Research Progress

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Research Progress

• Ryan Stillwater
• CAP Lab
• Virginia Tech
• 23 March 2004

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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

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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

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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

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Mars Atmosphere

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

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Titan Atmosphere

• Mostly N2, CH4, and H2
• Ions are 0.10 of atmosphere at 30000 km
• Atmosphere unstable
• Saturns solar wake

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Io Atmosphere

• Mostly SO2, S, and O
• Ions are 0.0039 of atmosphere at 400 km
• Atmosphere unstable
• Jupiters solar wake
• Ionosphere similar to Marss

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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

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Titan Forces

• Maximum relative force at 3000 km of 1.27E9 N
• Represents 38.6 percent increase
• Maximum force of 8.3E-8 N at 1100 km

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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

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Numerical Procedure

• Altitude gt atmosphere
• Small angle approximation
• Altitude lt atmosphere
• Enckes Method
• Neutral Force
• F0.5CdArV2
• Accelerated Force
• F0.5CdAr(V22eF/mi)

Enckes Method
Small Angle
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Neutral Orbit Determination

• Upon exiting atmosphere the position and velocity
  are used to determine the parameter,
  eccentricity, and true anomaly
• PR x V2/m
• e(V2-m/R)R-(R . V)V/m
• ncos-1(e . R)/(eR)
• True anomaly increased in small increments to
  determine intermediate positions and velocity

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Enckes Method
R

• One of the more accurate methods
• Uses intermittent corrections
• Rm/R3Rap true orbit
• Rm/R3R0 Osculating Orbit
• dRapm/R3R-m/R3R
• dRapm/R3(1-R3/R3)R-dR
• Use Runge-Kutta 4th order method to determine
  dR(todt) and dR(todt)

dR
R
Correction
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Enckes Method

• Knowing dR(todt) and dR(todt)
• Calculate R(todt) and R(todt)
• Check if dR/R gt max value, if so correct
• R(todt)R(todt)dR(todt)
• V(todt)R(todt)dR(todt)
• Test if R gt RplanetRatmosphere

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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
• Enckes method inside of the atmosphere