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Active Propellant Management: 

Active Propellant Management Dr. Boris Yendler Lockheed Martin Technical Operations Comsat Technical Services SpaceOps 2006, 19 -23 June, 2006 Rome, Italy,

Agenda: 

Agenda Background Goals APM implementation Re-pressurization Results Conclusion

Background: 

Problems of Operating spacecraft at End-Of-Life (EOL): Temperature difference between East and West tanks - daily Temperature difference between South and North tanks – seasonal Propellant migration due to temperature difference (thermal pumping) between should be taken into consideration at EOL when amount of propellant migrating in and out of the tank is comparable to propellant load of a single tank Propellant migration between tanks can lead to unstable orientation of the spacecraft (bad for imaging spacecrafts) during mission life Background

Background –cont’: 

Background –cont’ Thermal pumping can lead to depletion one of the tanks even though the total propellant load of the spacecraft does not indicate any possibility of tank depletion Reduction of propellant migration between tanks is usually done by controlling temperature difference between tanks Efficiency of temperature differential control to mitigate risk of tank depletion ?

GOALS: 

GOALS Determine efficiency of differential temperature control schemes to minimize thermal pumping Develop Active Propellant Management (APM) to minimize risk of accidental tank depletion Determine factors affecting APM procedures APM application for spacecraft re-pressurization

Slide6: 

MLI Tank wall Gas Liquid Radiation coupling North South West East Tank 1 Tank 2 Tank 3 Tank 4 MODELS Spacecraft model Tank model

SINDA/FLUENT Dynamic Model Network: 

SINDA/FLUENT Dynamic Model Network Gas node Fuel node Tank Wall node MLI node Gas + Fuel = constant volume fuel nodes are connected via pipe NE tank NW tank SE tank SW tank

Factor: Season: 

Factor: Season Daily Fuel Load variation at 12 kg total fuel load – NO differential temperature control Equinox, Winter and Summer Solstices The biggest variation in Equinox South tanks (SE or SW) have 1 kg less than North tanks during Winter Solstice North tanks (NE or NW) have 1 kg less than South tanks during Summer Solstice Winter Solstice

Factor: Ground Support: 

Factor: Ground Support Time spent by ground station operators to conduct the APM procedure Trade OFF : less ON/OFF heater toggle – more fuel movement IN and OUT (in the case of manual operation )

Minimum allowable fuel level: 

Minimum allowable fuel level Sump exposure to Helium leads to bubbles in fuel line (if bubble point is exceeded) Sump should be always submerged sump He Fuel sump He Fuel S/c maneuvering can shift fuel position Sump gets exposed to He Minimum fuel level should be high enough to keep sump submerged- Minimum Allowable Propellant Level (MAPL)

Factor: Maximum Allowable Propellant Migration: 

Factor: Maximum Allowable Propellant Migration Minimum propellant level = average tank load – maximum propellant migration Minimum Allowable Propellant Level (MAPL) determines Maximum Allowable Propellant Migration (MAPM) average MAPL MAPM

APM implementation: 

APM implementation APM driven by tank temperature difference between tanks on West and East sides (4 tank case) APM driven by time line (4 tank case) Tank temperature varies on the same s/c side during Winter and Summer solstices South tanks are hotter during Winter solstice North tanks are hotter during Summer solstice Problems with APM driven by temperature difference:

APM driven by East –West temperature difference: 

APM driven by East –West temperature difference Temperature Variation fuel migration reduced significantly only during half day fuel load is kept at low level – risk of accidental depletion is NOT reduced (SE tank) tank heaters must be switched every 2.5 hr to maintain 3oC dead band – difficult with manual operation Fuel Mass Variation APM starts

APM driven by time line: 

APM driven by time line Heaters turned ON and OFF according to pre-determined schedule Heaters on West or East sides turned ON/OFF ONCE a day Heaters on West or East sides turned ON/OFF TWICE a day

APM driven by time line- cont’: 

APM driven by time line- cont’ Reduction: 0.7 kg in NE/SE tank minimum level 0.3 kg in NW/SW tank minimum level

APM driven by time line- features: 

APM driven by time line- features Reduction of fuel migration where it is needed ( f. ex. IN&OUT of South tanks vs. North tanks during Winter solstice) Control over propellant distribution between tanks – schedule can be devised to increase minimum propellant level in order to reduce risk of depletion Increase number of heat pulses reduces fuel migration but increases operator involvement (in the case of manual operation)

Slide17: 

North South West East Tank 1 Tank 2 Tank 3 Tank 4 Re-Pressurization Spacecraft model Typically, propellant tanks need to be re-pressurized Imbalance of propellant tanks during re-pressurization can create problem at EOL Typical approach – run re-pressurization when tank temperatures are equal

Slide18: 

K4126 18 Re-Pressurization – cont’ Equality of temperature readings does NOT guarantee that propellant loads are equal Temperature sensor location is important

Conclusion: 

Conclusion APM reduces daily propellant migration APM driven by time line provides more control over propellant movement between tanks then typical APM driven by temperature difference APM driven by time line mitigates risk of accidental depletion of propellant tanks At certain conditions, typical APM driven by temperature difference does NOT reduce risk of tank accidental depletion Re-pressurization should be done with caution