SPACE PROPULSION SIZING PROGRAM (SPSP) Version 9 Let us create vessels and sails adjusted to the heavenly ether, and there will be plenty of people unafraid of the empty wastes. - Johannes Kepler in a letter to Galileo David North, Analytical Mechanics Associates Inc. Michael D. Scher, National Institute of Aerospace Michael Scher, National Institute of Aerospace David North, Analytical Mechanics Associates Inc. Student Session II Paper: GT.SSEC.F.6
SPSP description Overview Mass estimating approach Geometry sizing Spin-off Tools Benchmarking SPSP Demonstration Summary
Space Propulsion Sizing Program (SPSP) Add capability for reliable in-space propulsion system design. Originally designed for high-level sizing and trade studies. Ideal for rapid propulsion trade studies. Evolved into tool for high-level or detailed system design. Combines best mass estimating methods available. Simplified user interface in Microsoft Excel and Visual BASIC. Self-contained help documentation for fast assistance.
SPSP Program Structure V Input Parameters Payload Mass Type Chemical NTR Performance Thrust Propellant Type Number of Engines Structure Tank Configuration Materials Launch Vehicle Payload Envelope Excel Output Parameters Stage Gross Mass Subsystem Dry Masses Engine Tank Propellant Feed Reaction Control Sys Power Structures Avionics Main Propellant Mass RCS Propellant Mass Inert Propellant Masses Residual Propellants Reserve Propellants Pressurization Gas Mass Propellant Boil-Off Mass Burn Duration G-Loading Preliminary Propulsion System Geometry Parameters Geometry Output Ø Lfuel tank L tot L ox tank Leng Øeng Component C.G. s CAD
SPSP Modules and Options System Level Input-Output Module Engine Module Main Tank Module Propellant Feed Module RCS Module Structures Module Avionics Module Power Module Tandem FOT Tandem OOT Storable Cryogenic NTR Storable Cryogenic Storable Cryogenic* Battery Solar Panel Nested NP Nested P NEP/SEP* Solar Sail* Cold Gas Reaction Wheel* Multiple NTR RTG Fuel Cell * Future Development Geometry Generator
SPSP Top-Level Input Page
Help Example: Main Tanks Help Page Describes input requirements and output calculations in detail
Mass Estimating Methods Mass Estimating Methods Method Averaging Mass Est. Relationship Bottom-Up Calculation Regression Database METHOD MODULE Engine X X Main Tanks X X X Propellant Feed X X RCS X X X Power X Structures X Avionics X
Geometry Sizing 2-D cross-section using the Excel lin plot. 3-D CAD software Pro-Engineer imbedded into SPSP with capability to other software 0.00-0.70 0.30 1.30 2.30 3.30 4.30 5.30 6.30 7.30-1.00-2.00-3.00-4.00 17.0 m -5.00-6.00-7.00 Payload Adapter Forward Skirt Aft Compartment Aft Skirt 17.59 m -8.00 Thrust Structure -9.00 Engine Head Engine Nozzle -10.00-11.00 Oxidizer Tank Intertank Fuel Tank -12.00-13.00-14.00-15.00-16.00-17.00
Staging Tool with Optimizers Stacks up to 5 in-space, lander, or launch vehicle stages Each stage is modifiable with separate SPSP files Optimizes the stack to reduce total gross mass or to keep each stage identical Can also be used without optimizer to develop user-driven design
Tanker Sizing Tool Developed for propellant aggregation and propellant transfer trade studies. Identical to main SPSP but has no main engine. Due to similarity, also useful for sizing depots.
Lander Sizing Tool Same as main SPSP with additional structural mass for landing gear Additional structure is 3% of touchdown mass, based on Apollo lander Sizes un-crewed lander due to lack of crew habitat sizing capability
Launch Vehicle Design and Analysis Tool Combines staging tool with a MATLAB program which integrates the equations of motion Assumes simple g-turn trajectory Useful for determining relationship between insertion orbit and payload mass
Other SPSP capabilities Multiple Payload and/or V s Allow up to 5 different payloads and/or 5 different maneuvers Developed to analyze complicated rendezvous sequences Previously SPSP could only size for one payload through one maneuver Boil-off Estimates Added to account for potentially drastic cryogenic propellant losses Based directly on the fundamental physics Used as upper limit for zero boiloff hardware mass to make a positive impact on the propellant storage system
Benchmarking with Known Upper Stages Within an acceptable error Shows conservative estimate on inert masses Primary source of error believed to be avionics estimate Centaur III Delta IV Actual SPSP % error Actual SPSP % error Gross Mass (kg) 18960 19322 1.91% 30710 30564-1.63% Inert Mass (kg) 2180 2193 0.59% 3490 3507 0.49% Prop. Mass (kg) 16780 16972 1.14% 27200 26756-0.48% Mass Fraction 0.885 0.878-0.75% 0.89 0.875-1.67%
The S-IVB at Cutoff 100% Engine and Accessories 13.5% Engine and Accessories 13.9% 90% RCS 3.0% RCS 2.7% 80% Electrical 12.5% Electrical 15.8% 70% Purge and Propellant Feed 11.9% Purge and Propellant Feed 6.0% 60% 50% Tanks and Insulation 31.6% Tanks and Insulation 32.4% 40% 30% 20% Residual LH2 6.5% Residual LOX 1.1% Residual LOX 7.6% Residual LH2 4.6% 10% Structure 15.1% Structure 14.5% 0% Other Residuals 4.8% Other Residuals 2.5% Actual Estimated 12.85 t 12.88 t
Error less than 1% Geometry Comparison Cause of error likely due to shape of bottom tank 12.11 m 12.0 m
SPSP Testing with Known Vehicles Demonstrates inherent relationship between propellant mass fraction and vehicle gross mass. Improved propellant mass fraction estimates. 1 Propulsion System Gross Mass Vs. Propellant Mass Fraction 0.95 Propellant Mass / Propulsion Gross Mass 0.9 0.85 0.8 0.75 0.7 0.65 Delta IV 5-Meter Upper Delta IV 5-Meter Upper Stage Stage Gross Mass = 30.84 MT Prop Gross Mass Mass Fract = 30.84 = 0.882 MT Centaur Prop Mass IIIA Fract = 0.882 Centaur IIIA Gross Mass = 18.96 MT Prop Gross Mass Mass Fract = 18.96 = 0.885 MT Prop Mass Fract = 0.885 SPSP SPSP Nested Tanks Pressurized Nested Tanks Pressurized SPSP SPSP Tandem Tanks Fuel on Tandem Tanks Fuel on Top SPSP Top SPSP Nested Tanks Non Nested Tanks Non Pressurized Pressurized Saturn SIV-B Saturn SIV-B Gross Mass = 120 MT Prop Gross Mass Mass Fract = 120 = 0.893 MT Prop Mass Fract = 0.893 0.6 0 50 100 150 200 250 Gross Mass (MT)
SPSP/ProEngineer Demonstration
Summary Simple, robust package of tools Provides reliable estimates for high-level design and rapid trade studies Complete set of tools used to design from launch to in-space maneuvers to landing on a distant planet and returning to earth orbit