1、Lessons Learned Entry: 0364Lesson Info:a71 Lesson Number: 0364a71 Lesson Date: 1994-12-22a71 Submitting Organization: JPLa71 Submitted by: B. LarmanSubject: Galileo Retro Propulsion Module and Pyro Power System Interaction Abstract: Galileo design optimizations over the years exacerbated interaction
2、s between spacecraft power and the propellant tanks. During the cruise phase, high power and heat dissipation near the propellant tanks combined with an enhanced tank load to increase the tank pressure.A thorough analysis should be conducted before changes are made to one or more of the flight proje
3、ct elements that occur late in the development cycle or well into the test program. Description of Driving Event: Over a period of several years, design optimizations were made to the Galileo Spacecraft system including the increase in the Retro Propulsion Module (RPM) tank load from 84% to 94%. Thi
4、s was to assure adequate propellant to accomplish the mission objectives and was done late in the spacecraft development cycle. However, the change resulted in a high degree of coupling between the RPM tank pressure and the spacecraft system power demand due to the spacecraft power dissipation mecha
5、nism. During the cruise phase, the spacecraft power demand will be low and the excess electrical power is to be dissipated by shunt heaters located near the RPM tanks. The power dissipation increases the RPM tanks temperature with a concomitant rise in the RPM tank pressure. The RPM design is such t
6、hat relatively small temperature increases combined with the low ullage (tanks nearly full), will cause a dangerous increase in the internal RPM tank pressure. The shunt heater circuit already had a requirement for a minimum dissipation level in order to assure adequate power margin for blowing fuse
7、s in case of a spacecraft fault. The RPM tank pressure concern now added an upper limit on the shunt heat dissipations. Maintaining this dissipation within the required range causes a significant impact to the spacecraft system fault detection and control software. In addition, the operational seque
8、nce design after launch and during the cruise will be more complex and require the use of additional resources.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Lesson(s) Learned: Design of the various elements of a flight project (trajectories, scienc
9、e, mission operations, spacecraft design, spacecraft integration and test, etc.) is usually conducted in parallel. Although the designs are not conducted independently, there are always subtle but significant interactions which can occur within one of the elements or between several elements.Recomme
10、ndation(s): A thorough analysis should be conducted before changes are made to one or more of the flight project elements late in the development cycle where the test program is well advanced or actually may be completed for some of the elements. This analysis should be conducted in concert with des
11、igners of the other elements. If discovered after changes are made, these interactions and couplings may (1) reduce the flexibility to make later changes necessary to recover from failures, or (2) negate the opportunity to enhance future science return, or (3) require complicated and costly operatio
12、nal workarounds.Evidence of Recurrence Control Effectiveness: N/ADocuments Related to Lesson: N/AMission Directorate(s): N/AAdditional Key Phrase(s): a71 Configuration Managementa71 Test & VerificationAdditional Info: Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Approval Info: a71 Approval Date: 1986-09-30a71 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-,-,-
