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

2. This document is the property of Astrium. It shall not be communicated to third parties without prior written agreement. Its content shall not be disclosed. 23. 07. 2010Page 2 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 P/L LH2 LOX stage

3. This document is the property of Astrium. It shall not be communicated to third parties without prior written agreement. Its content shall not be disclosed. 23. 07. 2010Page 3 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 P/L LH2 LOX stage

4. This document is the property of Astrium. It shall not be communicated to third parties without prior written agreement. Its content shall not be disclosed. 23. 07. 2010Page 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. This document is the property of Astrium. It shall not be communicated to third parties without prior written agreement. Its content shall not be disclosed. 23. 07. 2010Page 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. This document is the property of Astrium. It shall not be communicated to third parties without prior written agreement. Its content shall not be disclosed. 23. 07. 2010Page 6 Illustration of discussed Issues

7. This document is the property of Astrium. It shall not be communicated to third parties without prior written agreement. Its content shall not be disclosed. 23. 07. 2010Page 7 LOX LH2 Center of mass of the upper stage (satellites are not shown). Stage will rotate around this point Attitude control thrusters firing VINCI engine Common Bulkhead side walls are hot due to radiation from sun leading to LH2 evaporation close contact from LH2 may cool down LOX too much Slewing Maneuver with no regard of fluid motion

8. This document is the property of Astrium. It shall not be communicated to third parties without prior written agreement. Its content shall not be disclosed. 23. 07. 2010Page 8 Slewing Maneuver with longitudinal Thrust in order to stabilize the fluid Position sloshing wave no contact LH2/LOX minimal wall contact

9. This document is the property of Astrium. It shall not be communicated to third parties without prior written agreement. Its content shall not be disclosed. 23. 07. 2010Page 9 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. Example of Barbecue Mode (0.3 deg/sec)

10. This document is the property of Astrium. It shall not be communicated to third parties without prior written agreement. Its content shall not be disclosed. 23. 07. 2010Page 10 Torque generated by spinning Propellant acting on the Upper Stage as computed by FLOW3d and coupled back into Fluid Motion Disturbance Torque in transversal axis (nutation control) spin-up spin-reversalnutation damping cmds Disturbance generated due to spin reversal Feedback Loop

11. This document is the property of Astrium. It shall not be communicated to third parties without prior written agreement. Its content shall not be disclosed. 23. 07. 2010Page 11 Structure of Coupled Simulation allowing the Analysis of the Sloshing Motion and Control in closed Loop

12. This document is the property of Astrium. It shall not be communicated to third parties without prior written agreement. Its content shall not be disclosed. 23. 07. 2010Page 12 Tank #1 Flüssigkeitsdynamik Tank #2 Flüssigkeitsdynamik Tank #n Flüssigkeitsdynamik Starrkörper Dynamik Regler (SCA Algorithmus) Linear and Upper Stage Reaction Forces and Moments Process #2..n+1: Flow3D- Process #1: Upper Stage Simulation Attitude and Rate Simulator Tank #1 Flüssigkeitsdynamik Tank #2 Flüssigkeitsdynamik Tank #n Flüssigkeitsdynamik Tank #1 FlüssigkeitsdynamikTank #1 Fluid Dynamics Tank #2 FlüssigkeitsdynamikTank #2 Fluid Dynamics Tank #n FlüssigkeitsdynamikTank #n Fluid Dynamics Starrkörper Dynamik Rigid Body Dynamics Controller (SCA Algorithms) angular Acceleration Complete Dynamics - or simplified models (spring/damper) Commanded Forces and Torques Simulator

13. This document is the property of Astrium. It shall not be communicated to third parties without prior written agreement. Its content shall not be disclosed. 23. 07. 2010Page 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)