Optimizing Commonality and Performance in Platform-Based Earth - PowerPoint PPT Presentation

Introduction Methodology Example of Application Conclusion Optimizing Commonality and Performance in Platform-Based Earth Observing SmallSat Architectures Zvonimir Stojanovski Daniel Selva March 10, 2017 Partially funded by the Cornell University Engineering Learning Initiatives 1/24

Introduction Methodology Example of Application Conclusion Background CubeSats and other small satellites are becoming important in Earth-observing systems [1] Often large constellations of similar or identical satellites Can we use commonality to reduce mission costs without sacrificing performance? Images from NASA.gov 2/24

Introduction Methodology Example of Application Conclusion Commercial Off-the-Shelf (COTS) Components Increasingly used for small satellites Can significantly reduce development cost Automated tool developed by Jacobs and Selva [2] Equipped with catalog of COTS components Generates and evaluates design for a CubeSat We want to extend this concept to families of satellites endurosat.com 3/24

Introduction Methodology Example of Application Conclusion Platform-Based Design Widely used in mature industries, e.g., automotive and aircraft [3] Scale-Based Variants obtained by scaling variables such as length or area E.g., Airbus A3xx family Modular – Used Here “Airbus A320 Variants obtained by combining different sets of Family,” Global Traffic . common components E.g., Volkswagen A family More appropriate for using COTS components 4/24

Introduction Methodology Example of Application Conclusion The Optimization Problem Maximize Performance and Minimize Cost subject to Feasibility Constraints Cost model accounts for commonality and modularity When commonality is used: Cost is typically lower but Design is not tailored specifically to each mission This is the main trade-off in this problem 5/24

Introduction Methodology Example of Application Conclusion How the Tool Works Catalog Requirements Genetic Select Module Algorithm Results Scheme Components (NSGA II) Selected for Each Mission Compute Cost Evaluated Apply No Platform Feasible? Penalty Design Yes Compute Performance 6/24

Introduction Methodology Example of Application Conclusion Representation of a Satellite Design Each satellite must have certain components We call these abstract components component slots Some slots may be empty (e.g., ADCS Actuator 2 and Propulsion) Components may be redundant To design a satellite means to select components from the catalog to fill the component slots. 7/24

Introduction Methodology Example of Application Conclusion Modules and Platforms A module is a set of one or more components that is assembled prior to the main assembly of the spacecraft A module may fill multiple component slots at once Modules are assembled from components from the catalog The module scheme indicates which component slots are placed together in modules A platform is a family of spacecraft with shared modules In a platform, all missions use the same module scheme 8/24

Introduction Methodology Example of Application Conclusion Cost Model for Mission Platform Total cost: C = C P + C IAT + C L (1) Component Cost C P : Sum of retail costs of COTS components Launch Cost C L : based on prices given by a launch provider Integration, Assembly and Testing (IAT) Cost C IAT : affected by modular design and commonality Assume other costs are not affected by choice of components or modules 9/24

Introduction Methodology Example of Application Conclusion IAT Cost of Modules Model based on Tsai, Chen, and Lo [4] � (2) A j = γ j m ij a ij i A j : IAT cost of module j a ij : non-modular IAT cost of component i m ij number of component i in module j γ j : “the savings ratio when module j is used” Learning curve is used for multiple identical modules Then A j is the first unit IAT cost of module j Small γ j is better—gives lower module IAT cost 10/24

Introduction Methodology Example of Application Conclusion Connectivity Coefficients For each pair of components { i , k }, we define a connectivity coefficient ǫ ik Note that ǫ ik = ǫ ki This is the cost increase or decrease factor when i and k are placed together in a module We compute γ j by averaging ǫ ik over all pairs of components in module j Sample Module j : Antenna Transceiver Battery ǫ Antenna \ Sym. = ⇒ γ j = 0.9 Transceiver 0.8 \ Battery 1.0 0.9 \ 11/24

Introduction Methodology Example of Application Conclusion Heuristic for Selecting Module Schemes Computationally expensive (if not impossible) to evaluate all module schemes 115 975 modules schemes for 10 component slots 1 382 958 545 for 15 slots Instead, we use a heuristic based on graph theory Groups components together based on two factors: Frequently occurring pairs (take advantage of learning factor) Low connectivity coefficients (lower first-time IAT cost) 12/24

Introduction Methodology Example of Application Conclusion Procedure for Determining Module Schemes (A part of) the initial graph 2 Propulsion ADCS Actuator 1 3 4 4 2.7 3.3 4 Antenna ADCS Actuator 2 2.7 4 5 5 3 5 5 Battery Transceiver 5 Weight: w ij = ǫ ij × (# distinct component pairs) 13/24

Introduction Methodology Example of Application Conclusion Procedure for Determining Module Schemes Edges are removed from heaviest to lightest Graph splits into n connected components, for n = 1,2,3,... This is for n = 3: Three Groups 2 Propulsion ADCS Actuator 1 2.7 Antenna ADCS Actuator 2 2.7 Battery Transceiver 14/24

Introduction Methodology Example of Application Conclusion Evaluating Performance for Mission Platforms Threshold and Target values given for performance metrics for each mission, e.g. Lifetime Downlink data rate Slew rate Pointing accuracy Each performance metric is normalized using a sigmoid function Performance of a mission is the average of its normalized performance metrics Platform Performance Score – to be maximized Weighted average of missions’ performance Weight used is the mission’s “importance” 15/24

Introduction Methodology Example of Application Conclusion Problem Overview Inputs – For Each Mission Payload Ouptuts Orbit Modular design for mission Threshold and Target values family for performance Total cost and cost Number of satellites breakdown (by mission, “Importance” number components, IAT, and launch) Feasibility constraints Basic requirements for Performance metrics for operational satellite missions E.g., solar panels produce sufficient power 16/24

Introduction Methodology Example of Application Conclusion Sample Missions – Used for Testing the Tool Mission #Sats Importance Orbit A 20 5 LEO, 400 km, Polar B 16 6 LEO, 600 km, Near-Polar C 8 8 SSO, 600 km, Morning D 5 10 SSO, 600 km, Afternoon E 15 10 LEO, 800 km, Polar F 5 15 SSO, 600 km, Morning 17/24

Introduction Methodology Example of Application Conclusion Payload Specifications for Sample Missions Mission Mass (g) Power (W) Height (mm) Data Rate (KB/s) A 1000 3 100 1.0 B 200 1 30 2.5 C 2000 20 150 12.5 D 3000 30 200 25.0 E 1200 10 100 5.0 F 1500 15 150 50.0 For all sample payloads: One-year reliability is 99.9% Length and width are 100 mm 18/24

Introduction Methodology Example of Application Conclusion Sample Mission Requirements Mission A B C D E F Lifetime (years) Thr. 0.4 0.4 1.5 4 1.8 2 Tar. 0.5 0.5 2 5 2.2 2.5 Pointing Accuracy (deg) Thr. 1 2 0.2 0.005 0.5 0.005 Tar. 0.5 1 0.1 0.001 0.1 0.001 Downlink Data Rate (kbit/s) Thr. 72 160 800 1600 320 3200 Tar. 80 200 1000 2000 400 4000 Slew Rate (sec. to slew 30 ◦ ) Thr. 150 — 90 45 90 120 Tar. 120 — 60 30 60 75 Thr. — Threshold value Tar. — Target value 19/24

Introduction Methodology Example of Application Conclusion Plot of All Feasible Designs Found 60 Dominated Non-Dominated 55 Cost ($1 000 000) 50 45 40 35 30 0.72 0.74 0.76 0.78 0.8 0.82 0.84 0.86 0.88 Performance Score 20/24

Introduction Methodology Example of Application Conclusion Sample Module Schemes Illustrate the trade-off between commonality and performance Highest-Performance Platform Lowest-Cost Platform Group Component Slots V Group Component Slots V 1 ADCS Sensor 3 1 ADCS Sensor 4 2 OBC 5 2 ADCS Actuator 1 2 3 Battery 4 3 ADCS Actuator 2 2 Antenna 4 OBC 4 4 3 Transceiver 5 Battery 6 ADCS Actuator 1 Antenna 6 3 5 ADCS Actuator 2 2 Transceiver Propulsion 7 Solar Panel 4 8 Structure 2 Structure 6 3 9 Propulsion 1 Solar Panel V is the number of variants of each module. 21/24

Introduction Methodology Example of Application Conclusion Limitations Performance model uses rough approximations Component catalog is small Cost model does not account for ground operations, etc. Connectivity coefficients are guesses Emphasis was on methodology 22/24