1、Public Lessons Learned Entry: 2496 Lesson Info: z Lesson Number: 2496 z Lesson Date: 2010-3-24 z Submitted by: Giovanni Rosanova Subject: High Voltage Power Supply Circuit Failure due to Hollow Core Resistor Abstract: On two simultaneous sounding rocket missions, science instrument high voltage powe
2、r supplies experienced in-flight failure. A subsequent investigation discovered that the OHMITE Maxi-Mox series resistors in the power supply circuitry have a hollow core, which, during the rapid ascent of the sounding rocket, did not have sufficient time to properly vent. This resulted in coronal a
3、rcing in the resistor and subsequent failure of the power supplys feedback op-amp. It is recommended that hollow core resistors only be used in situations where they are given sufficient time to reach vacuum prior to high voltage being applied. Description of Driving Event: After the missions were c
4、onducted and the data review indicated science instrument failure, University of Iowa personnel investigated the issue and tried to recreate the problem in their laboratory. The problem manifested itself as a failed op-amp in the feedback control circuitry when the high voltage supplies were placed
5、in vacuum and powered on. The feedback control is achieved through a resistor divider circuit on the output of the supply utilizing a 100Mohm and 100kohm resistor to provide a divide by 1000. This monitor of the output is the input of the drive controlling op-amp (the op-amp that would fail). The 10
6、0MOhm resistor was an OHMITE Maxi-Mox series resistor, which is rated for 10kV. Note: The failure never occurred on the bench in atmosphere, only during vacuum conditions. After multiple tests and a detailed review by a space flight high voltage power supply expert it was pointed out that the Maxi-M
7、ox series resistor was hollow. This resistor uses a hollow ceramic core for the mechanical support in the resistor; the core is hollowed in order to decrease the weight of the resistor. In atmosphere there is sufficient standoff of the voltage between the two ends of the resistor; however, as the am
8、bient pressure decreases the standoff voltage decreases and ultimately could break down. This results in the full voltage of the supply output, 2.5 kV, directly inputting into the feedback op-amp and damaging the op-amp. This failure mode was verified in testing 6 Maxi-mox resistors in vacuum, by se
9、tting up a test resistor divide network similar to the supply implementation, applying a set 2.5kV across the resistor network and measuring the voltage at the divide point. Five of the resistors arced and resulted in the full 2.5kV at the divide point. One resistor showed no indication of arcing. T
10、his was attributed to either the sealing around the core of the resistor being either very tight or very loose; the resistor either never reached the corona point or quickly pumped out past the corona point. Lesson(s) Learned: Provided by IHSNot for ResaleNo reproduction or networking permitted with
11、out license from IHS-,-,-The Maxi-Mox resistors could be used in space flight if a sufficiently long interval is allowed for the cavity in the core to reach vacuum; however, because the pump-out rate varies from resistor to resistor, the point at which the arcing occurs on the resistor is indetermin
12、ate and, therefore, these resistors are not suitable for use on sounding rockets or space flight applications where a long pump out is not feasible. This issue is only on the Maxi-Mox series; the Slim-Mox and Mini-Mox series are solid core resistors and do not suffer this problem. Recommendation(s):
13、 It is recommended that hollow core resistors only be used in situations where they are given sufficient time to reach vacuum prior to high voltage being applied. This requires the user to characterize, with sufficient reliability and confidence, the pump-out rate of the resistor. Evidence of Recurr
14、ence Control Effectiveness: University of Iowa personnel indicated that they have shared this lesson with other researchers in the sounding rocket community. Documents Related to Lesson: N/A Mission Directorate(s): z Space Operations z Science z Exploration Systems z Aeronautics Research Additional
15、Key Phrase(s): z Engineering Design (Phase C/D).Orbiting Vehicles z Engineering Design (Phase C/D).Launch Systems z Engineering Design (Phase C/D).Crew Survival Systems z Engineering Design (Phase C/D). z Systems Engineering and Analysis.Mission and systems trade studies z Systems Engineering and An
16、alysis.Engineering design and project processes and standards z Systems Engineering and Analysis. z Engineering Design (Phase C/D).Power z Safety and Mission Assurance.Reliability z Safety and Mission Assurance.Early requirements and standards definition z Safety and Mission Assurance.Advanced plann
17、ing of safety systems z Safety and Mission Assurance. z Engineering Design (Phase C/D).Spacecraft and Spacecraft Instruments Additional Info: z Project: All space flight projects and programs that utilize high Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-voltage power supplies. Approval Info: z Approval Date: 2010-05-20 z Approval Name: mbell z Approval Organization: HQ Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
