1、Lessons Learned Entry: 1390Lesson Info:a71 Lesson Number: 1390a71 Lesson Date: 2004-01-12a71 Submitting Organization: JPLa71 Submitted by: David Oberhettinger, Jim TaylorSubject: Test Telecommunications Links End-to-End, and Dont Forget the Doppler (2000) Abstract: A mission-critical error was disco
2、vered in the communications link between the Cassini spacecraft and its Huygens probe when it was determined that the radio frequencies would not adjust for Doppler effect. This parameter was not isolated during the pre-launch verification process. The recommendations affirm the need for (1) end-to-
3、end testing of communications links, (2) a high fidelity telecommunications testbed, and (3) referencing Doppler effects on subcarriers in an appropriate procedure.Description of Driving Event: A mission-critical error was discovered in the communications link between the Cassini spacecraft and its
4、Huygens probe when it was determined that the radio frequencies would not adjust for Doppler effect. With Doppler effect, the motion of a transmitter relative to a receiver causes the received frequency to differ from that sent from the transmitter. The effect on a probe-to-orbiter uplink may be esp
5、ecially severe in times of rapid velocity changes such as during planetary flybys and Saturn orbit insertion. An extensive in-flight end-to-end telecommunications test conducted in February 2000 (3 years after Cassini was launched) revealed anomalous characteristics of the Huygens-Cassini communicat
6、ions link. Extensive ground testing of the link subsequently confirmed that Doppler shift would cause unanticipated 10dB degradation in the link margin, resulting in a major loss of data during probe descent and landing. This parameter was not isolated during the pre-launch verification process. The
7、 baseline mission profile has been changed to increase the strength of the data signal and restore the Huygens mission. ReferencesProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-1. ”Huygens Communications Package Under Investigation,” ESA Press Relea
8、se, October 5, 2000.2. ”Ensure Test Facilities Can Accommodate Test-As-You-Fly,“ Lessons Learned No. 1335, March 31, 2003.3. ”Test As You Fly, Fly As You Test, And Demonstrate Margin,” Lessons Learned No. 1196, January 24, 2002.4. JPL Incident/Surprise Anomaly (ISA) report no. Z70967, February 14, 2
9、001.Additional Key Words: international partnering, telecommunications design, uplink design, link analysis, telecommunications subcarrier, subcarrier test, design margin, flight readiness, test and integration, telecommunications failure modes, fault tolerance, RF simulations Lesson(s) Learned: 1.
10、Despite prior incidents involving Doppler effects on the command subcarriers for Ulysses and Deep Space 1, designers still tend to overlook the subcarrier when analyzing and testing for Doppler effects on deep space communications links. 2. It is difficult to conduct realistic simulations of Doppler
11、 effect in testbeds that do not replicate communications frequencies and signal levels.3. Communication link design must be more carefully reviewed and verified by analysis when more than one organization is responsible for verifying through test that the transmitting and receiving spacecraft are co
12、mpatible under mission conditions.Recommendation(s): 1. Consider a history of deep space communications design difficulties as validation of the need for end-to-end testing of communications links.2. A telecommunications testbed should be capable of simulating space communications and environments (
13、e.g., Doppler, occultation, plasma effects) with the high fidelity needed to accurately mimic the end-to-end communications link.3. Doppler effects on subcarriers, as well as carriers, should be referenced in an appropriate procedure. If compensation for Doppler effects can be performed during missi
14、on operations, the applicable software, flight rule, or procedure should explicitly state the need for compensation and reference the numerical values to be used.Evidence of Recurrence Control Effectiveness: Corrective Action Notice No. Z84381 was opened by JPL on August 3, 2004 to initiate and docu
15、ment appropriate Laboratory-wide corrective action on the above recommendations.Documents Related to Lesson: Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-N/AMission Directorate(s): a71 Exploration Systemsa71 Sciencea71 Aeronautics ResearchAddition
16、al Key Phrase(s): a71 Communication Systemsa71 Facilitiesa71 Flight Operationsa71 Hardwarea71 Independent Verification and Validationa71 Safety & Mission Assurancea71 Spacecrafta71 Test & Verificationa71 Test FacilityAdditional Info: Approval Info: a71 Approval Date: 2004-04-26a71 Approval Name: Carol Dumaina71 Approval Organization: JPLa71 Approval Phone Number: 818-354-8242Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
