January 22, 1997
TO: Distribution
FROM: 700/Chief Engineer
SUBJECT: Summary/Findings of Balloon Failure Oversight Committee
At the request of Mary Kicza, I submit this memo to formally close out the Balloon Failure Anomaly investigation. The text that follows is essentially a reprint of the "E" mail that I had issued to all of you on September 16, 1996.
After a long history of experiencing many balloon flight successes and one or two failures each year, the balloon program reliability record took a dramatic turn beginning in August, 1995, when a system failed abruptly in flight upon reaching float altitude. Although this was a qualification flight of a new balloon design, the failure was blamed on a possible balloon material or balloon manufacturing deficiency coupled with higher flight loading inherent in this non-heritage balloon design. This failure was followed by 5 additional inflight failures and 3 aborted flight attempts. It was this string of failures that forced a suspension of the balloon program.
Of the 3 aborted launch attempts, one was caused by a sudden shift of wind on the launch line while two were caused by spontaneous firings of the terminate system. With the absence of specific causal data to the contrary, the Wallops Flight Facility (WFF) review board concluded that the most likely cause of these terminate failures was static discharge. The oversight committee concurred that this was a reasonable conclusion based on a number of factors: (1) 8 unshielded 200 foot wires are routed from the terminate electronics box to the Holex termination device along the length of the collapsed parachute; (2) the nylon chute and the plastic balloon materials provide an excellent media for static charge build-up as the materials are dragged across an insulated material prior to launch; (3) the protective Holex bleeder resistor is located in the electronics box rather than adjacent to the Holex device; (4) the bleeder was found to have been open circuited in at least one of the two failures; and (5) probably of most importance was the fact that 4 of the 8 referenced wires were added to the flight configuration as a change in June '94 as telltale wires to report whether the cutter had in fact severed the restraining cable. This 4 wire cable is unshielded (as are the other 4 wires), 2 wires run right through the Holex device while 2 are unused and unterminated, and although many missions were flown successfully after the addition of these wires, it is certainly possible that these wires could provide a smoking gun for the static charge scenario given appropriate humidity and environmental conditions. Regarding these failures, the oversight committee recommended that four actions be taken prior to sanctioning a return to flight: (1) incorporate a 10 ohm bleeder protective resistor directly in the vicinity of the Holex device; (2) shield and terminate shields on 4-200 foot conductors that connect the Holex devices to the terminate electronics; (3) eliminate the telltale and unused wires entirely; and (4) select the best electronic packages available for the subsequent flights, and perform a detailed inspection of this hardware in the field prior to declaring a readiness for flight.
In addition to the aborted flights referenced above, 6 missions were prematurely terminated during the time frame in question. One failure was attributed to a faulty protective aneroid switch that fired the terminate circuitry prematurely. The failure analysis regarding this aneroid concluded that the current aneroid switches may contain solder balls and may be slow to operate. Accordingly, it was recommended that: all aneroid switches be radiographically examined for extraneous particles that may have been introduced during the lead soldering process; and if a slow operate time is not desired, then additional screening may be required. Finally, they concluded that the Honeywell "HM" series microswitch would be a better choice for this application because it is hermetically sealed and has bifurcated gold contacts which are not susceptible to oxide films. A second failure involved the bursting of a pressurized (rather than a zero pressure) balloon at altitude, and although this was an experimental balloon, it burst at approximately one half its calculated burst pressure. A third failure resulted when a flight system failed abruptly upon reaching float altitude. This was the qualification flight of a new balloon design referenced in my first paragraph, and the failure was blamed on a possible balloon manufacturing deficiency coupled with higher flight loads than would have been present in a heritage design in spite of the fact that 5 balloons of this new design had already flown successfully. Three additional failures involved the inability of balloons to reach or remain at proper altitude. Each of these failures was attributed to balloon imperfections or tears. And although it was not possible to link all of the failed balloons to build dates that corresponded to poor balloon plant quality audits, or to only one of two balloon producing facilities, all of the balloons in question were manufactured during the time frame that one facility was being purchased by the other. Although the people and processes supposedly remained constant during the months preceding and subsequent to announcements of the buyout and of management changes, employee anxieties may have affected balloon quality during that time period. To this end, the oversight committee recommended not flying balloons manufactured during this turbulent time, at least in the near term. It was also suggested that nights be resumed using smaller and traditionally reliable balloons at first. Furthermore, since the balloon material is quite fragile (0.8 mil thick), it was recognized that handling, and the flight line operation itself could also contribute to in flight failures. Consequently, the committee recommended that some of the "old timers" be asked to perform an audit of the balloon factory and to witness a number of upcoming balloon flights and report their observations and findings to WFF management and to the oversight committee.
Based on the data that had been made available to us, and pending implementation of the recommendations stated above, the oversight committee recommended the resumption of balloon flights on a limited basis until the reliability record of the past has been restored. The committee recognized the importance of Flight Safety for the crew and for the population in the vicinity of the balloon flights. For these reasons, we recommended that WFF select safe fly zones that would minimize overflying populated areas especially during balloon climb out. The concern for safety must be the primary consideration regarding the balloon flight, and it must be shown for every flight that safety has not been compromised.
H. Richard Freeman
Distribution:
100/Mr. A. Diaz
180/Ms. M. Kicza
180/Mr. P. DeMinco
300/Mr. R. Baumann
600/Dr. S. Holt
700/Dr. A. Sherman
700/Mr. W. Keegan
800/Dr. A. Torres
cc:
313/Dr. R. Predmore
313/Mr. F. Gross
661/Dr. J. Tueller
704/Mr. J. Wolfgang
722/Mr. R. Farley
730/Mr. R Kichak
741/Mr. S. Meyers
842/Mr. H. Needleman
842/Mr. R. Nock
ret./Mr. W. Nagel
ret./Mr. S. Derdeyn
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