Coasting Phase Propellant Management for Upper Stages

Coasting Phase Propellant Management for Upper StagesPhilipp BehruziHans StrauchFrancesco de Rose

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New Requirements for next Generation cryogenic Upper Stages lead to new Problems in Propellant ManagementPerform multiple engine starts in order to enhance mission flexibilityun-defined propellant position due to weightless condition between main engine burnsoccurrence of bubbles due to slewing maneuvers and need for de-bubbling prior to re-ignition



New Requirements for next Generation cryogenic Upper Stages lead to new Problems in Propellant ManagementLong time period (ballistic flight mode) between engine shut down and re-ignitionincrease of the liquid hydrogen (LH2) temperature and pressure changes due the contact with the hot side walls of the tankde-crease of the temperature of the liquid oxygen (LOX) due to a common tank wall in case of a common bulked tank



New Requirements for next Generation cryogenic Upper Stages lead to new Problems in Propellant Management (contd)Second Boost for GTO+ OrbitsRemaining propellant mass for the second boost means higher sloshing mass compared to classical GTO missionsHigh sloshing mass effectsfirst 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)



Requirements from Propellant Managment Function toward the Attitude Control SystemThe perfect attitude controller (as seen from propellant management function)can control or at least restricts the motion of LOX and LH2 such thatLH2 minimizes its contact with the hot side wallskeeps LOX at a distance to LH2 in order to avoid LOX sub-coolingperforms 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 tankis robust against a high sloshing mass in such a way thatthe propellant used for attitude control during the long ballistic flight phase (up to 5 hours) is smallthe number of actuations commanded to the attitude thrusters is smallthe 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



Illustration of discussed Issues



LOXLH2Center of mass of the upperstage (satellites are not shown).Stage will rotate around this pointAttitude control thrusters firingVINCI engineCommon Bulkheadside walls arehot due to radiationfrom sun leading to LH2evaporationclose contact from LH2 may cool downLOX too muchSlewing Maneuver with no regard of fluid motion



Slewing Maneuver with longitudinal Thrust in order to stabilize the fluid Position sloshing waveno contact LH2/LOXminimal wall contact



Motion of the Launcher Roll Axis in the transverse plane during long ballistic flight phaseHitting the attitude threshold, which leads to a thruster commandThruster commands lead to linear and angularaccelerations, which excite the fluid motion.Example of Barbecue Mode (0.3 deg/sec)



Torque generated by spinning Propellant acting on the Upper Stage as computed by FLOW3d and coupled back into Fluid Motion



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





ConclusionsStrong coupling between propellant sloshing and stage motion A5ME upper stage requires coupled analyses for ballistic flight phasesWetting conditions strongly dependent on GNC (sloshing excitation) Impact on thermal tank conditions

Coupled Sim tool is operational for A5MENext steps: Coupling with thermal analysis tool (ESATAN)


Coasting Phase Propellant Management for Upper Stages

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