FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1967
1967 - 0889.PDF
FLIGHT International, 25 May 1967 867 Astronaut Donn F. Eisele demon- strates the new hatch door on an Apollo spacecraft mock-up. The new door opens outwards, by means of a handle which will re- lease 15 cam locks simultaneously in two to three seconds Spaceflight Apollo 204: final report T HE fourth and final report by the Apollo 204 ReviewBoard on the fire which, involving the Apollo capsule,resulted in the deaths of astronauts Virgil Grissom, Edward White and Roger Chaffee on January 27 was sent by the Board's chairman, Dr Floyd Thompson, to Mr James Webb, the NASA administrator, on April 5. The report describes the history of the Apollo capsule 012 which had been scheduled for the AS-204 flight, and the "plugs out" test to which it was being subjected at the time of the accident. The purpose of this test was, to quote the Board, "to demonstrate all space vehicle systems and operational pro- cedures in as near a flight configuration as is practical and to verify their capability in a simulated launch. System verifi- cation is performed, an abbreviated final countdown conducted and a flight simulation made. All communication and instru- mentation systems are activated and proper measurements are monitored at appropriate ground stations. At the start of the simulated flight, umbilicals are disconnected and the space- craft is on simulated fuel-cell power." The report goes on to describe the sequence of events in chronological order, up to and during the time of the fire (see Flight, March 9). It continues with a discussion of the likely causes leading to the fire (reproduced below in part), and con- cludes with the board's findings and recommendations, which we reproduce in full. Cause of the Apollo Fire The fire in Apollo 204 was most probably brought about by someminor malfunction or failure of equipment or wire insulation. This failure, which most likely will never be positively identified, initiateda sequence of events that culminated in the conflagration. A great deal of effort has been expended in an attempt to find this specificinitiator. Although unsuccessful in this search, this effort has pro- duced a fairly good understanding of the types of things that mayhave been the initiator and the types of things that probably could not have been the initiator. Electrostatic discharge, spontaneouscombustion of flammable material, mechanically produced heat by machinery and heat from the impact of a struck object have beeneliminated as reasonable possibilities of ignition of the fire. The flow of oxygen through orifices or metering valves can create heatthrough the excitation of resonating frequencies in the gas. However, a thorough examination of the hardware and evaluation of recordedPerformance of the equipment eliminates the energy of flowing oxygen as a possible initiator. The most obvious source of energy needed to initiate the fireexisted in the spacecraft's power distribution system. Current- carrying wires were distributed throughout every major region ofthe command module. The most likely ways in which electrical Power can initiate a fire are the following: (1) Through malfunction°f the equipment being powered which in turn ignites or initiates a nre in nearby combustibles. (2) Overload in the conductor resultingfrom shorts in equipment or wiring. This overload will cause the inductor to overheat and ignite nearby combustibles. (3) Electricarcs that are created when the insulation is defeated between power carrying conductors and the spacecraft structure or equipment. A large majority of the wires were left undamaged. However, there were a number of cases where exposed wire showed extensive burning, overheating or complete destruction. There was also several places where pitting of exposed conductors and adjacent structure indicate that an electric arc had occurred. Malfunction of Electrically Powered Equipment After removalfrom the spacecraft, each component or subassembly was critically examined to determine whether or not it could be associated withthe initiation of the fire. The vast majority of these could be classified as non-initiators on the basis of external examination andrecorded performance. If, however, there was any suspicion that an item was involved with the initiation of the fire, it was subjected tointensive scrutiny that involved one or more of the following procedures: Laboratory analysis of damage, electrical continuityand resistance tests, functional performance using established procedures for "bench checks" and careful disassembly whichincluded repeating some of the above steps on individual parts of the assembly. The results of this effort led to the conclusion thatnone of the electrically powered spacecraft systems or subassemblies was associated with the initiation of the fire. Electrically Overloaded Conductors The Apollo spacecraft wiringis protected with Teflon insulation. Teflon was chosen as the insulating material after a series of tests clearly showed that it wasthe least likely to burn when overheated by shorting. Individual conductors in a wire bundle using Teflon-insulated wires couldbe melted to destruction without initiating a sustained fire in the bundle when located in a 100 per cent oxygen atmosphere at51b/sq in absolute. The Teflon insulating material provided a high degree of fire protection to wire bundles which may containelectrically overloaded wires. Primary protection to wiring in the spacecraft, however, was provided by circuit-breakers and fuseswhich protected all power-carrying conductors. Critical analysis of all circuit-breaker installations showed that this protection wasprovided adequately with only a few exceptions. Several indications of shorted wiring were made the subject of individual detailedinvestigations. These investigations have all proved negative except for a few cases that could not be exonerated completely. Electric Arcs Teflon has excellent fire resistance but low resistanceto cold flow. The Teflon covering on the wire used in Apollo 204 could be damaged easily or penetrated by abrasion. The coveringcould also be damaged when forced against the structure by poor installation. The board found numerous examples in the wiring ofpoor installation, design and workmanship. (An example is shown . . . where a wrench socket was found in the spacecraft.)If a power conducting wire experiences penetration of its insulation by the metal structure of the spacecraft or spacecraft components,an instantaneous short to ground is created at the point of con- ductor contact. An arc or a series of arcs between conductor andstructure results. The arcing action may be terminated by the blowing away of molten metal at the point of contact, or ifsufficient mechanical pressure exists, fusion between the conductor and structure may occur to create a continuous short. The previousoccurrence of an arc can be determined through examination of hardware because a characteristic pit or crater is left at the locationof contact. Tests in a 16.51b/sq in absolute oxygen atmosphere have shown that sparks blown from arcs can ignite combustiblematerial several inches from the arc. Circuit-breakers and other practical circuit interrupting devices cannot act rapidly enough to
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
