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Research Progress

Research Progress . Ryan Stillwater CAP Lab Virginia Tech 23 March 2004. Aerobraking. Known as the free downhill Uses the planetary atmosphere to produce a drag force, thereby slowing spacecraft Only propellant used is for orbit correction burns at apoapsis

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Research Progress

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  1. Research Progress Ryan Stillwater CAP Lab Virginia Tech 23 March 2004

  2. Aerobraking • Known as the free downhill • Uses the planetary atmosphere to produce a drag force, thereby slowing spacecraft • Only propellant used is for orbit correction burns at apoapsis • Used successfully in orbit around Earth, Venus, and Mars

  3. Magellan • Arrived in Venus orbit in August of 1990 • Reduced apoapsis from 8470 km to 541 km • Performed 730 aerobraking orbits • Performed 13 periapsis correction burns • Maximum drag force of 4.8 N

  4. Mars Global Surveyor • Arrived in Mars orbit in September of 1997 • Reduced the apoapsis from 54000 km to 450 km • Performed 450 aerobraking orbits • Maximum drag force of 3.9 N • Dust storm spiked drag force to 15.3 N

  5. Mars Atmosphere • Mostly CO2, N2, and O • Ions are 0.15% of atmosphere at 300 km • Atmosphere unstable • Dust storms

  6. Titan Atmosphere • Mostly N2, CH4, and H2 • Ions are 0.10% of atmosphere at 30000 km • Atmosphere unstable • Saturn’s solar wake

  7. Io Atmosphere • Mostly SO2, S, and O • Ions are 0.0039% of atmosphere at 400 km • Atmosphere unstable • Jupiter’s solar wake • Ionosphere similar to Mars’s

  8. Mars Forces • Maximum relative force at 300 km of 1.06E-7 N • Represents 8.9 percent increase • Maximum force of 5.3E-6 N at 130 km

  9. Titan Forces • Maximum relative force at 3000 km of 1.27E–9 N • Represents 38.6 percent increase • Maximum force of 8.3E-8 N at 1100 km

  10. Io Forces • Maximum relative force at 400 km of 1.98E-7 N • Represents 0.92 percent increase • Maximum force of 1.73E-6 N at 100 km

  11. Numerical Procedure • Altitude > atmosphere • Small angle approximation • Altitude < atmosphere • Encke’s Method • Neutral Force • F=0.5CdArV2 • Accelerated Force • F=0.5CdAr(V2+2eF/mi) Encke’s Method Small Angle

  12. Neutral Orbit Determination • Upon exiting atmosphere the position and velocity are used to determine the parameter, eccentricity, and true anomaly • P=|R x V|2/m • e=[(V2-m/R)R-(R.V)V]/m • n=cos-1[(e.R)/(e*R)] • True anomaly increased in small increments to determine intermediate positions and velocity

  13. Encke’s Method R • One of the more accurate methods • Uses intermittent corrections • R”+m/R3*R=ap – true orbit • R”+m/R3*R=0 – Osculating Orbit • dR”=ap+m/R3*R-m/R3*R • dR”=ap+m/R3[(1-R3/R3)R-dR] • Use Runge-Kutta 4th order method to determine dR’(to+dt) and dR(to+dt) dR R Correction

  14. Encke’s Method • Knowing dR(to+dt)and dR’(to+dt) • Calculate R(to+dt) and R’(to+dt) • Check if dR/R > max value, if so correct • R(to+dt)=R(to+dt)+dR(to+dt) • V(to+dt)=R’(to+dt)+dR’(to+dt) • Test if R > Rplanet+Ratmosphere

  15. Summary • Aero braking saves money • Minimal ionosphere on most planets • Most plasma braking forces on the order of 10-7 Newtons • Small angle approximation outside of atmosphere • Encke’s method inside of the atmosphere

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