Computers in Spaceflight: The NASA
Experience
- [399-401] Appendix III: GOAL,
A Language for Launch Processing
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- GOAL is a high-level language that uses
the terminology of test engineers to write tests and procedures to
certify that a Shuttle vehicle is ready for launch. When the first
automated preflight checkout programs were written in the
mid-1960s, Marshall Space Flight Center originated ATOLL, a
special high-level language for use in preparing test procedures.
GOAL superseded that language in the early 1970s.
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- Fig. III-1 is a segment of a GOAL program
used to safe various spacecraft systems if a NOGO condition causes
the final countdown to be suspended. Note that names of data items
held in common in the Launch Processing System appear within
brackets, <>, and data local to the program is named between
parentheses, (). Statements familiar to high-level programming
language users, such as READ, IF-THEN-ELSE, and LET, have similar
functions in GOAL. Additional statements, such as VERIFY, make it
possible for the engineers to test whether valves or switches are
set properly or whether a value is within a specified range. SET
permits switches to be activated.
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- Although seemingly highly structured, GOAL
allows engineers to frequently repeat the most common error of
their peers using FORTRAN: excessive unconditional jumps such as
the one on line 2030, making it difficult for someone to read and
modify the program. Whereas in older versions of FORTRAN it was
necessary to create structures such as those found between lines
2026 and 2039 to handle multiple statements in the THEN and ELSE
blocks of a selection structure, later versions of the language
and GOAL itself (see lines 1980 through 1988) permit multiple
lines of code to be included within the blocks. Therefore, the
GOTO statements are often used less to create structure than to
provide a "quick fix" when the logic of the program needs
expanding.
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- GOAL is used both at the Kennedy Space
Center and Vandenberg Air Force Base in launch processing systems
and is expected to last for the duration of the Shuttle
program.
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- Further information about GOAL is
contained in the following documents:
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- - IBM Corporation, Launch Processing
System Checkout, Control and Monitor Subsystem Detailed Software
Design Specifications, Book 2, Part 1: GOAL Language Processor,
KSC-LPS-IB-070-2, pt. 1, release S33, Cape Canaveral, FL, June 3,
1983.
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- - IBM Corporation, Launch Processing
System Checkout, Control, and Monitor Subsystem: GOAL On-Board
Interface Language, KSC-LPS-OP-033-4, release S33, Cape Canaveral,
FL, April 27, 1983.
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FIGURE III-1
FIGURE III-1- continued
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