SNAP Propulsion System:
SNAP Propulsion System FUNTIONAL REQUIREMENTS
Provide capability for multiple burn, 136 m/s DV
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”
SNAP Propulsion System Design Trade:
“Low Power” EP Assumptions SNAP Propulsion System Design Trade
SNAP Propulsion System Design Trade Conclusions:
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.
SNAP Propulsion System:
SNAP Propulsion System 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
15o off X-axis
Orbit Ave Power (@25% D.C.) = 23 W
Catalyst Bed + Thruster Power (During Firing)
= 10.2 W per thruster
15o X Y Z Z
SNAP Propulsion System:
SNAP Propulsion System
SNAP Propulsion System:
Regulated BiPropellant
System Option
SNAP Propulsion System