Description of Driving Event:
Lack of Dependency Matrix for I-Load Recalculation
Lesson(s) Learned:
There is no formal requirement that dependent Space Shuttle I-loads be recalculated or checked when an I-load patch is to be uplinked.
Recommendation(s):
NASA should create a dependency matrix of all I-loads. Furthermore, it should assess its Space Shuttle and ISS procedures and ensure that they are all fully documented.
Evidence of Recurrence Control Effectiveness:
NASA believes that we already meet the intent of the recommendation. Flight Operations processes and documentation ensures proper I-load change implementation for all flight design I-loads, including uplinkable I-loads. These procedures include positive verification that the selected or uplinked values do not violate sub-system, element, or integrated vehicle certification and that the update meets mission requirements. I-load dependencies are verified as part of the certification assessment. Procedures for verifying I-loads to be uplinked vary. In some instances uplinked I-loads change vehicle response in a way that impacts several of the remaining I-loads; i.e., Day-of-Launch I-load Update (DOLILU). Those verification assessments include an analysis, which uses a high fidelity computer model to simulate integrated vehicle response to the new I-loads. These simulations include models of the onboard flight software of sufficient detail to verify that all applicable I-load interactions are assessed. In other cases, specific I-load dependencies are evaluated. A number of flight design uplinks involve an uplink of values that are generated and verified days or sometimes months before launch. These I-loads include vehicle navigation, targeting, and abort parameters. Verification procedures for these I-loads are identical to that used during the normal flight design template. For all cases, procedures clearly specifying verification requirements including specific I-load dependency evaluations, as applicable, are in place and under configuration control.
Documents Related to Lesson:
N/A
Mission Directorate(s):
- Exploration Systems
- Space Operations
- Aeronautics Research
Additional Key Phrase(s):
- Aerospace Safety Advisory Panel
- Computers
- Launch Process
- Risk Management/Assessment
- Software
- Spacecraft
Additional Info:
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