1、Lessons Learned Entry: 1185Lesson Info:a71 Lesson Number: 1185a71 Lesson Date: 1991-01-10a71 Submitting Organization: KSCa71 Submitted by: W. Irby Moore/Eric RaynorSubject: Mighty Mouse 2.75 Inch Folding Fin Aircraft Rocket (FFAR) Inadvertent Launch Mishap Investigation Board Report of October 10, 1
2、991 Description of Driving Event: On August 26, 1991 a 2.75 inch Folding Fin Aircraft Rocket (FFAR) with a French Payload aboard was being prepared for launch at the Rocket Triggered Lightning Site (RTLS), KSC. Preparations were in process using Procedure Rocket Triggered Lightning Project (RTLP) Te
3、chnical Operating Procedure (TOPS) 2 Rev B dated 8/20/91. Two French scientists/engineers were working on the rocket making the final payload adjustments. One French scientist was standing on the launcher assembly checking the lanyard connector, which disables the field mil motors. It was at this ti
4、me that the rocket motor inadvertently ignited and launched. The time was approximately 1:11 p. m. EDT. The rocket exhaust and flame was deflected by the concrete launch pad into the left pant leg of the flame retardant white cotton coveralls reportedly causing first and second degree burns from the
5、 ankle to the knee on the shin area. Injured person was transported to Jess Parrish Hospital in Titusville, FL, was treated and released, and later returned to the launch site.The payload and rocket are not intended for recovery; however, since no data was retrieved, the launch was a total loss. Att
6、empts to recover the payload for investigation were unsuccessful. The investigation team reviewed the RTLS operation procedures and witness statements. Key personnel from the RTLS and U.S. Air Force personnel working at the site were interviewed. In addition, the team consulted various people with e
7、xpertise on the 2.75 inch FFAR, including personnel at NASA Wallops Flight Facility. Laboratory support was provided by the Materials Science Laboratory (MSL) personnel and KSC Electromagnetic Analysis (EMA) Group.Lesson(s) Learned: On Friday August 30, 1991 the EMA Group performed radio frequency (
8、RF) field intensity measurements at the launch site within 3 feet of the launcher. The ambient environment was Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-measured to be less than or equal to one volt/meter. These same levels were observed when a
9、n idling automobile was in the area. Two local radars were analyzed showing approximately zero volts/meter. The hand held radios were tested, as well as the base station. All RF measured sources were not, in the opinion of the EMA, considered to be of sufficient strength to cause a RF induced igniti
10、on of the rocket.The MSL personnel made an analysis of the electrostatic conditions at the time of the mishap. The French scientists clothing and shoes were tested for electrostatics, and were ruled out as having contributed to the incident. The fiberglas launcher was evaluated and an electrostatic
11、charge could be induced on the launch tube; however, MSLs opinion was that it was not sufficient enough to be a contributing factor. In addition, the humidity levels recorded at the time of the mishap were 80 percent or greater which in the expert opinion of the MSL personnel would not enhance elect
12、rostatic characteristics. Therefore, electrostatic phenomenon was ruled out as a credible contributing factor.One additional area that was addressed was that of the dissimilar metals used in the construction of the launcher. MSL personnel measured this galvanic action and found that the assembly was
13、 producing 60 millivolts of electricity at 12 milliamps of current. This is insufficient current to ignite the rocket motor. The manufacturers specification on the igniter is 200 milliamps no fire current and 300 milliamps all fire current.The board has also reviewed related incidents at Wallops Isl
14、and and found that there were internal grounding changes made to the Mighty Mouse because of fin connection and other reasons. Wallops, however, has had no specifically related incidents, (due to payload power supplies).The primary cause of the mishap was a “sneak circuit“ that existed between the 1
15、3.5 Volts Direct Current (V DC) payload power supply and the “Bridge Wire“ squib which ignites the booster rocket propellant. This “sneak circuit“ actually used all of the normal firing circuit safety switches and shorting jumpers as an electrical path to ignite the motor. A mini phone plug is inser
16、ted to open the 13.5 V DC payload power circuit. Previously, a non-conductive lanyard had been remotely actuated to withdraw the mini plug just prior to launch to activate the payload power circuit. On August 26, 1991 a piece of electrical wire was substituted as a lanyard. The wire was soldered to
17、the mini plug on one end and attached to a small pneumatic withdrawal piston on the other end. This connection made electrical contact with the piston clevis, which is grounded to the launcher structure. As the mini plug is inserted into the payload jack it momentarily contacts the + 13.5 V DC power
18、 supply circuit which then charges the launcher frame to 13.5v DC.The spring loaded “J-hook“ which secures the rocket from falling through the tube and normally would supply the negative side of the 27 V DC booster firing circuit inadvertently contacts the launcher frame due to rotation when loaded
19、by the rocket fin in the launch tube. At this point the J-hook sees the +13.5 V DC which is now conducted to the center of the “hot shoe“ of the bridge wire squib by the conductive copper safety shorting tape. This applied a +13.5 V DC to one side of the bridge wire.Provided by IHSNot for ResaleNo r
20、eproduction or networking permitted without license from IHS-,-,-Normally this condition would not allow a difference in potential across the bridge wire since the circuit shorted to the motor case and the fin with the tape jumper is also grounded to the motor case. The fin to motor case connection,
21、 however, is made with a roll pin, which allows the resistance to vary (loose ground). Current will flow through the 1.5 ohm bridge wire igniter circuit if the fin to rocket connection is greater than 1.5 ohms. This connection was measured by the MSL to vary to over 400 ohms. Current flow was also m
22、easured at greater than 1 amp in field tests. The squib is specified to no-fire at 200mA and fire at greater than 300mA.Primary Cause: The existence of a sneak circuit along with the fact that the payload power source was being interrupted/connected at the time of the incident, caused the inadverten
23、t ignition of the 2.75 inch FFAR/Mighty Mouse Rocket.Contributing Causes:1. The design and construction of the 2.75 inch FFAR does not provide a reliable electrical connection between the rocket fins and the nozzle plate. Electrical resistance at this point caused current to flow through the lower r
24、esistance ignitor circuit.2. The payload arming device, which switches the payload motors on and off with a mini phone plug, was connected to the pneumatic withdrawal piston with a piece of electrical wire. The electrical wire was soldered to the mini plug and secured to the piston with a screw, com
25、pleting an electrical flow path.3. The RTLP TOPS 2, Rev B, “Test Operation of 2.75 FFAR11 needs additional review. The procedure does not detail the step by step operations of preparing, loading and launching the 2.75 FFAR. All agencies (NASA, US Air Force and the French operations) should make thes
26、e necessary modifications. In addition, the procedure needs warnings for “Hazardous Steps“ and notes indicating “End of Hazardous Step“ within each section of sequences.4. During the inadvertent launch, there was a person fishing from a boat within the designated control area of Mosquito Lagoon. The
27、 fisherman indicated that the rocket came within 300 yards of his boat.Observations:5. There was no safety professional/observer required on site while handling, loading and preparing the 2.75 FFAR for launch readiness. The RTLP Tops 2, Rev B only requires a safety concurrence, which was done by pho
28、ne on the day of the mishap.6. The 2.75 FFAR Launcher Assembly was fabricated with dissimilar metals (aluminum, steel, and cadmium plated bolts). Galvanic action was measured and found to provide 12 mA, which is insufficient current to ignite the rocket motor. However, over a long period of time, th
29、is could result in corrosion problems. The current flow is very undesirable.7. The RTLP TOPS, Rev B did not specify the required control/clear area around the staging site and launcher assembly area. In addition, there were no man loading requirements identifying the number of personnel required to
30、complete the hazardous steps for each operation.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-8. The RTLP TOPS, Rev B did not specify the required control/clear area around the staging site and launcher assembly area. In addition, there were no man
31、 loading requirements identifying the number of personnel required to complete the hazardous steps for each operation.9. It was noted during the removal of the two unused 2.75 FEAR from the launcher (tubes 1 and 4) that the U.S. Air Force M/Sgt took steps to avoid possible electrical static charge d
32、issipation into the launch system. Before touching the ordnance, he grounded himself to earth ground then to the launcher frame.10. It was noted that the injured person was standing on the launcher assembly while making adjustments to the payload arming device (mini plug). There was a portable work
33、stand within 10 feet of the launch assembly available for use while working on the rocket and its payload.11. It was noted that the French personnel were wearing personally owned white coveralls. The procedure called for NASA roved “Blue Collar“ coveralls. The French were given verbal approval for u
34、se of their own coveralls. There was no deviation or waiver documented to approve the change.Recommendation(s): 1. Provide a means to assure there is no source or path of electrical connections to allow a sneak circuit between the payload power source or other external electrical power supply to the
35、 2.75 FFAR igniter. Also, power transfer above 1.5V DC should usually be done remotely.2. Do not use the fins as part of an electrical grounding circuit, unless provision is made to assure adequate electrical connections.3. Redesign the arming device to provide electrical isolation from the battery
36、and connect to the withdrawal piston with a non conductive lanyard.4. Review and amend the 2.75 FFAR procedure to assure that it meets NASA, KSC requirements such as those outlined in KMI 1710.13 and other supporting documents.5. Revise the 2.75 FFAR procedure to require the down range impact area a
37、nd air space be secured and cleared of all unauthorized personnel and aircraft before loading and preparing the 2.75 FFARs and their payloads.6. Revise the 2.75 FFAR procedure to require a safety professional/observer to be on site during all hazardous operations.7. Redesign the launcher assembly to
38、 use insulating devices between dissimilar metals, or use materials that are compatible.8. Revise the procedure to indicate the required control/clear area and show the man loading charts that identify the personnel required to perform the hazardous steps/task.9. During the pre task/test briefing pe
39、rsonnel must be reminded of the necessity to discharge any potential of static buildup within their body/clothing just before handling ordnance (regardless of the humidity levels). Use leg stats/wrist stats as required.10. Personnel should use the proper equipment. The use of the work stand would ha
40、ve minimized, if not eliminated the injury received during the inadvertent launch.11. When any change to the procedure is needed, a written deviation or waiver must be signed and approved as required by KMI 1710.13.Provided by IHSNot for ResaleNo reproduction or networking permitted without license
41、from IHS-,-,-Evidence of Recurrence Control Effectiveness: N/ADocuments Related to Lesson: N/AMission Directorate(s): a71 ScienceAdditional Key Phrase(s): a71 Air-Traffic Managementa71 Energetic Materials - Explosive/Propellant/Pyrotechnica71 Energya71 Environmenta71 Explosives Handlinga71 Flight Eq
42、uipmenta71 Flight Operationsa71 Ground Equipmenta71 Hardwarea71 Human Factorsa71 Launch Processa71 Mishap Reportinga71 Personal Protective Equipmenta71 Range OperationsMishap Report References: Mighty Mouse 2.75 Inch Folding Fin Aircraft Rocket (FFAR) Inadvertent LaunchAdditional Info: Provided by I
43、HSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Approval Info: a71 Approval Date: 2002-04-30a71 Approval Name: Gena Bakera71 Approval Organization: KSCa71 Approval Phone Number: 321-867-4261Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
