**Investigation of the Magnetosphere
of Ganymede with Galileo's Energetic Particle Detector**

*Ph.D. dissertation by Shawn M. Stone, University of Kansas,
1999.*

*Copyright 1999 by Shawn M. Stone. Used with
permission.*

**4.9 The Divergence of Magnetic Field in Models M1 and M2**

**Figure 4.35** The
divergence of a magnetic field line starting from 45º
latitude and 90º West longitude in a GSII coordinate system
for model M1. The distance scale chosen to implement the
derivatives was 100 km.

**Figure 4.36** The
divergence of the magnetic field along the field line
presented in figure 4.31 for model M2. The distance scale
chosen to implement the derivatives was 100 km.

**4.10** Using the EPD
Instrument to Check for Aberration of the Plasma Direction

It is possible to use the ion rate data to imply a set of aberration angles from the direction of corotation. This can be done by locating the direction of the maximum rate and the minimum rate in a complete stepping sequence. The ideal case would find these directions to be 180º apart, but due to the fact that the spacecraft is translating and the angular coverage is in discrete steps, these two vectors are only approximations. This procedure produces for G2 (stepping sequence 3-4-5-4-3), during the inbound trajectory outside of the magnetopause and the outbound, the aberration angles in Table 4.11. For G7 this procedure is plagued by a more complete angular coverage of the 4π sphere. This seems contradictory, but the 1-2-3-4-5-6-7-6-5-4-3-2-1 stepping sequence allows for a longer translation range (4 minutes worth), and a greater probability that the maximum and minimum vectors will be less than 180º apart. This procedure yields for G7 the aberration angles in Table 4.11.

**Table 4.11** Aberration
angles of the corotational plasma flow as ascertained from
the look directions of the maximum and minimum rates. The
angles α and β are
calculated from the orientation of the maximum look
direction relative to the theoretical corotation direction
in GSII coordinates {0,-1,0}.

Encounter |
Angle betweenMax and Min |
Aberrationangle β |
Aberrationangle α |

G2 inbound | 104º | -49º | 10º |

G2 outbound | 118º | -23º | 9º |

G7 inbound | 107º | 70º | 13º |

G7 outbound | 111º | 33º | 28º |

Next: Chapter 5 The Simulation: Time Reversed Particle Following

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Galileo Table of Contents Page.

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Technologies Home Page.

Updated 8/23/19, Cameron Crane

## QUICK FACTS

**Manufacturer:**The Galileo Spacecraft was manufactured by the Jet Propulsion Laboratory, Messerschmitt-Bölkow-Blohm, General Electric, and the Hughes Aircraft Company.

**Mission Duration:**Galileo was planned to have a mission duration of around 8 years, but was kept in operation for 13 years, 11 months, and 3 days, until it was destroyed in a controlled impact with Jupiter on September 21, 2003.

**Destination:**Galileo's destination was Jupiter and its moons, which it orbitted for 7 years, 9 months, and 13 days.