1、Lessons Learned Entry: 0566Lesson Info:a71 Lesson Number: 0566a71 Lesson Date: 1996-05-20a71 Submitting Organization: MSFCa71 Submitted by: Peter MessoreSubject: Tethered Satellite System 1 Reflight (TSS-1R) Failure Description of Driving Event: On February 22, 1996, the STS-75 Space Shuttle Columbi
2、a was launched at 53/20:18 GMT. The orbiter was inserted into a 296 km (160 nautical mile) orbit at an inclination of 28.5 degrees. The crew consisted of 7 members, including commander, pilot, 3 mission specialists, 1 payload commander, and 1 payload specialist. The TSS-1R payload was a reflight of
3、TSS-1 in 1994, where deployer mechanism problems limited the tether deployment to slightly less than 300 m. The planned duration of the flight was 14 days. The payload bay configuration consisted of the Tethered Satellite System (TSS) experiments, two U.S. Microgravity Lab pallets (USMP-3), Orbiter
4、Acceleration Research Experiment (OARE) pallet, and Extended Duration Orbiter (EDO) pallet.Deployment of the satellite began at 56/20:46 GMT. On 57/01:29:26 GMT, at a tether length of 19.7 km, the satellite tether broke within the 12 m deployer boom, and the satellite separated from the orbiter. The
5、 rate of tether deployment was under control of the science computer. At the time of the tether separation, the deployment rate was being ramped down, per timeline, in preparation for halting at 20.7 km tether length. The tether deployment rate was approximately 1 m/s when it separated. There were n
6、o injuries and no damage to the orbiter or its subsystems due to the tether break.The orbiter was located at 2 degrees N latitude and 100.4 degrees W longitude, and was at an altitude of 296 km (160 nautical miles) at the time of tether break. The TSS-1R experiments were in the passive mode, with no
7、 current flowing in the tether. The tether had an electric potential of -3500 VDC with respect to the orbiter ground, as planned, during this mode.Telemetry from the orbiter and the satellite was operating prior to, during, and after the tether separation. Video imagery of the tether was available a
8、fter the separation, but no video coverage exists showing the break itself. Video and still photography were taken during the mission of the Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-failed end of the tether within the boom. The tether remainin
9、g in the boom was rewound on the reel during the mission.Post flight inspection of the tether end showed it to be charred, with an apparent final tension failure of a few strands of Kevlar. The TSS-1R Mission Failure Investigation Board established that the tether failed as a result of arcing and bu
10、rning of the tether, leading to a tensile failure after a significant portion of the tether had burned away.This photo shows the frayed tether end under high intensityThis photo shows the frayed tether end under ambient lighting.Pictures of the frayed tether end The arc started in the Lower Tether C
11、ontrol Mechanism (LTCM), resulting in a 1 A current discharge to orbiter ground in the LTCM. This event occurred during a passive mode of science operations, with -3500 VDC on the tether conductor. The arc continued intermittently for 9 s, as the breached part of the tether traversed at 1 m/s throug
12、h the remaining deployer mechanisms and into the 12 m deployer boom, where the space plasma provided the current return path. This arcing produced significant burning of most of the tether material in the area of the arc. The nominal load on the tether, 65 N (15 lb.), finally separated the tether at
13、 the burn location, while it was within the deployer boom. The upper tether section was pulled through the Upper Tether Control Mechanism (UTCM), away from the orbiter at a speed of 3 m/s, due to tether dynamics and the satellite movement away from the orbiter. The lower section of the tether remain
14、ed within the boom, and was recovered after the flight.The arc initiated at a breach in the FEP insulation layer of the tether. Pressure within the LTCM, the proximity to a ground plane at the LTCM entry pulley, and the high voltage on the conductor, provided the favorable environment based on press
15、ure-distant relationships (Paschens Law)* for the conductor to arc through the breach in the tether insulation.Although the damaged area of the insulation was destroyed due to burning, the TSS-1R Mission Failure Investigation Board found sufficient evidence from test and analysis to establish foreig
16、n object penetration, or damage to the FEP insulation layer in manufacturing or handling, as the probable cause of the breach of the insulation layer.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-D The satellite and tether moving away from the shut
17、tle D Scan of the boom with the slack tether in the shuttle cargo bay Manufacturing and inspection records show that the tether fabrication task was very difficult, and that numerous problems were encountered in the extrusion and braiding processes of this very long tether. The fabrication of the te
18、ther was carried out in a normal manufacturing shop environment.Metallic and non-metallic contamination was found within the FEP insulation layer of the flight tether, including the 9 m that had gone through the lower deployer mechanisms prior to the failure. Non-metallic and metallic contamination
19、was also found between the Nomex and insulator layers of several samples of flight tether. EDS analysis revealed foreign material near the failed end.In addition to the contamination found within the tether, debris was found in several locations within the deployer mechanism. Metallic debris, large
20、enough to breach the FEP, was found in the LTCM, the deployer boom assembly, and the reel housing. In the LTCM, a small piece of very fine silver plated wire, aluminum shavings, and unidentified non-metallic debris were found. Small metallic shavings were found attached to the back of small screw ho
21、les in the boom assembly.Damage to the copper conductor was found in both the returned flight tether, and in a section of qualification tether examined after a special spark test. This damage appeared to have taken place during fabrication of the tether.The final wind of the tether onto the flight r
22、eel was at a tether tension of 50 N. This results in high compression forces on the tether layers deep within the reel. The TSS-1R Mission Failure Investigation Board calculated that compressive forces at the layer where the tether breach was located, were as high as 35 N/mm for several days after t
23、he winding process. This compressive force is more than sufficient to force small debris through the insulation layer of the tether.The TSS-1R Mission Failure Investigation Board found one contributing cause was that the degree of vulnerability of the tether insulation to damage was not fully apprec
24、iated. A second contributing cause was high voltage effects on the insulator itself. Concern over the environment inside the LTCM led to the analyses involving Pashcens Law relating voltage break down propensity as a function of the pressure-distance parameter.* - In 1889 Paschen introduced a genera
25、lization to the complex subject of gas break down in the law bearing his name. This law states simply that in a uniform field the sparking potential of a gas depends only upon the product of the gas pressure and the electrode separation.Provided by IHSNot for ResaleNo reproduction or networking perm
26、itted without license from IHS-,-,-The TSS-1R Mission Failure Investigation Board was able to conclusively eliminate several major areas as causal. They included:a71 Satellite Hardware and Operationsa71 Core Science Equipment and Operationsa71 Hardware and Operations of the Experimentsa71 Mission Op
27、erations (Ground and Flight)a71 Induced Loads (static or dynamic)a71 Pyrotechnic Tether Cuttersa71 Heating of the Tether During Commanded and Controlled Current Flowa71 Design Changes Made to TSS-1a71 Aging of the Components (shelf life)a71 Micrometeoroid or Orbital Debris Collisiona71 Electrical St
28、orm ActivityReference(s): TSS-1R Mission Failure Investigation Board - Final Report, May 20, 1996.Lesson(s) Learned: The TSS-1R Mission Failure Investigation Board made several observations in the course of the investigation. Among these are that:1. the tether failure is not indicative of any fundam
29、ental problem in using electrodynamic tethers;2. there was a significant amount of scientific data secured from the flight, before the tether separated;3. the science, engineering and support teams were highly competent, motivated, and committed to the experiment;4. electrostatic charge build-up cou
30、ld be an issue in the future;5. the documentation provided by the project to the Board was appropriate;6. the tether configuration was affected by the winding loads on the reel;7. the load paths of the composite tether are complex;8. closed areas with a favorable pressure-distance combination (Pasch
31、ens Law) can cause arcing if not vented.The TSS-1R Mission Failure Investigation Board finally observed that the long time span between the fabrication of the hardware and the flight missions increased the exposure of the hardware to contamination and damage. Recommendation(s): The TSS-1R Mission Fa
32、ilure Investigation Board made the following recommendations:Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-1. use rigid standards for fabrication and handling of the high voltage cable;2. ensure that the deployer path is free of debris;3. reduce, t
33、hrough design and operations, the possibility of arcing;4. conduct electrical integrity tests as close to the flight date as possible;5. conduct high fidelity tests on critical subsystems;6. strengthen the integrated systems development approach.Evidence of Recurrence Control Effectiveness: N/ADocum
34、ents Related to Lesson: N/AMission Directorate(s): N/AAdditional Key Phrase(s): N/AAdditional Info: Approval Info: a71 Approval Date: 1997-10-01a71 Approval Name: Frank Hepburna71 Approval Organization: CR10a71 Approval Phone Number: 205-544-4155Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
