1、Lessons Learned Entry: 1485Lesson Info:a71 Lesson Number: 1485a71 Lesson Date: 2004-05-17a71 Submitting Organization: JPLa71 Submitted by: David OberhettingerSubject: The Risk Reduction From ?Two-fers? (Multiple Sister Spacecraft) May Outweigh the Incremental Cost (2002) Abstract: NASA elected at th
2、e end of MER Phase A to build a second Mars Exploration Rover at an estimated cost of $243 million. In addition to potentially doubling science return from Mars and mitigating the program impact were a rover to fail, this “two-fer” approach proved helpful in controlling development risks. Consider t
3、he benefits to system development and I&T that may accrue from building a “sister” spacecraft and from maintaining multiple testbeds.Description of Driving Event: At the end of Mars Exploration Rover (MER) Phase A development in July 2000, the cost of a single rover was estimated at $445.5 million,
4、including 20 percent budget reserves. The following month, JPL committed to a two-rover mission with an estimated cost of $243 million for the second rover. In addition to potentially doubling science return from Mars and mitigating the program impact were a rover to fail, this “two-fer” approach pr
5、oved helpful in controlling development risks.Having two rovers under development provided enhanced flexibility to the Integration & Test process (referred to as “ATLO” at JPL). ATLO (Assembly, Test, and Launch Operations) began in late February 2002 for MER-1, and in early May 2002 for the second r
6、over. Experience with MER-1 permitted an abbreviated ATLO for MER-2 and the availability of the additional MER-2 hardware in ATLO helped to isolate problems experienced by MER-1. The MER-2 funding also covered procurement of extra spare assemblies. Schedule risk was mitigated by this “hardware-rich”
7、 ATLO test environment, and was also alleviated by parallel development using four main testbeds run by separate teams. Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-DThe complex rovers were developed under major schedule risk. The MER schedule pro
8、vided for only 34 months from program approval in July 2000 to the opening of the launch window in May 2003. The Aerospace Corporation (Reference (1) rated MER as having a complexity comparable to traditional NASA missions such as Cassini and Galileo. The shortest of these traditional, large scale p
9、rojects took 80 months to develop. The development of dual rovers helped improve the system-level test program and helped to mitigate the risk associated with the compressed MER development schedule. References 1. M.A. Dornheim, “Can $ Buy Time: Complex Rovers Were Developed in a Dangerously Short P
10、eriod,” Aviation Week & Space Technology, May 26, 2003, p.56.Additional Key Words: integration and test, flight spares, schedule margin, schedule constraints, system testbed, test bed Lesson(s) Learned: The incremental cost of building a second copy of a spacecraft may be exceeded by the value added
11、 by the extra risk reduction.Recommendation(s): Mission schedule and technical risk mitigation strategies should consider the benefits to system Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-development and ATLO that may accrue from funding develop
12、ment of a second, “sister” spacecraft. Multiple testbeds operated in tandem may help to accrue the full benefits of concurrent development of duplicate spacecraft. Evidence of Recurrence Control Effectiveness: Corrective Action Notice No. Z84117 was closed by JPL on August 24, 2005. The measure take
13、n to implement Laboratory-wide corrective action on the above recommendation was a revision to the JPL risk management guidelines (JPL D-15951). The Risk Planning section now calls for consideration of the initial investment in risk reduction by addition of spare components, including twin missions
14、like MER, and especially when the launch window is a critical resource.Documents Related to Lesson: Flight Project Practices (Requirement), Jet Propulsion Laboratory (JPL) Document No. 58032, February 27, 2003, Section 5.7: “Spares, Testbeds, and Models.”Mission Directorate(s): a71 Exploration Syste
15、msa71 Aeronautics Researcha71 ScienceAdditional Key Phrase(s): a71 Flight Equipmenta71 Hardwarea71 Policy & Planninga71 Program and Project Managementa71 Risk Management/Assessmenta71 Spacecrafta71 Test & Verificationa71 Test ArticleAdditional Info: Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Approval Info: a71 Approval Date: 2004-09-22a71 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-,-,-
