1、Public Lessons Learned Entry: 3157Lesson Info:a71 Lesson Number: 3157 a71 Lesson Date: 2010-06-8 a71 Submitting Organization: KSC a71 Submitted by: Annette Pitt Subject: Environmental Control System (ECS) Purge Support Requirements Abstract: When Environmental Control System (ECS) purge support requ
2、irements for the Orbiter were originally developed, they identified the parameters of the purge and when a purge should be started and ended while the Orbiter was in different locations. The requirements did not address unplanned purge outages or times when excursions outside the purge parameters oc
3、curred. At some point actual testing should be performed to determine the effects of a purge outage or temperature/humidity excursion on the spacecraft. Description of Driving Event: It was believed that outages and excursions would occur infrequently and would be addressed by waivers to the ECS req
4、uirements. The problem was that, because the ECS purge was being supplied 24 hours a day, 7 days a week for months at a time, the likelihood that a purge outage or excursion would occur increased dramatically, and numerous waivers were being written, sometimes more than once per flight. A general re
5、quirement with a broader range but a shorter time span was developed to accommodate short excursions outside the acceptable parameters for temperature, flow rate, and humidity. The general requirement also allowed short-duration purge outages as long as certain environmental conditions were met. Thi
6、s new general requirement was implemented in 1988 after 25 outage/excursion waivers were generated in 1987. Initially, the general requirement addressed a limited number of purge outages and excursions; but by 2002, it encompassed all purge outages and excursions. Lesson(s) Learned: If you plan to p
7、rovide an ECS purge for long periods during spacecraft ground processing, it is better to have a requirement to cover unplanned purge outages and excursions from the beginning. Recommendation(s): Determining the limits for this type of requirement would be difficult to do before the hardware is buil
8、t because of the lack of information on the Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-external environment and the actual effect the purge would have on the hardware being protected. However, a placeholder for a general requirement could be put
9、 in place. At some point, a completed pathfinder spacecraft will be built and actual testing could be performed using temporary surface temperature sensors and humidity sensors to determine the effects of a purge outage or temperature/humidity excursion on the spacecraft. Evidence of Recurrence Cont
10、rol Effectiveness: N/A Documents Related to Lesson: N/A Mission Directorate(s): a71 Space Operations Additional Key Phrase(s): a71 1.Ground processing and manifesting a71 1.Configuration control and data management a71 1.Mission concepts and life-cycle planning a71 1.Ground support systems a71 1.Planning of requirements verification processes Additional Info: a71 Project: Space Shuttle Program Approval Info: a71 Approval Date: 2010-10-08 a71 Approval Name: mbell a71 Approval Organization: HQ Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
