1、Lessons Learned Entry: 1113Lesson Info:a71 Lesson Number: 1113a71 Lesson Date: 1999-02-01a71 Submitting Organization: HQa71 Submitted by: David M. LengyelSubject: International Space Station (ISS) Program/Extravehicular Activity (EVA)/Simplified Aid for EVA Rescue (SAFER) Description of Driving Even
2、t: Lack of Sufficient Operational Assets to Procure Necessary Safety HardwareLesson(s) Learned: The EVA project lacks sufficient operational assets to meet unplanned contingencies. There are no spare Extravehicular Mobility Units (EMUs). Only five U.S. Simplified Aid for EVA Rescue (SAFER) flight un
3、its will be available to meet a requirement to maintain three units on orbit. In addition, only four Russian SAFER units are planned.Recommendation(s): To meet contingencies that are almost certain to arise, additional EMUs and SAFER units or their critical long lead components should be procured as
4、 soon as possible.Evidence of Recurrence Control Effectiveness: NASA concurs with the ASAP recommendation. With respect to the EMU, the inventory of life support system (LSS) hardware will be 14 (13 Class I and 1 Class II) by October 1999.Exceedences to our supply begin in 2000. In order to achieve
5、a 90 percent probability of sufficiency, NASA must increase its inventory by two LSSs. NASA plans on addressing this issue within the Program Operating Plan (POP) 99. We plan to upgrade the current Class II LSS to Class I and upgrade the certification unit to Class II. This will increase our invento
6、ry to 15. NASA also plans to go forward with the recommendation to procure an additional LSS to achieve 16 LSSs. Additionally, the current space suit assembly (SSA) flight hardware models predict SSA demand beyond the current inventory Provided by IHSNot for ResaleNo reproduction or networking permi
7、tted without license from IHS-,-,-of 15. The demand peaks at 23 for one month, but there are 15 months where it is at 18 through 2004. The current plan is to procure hardware to 18 through the POP 99.SS. A hardware shortages can be determined once crewmembers are selected. The lead times for SSA har
8、dware are such that once shortages are determined, specific hardware shortages can be procured. The current training model for the EMU predicts demand not to exceed the procured inventory of 10; therefore, sufficient inventory exists for training.With respect to the USA SAFER, NASA concurs with the
9、ASAP recommendation on obtaining critical long lead components. In fact, the majority of the long lead components have already been procured. These components are expected to support the USA SAFER flight units for their 7-year life.NASA can normally support the requirement to maintain three USA SAFE
10、R flight units on orbit with five flight units in service. The current rotation plan utilizes two of the flight units to accommodate rotation of back-to-back missions where the turn-around time is approximately 1 month. With one flight unit out of service, four USA SAFER flight units can be rotated
11、to maintain three units on orbit for 92 percent of the flights per the International Space Station (ISS) assembly sequence dated February 22, 1999.The remaining 8 percent of the flights can also be supported with contingent coordination ahead of time to reduce the turnaround time from approximately
12、1.5 months to approximately 1 month.Another option was already planned to deal with the margin in the rotation of five USA SAFER flight units. In order to increase the USA SAFER logistics margin, an extension of the 1-year certification will be assessed based on flight performance. Being able to lea
13、ve the units on orbit longer will allow the rotation rate to decrease sufficiently to eliminate any problems with having one unit out of service. Data will be collected for analysis immediately after the flight units are declared fully operational. At the present, additional USA SAFER flight units a
14、re not needed for the following reasons:1. The rotation of five flight units can fully support the flight requirement2. The rotation of four flight units can support the flight requirement for at least 92 percent of the current ISS assembly flights3. The turnaround time can be reduced for special ca
15、ses4. The on-orbit certification is expected to be extended with additional flight data.However, in the event a USA SAFER flight unit is not available for any reason, the EVA crew is trained to use the two-fault tolerant tethering scheme to meet the safety requirement. This tethering scheme is fully
16、 certified and has been used successfully during several EVAs, including those on the recent STS-88 mission. Lastly, with respect to the Russian SAFER, NASA has revised its plan and will now produce five flight units, rather than four, in order to support the logistics model consistent with the USA
17、SAFER plan.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Documents Related to Lesson: N/AMission Directorate(s): a71 Space Operationsa71 Exploration SystemsAdditional Key Phrase(s): a71 Aerospace Safety Advisory Panela71 Extra-Vehicular Activitya71
18、 Flight Equipmenta71 Procurement Small Business & Industrial Relationsa71 Research & DevelopmentAdditional Info: Approval Info: a71 Approval Date: 2002-02-12a71 Approval Name: Bill Loewya71 Approval Organization: HQa71 Approval Phone Number: 202-358-0528Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
