1、Public Lessons Learned Entry: 4417 Lesson Info: Lesson Number: 4417 Lesson Date: 2010-08-31 Submitting Organization: KSC Submitted by: Annette Pitt Subject: Shuttle Orbiter Airlock Hatch Failure Caused By Loose Screw On STS-80 Prevented Two Planned Mission EVAs Abstract: During the Space Shuttle STS
2、-80 mission, the two planned Extravehicular Activities (EVA) were scrubbed when the astronauts discovered that the outer airlock hatch would not open. This impacted the plan to evaluate the EVA tools that would be used for the construction and maintenance of the International Space Station. Upon ret
3、urn from the mission, troubleshooting revealed that the airlock actuator that is used for latching and unlatching the hatch was defective. This actuator was removed and replaced. Troubleshooting on the removed actuator revealed that a small screw had come loose from an internal assembly and lodged i
4、n the planetary gears of the actuator. Space Shuttle Program Corrective Action Record Number AE0959-010 documented this problem. The Failure/Problem Report Number NSLAD-RE-97-044 documented the actuator findings. Both of these reports are attached to this Lesson Learned input. Description of Driving
5、 Event: The Space Shuttle mission STS-80 was launched on October 31, 1996. The mission planned for two EVAs to evaluate tools that would be used for the construction and maintenance of the the International Space Station (ISS). However, when the astronauts attempted to open the outer airlock hatch,
6、the hatch would not unlatch. The decision was made by the mission managers not to attempt the EVAs since they did not want to risk damage to the hatch or seals. When Columbia returned to the Kennedy Space Center (KSC), following the mission, troubleshooting revealed that the outer airlock hatch actu
7、ator assembly was faulty. A new actuator assembly was installed on Columbia and the outer airlock hatch opened and closed normally. Troubleshooting on the bench revealed that one of the two Number 4-40 fasteners that hold the no-back/clutch assembly together had backed out and was lodged between a p
8、lanetary gear and the ring gear within the actuator gearbox. Furthermore, the second fastener was partially backed out and was loose (no running torque). It was also found that the threaded inserts used with the fasteners were a non-locking type when the drawing specified that a locking threaded ins
9、ert should be used. Additionally, the vendor drawing did not specify a torque value for these fasteners. To resolve this issue, all actuators in the fleet were reworked to install locking threaded inserts. The vendor drawing was also updated to specify a torque on the fasteners and to verify running
10、 torque during the installation. Below is a video discussion of this lesson Click this link to see the video transcript Lesson(s) Learned: The science of Human Spaceflight is a very non-forgiving process. In this case, a dislodged screw jammed a gear assembly thus preventing a hatch from opening dur
11、ing a space mission. This impacted the mission by preventing the EVAs from occurring. Something as simple as a small screw provided a major impact to the mission objectives. Attention to the details of installing the screws in the actuator gearbox and not noticing that there was no running torque pr
12、ovided the conditions where the screw fell out and jammed the actuator gear. Additionally, there was no simple way to screen for this failure. This hatch had successfully flown on a number of previous missions and had successfully passed the pre-flight functional check-out and closed nominally prior
13、 to launch, but then failed to operate properly during the mission. Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-STS-80 Actuator Gear Box Assembly with embedded screw in gears Provided by IHSNot for ResaleNo reproduction or networking permitted wi
14、thout license from IHS-,-,-STS-80 Actuator Gear Box Assembly showing missing and loose screws Recommendation(s): A uniform methodology for the installation of all fasteners should be provided early in the design phase of the program. This fastener specification should be imposed on all vendors/contr
15、actors responsible for hardware assemblies on the space vehicle. Where applicable, locking threads with running torques and final torques should be imposed on all assembly drawings. Additionally, the Shuttle Orbiter hatch actuators are essentially multi-geared torque multipliers containing numerous
16、small parts which cannot be easily maintained. Despite several successful ground cycles of the hatch actuator, the problem was not identified until flight, and was not repairable in-flight. Future designed should give serious consideration to less elegant designs. Designs with less complexity, lower
17、 parts count, and the ability for in-flight maintenance, in-flight repair or in-flight work-around should be given a higher priority in design trade studies. It is easy to design something more complicated with added features and additional failure modes, but more difficult to build it to be simple
18、and robust with fewer failure modes; future designers should strive for the latter. Evidence of Recurrence Control Effectiveness: There have been no recurrences of the actuator hatch screw issue since STS-80 after all the actuators were reworked. Documents Related to Lesson: Space Shuttle Program Co
19、rrective Action Record Number AE0959-010 Failure/Problem Report Number NSLAD-RE-97-044 Click here to download communication document. Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Mission Directorate(s): Space Operations Exploration Systems Additio
20、nal Key Phrase(s): Logistics and maintenance Launch Systems Lander Systems Level II/III requirements definition Engineering design and project processes and standards Additional Info: Project: Space Shuttle Programs Approval Info: Approval Date: 2011-08-01 Approval Name: mbell Approval Organization: HQ Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
