1、Lessons Learned Entry: 1397Lesson Info:a71 Lesson Number: 1397a71 Lesson Date: 2003-09-01a71 Submitting Organization: GSFCa71 Submitted by: James Tomaka/Yen WongSubject: Space Network (SN) Ka-band Infrastructure - Design, Integration, and Test Issues Abstract: A Ka-band return infrastructure was imp
2、lemented for NASAs Space Network under the GSFC Ka-Band Transition Project (KaTP). Throughout the requirements development, design, implementation, and testing activities for this ground terminal, there were a number of events or circumstances that caused lessons to be learned. These events and less
3、on learned are listed below.Description of Driving Event: The KaTP was instituted at the White Sand Complex by December 2002 and consisted of two major functions: Modify the existing 225 MHz Ku-band downconverters to support the Ka-band Space Network Interoperability Plan (SNIP) frequencies and inst
4、all a Ka-band wideband architecture consisting of waveguide equalizers, downconverters and IF Switch. Associated software and firmware changes were also required. A demonstration test was conducted to validate the overall performance of the KaTP infrastructure using high data rate technologies that
5、could support future NASA near-earth missions. 1. System Requirements Document (SRD) DevelopmentThe SRD encompassed too many requirements, some of which were not directly applicable to the immediate KaTP. 2. AnalysisThe WSC KaTP team spent unscheduled resources performing analysis on the “RF solutio
6、n” Waveguide Equalizer. The vendor produced simulation results based on group delay, while the KaTP SRD had results in deviation from best-fit phase (phase nonlinearity). The KaTP team also spent Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-consid
7、erable unscheduled time performing analysis on the effects of phase non-linearity on system performance. 3. Vendor DeliveryThe KaTP was adversely affected by the late delivery of vendor-developed equipment. The downconverter vendor has originally proposed a 6-month delivery schedule that extended to
8、 19 months. The vendor had difficulty meeting several downconverter specifications and had spent several months redesigning modules. The IF Switch delivery was also extended from 6 months to 10 months based on vendor inexperience with developing the product. 4. Equipment ProcurementThe KaTP contract
9、or team underestimated the time and effort to initiate procurements through the GSFC Consolidated Logistics Facility (CLF). The KaTP contractor accounted for the time required to perform RFP technical reviews, however processes required for large-ticket items (i.e. downconverters) require additional
10、 vendor paperwork that was not accounted for by the team. While the KaTP contractor team set up communications with the buyer at the CLF to speed the procurement process, the schedule estimates were far too optimistic (usually assuming 1 week) to get vendors under contract. 5. Project BudgetThe KaTP
11、 team exceeded the initial budget estimate allocated for the project. The KaTP provided many unique design challenges that were magnified by the limited funds available for the task. The KaTP team was required to modify a total of 28 downconverters (225 MHz), and install a Ka-band architecture consi
12、sting of 650 MHz downconverters, waveguide equalizers in multiple equipment chains interfaced to a common IF Switch. Some of the budgetary problems encountered can be attributed to the growth of the project and additional testing required by the customer. 6. Waveguide Equalizer Equipment DefinitionT
13、he KaTP team initially focused on the Waveguide Equalizer operating at the IF frequency similar to the legacy design The KaTP Waveguide Equalizer procurement was delayed while a vendor performed a feasibility study. There were considerable additional amounts of time (approximately 9 months) and mone
14、y ($47,000) before the IF solution was scrapped in favor of an RF solution. 7. 225 MHz Downconverter ModificationsThe KaTP project called for the modification of an existing set of unique downconverter chassis. These units were not consistent in their implementation when initially manufactured a dec
15、ade earlier. There were unanticipated differences in the original implementation between each chassis such as Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-cable routing and parts supplied by different vendors. This caused some additional “lost tim
16、e” in having to deal with these subtle differences, and realignments. 8. Interference with TDRS Telemetry SignalDuring KaTP Demonstration tests interference of the TDRS telemetry signal was noted while a CW signal was present on the Ka- wideband channel. The KaTP attempted to support the SNIP wideba
17、nd frequency plan where the downlink signal of 13.720 GHz was shifted to 13.725 GHz. It was the view of the KaTP team that sufficient isolation existed between the Ka-band downlink signal on one polarization and the TDRS telemetry signal at 13.725 GHz on the opposite polarization. The KaTP team did
18、not account for the potential for a user spacecraft going to CW mode. 9. SN DemonstrationDuring the KaTP 600 Mbps demonstration, a high end-to-end implmentation loss was measured. This high implementation loss occurred as a result of using non-optimum test equipment to test the channel. The test tra
19、nsmitter, receiver, upconverter, downconverter and high-powered amplifier (HPA) all contributed to the channel distortions that degraded performance. The KaTP demonstration tram spent unscheduled resourced performing analyses and simulations in order to determine the reason for the high end-to-end i
20、mplementation loss. Lesson(s) Learned: 1. System Requirements Document (SRD) Development2. The SRD development task unnecessarily grew in scope and began to encompass future follow-on work. In addition to Ka-band IF requirements, several versions of the SRD included performance issues related to CCS
21、DS data routing. Considerable time and effort was expended on reviewing documentation that was not pertinent to the task at hand. The SRD should have focused on the function and performance requirements of the Ka-band IF implementation task 2. AnalysisThe WSC KaTP team did not originally allocate an
22、y labor costs or schedule impacts associated with performing analysis to the waveguide and phase nonlinearity issues. Delays to the KaTP project were incurred while a contractor team was called on to perform additional “impact to system performance” analysis. An example of this was experienced durin
23、g the decision on total amounts of phase nonlinearity allowable for the KaTP infrastructure during the Waveguide Equalizer procurement. On a project with the scope, complexity and challenges of the KaTP, the team must consider budgeting additional hours for these unforeseen problems. 3. Vendor Deliv
24、eryProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-While the KaTP implementation schedule was aggressive, one could not account for the large delays encountered from the vendors. The contractor team spent considerable time and energy working with the
25、 vendor and pushing for delivery. In future large procurements, the contractor team should account for some vendor delays when forecasting schedule and there should be some way of enforcing vendors to deliver hardware on time (either through incentives or penalties incorporated into the contract). T
26、he procurement office should have been involved earlier and they may have worked the delivery issues since they control the payments and have more clout with the vendor. Additional time in schedule should be allocated to do more work on vendor surveys and “requests for information” from prospective
27、vendors. This may have given the KaTP team a better feel for aggressive specifications and alternative architectures. In some cases the team received one vendor quote, which implies the specifications may have been too restrictive. 4. Equipment ProcurementThe KaTP contractor team has learned to proj
28、ect more time into a schedule to account for RFP technical evaluations, initiating procurements through the CLF, and getting vendors under contract. For large acquisitions, this process can take four to eight weeks. 5. Project BudgetThe size and complexity of the KaTP presented several unique challe
29、nges. From the onset, NASA project management stated the project had limited funds, however, they wanted to accomplish all of the goals of the project. The KaTP team attempted to achieve a system that met all the requirements with a minimal amount of risk to the project budget and schedule. This app
30、roach drove the team to implement an architecture similar to the legacy design and in the future the team should evaluate the critical parameters that impact system performance and choose an architecture that would minimize this risk. 6. Waveguide Equalizer Equipment DefinitionThe KaTP team focused
31、on an IF frequency Waveguide Equalizer too quickly without weighing other options. This decision was based somewhat on the legacy equipment design using an IF-based equalizer. The team should have explored other possibilities concurrently but the time and effort was not allocated into the schedule.
32、7. 225 MHz Downconverter ModificationsThe legacy 225 MHz downconverters were built as custom units and the implementation varied from chassis to chassis. This problem could not have been foreseen, a realistic schedule should allot additional time to handle unforeseen problems. Provided by IHSNot for
33、 ResaleNo reproduction or networking permitted without license from IHS-,-,-8. Interference with TDRSS Telemetry SignalThe KaTP team should have contacted the NASA spacecraft engineering group charged with the development of the TDRS- HIJ series spacecraft to determine the rationale for their freque
34、ncy plan. The spacecraft manufacturer chose to design a specific frequency plan for the TDRS-HIJ series satellites that was not compatible with the SNIP frequency plan. The KaTP team should have researched this issue more thoroughly during the design and implementation of the ground infrastructure.
35、9. SN DemonstrationThe KaTP was hindered during the SN Demonstration tests by test equipment that exhibited higher than expected implementation losses. A considerable amount of time was spent verifying the test equipment, understanding and characterizing the losses inherent in the various test confi
36、gurations. It is recommended that test receivers should be optimized for the data rate under test. Future testing should incorporate test equipment that meets or exceeds the fidelity one is trying to demonstrate. Suspect test equipment reduces the confidence in the test results and impacts the sched
37、ule and budget. Recommendation(s): Recommendations are provided above as part of the lesson learned for each topic. Evidence of Recurrence Control Effectiveness: N/ADocuments Related to Lesson: N/AMission Directorate(s): a71 ScienceAdditional Key Phrase(s): a71 Communication Systemsa71 Facilitiesa71
38、 Ground Equipmenta71 Ground Operationsa71 HardwareProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-a71 Independent Verification and Validationa71 NASA Standardsa71 Parts Materials & Processesa71 Research & Developmenta71 Test & Verificationa71 Test Articlea71 Test FacilityAdditional Info: Approval Info: a71 Approval Date: 2004-05-19a71 Approval Name: Al Galloa71 Approval Organization: GSFCa71 Approval Phone Number: 301-286-3756Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
