1、Best Practices Entry: Best Practice Info:a71 Committee Approval Date: 2000-04-19a71 Center Point of Contact: MSFCa71 Submitted by: Wil HarkinsSubject: Solid Rocket Booster (SRB) Refurbishment Practices Practice: Engage in refurbishment activities to rebuild and prepare for reuse of the Solid Rocket
2、Boosters (SRBs) after each Space Shuttle Orbiter launch. These refurbishment activities include: (1) inspection, (2) reworking of anomalies to specification, (3) material review board (MRB) acceptance or scrapping, (4) cleaning, (5) corrosion protection and prevention, (6) scheduled part replacement
3、, (7) test and checkout, and (8) preparation for storage or return to flight buildup.Programs that Certify Usage: This practice has been used on Space Shuttle Solid Rocket Booster (SRB), Space Shuttle Solid Rocket Motor (SRM).Center to Contact for Information: MSFCImplementation Method: Benefit:This
4、 Lesson Learned is based on Maintainability Technique number OPS-01 from NASA Technical Memorandum 4628, Recommended Techniques for Effective Maintainability.Implementation Method:Refurbishment of SRB components is cost effective and conserves resources. This allows for reuse Provided by IHSNot for
5、ResaleNo reproduction or networking permitted without license from IHS-,-,-of SRBs, thus saving money for the program versus building new SRBs for each launch.Solid Rocket Booster (SRB) Refurbishment encompasses the activities required to return the reusable SRB component to a flightworthy condition
6、 after SRB ignition, liftoff, and flight; separation from the external tank; descent (free fall and parachute); ocean impact; and retrieval. When the decision was made to recover and reuse the SRB hardware, a design team was organized to formulate the maintainability criteria for a reusable booster.
7、 The SRB Flow Chart for Maintainability is shown in Figure 1. The maintainability design team produced the Solid Rocket Booster Maintainability Design Criteria Document (reference 1), a document that was used by designers as they conceived each design feature, performed the necessary tradeoffs of th
8、e design parameters, and made other design and product engineering decisions. The design team included maintainability as a design goal and incorporated the desired maintainability features into components of the end item throughout the design process. Maintainability factors that were considered du
9、ring the design of the SRB are shown in Table 1.refer to D descriptionD Figure 1. SRB Flow Chart for Maintainability 1. Accessibility2. Commonality of Fasteners3. Electrical Subsystem Installation and Removal4. Thrust Vector Control (TVC) Subsystem Installation and Removal5. Markings and Color Codin
10、g6. Unitization of Subsystems7. Irreversibility of Connectors8. Tool and Equipment Design9. Spares ProvisioningTable 1. SRB Maintainability Factors Design Process ConsiderationsProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Table 2 lists typical mai
11、ntenance actions that were considered during the design process. The SRB was designed to withstand launch, water impact, and towback environments, incorporating the capability of 10 flights for the parachutes; 20 flights for electrical/electronic components, Thrust Vector Control (TVC) components, a
12、nd SRM components; and 40 flights for the structures. SRB structures are typically welded and/or mechanically fastened aluminum except for the external tank attach ring, which is mechanically fastened steel. All aluminum structural assemblies are first painted and then coated with an ablative insula
13、tion. The SRM segments are forged D6AC steel. All structural components are cleaned and/or alodined as appropriate, before being primed and top coated with paint. The mechanically fastened aluminum and steel structural components are designed to be protected from salt water intrusion by applying sea
14、lant between adjoining surfaces, installing the fasteners with sealant, torquing the fasteners, and applying a fillet of sealant along the edge of brackets where they join the main structure. The electronic/electrical components exposed to salt water are sealed, and the external surfaces of these co
15、mponents are painted. The TVC hydraulic system is a closed-loop system that does not permit the intrusion of sea water. The SRM segments external surfaces are protected with an epoxy paint finish, and the internal surfaces are protected by the propellant insulator that is bonded to the inside surfac
16、es of the SRM segments. Areas not protected with paint or bonded-on insulation are protected with a water-repellent grease.1. Inspection2. Troubleshooting3. Calibration and Adjustment4. Repair5. VerificationTable 2. Maintenance Actions Specific ImprovementsTypical areas of the SRB that have been red
17、esigned or modified as a result of trouble areas found during recovery and refurbishment are discussed below:1. Galvanic corrosion occurred in the aft skirt of the first few SRBs recovered. To prevent this from recurring the design team added a zinc coating to selected metal components, and bolted a
18、nodes (Zinc bars) to some components of the TVC system.2. The aft skirts of the first few SRBs experienced water impact damage. The corrective action included the addition of gusset reinforcements to the structural rings. Foam was sprayed on the interior of the aft skirt to protect the reinforcement
19、 rings and the TVC components. Impact force with the water was reduced by increasing the diameter of the main parachutes from 115 feet to 136 feet. The larger parachutes decreased the SRBs water impact velocity from 88 ft/sec to 75.5 ft/sec (60 mph to 51.5 mph, respectively).3. During initial teardo
20、wn and inspection, water and corrosion were found between the mating Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-surfaces of structural members. To correct this problem, the sealant application specifications were modified to require the sealant
21、to be applied to both surfaces before joining.4. To eliminate potential water entry into the forward skirt, the following areas were modified or redesigned:1. The aft seal on the forward skirt was changed from a rectangular to a “D“ configuration to allow better contact between the forward skirt and
22、 the forward dome of the SRM.2. A fillet of sealant was added between the access door and the surrounding structure after final close-out of the forward skirt.3. Sealant was added to the mating surfaces and the installation bolts of the separation nut housing for the main parachute attach fittings.6
23、. The following practices improved maintainability, parachute deployment, and parachute inflation:1. To avoid abrasive damage that occurred during main parachute deployment, foam and ablative material were added to portions of the frustum and the main parachute support structure.2. To avoid damage t
24、o the parachutes during deployment, the parachutes are now packed in a circular pattern rather than the previous zig-zag pattern.3. The opening at the top of the main parachute canopy was decreased in diameter to allow quicker inflation of the parachute.8. After every flight electronic components we
25、re being returned to the vendor for refurbishment. After refurbishment, acceptance test procedures (ATP) were performed, including vibration and thermal testing. The vibration level of these tests caused the remaining life of the component to be reduced. To prevent the excessive expenditure of compo
26、nents lifetime (except for the range safety system components) vibration and thermal testing has been eliminated during normal turnaround. The constant improvement of electronic parts by the manufacturer presents a unique problem to the SRB refurbishment effort because the improved parts are often n
27、ot interchangeable with their predecessors. A sufficient quantity of spare parts must be procured to meet logistics requirements until the components are redesigned to use the improved parts.Typical Refurbishment ProceduresFigure 2 depicts the SRB flight configuration. After approximately 125 second
28、s into the Shuttle flight, the SRBs are jettisoned from the external tank. During reentry, the nose cap is jettisoned (it is not recovered), deploying the drogue parachute. After the SRB is stabilized in a vertical position, the frustum is jettisoned and descends into the ocean. Its descent is held
29、to a safe velocity by the drogue parachute. In the meantime, the jettisoning of the frustum deploys the three main parachutes, lowering the remaining portion of the SRB into the ocean. Once in the ocean, the parachutes (which are jettisoned at water impact) and the frustum are removed by the recover
30、y team and positioned onto the recovery vessel. A plug is inserted into the SRM nozzle throat and the SRB is dewatered. Removal of the water from the SRB allows the SRB to be positioned from a vertical position to a horizontal position. The SRB is then towed to the disassembly area dock.Provided by
31、IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-refer to D descriptionD Figure 2. SRB Flight Configuration At dockside, the SRB is lifted from the water and placed on dollies. The SRB pyrotechnics are disarmed, the TVC fuel system is depressurized, and an assess
32、ment team inspects and documents anomalies that may have occurred during flight. Then the SRB is washed with a detergent solution in a semiautomated wash facility. The aft skirt is removed and routed to the TVC disassembly facility. Table 3 lists a typical flow sequence for major structure refurbish
33、ment. After the aft skirt is removed, the remainder of the SRB is routed to the disassembly facility.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-1. Tow SRB from water impact area to dock2. Remove SRB from ocean, Rinse with potable water.3. Place
34、SRB on transporter.4. Safe SRB Ordnance and Hydrazine Systems.5. Assessment Team Inspection.6. Wash SRB with detergent solution and rinse.7. Remove aft skirt assembly.8. TVC refurbishement facility.9. Remove TVC Components.10. Disassembly area; remove components.11. Critical dimension check.12. Ther
35、mal protection system removal, robotic hydrolaser.13. Inspect, Visual and NDE (XRAY and Ultrasonics).14. Rework, Touch-up paint (repaint every fifth use.)15. Inspect and identify.16. Preflight storage.Table 3. Typical Structure Refurbishment Flow As the SRB components are removed, they are identifie
36、d by attaching a metal tag with their part number and dispositioned per the Predisposition List for SRB Flight Hardware (reference 2). The SRB component is then routed to the refurbishment area where a prepared refurbishment procedure document is attached to the part. The part is reworked to conform
37、 to the Refurbishment Engineering Specification. This specification lists the requirements for refurbishing each component to flightworthy condition before it is returned to storage.The SRM segments are disassembled in the disassembly facility at dockside, placed on rail cars, and transported to the
38、 SRM contractor located in Utah. At the contractors plant, the segments are off-loaded and routed to refurbishment areas. All segments that are to be reused must meet the requirements of specification STW7-2744 (reference 3). If segment dimensions fall outside the acceptable requirements of this spe
39、cification, an individual analysis is required to determine the effect on the structural and sealing capability before reusability is determined. All documented nonconformances are reviewed to determine if the condition of the hardware has changed. The most critical areas to be reviewed are case mem
40、brane thickness, vent port and leak port threaded areas and sealing surfaces, and aft segment stiffener stubs. No surface defects (corrosion, pitting, scratches, noncrack-like flaws, etc.) deeper than 0.010 inch are permitted. All segments are hydrotested to 1.125 times the Maximum Expected Operatin
41、g Pressure and magnetic-particle inspected.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-1. Major Structures (Frustrum, Forward Skirt, Aft Skirt, External Tank Attach (ETA) Ring, Solid Rocket Motor (SRM) Segments, etc.2. Electronic Components: Inte
42、grated Electronic Assembly (IEA), Integrated Receiver Decoder (IRD), etc.3. Electrical Cables.4. TVD Components Auxiliary Power Unit (APU), Hydraulic Pump, Hydraulic Reservoir, Fuel Service Module (FSM), etc.5. ParachutesTable 4. Types of Hardware That Have Been Successfully Refurbished References:1
43、. NASA/MSFC: Solid Rocket Booster Maintainability Design Criteria Document, SE-019-022-2H, NASA/Marshall Space Flight Center, AL.2. USBI: Predisposition List for SRB Flight Hardware, 10PLN-0027, USBI, United Technologies, Huntsville, AL.3. Thiokol: Space Shuttle SRM Refurbished Case Acceptance Crite
44、ria, STW7-2744, Thiokol Corporation, Space Operations, Brigham City, Utah.4. NASA/MSFC: Sealing of Faying Surfaces Subject to Sea Water Exposure on the SRB Excluding the SRM, 10A00526, NASA/Marshall Space Flight Center, AL.5. NASA/MSFC: Sealing of Fasteners Subject to Sea Water Exposure on the SRB E
45、xcluding the SRM, 10A00527, NASA/Marshall Space Flight Center, AL.6. NASA/MSFC: Protective Finishes for Aluminum and Steel Alloys Subject to Seawater Exposure on the SRB Excluding the SRM, 10A00528, NASA/Marshall Space Flight Center, AL.7. NASA/MSFC: Solid Rocket Booster Flight Hardware Ground Opera
46、tions Plan, SE-019-040-2H, NASA/Marshall Space Flight Center, AL.8. NASA/MSFC: Solid Rocket Booster Flight Hardware Refurbishment Requirements, SE-019-050-2H, NASA/Marshall Space Flight Center, AL, Systems Analysis and Integration.9. Thiokol: Space Shuttle SRM, Requirements and Acceptance for Refurb
47、ishment Nozzle Metal Components, STW7-2863, Thiokol Corporation, Space Operations, Brigham City, Utah.10. Thiokol: Space Shuttle SRM, Process Finalization Requirements for Nozzle Metal Hardware, STW7-3450, Thiokol Corporation, Space Operations, Brigham City, Utah.11. Thiokol: Space Shuttle SRM, Acce
48、ptance Criteria, New and Modified Case, STW7-3489, Thiokol Corporation, Space Operations, Brigham City, Utah.12. Thiokol: Space Shuttle SRM, Acceptance Criteria for Refurbished Igniter Chambers and Igniter Adapter, STW7-3861, Thiokol Corporation, Space Operations, Brigham City, Utah.13. Thiokol: Ref
49、urbishment and Acceptance Criteria for Redesigned Barrier-Booster Assembly, STW7-3888, Thiokol Corporation, Space Operations, Brigham City, Utah.14. Thiokol: Manufacturing Plan for Space Shuttle Redesigned Solid Rocket Motor (RSRM) Project, TWR-10341(CD), Prepared for NASA by Thiokol Corporation. Brigham City, Utah.Provided by IHSNot for ResaleNo reproduction or networking permitted without license
