1、Lessons Learned Entry: 1739Lesson Info:a71 Lesson Number: 1739a71 Lesson Date: 2005-10-21a71 Submitting Organization: JPLa71 Submitted by: David Oberhettingera71 POC Name: Glenn Tsuyuki, Mark Boyles, Steve Squyresa71 POC Email: Glenn.T.Tsuyukijpl.nasa.gova71 POC Phone: 818-354-2955Subject: Thermal S
2、ensor Installation Failures Remain a Problem (2003) Abstract: There is an extensive history of resistance thermal device (RTD) failures on NASA and DOD missions due to thermally-induced mechanical stress. Recent MER ground and in-flight failures, including some failures in mission critical MER appli
3、cations, suggest that these devices remain sensitive to variations in the mounting configuration. Perform Package Qualification Verification (PQV) for all critical RTD applications. For non-critical applications, develop standard, flight qualified installations and methods, and track the part pedigr
4、ee.Description of Driving Event: During Mars Exploration Rover (MER-2) system-level thermal-vacuum (STT) test, it was discovered that one of two platinum resistance thermometers (PRTs) that provide temperature calibration for the Miniature Thermal Emission Spectrometer (MTES) had failed (Reference (
5、1). The PRTs had been installed by the contractor using a liberal amount of a rigid adhesive that transferred the thermal strain directly to the relatively brittle ceramic body of the PRT, overstressing it to failure. The mounting method had not been subjected to Package Qualification Verification (
6、PQV), and subsequent coupon tests showed that the mounting method was consistent with failure within a few thermal cycles. One internal calibration target PRT on each of the Mars rovers was reworked by JPL using a ribbon of RTV, a configuration that passed PQV. (The others were not replaced because
7、it would have invalidated the calibration.) Three months after landing on Mars, 6 internal and external calibration target PRTs on Rovers MER-1 and MER-2 that were bonded using the original method failed, but the 2 reworked PRTs subjected to PQV functioned properly. The loss of a temperature Provide
8、d by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-sensor on the MTES could result in the loss of a major portion of the rovers science return.In an unrelated incident during an STT of MER-1 (Reference (2), the azimuth actuator PRT failed on the Instrument Dep
9、loyment Device (IDD, or rover arm). This failure occurred shortly after the IDD heaters, used at the conclusion of the test to return the spacecraft to ambient temperature, were powered off. In this case, bonding adhesive likely migrated from under the PRT body and onto the lead wires (Figure 1), an
10、d the different coefficients of thermal expansion caused the contracting platinum wire to break and open at cold temperature. Figure 1 is a color photo of a small motor, a barrel-shaped device about one inch in diameter and 2 inches in length. An amber-colored, rectangular, piece part is affixed to
11、the outside surface of the motor casing. A clear gel-like coating covers the part, and the coating also extends to cover two looped, hair-thin, silver lead wires that extend from the body of the piece partFigure 1. PRT bonded to the actuator case with excessive epoxy adhesive, covering the leads (sm
12、all wire loops indicated by arrow)Also, a PRT on the MER-2 Lander Petal Actuator failed in flight (Reference (3).Thermal sensors provide vital information on spacecraft and instrument health, and are sometimes essential to subsystem function. A 1994 study (Reference (4) documented a trend of in-flig
13、ht failures of resistance thermal devices (RTDs) on JPL, Goddard Space Flight Center, and U.S. Air Force missions. Although electrostatic discharge and radiation also caused failures, design and implementation of the sensor mounting configuration was the probable cause of most failures. For installa
14、tions lacking adequate strain relief, thermal dwell or cycling may induce different expansion and contraction rates in the (internal) sensing wire (0.0006 inch diameter), or the lead wire (0.012 inch diameter), versus the sensor body. Fracture of an RTD wire typically resulted in erratic readings (a
15、s the wire intermittently regained contact), followed by full scale temperature readings indicating an open circuit. Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-References: 1. JPL Problem/Failure Report No. Z79528, February 21, 2003 2. JPL Proble
16、m/Failure Report No. Z79691, March 5, 1003. 3. JPL Problem/Failure Report No. Z81188, July 10, 2003 4. D. Oberhettinger, “NASA Unmanned Flight Anomaly Report: Investigation of Thermal Sensor Failures Aboard Unmanned Spacecraft“ (JPL D-11377), April 1994. Lesson(s) Learned: When viewed against a hist
17、ory of RTD failures related to mechanical stress during NASA and military missions, recent JPL failures suggest that these devices remain sensitive to variations in bond joint geometry and in device and surface mount materials. Hence, package qualification verification (PQV) may be particularly suit
18、ed to predicting RTD failure - arguably more suited than a collective mechanical design guideline for packaging (e.g., 155 deg C range for 200 cycles). The need for PQV may be overlooked in plans and contracts because hardware featuring RTDs may be mistakenly considered to be purely mechanical assem
19、blies. Also, a problem with qualifying a single standard mounting configuration is the lack of analytical insight into what changes may invalidate the flight qualification.Recommendation(s): 1. Perform PQV to verify the peer-reviewed packaging design for all critical RTD applications used in both cl
20、osed and open control loops. 2. Develop a set of standard, flight qualified, mounting configurations, installation procedures, and workmanship standards for RTDs not intended for critical applications. Review the established engineering specifications and procedures on the use of bonding and potting
21、 compounds, and issue guidelines that account for adhesive properties, the need for mechanical stress relief, and the effects of environmental stress on RTDs. 3. Assure that all piece part RTDs have a qualification paper trail from the manufacturer. Evidence of Recurrence Control Effectiveness: JPL
22、opened Preventive Action Notice (PAN) No. Z87688 on October 24, 2005 to initiate and document appropriate Laboratory-wide action on the above recommendations.Documents Related to Lesson: N/AProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Mission Dire
23、ctorate(s): N/AAdditional Key Phrase(s): a71 Additional Categories.Flight Equipmenta71 Additional Categories.Hardwarea71 Additional Categories.Payloadsa71 Additional Categories.Spacecrafta71 Additional Categories.Test & Verificationa71 Additional Categories.Test ArticleAdditional Info: a71 Project: MERApproval Info: a71 Approval Date: 2006-12-06a71 Approval Name: ghendersona71 Approval Organization: HQProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
