NASA Task Order NNN06AA01C Interstellar Probe Reliability Engineering Discussion Glen H. Fountain, Clayton A. Smith, Sally Whitley, Steve Jaskulek The Johns Hopkins University Applied Physics Laboratory, Laurel, MD, USA. Acknowledgement: Almost 200 professional scientists and engineers world-wide actively working in support for Interstellar Exploration 17 November 2020 1 Reliability Engineering Topics NASA Task Order NNN06AA01C § Challenge of 50 years § Interplanetary mission duration experience § Overall framework to assess mission reliability § Robustness of Science Requirements and Instrument Suite § Reliability of spacecraft bus § Physics of failure methods 17 November 2020 2 Longevity Study Goal and Relevance to Other Long Duration Missions NASA Task Order NNN06AA01C § The Space Mission Life Time Study is part of the Interstellar Probe (ISP) initiative to study the environment well beyond the Heliosphere § An aspirational goal is to operate for 50 years or longer § The study has two principal goals: § Identify the processes for both the flight system, the supporting ground infrastructure, and mission staffing to assure a successful outcome when mission success requires 50 plus years of successful operation § Provide information about current and past missions with supporting analysis that will provide stakeholders with the confidence necessary to support such a mission § Interstellar Probe can provide a path and the basis for community support for other proposed missions § Many missions under study for the upcoming National Academy Decadal Survey may require mission durations exceeding 20 years § Electronic parts industry is dominated by short life-span consumer products § Historical record will need to be augmented with analysis and testing to provide confidence for decades long missions § Real trade space exists for space-based infrastructure of longevity vs tech refresh § Failure free / robust designs can support human missions of long duration where sparing up-mass and volume represent significant constraints 17 November 2020 3 Reliability Study Goals NASA Task Order NNN06AA01C § Longevity and reliability analyses are part of the Interstellar Probe (ISP) initiative to study the environment well beyond the Heliosphere with an aspirational goal is to operate for 50 years or longer § Reliability assessment questions § What does the historical record tell us about long duration missions? § What are the major technical challenges in building a long lasting spacecraft? § What is the analytical framework for providing sufficient confidence to decision-makers and the science community? § Assess the reliability of a baseline design § Identify risk drivers and mitigations § Quantify the uncertainty of such a system 17 November 2020 4 Building to Last NASA Task Order NNN06AA01C § Can we make systems that last long times without maintaining them? Oxford Bell (The Clarendon Dry Pile) Setup in 1840 is still ringing. The frequency of its oscillation is about 2Hz; so far the bells have been rung on the order of 10 billion times. Voyager 1 & 2 spacecraft – Launched in 1977 and still operational. Source: University of Oxford Department of Physics webpage § These systems were not designed to last this long § Survivors bias – caution on taking these examples as proof 17 November 2020 5 Literature Review NASA Task Order NNN06AA01C § Identified 50+ papers relating to spacecraft lifetimes § Examples of missions discussed: § Matsumoto, S.K., “Voyager Interstellar Mission a Very Old Spacecraft on a Very Long Mission” (2016). § Top level overview of operating configurations, FSW modifications, transitions of Ground Sys., etc. § Brown, N., N. Cohen, M. Cavanaugh and G. Richardson, “Spacecraft Lifetime Study (2018). § Analysis of 283 spacecraft launched between 1980 – 2010, satellite life has increased and exceeds design life, study does not properly take into account spacecraft that are designed for lifetimes greater than 8 years § Weaver et al., “In-Flight Performance and Calibration of the Long Range Reconnaissance Imager (LORRI) for the New Horizons Mission” (2019). § Documents the LORRI performance from shortly after launch (2006) through early 2019, data demonstrates no change in instrument performance (> 1%) over that period. 17 November 2020 6 Literature Review NASA Task Order NNN06AA01C § Unlike the often-assumed constant failure rate models, spacecraft failure rates decrease over time § MIL-HDBK-217F is a defacto standard for determining failure rates and reliability for many systems, pervasive throughout DoD and government (lots more latter) § Better modeled as a Weibull distribution Sarsfield, L. P. (1998). The Cosmos on a Shoestring: Small Spacecraft for Space and Earth Science. Santa Monica, CA, RAND Corporation. § Spacecraft last longer than required design life § Plot shows Actual Life (vertical axis) versus Design Life (horizontal axis) for all satellites § Points above the 45° upward sloping light dotted line are satellites that have exceeded their design life § Red circles denote satellites that have either died due to technical failures of components, depletion of station keeping fuel, or loss of service/mission demand Fox, G., R. Salazar, H. Habib-Agahi and G. F. Dubos (2013). A satellite mortality study to support space systems lifetime prediction. Aerospace Conference, 2013 IEEE, IEEE. 17 November 2020 7 Time Dependent Failure Models NASA Task Order NNN06AA01C § Weibull fits generated for mission types and systems § Saleh, Joseph Homer, and Jean-François Castet, ”Spacecraft reliability and multi-state failures: a statistical approach.” John Wiley & Sons, 2011. § Same behavior seen in Interplanetary spacecraft data 17 November 2020 8 Historical Record NASA Task Order NNN06AA01C § Interplanetary missions § 179 classified as interplanetary* § 71 missions after removal of launch failures, technology demonstrators, short-lived landers/impactors, etc. § Represents nearly 725 years of on-orbit experience § Large majority are still active or ended without failure § Mission failures not dominated by any one cause § Full analysis to be published at RAMS conference, January 2021 * SpacTrak database. https://www.seradata.com/products/spacetrak/ 17 November 2020 9 Examination of Mission Duration NASA Task Order NNN06AA01C § History suggests that spacecraft Design Life vs Actual Life - Interplanetary Spacecraft operational lifetimes frequently 45 Voyagers 1&2 reflect intentional mission design decisions rather than poor reliability 40 or limits in engineering capability 35 Pioneer 6 § Spacecraft tend to last much longer that Explorer 50 design life 30 Pioneer 10 § Majority of failures occurred after design life 25 Retired Pioneer 11 Failed 20 Cassini Active Actual Life [years] Design Life = Actual Life 15 New Horizons 10 5 0 0 2 4 6 8 10 12 14 16 Design Life [years] 17 November 2020 10 Examination of Mission Duration NASA Task Order NNN06AA01C § Mission Duration § Since many missions still operational or operational when retired, cannot take average of mission times § Survival analysis is reliability engineering technique to evaluate special type of random variable of positive values with censored observations, of which failure time or survival time events are the most common § A particular challenge in analyzing survival data is information censoring, i.e., the observation of survival times is often incomplete § Right censoring or truncation where the observation is terminated at a fixed time 90% Confidence limits § Spacecraft retired before a failure was observed § Spacecraft still active, no failure observed Percentage of spacecraft survived § Survival Analysis shows mission duration to be Estimated Weibull distributed Weibull distribution § Shape factor < 1 indicating an decreasing failure rate over time § Consistent with finding in literature § Mean duration ~ 53 years 17 November 2020 11 Examination of Mission Duration NASA Task Order NNN06AA01C § With a majority of data set being right censored, Bayesian analysis provides quantification of the uncertainty in the results Joint probability distribution of Weibull parameters 5th = 37 years 95th = 150 years § Caution with these results as they do not account for real physical limitations of hardware 17 November 2020 12 Reliability Modeling NASA Task Order NNN06AA01C § To augment Reliability engineering products, special attention is given to failure mechanisms § Develop an understanding for how devices and materials can fail in the presence of various radiation and thermal environments and characterize the physics of degradation processes out to 50 years § Provide inputs to testing campaign to assure the project and sponsor of viability at 50 years § Design tests to discover behavior of systems, subsystem, components, and materials at End of Life § Include tests to characterize lifetime uncertainties for components and materials § Employ various acceleration methods to test at 50 years § Identify dependencies when various redundancy and/or hibernation schemes are explored § Evaluate system resilience with a view including potential failures, health monitoring, and fault management behavior 17 November 2020 13 Reliability Modeling NASA Task Order NNN06AA01C § Over-arching model ties spacecraft, instruments, and science objectives together in order to evaluate the combination of failures Does the Yes Loss of that represent a loss of mission Spacecraft Bus Fail Mission No § Event sequence diagram shows logical flow for potential end-states Are Threshold Yes (diamonds) Mission