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Choices: Some Considerations in Configuring Launch Systems

Choices: Some Considerations in Configuring Launch Systems. Dr. John M. Jurist Adjunct Professor of Space Studies, Odegard School of Aerospace Sciences, and Adjunct Professor of Biophysics and Aviation, Rocky Mountain College

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Choices: Some Considerations in Configuring Launch Systems

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  1. Choices: Some Considerations in Configuring Launch Systems Dr. John M. Jurist Adjunct Professor of Space Studies, Odegard School of Aerospace Sciences, and Adjunct Professor of Biophysics and Aviation, Rocky Mountain College Note: This material was used in various seminars at the above institutions, and is not to be reused without attribution

  2. Target Audience: • People not trained in the physical or engineering sciences • People with a general interest in why space launch technology is so complex

  3. A Great Resource for Those Who Wish to Dig Deeper: George Sutton’s books: Rocket Propulsion Elements (multiple editions over 60+ years)

  4. Goals: • Give a sense of the kinds of choices that are made in configuring a launch system. • Show how choices made early in the process affect later options.

  5. Relevant Quote: “Statements in the first 2 years of the company should be disregarded due to idiocy.” -- Elon Musk, ISDC 2008 remarks at Capital Hilton in Washington, DC on SpaceX scheduling problems

  6. Primary Parameters: Define payload mass to specified trajectory Example: 2,000 pounds to 200 km LEO at 23 deg inclination launched to east Translates to mission velocity change (delta-V) Orbital velocity plus margins for gravity and aerodynamic losses = mission delta-V

  7. The Basic Rocket Equation: Mo/Mf = e(v/c) or v = c * loge(Mo/Mf) Mo = GLOW = liftoff mass Mf = burnout mass c = g * Isp = exhaust velocity v = ideal burnout velocity

  8. Useful Reading Material: For a narrative of the implications of the rocket equation: http://www.nasa.gov/mission_pages/station/expeditions/expedition30/tryanny.html

  9. Options Narrowed: Select propellant (solid vs liquid, hydrocarbon vs liquid hydrogen, etc.) Propellant combination determines specific impulse from rocket equation C* = g * Isp = exhaust velocity

  10. Tradeoffs -- 1: Solid vs Liquid: • Simple vs complex (especially with pumps) • Reliable vs less reliable ignition • Storable vs less storable • Lower vs higher potential impulse density • Lower vs higher mass efficiency for larger (pumped) systems

  11. Tradeoffs -- 2: Solid vs Liquid: • Toxic components and/or exhaust products • Ammonium perchlorate • Liquid oxygen • Hydrocarbon • Hydrazine • Liquid hydrogen

  12. Tradeoffs -- 3: Solid vs Liquid: • Handling • Hydrocarbon vs liquid hydrogen • Lower vs higher specific impulse • Higher vs lower density (tank mass) • Insulation (tank mass)

  13. Options Narrowed -- 1: Selected propellant C* gives required mass ratio from rocket equation for given mission delta-V: (Mo/Mf), where Mo = GLOW = liftoff mass and Mf = burnout mass

  14. Options Narrowed -- 2: Staging to Ease Mass Ratio Constraints: • More stages = more complexity and less reliability • No ullage or separation motors required for solids but required for liquids unless hot-fire staging used

  15. Discussion Limitation: Assume two stage liquid propellant system from this point forward

  16. Mass Budget -- 1: Once payload mass, mission delta-v, propellant combination, staging, and mass ratio defined, characterization of each stage can proceed: • Structural elements • Tankage (and insulation if required) • Attitude control system • GNC (guidance, navigation, and control)

  17. Mass Budget -- 2: • Payload shroud (eject when out of atmosphere) • Interstage assembly (divide between lower and upper) • Ullage systems (stage separation and propellant settling for upper stage ignition) • Destruct system

  18. Mass Budget -- 3: • Propulsion system: • Motors : Nozzles behave differently at sea level and in vacuum so compromises needed in design • Pumps • Plumbing • Gimbals

  19. Mass Budget -- 4: • Multiple iterations required • Interactions/relationships • Reusability implies: More robust (and massive) structure, and Thermal fatigue and shock issues for motors

  20. Illustrative Interaction -- 1: A new definition: Net structural mass fraction NFS or NMF = ( Ms - Mm ) / Mp Ratio of structural mass less motor to propellant mass – also called net mass fraction or NMF

  21. Illustrative Interaction -- 2:

  22. Variations: Multiple motors: • Shut down and drop some motors part way through burn • Atlas missile Propellant Transfer • Shift propellant from tanks that can be dropped • SpaceX Falcon Heavy?

  23. An Alternative to Propellant Transfer: • Instead of similar core and 2 side boosters with fuel transfer to core, have similar tankage with more motors supplied from side boosters and fewer from central core • Eject side boosters and motors when fuel depleted

  24. Cost Considerations: Dr. Dietrich E. Koelle: Transcost • Statistical-analytical model for cost estimation and economical optimization of launch vehicles • Parametric cost estimation: Method of estimating cost per unit mass • See Launch Vehicle Business Workshop .ppt

  25. Political and Regulatory Considerations: To be discussed

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