1、Lessons Learned Entry: 0478Lesson Info:a71 Lesson Number: 0478a71 Lesson Date: 1995-06-12a71 Submitting Organization: LERCa71 Submitted by: Judy TerlepSubject: Transmit Antenna Adjustment Limits vis Bi-axial Drive Assembly - ACTS Description of Driving Event: The transmit antenna on the Advanced Com
2、munications Technology Satellite (ACTS) has the capability to traverse in both elevation (north-south) and azimuth (east-west) directions in order to adjust the alignment between the transmit and receive antennas. The adjustment was to be accomplished by using a bi-axial drive assembly mounted betwe
3、en the transmit antenna and the spacecraft. The bi-axial drive assembly consists of two axial drive mechanisms mounted orthogonally. Each drive mechanism contains a stepper motor capable of rotating a minimum of 0.30 degrees in either direction, in steps of 0.0075 degrees +/- 0.0015.The structural j
4、oint between the bi-axial drive assembly and the transmit antenna was designed to accommodate final adjustments for final positioning or alignment of the transmit antenna. The joint was held by friction with shims via four bolts through large holes to allow for adjusting or shifting of the transmit
5、antenna for final RF alignments.The mechanical joint between the bi-axial drive assembly and its mounting to the spacecraft allowed the transmit antenna to shift locations during launch aboard STS-51. The four bolts did not maintain the proper preload and the joint slipped during launch loading. Thi
6、s has reduced the available design adjustment range for the ACTS transmit antenna.Lesson(s) Learned: Friction is not sufficient to maintain precise alignments of mechanical attachment-type joints during any type of loading, especially launch loads.Recommendation(s): Provided by IHSNot for ResaleNo r
7、eproduction or networking permitted without license from IHS-,-,-Matched drill alignment joints with body-bound bolts or drill and pin joints after assembly.Evidence of Recurrence Control Effectiveness: N/ADocuments Related to Lesson: N/AMission Directorate(s): N/AAdditional Key Phrase(s): a71 Fligh
8、t Equipmenta71 Hardwarea71 Parts Materials & ProcessesAdditional Info: Approval Info: a71 Approval Date: 1996-11-06a71 Approval Name: Sell Jamesa71 Approval Organization: 501-4a71 Approval Phone Number: 216-433-8618Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
