Fixed Main Engine versus Gimbal Mounted Alternative Current Tasks: Gimbal Mount Alternative Separation Landing Alternative Minimizing Thruster Cost 2/19/09 Kris Ezra Attitude Group Translunar Phase 1

Gimbal System Explanation Advantages: Thrust vectoring implies possible decrease in attitude control prop Disadvantages: Extra complexity and mass Gimbal Mount Specifications: Approximate mass of 6 kg Angular maximum motion of 20º 3 Axis Gimbal Relatively low complexity Design, build, and test in house <$1,000 20º 1.06 m 0.3858 m Kris Ezra Attitude Group Translunar Phase

Comparison of Alternatives Determination Method Prop. Mass (kg) Moment Calculation (no rxn wheels Engine) 228 Moment Calculation (no rxn wheels Attitude) 80 Moment Calculation (rxn wheels) Specific Thrust Manip. (Attitude Desaturation) 6.287 Specific Thrust Manip. (Engine Desaturation 17.925 Lowest Total Mass Penalty: Attitude Thrusters: 6.287 kg Gimbaled Engine: 23.925 kg Recommendations: Because of limited use of gimbaled main engine in other phases due to thrust magnitude, recommend fixed main engine Gimbaled Thrust Additional Costs: 17.638 kg mass increase < $1,000 Design, build, test cost Additional power sufficient to run 3 actuators Gimbal controllers (mass, power, cost yet unknown) Kris Ezra Attitude Group Translunar Phase

Mass Calculation Methods m is the time averaged mass M is the induced moment g is the gravitation constant of 9.80665 m/s^2 Isp is the specific impulse of H202 L is the distance from the thruster to the center of mass Method 2: M is the total propellant mass D is mission duration in days n is the average number of desaturation maneuvers per day J is the maximum torque provided by reaction wheels (Nm) T is an estimate of the specific thrust of the propellant for a given engine (N/kg) L is the moment arm of the desaturation device (m) Kris Ezra Attitude Group Translunar Phase

Specific Data Method 1: Method 2: Reaction Wheel Torque (Nm) 0.02 Mission Length (days) 365 Engine Thrust (N) 0.2 Desaturation Maneuvers (#/day) 6 Thrust Offset (m) 0.022 Max Reation Wheel Torque (Nm) 0.03 Isp (s) 161 H202 Specific Thrust (N/kg) 9.5 Attitude Moment Arm (m) 1.1 g (m/s^2) 9.80665 Engine Moment Arm (m) 0.3858 Mission Length (s) 31536000 Total mass (kg) (Attitude DS) 6.287081 Without rxn Wheel Torques: Total mass (kg) (Engine DS) 17.92584 mbar (kg/s) (no rxn wheels) 2.53346E-06 Total Mass (kg) (no rxn wheels) 79.89508197 With rxn Wheel Torques: mbar (kg/s) Total Mass (kg) Kris Ezra Attitude Group Translunar Phase

Determination of Specific Thrust FUEL STORAGE H2O2 %= 90.0 Kappa= 1.33 R = 369.67 M,gasmix 22.4906 Density= 1.391 kg/liter Run time= 120 sec V = 4.4 liter 1.17 US gallons w = 6.2 kg 13.7 lbs FUEL PUMP Fuel Flow= 0.0513 kg/sec 3.1 kg/min 0.04 lit/sec 2.2 lit/min 0.11 lbs/sec 0.59 gpm P= 23.7 bar(e) FLOW DISTRIBUTION TRAY Total tray hole area= 8 mm2 Pr.Drop= 0.1 bar (0.1 to 0.3 bar is recommended) Hole velocity= 4.43 m/s Hole diam 4 mm Number of holes 1 pcs Obtained and modified from http://www.peroxidepropulsion.com/article/5 Kris Ezra Attitude Group Translunar Phase

Determination of Specific Thrust CATALYST PACK Temp= 739 oC 1012 K Catalyst activity= 75 kg H2O2/liter catalyst,minute D= 17 mm Rem: The practical experiance so far is that maximum about 100 kg hydrogen peroxide Length= 187 373 screens (when using stacked silver screens ,0.5 mm thick) per liter of silver catalyst volume and minute, can be decomposed Volume= 0.04 liter Tot. screen area 0.082 m2 Weight of screen pack = 82 gram Pressure drop over the catpack = 14.6 bar Liquid feed load= 0.014 kg/mm2,min (typical value=0,010) 20.07164 lb/in2,min ROCKET NOZZLE D, inlet= A,inlet = 0.0002 P,inlet= 10 bar (abs) 147 psia c,inlet= 87 m/s v,inlet= 0.374102 m3/kg D,throut= 7.7 A,throut= 4.66E-05 P,throut 5.4 79 c,throut= 654 0.396468029 T,throut= 867.896 v,throut= 0.594136 594.896 C D,exit= 11.0 A,exit= 9E-05 P,exit 1 14.7 c,exit 1148 0.563259098 0.563259 THRUST= 58.86 N = 6 kgf = 13.33 lbf Kinetic power= 34 kW = 45 HP Obtained and modified from http://www.peroxidepropulsion.com/article/5 Kris Ezra Attitude Group Translunar Phase

References Bengtsson, Erik. “Peroxide Propulsion” Accessed 18 Feb 2009, URL: http://www.peroxidepropulsion.com/ Vaughan, David A., “Gimbal Development for the NEXT Ion Propulsion System” AIAA Joint Propulsion Conference & Exhibit, 2005. Lukasak, J. “Propellant Requirements: Attitude Control Thrusters with Low Thrust Orbit Trajectories,” 12 Feb. 2009. Erson, B. “Attitude Control Systems,” 19 Feb. 2009. Kris Ezra Attitude