1、Lessons Learned Entry: 0404Lesson Info:a71 Lesson Number: 0404a71 Lesson Date: 1996-04-26a71 Submitting Organization: JPLa71 Submitted by: J.A. RobertsSubject: Traveling Wave Tube Amplifier on Martian Surface: Failure Due to Corona (1976) Abstract: When commanded to switch on, TWTA No. 1 on Viking L
2、ander 2 failed to produce an S-band RF downlink, probably due to RF breakdown of the high-voltage power converter. High-voltage circuits designed to operate within the Martian atmosphere require special design precautions, such as insulation from ground potential, to avoid corona or other forms of h
3、igh-voltage breakdown.Description of Driving Event: (Relevant Historical Lessons Learned)Traveling Wave Tube Amplifier (TWTA) No. 1 on Viking Lander 2 failed to produce an S-band RF downlink when commanded “ON“ October 13, 1976. The most probable failure model is that the high-voltage power converte
4、r developed a corona breakdown. A subsequent attempt to operate this TWTA during the extended mission late in 1978 also failed to produce downlink.From Martian day one (SOL 1) after Lander 2 touchdown, TWTA No. 2 had been used and it had performed very well. On SOL 33, the link was switched to TWTA
5、No. 1 because it ran cooler than No. 2, and the increasing solar angle was beginning to raise the Lander ambient temperature. TWTA No. 1 produced normal carrier and telemetry sidebands; however, the ranging subcarrier was suppressed by noise by 6 to 8 dB. These symptoms continued from SOL 33 to SOL
6、38. On SOL 39, no signal was observed at the Deep Space Stations after the TWTA “ON“ command. Subsequent telemetry via the UHF relay link (not involved) showed the TWTA bay temperature did not make its usual climb. The TWTA went through its 90-second cathode warm-up period, and the failure must have
7、 occurred shortly after the high-voltage was programmed to come on.Other failure mechanisms examined and discarded include: sequence error, spurious signals on the Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-uplink from the stations, “power-on“ s
8、witch failures, exciter spurious signals, and command link failure. It was concluded the failure was within TWTA No. 1.Reference(s):a71 Viking Incident Surprise Anomaly Report No. 15643 (dated 13 Oct. 1976)a71 JPL IOM 3363-76-059, “Narrative on the Viking No. 2 Lander TWTA Failure,“ Lloyd Derr to Le
9、e Randolph, 29 Oct. 1976Lesson(s) Learned: High-voltage circuits designed to operate within the Martian atmosphere require that special design precautions be taken to avoid corona or other forms of high-voltage breakdown.Recommendation(s): The TWTA has numerous high-voltage areas needing protection
10、from ground potential, by means of either insulated wire or potting compound.Note: The Martian atmosphere consists mainly of 95% carbon dioxide and about 3% argon. The ambient pressure at the Lander site is 7.2 millibars, corresponding to an Earth pressure of 5.2 torr. This constitutes a very critic
11、al pressure region in an atmosphere of “active“ gasses. (Experimental experience with electrostatic discharge indicates that carbon dioxide produces corona at a voltage 19% lower than required for air, and argon at a voltage 60% lower than air.) Corona breakdown in Martian atmosphere could occur as
12、low as 50 volts. The TWTA power converter has output voltages ranging up to 2 kV. The failure analysis concluded that somewhere in the TWTA system, a high-voltage point developed a gap between itself and circuit ground which then filled with Martian air. Lack of precise telemetry data from the Lande
13、r made it impossible to define the breakdown area any closer than the TWTA No. 1 as a whole. Power converter corona RF noise could have found its way into the ranging system via the radio system or power line pickup.Evidence of Recurrence Control Effectiveness: N/ADocuments Related to Lesson: N/AMis
14、sion Directorate(s): Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-N/AAdditional Key Phrase(s): a71 Ground Operationsa71 Softwarea71 SpacecraftAdditional Info: Approval Info: a71 Approval Date: 1996-01-04a71 Approval Name: Carol Dumaina71 Approval Organization: 125-204a71 Approval Phone Number: 818-354-8242Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
