REG NASA-LLIS-0390-1995 Lessons Learned - Voyager Subsystem Interface Noise Problems.pdf

1、Lessons Learned Entry: 0390Lesson Info:a71 Lesson Number: 0390a71 Lesson Date: 1995-03-21a71 Submitting Organization: JPLa71 Submitted by: B. LarmanSubject: Voyager Subsystem Interface Noise Problems Abstract: Problems due to waveform irregularities and the resultant induced noise on the Voyager Spa

2、cecraft system interfaces were not validated until 500 hours of system testing had been completed. Lessons involve the need for early system tests to determine subsystem compatibility and design requirements for electrical noise and transients, and extensive interface testing under flight-like condi

3、tions.Description of Driving Event: Problems due to waveform irregularities and the resultant induced noise on the Voyager Spacecraft system interfaces were not validated until after in excess of 500 hours of system testing had been completed. The problem manifested itself in the following two ways:

4、1. A digital, coded interface design was utilized on the Voyager Spacecraft for transferring command data between the Computer Command Subsystem (CCS) and the power subsystem. This interface, under certain spacecraft system loading configurations with the support equipment disconnected, resulted in

5、several cases of either “no response“ or “incorrect response“ to commands. The problem was traced to the 2.4 kHz power subsystem waveform transitions (variable with system load configuration) coupling into the command circuits via its circuit returns causing spurious clock pulses.2. A related but no

6、t identical problem occurred on the CCS to the Attitude and Articulation Control Subsystem (AACS) Command Interface. In this case, waveform transition irregularities of the 2.4 kHz clock signal (again, variable with system load configuration) could, under certain conditions, result in trigger circui

7、ts interpreting these irregularities as clock pulses.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-To correct these problems required circuit modifications to all affected subsystems which entailed extensive regression testing. Details can be found

8、 in Voyager PFR 39802 and IOM 3132-76-179.Lesson(s) Learned: 1. Early testing of subsystem compatibility can detect problems and avoid extensive subsystem modifications.2. Waveform transition irregularities and resultant induced noise problems on spacecraft system interfaces, if not validated prior

9、to system testing of flight hardware, can require circuit modifications to affected subsystems and extensive regression testing.3. It is virtually impossible to simulate the real noise environment of the complete spacecraft in the subsystem test facility.Recommendation(s): 1. System tests to determi

10、ne subsystem compatibility should begin as early as possible using prototype or breadboard hardware. Testing of the system without the subsystem support equipment cables attached should also be conducted as early as possible. It has been found that these cables can alter the flight configuration noi

11、se environment considerably.2. Critical system level interface electrical noise and transient design requirements should be generated early by systems engineering. These should be reviewed and understood by the subsystem design engineers prior to circuit design. Critical subsystems interface circuit

12、 design should be reviewed by the system engineer prior to implementation.3. It is essential that early and extensive interface testing be conducted with as many system loading and flight-like conditions as possible. Where noise immunity is critical, injection of noise on the signal lines during sub

13、system tests may be necessary to demonstrate adequate margins.Evidence of Recurrence Control Effectiveness: N/ADocuments Related to Lesson: N/AMission Directorate(s): N/AAdditional Key Phrase(s): Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-a71 Spacecrafta71 Test & VerificationAdditional Info: Approval Info: a71 Approval Date: 1987-01-02a71 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-,-,-