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LEO Atmospheric Drag Analysis and Lunar Orbit Circularization

February 19, 2009. LEO Atmospheric Drag Analysis and Lunar Orbit Circularization. 1. Atmospheric Drag for Circular Parking Orbits. Assume Thrust of 110 mN Assume C D = 1.0 Analysis based on cross section area of: Solar Panels ~ 8 m 2 OTV ~ 4 m 2 Total Area ~ 12 m 2.

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LEO Atmospheric Drag Analysis and Lunar Orbit Circularization

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  1. February 19, 2009 [Andrew Damon] [Mission Ops] LEO Atmospheric Drag Analysis and Lunar Orbit Circularization 1

  2. Atmospheric Drag for Circular Parking Orbits • Assume Thrust of • 110 mN • Assume CD = 1.0 • Analysis based on cross section area of: • Solar Panels ~ 8 m2 • OTV ~ 4 m2 • Total Area ~ 12 m2 Recommend: Parking Orbit of 400 km – Drag drops to less than 5% of Thrust, Within capabilities of Dnepr Launch Vehicle [Andrew Damon] [Mission Ops] 2

  3. Lunar Orbit Circularization [Andrew Damon] [Mission Ops] “Step-down” of lunar orbit by thrusting near periapsis (braking) Goal of 110 km circular parking orbit EP thruster fired from -45o to 45o Modeled as impulsive maneuver to approximate benefit ΔV ≈ .38 m/s delivered near perilune with EP system Circularization time on the order of 4 years – not acceptable Solutions: - Raise parking orbit - Extend Earth outbound spiral - Use chemical system to deliver some ΔV 3

  4. Backup Slides Curve fit for density based on altitude: Where h is altitude in km and ρ is in ng/m3 [Andrew Damon] [Mission Ops] Drag Calculations FD ~ Newtons ρ ~ kg/m3 CD ~ dimensionless v ~ m/s A ~ m2 **Can be incorporated as part of EOMs 4

  5. [Andrew Damon] [Mission Ops] EP ΔV approximation -TOF for -45oto -45o determined - mo is known from time history - mdot assumed to be constant for EP - mf= mo - mdot(TOF) Just apply ideal rocket equation… Isp for system is known • ΔV = Isp*go*ln(mo / mf) • Because ΔV was applied symmetric to periapsisand this TOF was a small portion of the orbital period, the ΔV was considered impulsive for this “step-down” analysis 5

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