AAE450 Spring 2009 Propellant Requirements Attitude Control Thrusters with Low Thrust Orbit Trajectories [Josh Lukasak] [Attitude Group Lead]

AAE450 Spring 2009 Attitude Problem  Main Thruster Offset is the largest source of attitude perturbations. –Electric Propulsion uses a constant thrust for the orbit transfer phase. –Attitude control thrusters must be used along with reaction wheels.  Assumptions –Cubic craft with 1 meter sides,.5 N thrust, and an engine offset of 5 cm flying a 1 month transfer orbit. [Josh Lukasak] [Attitude Group Lead] (1)

AAE450 Spring 2009 Mass Estimates  Using basic kinematics the torque created by offset is Nm.  If a reaction wheel with a nominal torque of 0.02 Nm is used in the opposite angular direction the total torque is reduced along with the propellant mass.  Using these torques the total Monopropellant Hydrazine mass required is 14 kg. [Josh Lukasak] [Attitude Group Lead] (2)

AAE450 Spring 2009  Back Up Slides [Josh Lukasak] [Attitude Group Lead] (3)

AAE450 Spring 2009 Reaction Wheel  Vectronic Aerospace Reaction Wheel Type RW-01 [Josh Lukasak] [Attitude Group Lead] (4) Nominal Torque20 mNm Mass1.8 kg Power4 W Temperature Range-20 C to 70 C

AAE450 Spring 2009 Mass Calculations  M=F x r –M is the induced moment –F is the force or thrust –r is the radius from the force to the center of mass –m is the time averaged mass –M is the induced moment –g is the gravitation constant of m/s^2 –Isp is the specific impulse of Monopropellant Hydrazine –L is the distance from the thruster to the center of mass [Josh Lukasak] [Attitude Group Lead] (5)

AAE450 Spring 2009 Sample Calculations [Josh Lukasak] [Attitude Group Lead] (6)

AAE450 Spring 2009 Possibility of Thruster Gimbals  Thruster Gimbals are a distinct possibility for reducing mass and perhaps cost for attitude control.  Essentially the gimbals change the direction of the thrust vector and control the attitude of the spacecraft.  NASA research shows that these systems can be as small as 2.6 kg. [Josh Luksak] [Attitude Group Lead] (7)

AAE450 Spring 2009 References  Vectronic Aerospace Reaction Wheel Type RW-01 Vectronic Aerospace 28 January  Steven Oleson, Leon Gefert, Scott Benson, and Michael Patterson Mission Advantages of NEXT: NASA's Evolutionary Xenon Thruster September 2002  Rauschenbakh, Boris, Michael Ovchinnikov, and Susan McKenna-Lawlor. Essential Spaceflight Dynamics and Magnetospherics. Dordrecht, The Netherlands: Kluwer Academic Publishers, [Josh Lukasak] [Attitude Group Lead] (8)