1、Lessons Learned Entry: 1180Lesson Info:a71 Lesson Number: 1180a71 Lesson Date: 2002-04-25a71 Submitting Organization: GSFCa71 Submitted by: Marco ToralSubject: TDRS-H S-Band Multiple Access Antenna Performance Shortfall Description of Driving Event: The TDRS-H was launched on June 30, 2000. The sate
2、llite is the first of a new series of Tracking Data Relay Satellites. The satellite incorporated a number of new communication technologies including the Single Access Springback Reflector Antenna, transmitters and receivers operating at Ka-band and the S-band microstrip patch antenna elements used
3、in the Multiple Access (MA) phase arrays. During In-Orbit Test (IOT), performance deficiencies were observed in the MA forward (MAF) and return (MAR) channels. The MA phase array system is complex in design and relies on both hardware and software to perform the on-board beam forming to track user s
4、atellites. Based on analysis of test data, a few minor deficiencies were corrected through changes to the software (sign error) and calibration error (phase shift settings). However, the MAR formed beam G/T performance remained significantly below predicted performance. Performance testing of indivi
5、dual return array elements was initiated revealing widely divergent gain and axial ratios for the elements when compared to pre launch factory measurements. In one case, the performance of a single element was seen to degrade significantly in a 12-hour period. BSS initiated a comprehensive anomaly i
6、nvestigation incorporating: 1) On-orbit testing of TDRS-H; 2) Laboratory performance investigation of flight MA antenna elements; and 3) Factory satellite system level MA testing using the TDRS-I then undergoing integration and test. Ultimately, BSS determined that the most probable cause of the obs
7、erved performance was due to the MA array sunshield (thermal blanket) coming into contact with the antenna array elements. Such contact creates a dielectric loading of the microstrip patch radiators and transmission lines altering the phase relationship of the radiators and shifting the resonant fre
8、quency of the elements. Altering the phase relationship causes the element gain pattern to “squint“ or move off axis by some 8 degrees. The peak directivity, resistive loss and VSWR (Voltage Standing Wave Ratio) performance of the MA antenna elements degraded as a result of the close proximity of th
9、e sunshield. The sunshield is held in contact with the elements by electrostatic force created by deep charging of the dielectric materials used in the construction of the antenna elements. In response, a negative “image“ charge appears in the sunshield (since it is conductive and grounded), and the
10、 electrostatic attractive force field is created.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Lesson(s) Learned: 1. The use of microstrip patch elements was a new design to BSS, and as such, received substantial attention during the design, develo
11、pment and test phase. However, the interrelated physics of the sunshield contact and performance shortfall were never fully understood.2. Designers assumed that the designed spacing between the elements and the sunshield would be achieved. (The designed spacing of approximately 1/2 inch is more than
12、 sufficient to eliminate the effect.)3. Designers of the sunshield mechanical retention were unaware of the electrostatic attraction force and assumed that the sunshield would maintain clearance in the zero gravity space environment.4. While formed beam (gain and axial ratio) tests were performed on
13、 the assembled MA array without the sunshield in flight configuration, and continuity tests were performed on each element after installation of the sunshield, there was no test designed to compare individual element gain and axial ratio performance between pre and post installation of the sunshield
14、.5. During the anomaly investigation, laboratory tests of elements with the sunshield “touching“ the elements yielded no significant effect. This was a false conclusion based on a test configuration that pulled the sunshield away from the element due to gravity.Recommendation(s): 1. The Systems Engi
15、neering activity should, as part of the Systems Requirements Review, conduct a thorough review of all derived requirements, including interfaces, to establish that all requirements are identified, documented, and have been included in the verification process.2. During the proposal and initial desig
16、n phases of the project, carefully and thoroughly evaluate the heritage and prior application of the technology. In this case, the sunshield had been used in prior applications, but not with microstrip patch antenna elements.3. During the Integration and test phases of the project, test the entire s
17、ystem in the final flight configuration. In this case the concern was focused on the RF loss of the sunshield rather than the dielectric loading impact.4. Examine in detail all analyses of the on-orbit environment impact on the system. Not all aspects of the environment are easily simulated or teste
18、d (e.g. solar input, high energy plasma, etc) and verification of performance rests with the completeness and thoroughness of the environmental analyses.5. During anomaly investigations, check and recheck conclusions, analyses and tests. It is easy to go down the wrong path when results of tests yie
19、ld answers that match pre-conceived ideas.6. Design the system for on-orbit test. In this case there was an ability to examine the performance of individual elements. In many systems, this is not the case.7. Assure adequate clearance of dielectric or conductive material from resonant structures such
20、 as the microstrip circuitry including radiating RF antenna elements and transmission lines.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Evidence of Recurrence Control Effectiveness: 1. The design was altered to include standoffs over each forward
21、 and return antenna element. The standoffs assure a minimum separation of the element and the sunshield to avoid the RF performance impact.2. Specific tests of TDRS-I were incorporated to determine if an individual element were exhibiting performance similar to one with a sunshield in forcible conta
22、ct.3. The entire TDRS-I system is tested in the final flight configurationDocuments Related to Lesson: N/AMission Directorate(s): a71 Exploration Systemsa71 Sciencea71 Space Operationsa71 Aeronautics ResearchAdditional Key Phrase(s): a71 Communication Systemsa71 Parts Materials & Processesa71 Spacecrafta71 Test & VerificationAdditional Info: Approval Info: a71 Approval Date: 2002-04-01a71 Approval Name: Jay Liebowitza71 Approval Organization: GSFCa71 Approval Phone Number: 301-286-4467Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
