25 connector may be configured as a modem (DCE) or a computer (DTE) with a switch, which exchanges pins 2 and 3. There is no handshaking capability between the DADS and the experiments. The outputs are opto-isolated, and the RS-232-C drivers are current limited. The serial protocol is one start bit, 8 data bits, no parity, and one stop bit. Table F6 shows the pinout of the DADS box DB-25 connectors.