1. Competition Sensitive Dennis Asato June 28, 2001 XSuperNova / Acceleration Probe (SNAP) Propulsion

2. SNAP, June 28, 2001 Goddard Space Flight Center Propulsion Page 2 SNAP Propulsion System FUNTIONAL REQUIREMENTS Provide capability for multiple burn, 136 m/s  V Provide capability for 3-axis momentum unload KEY DESIGN DRIVERS Initial payload mass = 1619 kg ACS momentum unload = 3.5 kg/yr for 5 yrs No S/C orientation constraints during orbit transfer thruster firings (e.g., instrument protected with covers) Contamination sensitive instrument & sensors S/C power constrained to “several hundred watts”

3. SNAP, June 28, 2001 Goddard Space Flight Center Propulsion Page 3 123 – 250 mN 22 N THRUST OPTION 500- 1765 300 220 ISP (s) 1800 - 2200 W 5 W/thruster during firing + TBD W orbit ave. 9.1 W orbit ave.@ 25% d.c.+ 10.2 W/thruster during firing POWER (W) (+) High Isp (-) High power (-) Thrust too low for orbit transfer; better suited for attitude control, SK, drag compensation (-) High Cost for low  V mission 13 – 44 (excl. ACS) “Low Power” EP Options  Hall  PPT  Arcjet (+) Higher Isp than N2H4 (+) Lower orbital ave. heater power than N2H4 system (-) Complex fuel/oxidizer manifold design (?) Fuel slosh issues during science (TBD) (?) Plume contamination issue (TBD) 91MMH/NTO (+) Simple manifold design, low plume contamination, low HW mass (-) Low Isp (?) Fuel slosh issues during science (TBD) 117N2H4 COMMENTSPROPELLANT MASS (kg) OPTIONS “Low Power” EP Assumptions POWER (kW)ISP (s)THRUST (mN)EP SYSTEM 1.8500250N2H4 Arcjet 2.21765123Xe Hall SNAP Propulsion System Design Trade

4. SNAP, June 28, 2001 Goddard Space Flight Center Propulsion Page 4 SNAP Propulsion System Design Trade Conclusions  Baseline Design: “Blowdown” (unregulated pressure) N2H4 System with 4x22N canted thrusters & three  48.3 cm dia. propellant tanks  Merits: Simple manifold design, low contamination, relatively low component mass & orbital ave. power  Negatives: Low Isp (large tanks)  Propulsion System Options to Reduce Volume  MMH/NTO, pressure-regulated bipropellant system option would reduce the propellant tank diameter to 35 cm (4 tanks) + a 20 cm dia. pressurant tank.  Orbit transfer with single high DV burn would allow use of solid motor + small N2H4 system (ACS unload & small DV orbit adjust)  2 kW power system would be required to use EP thrusters (N2H4 arcjet, Xe Hall) – low thrust; long orbit transfer time.

5. SNAP, June 28, 2001 Goddard Space Flight Center Propulsion Page 5 SNAP Propulsion System F/D Valve N2H4 Tanks w/ AFE-332 or PMD Pressure Transducer P Filter Latching Isolation Valve LV Primary & Redundant 22 N Thrusters with Dual Seat Valves SNAP N2H4 PROPULSION SYSTEM N2H4 Propulsion System Design N2H4 mass (10% contingency) = 130 kg “Dry” mass (4 Tank Design) = 34.1 kg Three 48.3 cm dia tanks with AFE-332 elastomer diaphragm Primary & Redundant set of 22N thrusters mounted on –X axis & canted 15 o off X-axis Orbit Ave Power (@25% D.C.) = 23 W Catalyst Bed + Thruster Power (During Firing) = 10.2 W per thruster 15 o XY ZZ

6. SNAP, June 28, 2001 Goddard Space Flight Center Propulsion Page 6 SNAP Propulsion System

7. SNAP, June 28, 2001 Goddard Space Flight Center Propulsion Page 7 Regulated BiPropellant System Option SNAP Propulsion System