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.

Chapter 3. Instrument Characteristics and Coordinate Systems

The first charged particle detectors flown into space were simple Geiger counters [Van Allen, 1958] that counted the presence of particle radiation from all directions. They were not capable of distinguishing between species or energy of the impacting particles. After much development over the years, particle detectors are now able to detect and distinguish particles of many species and energies. Also, when mounted on spinning spacecraft platforms, sensors are able to measure the direction of the radiation over a wide range of angles. Galileo is a spacecraft that incorporates the best of these designs.

The Galileo spacecraft, shown in Figure 3.1, has 10 scientific instruments on board [Johnson et al., 1992] distributed over two sections, a spun and a despun section. Instruments that need to be stationary, such as the near-infrared mapping spectrometer and solid-state imaging camera, reside on the despun section. The instruments that sample particles and fields are mounted on the spun section, which makes a complete revolution about every 20 s. The two instruments that are integral to this work are the magnetometer [Kivelson et al., 1992] and the Energetic Particle Detector or EPD instrument, which is discussed below in detail. In this chapter, along with the instrumentation, is a discussion of the important coordinate systems and transformations used throughout this work.

Figure 3.1 A schematic representation of the Galileo spacecraft. Depending on their function, each instrument sits upon a spun or despun section of the of the spacecraft. Imaging and remote sensing equipment require a relatively stationary position since they observe a single object for long durations; hence they are mounted upon the despun section. The instruments that sample particles and fields need to cover a large angular area and reside on the spun section [Johnson et al., 1992].

• 3.1 The EPD Instrument
• 3.2 Low-Energy Magnetospheric Measurement System (LEMMS)
• 3.3 Count Rate and Differential Particle Flux
• 3.4 Inertial Reference Frames and Coordinate Systems
• 3.5 Coordinate Transformations and SPICE Kernels
• 3.6 State Vectors and EPD Look Directions

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