1、Public Lessons Learned Entry: 6636 Lesson Info: Lesson Number: 6636 Lesson Date: 2012-04-10 Submitting Organization: JPL Submitted by: David Oberhettinger Subject: Conduct a Final Mechanical Walkdown Prior to Spacecraft Integration with the Launch Vehicle Abstract: Where previous JPL spaceflight pro
2、jects relied solely on interim inspections and walkdowns during ATLO, the in-house MSL project conducted a formal, final, mechanical walkdown of the as-built configuration prior to vehicle stacking at the launch site. Because NuSTAR was an out-of-house build, an assessment and final walkdown was per
3、formed independent of the system contractor that similarly produced findings and observations. Conduct a final mechanical walkdown of the spacecraft prior to stacking or encapsulation for launch. Description of Driving Event: In-House Build The Mars Science Laboratory (MSL) spacecraft is an extremel
4、y complex system that was designed and built by the NASA/Caltech Jet Propulsion Laboratory (JPL) and is comprised of a Rover, Descent Stage (DS), Cruise Stage (CS), Backshell (BS), and Heatshield (HS). Prior to the stacking of these spacecraft vehicles for launch at the NASA Kennedy Space Center, a
5、final mechanical walkdown of each vehicle was performed in August 2011 (Reference (1) to identify workmanship discrepancies that would not be discernable after the vehicle had been stacked, including: Cabling: nicks, tight bend radii, routing over sharp edges, non-staked connectors, unsupported leng
6、th, etc. Multi-Layer Insulation: torn, not fully closed, ungrounded, improperly secured for bellowing, adjacent to sharp edges, etc. Structural: loose items, inverted washers, presence of non-flight hardware or material (e.g., tape, debris), cracks, dings, delamination, chipping/cracking paint, etc.
7、 Obstacles to Spacecraft Separation: lacing cord tied across a joint, defects in critical mating/faying surfaces (cups/cones), deployment/separation envelopes, and potential hazards or snag points. Close Clearances: Identify any possible unknown close clearances. Paperwork Closeout and Vehicle Readi
8、ness: review the status of open items on inspection reports (IRs), assembly metrology, alignment, and electrical bonding measurements; close clearance measurements; final sampling for planetary protection and contamination control, etc. The objective of this detailed examination of the spaceflight h
9、ardware in its final configuration was to assess the overall readiness to proceed with the MSL launch from an “as-built“ hardware perspective. The mechanical walkdown was not intended as a design review or an opportunity to question the “as-designed“ configuration. The walkdown participants included
10、 generalists and specialists (e.g., mechanical, cabling, thermal engineering, telecommunications engineers) from the hardware-delivering organizations. The intent was to include participants who could provide a fresh look at the hardware in the Assembly, Test, and Launch Operations (ATLO) configurat
11、ion. The number of participants in the Rover (Figure 1), DS (Figure 2), CS, BS, and HS walkdowns was limited to eight generalists and from three to seven specialists for each vehicle in order to: Keep the hardware safe from inadvertent contact. Provide participants with unobstructed and complete acc
12、ess to the hardware. Allow participants ample opportunity to ask questions of the vehicle engineers and Quality Assurance (QA). Permit the ATLO team to fully capture the details of each finding. Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Figure
13、1. Configuration of the MSL Rover for the final mechanical walkdown Figure 2. Configuration of the MSL Descent Stage for the final mechanical walkdown The final mechanical walkdown for MSL took two days to complete. At the end of each day, the ATLO team met with the participants to ensure that their
14、 notes and lists of discrepancies were accurate. To ensure closed-loop resolution of the walkdown results, each finding was documented by the ATLO Vehicle Leads and ATLO Lead QA. Accepted findings were added to each vehicles final IR and tracked to resolution. Reference (2) is an example status repo
15、rt for the MSL DS. Prior to MSL, JPL did not conduct formal final walkdowns of in-house builds. Also, JPL did not produce a formal walkdown package reporting pre-stack or pre-encapsulation mechanical discrepancies, subject to closed-loop resolution. Previous JPL projects relied only on interim inspe
16、ctions and walkthroughs conducted during ATLO. Although MSL also performed these interim inspections and walkthroughs during ATLO, the final MSL walkdowns discovered discrepancies such as the sharp edges and close clearances listed for the DS in Reference (2). Out-of-House Build For out-of-house bui
17、lds performed for JPL, like the Nuclear Spectroscopic Telescope Array (NuSTAR) project, the system contractor is responsible for vehicle readiness and paperwork closeout. To gain greater JPL project visibility into contractor preparations for spacecraft integration, an additional independent assessm
18、ent step may be useful. Based on experience gained with the MSL walkdown process, walkdowns of the NuSTAR spacecraft (Figure 3) were performed by JPL during final integration at the contractor facility and at the Vandenberg Air Force Base launch vehicle integration site. Since these final walkdowns
19、took place after NuSTAR was assembled (i.e. after the Optics Bench, Focal Plane Bench, and Bus were mated), the objective was limited to ensuring that the spacecraft was properly closed out for launch including its readiness to mate with the launch vehicle. This was accomplished by thorough inspecti
20、ons of the spacecraft exterior surfaces, and by randomly selected spot reviews of closeout procedures and processes. Unlike MSL, the independent final walkdown process did not include responsibility for implementation of corrective action on the walkdown findings. Provided by IHSNot for ResaleNo rep
21、roduction or networking permitted without license from IHS-,-,-Figure 3. Final configuration of the NuSTAR spacecraft Although the final walkdowns of this out-of-house build were less comprehensive (i.e., scope, duration, and number of participants) than the in-house MSL projects, the independent pr
22、ocess produced some significant findings and observations that were documented in a report (Reference (3). References: 1. Ben Thoma, MSL Assembly, Test, and Launch Operations: Final Mechanical Walkdowns, August 25, 2011. 2. Mark Yerdon, Descent Stage Walkdown (PHSF/KSC August 30, 2011) report, updat
23、ed September 29, 2011. 3. Ben Thoma, Report on Final Independent Walkdowns of the NuSTAR Spacecraft, JPL IOM 352M-BLT-1201, February 27, 2012. 4. Ben Thoma, et al, MSL Assembly, Test, and Launch Operations: Paper Closeout Status & Vehicle Readiness Rover, August 21, 2011. 5. Ben Thoma, et al, MSL As
24、sembly, Test, and Launch Operations: Paper Closeout Status & Vehicle Readiness Descent Stage, August 30, 2011. Lesson(s) Learned: 1. A final mechanical walkdown of an in-house build (MSL), conducted formally prior to spacecraft integration with the launch vehicle, discovered, tracked, and corrected
25、discrepancies in the as-built configuration. These included items (e.g., close clearances that were not previously measured) that were not identified during the interim inspections and walkdowns conducted throughout ATLO. 2. For an out-of-house build (NuSTAR), a less comprehensive final mechanical w
26、alkdown of the as-built configuration was performed by JPL independent of the contractor. This also produced and documented findings and observations. Recommendation(s): 1. For all in-house spacecraft builds, conduct a final mechanical walkdown of the spacecraft prior to stacking or encapsulation fo
27、r launch. Use a formal walkdown process similar to MSLs, including preparation of a formal walkdown package (References (1), (4), and (5), careful selection of expert participants, exercising appropriate caution to avoid hardware damage, conducting periodic debriefs of the Provided by IHSNot for Res
28、aleNo reproduction or networking permitted without license from IHS-,-,-participants, and documenting findings for closed-loop tracking to resolution. 2. For out-of-house builds by a spacecraft system contractor, conduct an independent final walkdown and assessment at the contractor facility and the
29、 launch vehicle integration site that includes thorough inspections of the spacecraft exterior surfaces, and at least randomly selected spot reviews of closeout procedures and processes. For out-of-house builds, it is necessary to prepare a formal report for the attention of project management. Evid
30、ence of Recurrence Control Effectiveness: JPL has documented the final mechanical walkdown process in a JPL procedure (https:/jplwiki.jpl.nasa.gov:8443/display/wired/Mechanical+Walkdowns) last updated on August 25, 2011. Documents Related to Lesson: N/A Mission Directorate(s): Science Exploration Sy
31、stems Additional Key Phrase(s): Integration and Testing Additional Categories.Safety & Mission Assurance Additional Categories.Payloads Additional Categories.Hardware Additional Categories.Ground Operations Additional Categories.Flight Equipment Safety and Mission Assurance.Quality Additional Catego
32、ries.Test & Verification Additional Categories.Spacecraft Additional Info: Project: Mars Science Laboratory, Nuclear Spectroscopic Telescope Array Approval Info: Approval Date: 2012-10-25 Approval Name: mbell Approval Organization: HQ Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
