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Coasting Phase Propellant Management for Upper Stages

Coasting Phase Propellant Management for Upper Stages. Philipp Behruzi Hans Strauch Francesco de Rose. P/L. stage. P/L. LH2. LOX. New Requirements for next Generation cryogenic Upper Stages lead to new Problems in Propellant Management.

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Coasting Phase Propellant Management for Upper Stages

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  1. Coasting Phase Propellant Management for Upper Stages Philipp Behruzi Hans Strauch Francesco de Rose

  2. P/L stage P/L LH2 LOX New Requirements for next Generation cryogenic Upper Stages lead to new Problems in Propellant Management • Perform multiple engine starts in order to enhance mission flexibility • un-defined propellant position due to weightless condition between main engine burns • occurrence of bubbles due to slewing maneuvers and need for de-bubbling prior to re-ignition

  3. P/L stage P/L LH2 LOX New Requirements for next Generation cryogenic Upper Stages lead to new Problems in Propellant Management • Long time period (ballistic flight mode) between engine shut down and re-ignition • increase of the liquid hydrogen (LH2) temperature and pressure changes due the contact with the hot side walls of the tank • de-crease of the temperature of the liquid oxygen (LOX) due to a common tank wall in case of a common bulked tank

  4. New Requirements for next Generation cryogenic Upper Stages lead to new Problems in Propellant Management (cont‘d) • Second Boost for GTO+ Orbits • Remaining propellant mass for the second boost means higher sloshing mass compared to classical GTO missions • High sloshing mass effects • first payload separation phase high controller bandwidth during separation phase (achieving high pointing accuracy) may lead to stability problem when combined with high sloshing mass • long ballistic flight phase between first separation phase and re-ignition generation of disturbance torque by fluid motion will lead to controller commands (increase of number of thruster actuations, attitude propellant consumption)

  5. Requirements from Propellant Managment Function toward the Attitude Control System • The “perfect” attitude controller (as seen from propellant management function) • can control or at least restricts the motion of LOX and LH2 such that • LH2 minimizes its contact with the hot side walls • keeps LOX at a distance to LH2 in order to avoid LOX sub-cooling • performs large angle re-orientation maneuver such that LH2 and LOX stays at the bottom in order to avoid the generation of bubbles due to un-controlled splashing of the fluids in the tank • is robust against a high sloshing mass in such a way that • the propellant used for attitude control during the long ballistic flight phase (up to 5 hours) is small • the number of actuations commanded to the attitude thrusters is small • the closed loop is stable despite the high sloshing mass Need of a tool to simulate the controller commands (including algorithm, sensors and thrusters), motion of the stage, motion of the fluids and their mutual interaction

  6. Illustration of discussed Issues

  7. Slewing Maneuver with no regard of fluid motion Center of mass of the upper stage (satellites are not shown). Stage will rotate around this point Common Bulkhead LOX LH2 Attitude control thrusters firing side walls are hot due to radiation from sun leading to LH2 evaporation close contact from LH2 may cool down LOX too much VINCI engine

  8. Slewing Maneuver with longitudinal Thrust in order to stabilize the fluid Position minimal wall contact sloshing wave no contact LH2/LOX

  9. Example of Barbecue Mode (0.3 deg/sec) Motion of the Launcher Roll Axis in the transverse plane during long ballistic flight phase Hitting the attitude threshold, which leads to a thruster command Thruster commands lead to linear and angular accelerations, which excite the fluid motion.

  10. Disturbance Torque in transversal axis (nutation control) Disturbance generated due to spin reversal spin-up spin-reversal nutation damping cmds Feedback Loop Torque generated by spinning Propellant acting on the Upper Stage as computed by FLOW3d and coupled back into Fluid Motion

  11. Structure of Coupled Simulationallowing the Analysis of the Sloshing Motion and Control in closed Loop

  12. Process #1: Upper Stage Simulation Simulator Simulator Commanded Forces and Torques Controller Regler Attitude and Rate (SCA Algorithmus) (SCA Algorithms) Starrkörper Rigid Body Starrkörper Dynamik Dynamics Dynamik Tank #1 Flüssigkeitsdynamik Tank #1 Flüssigkeitsdynamik Tank #1 Fluid Dynamics Tank #1 Flüssigkeitsdynamik Linear and Reaction Forces and Moments Tank #2 Flüssigkeitsdynamik Tank #2 Flüssigkeitsdynamik angular Acceleration Tank #2 Fluid Dynamics Tank #2 Flüssigkeitsdynamik Tank #n Flüssigkeitsdynamik Tank #n Flüssigkeitsdynamik Tank #n Fluid Dynamics Tank #n Flüssigkeitsdynamik Complete Upper Stage Dynamics Process #2..n+1: Flow3D - - or simplified models (spring/damper)

  13. Conclusions • Strong coupling between propellant sloshing and stage motion  A5ME upper stage requires coupled analyses for ballistic flight phases • Wetting conditions strongly dependent on GNC (sloshing excitation)  Impact on thermal tank conditions Coupled Sim tool is operational for A5ME Next steps:  Coupling with thermal analysis tool (ESATAN)

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