X-ray Wide Field Imager

1. X-ray Wide Field Imager Propulsion Bob Estes 16 – 20 April, 2012

2. Summary • Monopropellant (Hydrazine) Propulsion subsystem operating in a blow-down mode • Three 22 inch spherical propellant tanks with diaphragms • Thrusters: Twelve 22N thrusters (Aerojet MR-50E) • Propellant Mass: 148.6 kg (6.4 kg GN2) based on 3300 kg wet • Subsystem Dry Mass: 38.1 kg • Subsystem is single-fault tolerant (dual-fault tolerant wrt Range Safety) • All components are TRL9

3. Propulsion Subsystem Schematic N2 N2H4 N2 N2H4 N2 N2H4 P P P Diaphragm Tanks F 22 N Thrusters FD Valves Pressure Transducer Filter Latch Valve F P

4. Propulsion Subsystem Drivers • Provide ΔV for 3300 kg maximum launch mass (wet mass) • Provide 6 DOF to spacecraft via thrusters • Unload momentum wheels • Size the propulsion system for 5 years at L2 at maximum launch mass • Single fault tolerant, graceful degradation • Dual fault tolerant with respect to range safety • Minimize plume contamination to mirror and radiators • Minimize product qualification Total = 91 m/sec

5. Propulsion Subsystem Description • Mono-Propellant, blow-down system using hydrazine fuel • Three diaphragm propellant tanks • Diameter ~22 inch • Each holds up to 63.5 kg of fuel in blowdown mode (required = 49.5 kg each) • Twelve 22-N thrusters • Thrusters arranged in 2 banks to provide redundancy • Thrusters provide 6 DOF • Dual coil thrusters • Dual coil latch valves • Pressurant side of tanks isolated to ensure equal draining • Dedicated transducers provide propellant knowledge for individual tanks P P P N2 N2H4 N2 N2H4 N2 N2H4 Diaphragm Tanks F 22 N Thrusters FD Valve Latch Valve Pressure Transducer Filter F P

6. ΔV Budget • Propellant was budgeted for a 3300 kg S/C (including propellant mass) • Nominal ΔV = 91 m/s. Adding 10% Attitude Control (AC) tax and 0% Margin increases total ΔV to 100.1 m/s. • ΔMass Sensitivity chart for tank capacity margins • Specific Impulse (Isp) assumes 10⁰ degree cant in two planes. (227 sec represents average over full pressure range) • Total propellant mass = 148.6 kg • Maximum continuous burn = 2295 seconds (~38 minutes), Launch Window+Dispersion

7. ΔMass Sensitivity • Baseline = 148.6 kg • Propellant was budgeted for 91 m/sec + 10% ACS penalty = 100.1 m/sec • Isp = 227 sec (10⁰+ 10⁰ cant) 22 N class thrusters • Max load = 191.5 kg (3 x 5555 in3 tanks, 400 – 100 psi blowdown, 50 – 10 C)

8. Propellant Tanks • 3 spherical diaphragm tanks with tab mounts • ATK Part No. 80259-01 • Volume = 5,555 in3 (one tank) • Propellant Capacity • 72 kg each (qualified max) • 64 kg for 400 – 100 psi blowdown, 50 – 10 ⁰C • Titanium Construction • Mass = 7.27 kg each (standard, light version = 6.4 kg) • Diameter = 22.14 in. • MEOP = 475 psi • BOL 400 psi @ 50C for this mission • Tank will blow down to ~ 164 psi at 10 ⁰C

9. Blow-Down Curve BOL L2 Thruster Operating Range Launch Window LV Dispersions MCC Orbit Maintenance

10. Thrusters • Twelve Aerojet MR-50E monopropellant thrusters • 22 N (5 lbf), • Extensive flight heritage • Sizing: • ΔV • Four 22N thrusters complete largest maneuver (Launch window+LV Dispersion Correction - 55 m/s) in about 38 minutes • Thruster qualified for hundreds of minutes continuous firing • ΔH (momentum change) • Unloads expected to be infrequent (~ 75 days) • Minimum impulse bit @ 400 psi~ 0.4 Ns x moment arm • Estimated propellant required for ΔH is 0.5 kg • Assume unloading 122.5 Nms every 75 days for 5 years • Pulse Life • Maximum number of pulses ~ 12000 for ΔH • Thruster qualified for >> 100,000 pulses

11. Thruster Installation(Note: 3.5m Bus Hex Shown) Provide 6 DOF and redundancy in the event of thruster failure 8 Thrusters canted 10⁰ in two planes Thrusters arranged in balanced couples as seen by intersecting lines of action Cover/Shade Three Tanks 4 Thrusters canted 45⁰ in one plane Notional CG Solar Array Lines of Action

12. Master Equipment List • All components are TRL-9 • Power • Thruster Cat-Bed Heaters = 3.85 Watts each. Minimum of 4 heaters powered for one hour before maneuvers • Pressure Transducers = 1 Watt each. 2 pressure transducers powered continuously • Valve, line and tank heaters booked by Thermal subsystem

13. Issues and Concerns & Future Work • Investigate current BL thruster configuration for adequacy • Torque “bit” • Redundant modes • Latch valve grouping • Cant angles • Low mass of S/C may allow 1 lbf (5N) thrusters • Radiator location and sensitivity to plume not yet defined • Reported propellant budgets based on estimated launch masses • Atlas LV has launch capacity beyond BL tankage capacity • Falcon 9 launch mass (~2400 kg) may be possible • Investigate other configurations • May be able to use single PMD tank (saves 12 kg in tank mass + fewer components) • Smaller diaphragm tanks save (4 kg) • Match thruster class and position to torque requirements (with margin) – smaller thrusters?

14. Acronym list AC – Attitude Control BL – Baseline BOL – Beginning of Life Cat-Bed – Catalyst Bed (thruster) DOF – Degree of Freedom FD Valve – Fill and Drain Valve GN2 – Gaseous Nitrogen ΔH – Momentum change Isp – Specific Impulse, sec LV – Launch Vehicle MCC – Mid-Course Correction MEOP – Maximum Expected Operating Pressure MR – Monopropellant Reaction (Engine) PMD – Propellant Management Device sec - seconds ΔV – Change in velocity

15. Backup

16. Propulsion Labor • Total FTEs = 12.9 • Cost assumes In-House build at GSFC and covers the following tasks: • Propulsion subsystem design and analysis • Procurement activities (component purchases and contract management) • Propulsion subsystem assembly • Propulsion subsystem testing • Propulsion support during S/C level I&T • Launch site support • Note: FTEs do not include thermal design, drawing production, support structure fabrication, or electrical harness integration.