The following describes best case performance load calculations for each commanding function performed during a contact. Figure C-8 displays a summary of commanding loads under best case commanding rates.
Execute Command Plan - It is assumed that the best case commanding load is 1 Kbps, and that a command word contains 30 bits. This translates into 33.33 words/second, which is a negligible processing load.
Constraint Check - As stated above, the worst case command loading would be a block command with each command step in the block having one separate command constraint check. In the best case scenario, each command step in the block would require evaluation of one constraint check at the best case commanding rate. Since the 1 Kbps rate translates into 33.33 commands/sec (see above), a maximum constraint check rate of 33.33 checks/sec is needed. It was determined from analysis that the maximum number of rules for a command constraint is approximately four. Based on these assumptions, best case constraint checking would require (33.33*4) 133.3 rules/second. Based on benchmarks of leading real-time rule-based expert system shells, it was determined that they can support ~270 rules/sec/SPECint92, resulting in a total constraint check load of 0.49 SPECint92.
Transmit - This function is included in Execute Command Plan and is a negligible load.
Verification - As stated above, it is also assumed that commanding functional verification will be done using rule bases. It is estimated that the maximum number of rules used for functional evaluation would be about ten. Since we assume ten verification rules/command and 33.33 commands/sec, 330 verification rules/sec must be supported. This equates to a verification load of 1.24 SPECint92.
Display - The display load is included in Telemetry as a combination of telemetry and commanding loads for a contact.