Scientific instruments to measure fields and particles were mounted on the spinning section of the spacecraft, together with the main
antenna, power supply, the propulsion module and most of
Galileo computers and control electronics. The sixteen instruments, weighing altogether, included
magnetometer sensors mounted on an boom to minimize interference from the spacecraft; a
plasma instrument for detecting low-energy charged particles and a plasma-wave detector to study waves generated by the particles; a high-energy particle detector; and a detector of cosmic and Jovian
dust. It also carried the Heavy Ion Counter, an engineering experiment to assess the potentially hazardous charged particle environments the spacecraft flew through, and an
extreme ultraviolet detector associated with the UV spectrometer on the scan platform. The CCD had radiation shielding a thick layer of
tantalum surrounding the CCD except where the light enters the system. An eight-position filter wheel was used to obtain images at specific wavelengths. The images were then combined electronically on Earth to produce color images. The spectral response of the SSI ranged from about 400 to 1100 nm. The SSI weighed and consumed, on average, 15 watts of power.
Near-infrared mapping spectrometer (NIMS) The NIMS instrument was sensitive to 0.7-to-5.2-
micrometer wavelength
infrared light, overlapping the wavelength range of the SSI. NIMS used a aperture reflecting telescope. The
spectrometer used a grating to disperse the light collected by the telescope. The dispersed spectrum of light was focused on detectors of
indium,
antimonide and
silicon. NIMS weighed and used 12 watts of power on average.
Ultraviolet spectrometer / extreme ultraviolet spectrometer (UVS/EUV) The
Cassegrain telescope of the UVS had a aperture. Both the UVS and EUV instruments used a ruled
grating to disperse light for spectral analysis. Light then passed through an exit slit into
photomultiplier tubes that produced pulses of electrons, which were counted and the results sent to Earth. The UVS was mounted on
Galileo scan platform. The EUV was mounted on the spun section. As
Galileo rotated, EUV observed a narrow ribbon of space perpendicular to the spin axis. The two instruments combined weighed about and used 5.9 watts of power.
Photopolarimeter–radiometer (PPR) The PPR had seven radiometry bands. One of these used no filters and observed all incoming radiation, both solar and thermal. Another band allowed only solar radiation through. The difference between the solar-plus-thermal and the solar-only channels gave the total thermal radiation emitted. The PPR also measured in five broadband channels that spanned the spectral range from 17 to 110 micrometers. The radiometer provided data on the temperatures of Jupiter's atmosphere and satellites. The design of the instrument was based on that of an instrument flown on the
Pioneer Venus spacecraft. A aperture reflecting telescope collected light and directed it to a series of filters, and, from there, measurements were performed by the detectors of the PPR. The PPR weighed and consumed about 5 watts of power.
Spun section Dust-detector subsystem (DDS) The
dust-detector subsystem (DDS) was used to measure the mass, electric charge, and velocity of incoming particles. The masses of dust particles that the DDS could detect go from to grams. The speed of these small particles could be measured over the range of . The instrument could measure impact rates from 1 particle per 115 days (10 megaseconds) to 100 particles per second. Such data was used to help determine dust origin and dynamics within the
magnetosphere. The DDS weighed and used an average of 5.4 watts of power.
Energetic-particles detector (EPD) The energetic-particles detector (EPD) was designed to measure the numbers and energies of ions and electrons whose energies exceeded about . The EPD could also measure the direction of travel of such particles and, in the case of ions, could determine their composition (whether the ion is
oxygen or
sulfur, for example). The EPD used silicon solid-state detectors and a
time-of-flight detector system to measure changes in the energetic particle population at Jupiter as a function of position and time. These measurements helped determine how the particles got their energy and how they were transported through Jupiter's magnetosphere. The EPD weighed and used 10.1 watts of power on average.
Heavy-ion counter (HIC) The HIC was, in effect, a repackaged and updated version of some parts of the flight spare of the
Voyager cosmic-ray system. The HIC detected heavy
ions using stacks of single crystal silicon wafers. The HIC could measure heavy ions with energies as low as and as high as per nucleon. This range included all atomic substances between
carbon and
nickel. The HIC and the EUV shared a communications link and, therefore, had to share observing time. The HIC weighed and used an average of 2.8 watts of power.
Magnetometer (MAG) The
magnetometer (MAG) used two sets of three sensors. The three sensors allowed the three orthogonal components of the
magnetic field section to be measured. One set was located at the end of the magnetometer boom and, in that position, was about from the spin axis of the spacecraft. The second set, designed to detect stronger fields, was from the spin axis. The boom was used to remove the MAG from the immediate vicinity of
Galileo to minimize magnetic effects from the spacecraft. However, not all these effects could be eliminated by distancing the instrument. The rotation of the spacecraft was used to separate natural magnetic fields from engineering-induced fields. Another source of potential error in measurement came from the bending and twisting of the long magnetometer boom. To account for these motions, a calibration coil was mounted rigidly on the spacecraft to generate a reference magnetic field during calibrations. The magnetic field at the surface of the Earth has a strength of about 50,000
nT. At Jupiter, the outboard (11 m) set of sensors could measure magnetic field strengths in the range from ±32 to ±512 nT, while the inboard (6.7 m) set was active in the range from ±512 to ±16,384 nT. The MAG experiment weighed and used 3.9 watts of power.
Plasma subsystem (PLS) The PLS used seven fields of view to collect
charged particles for energy and mass analysis. These fields of view covered most angles from 0 to 180 degrees, fanning out from the spin axis. The rotation of the spacecraft carried each field of view through a full circle. The PLS measured particles in the energy range from . The PLS weighed and used an average of 10.7 watts of power.
Plasma-wave subsystem (PWS) An electric
dipole antenna was used to study the electric fields of
plasmas, while two search coil magnetic antennas studied the magnetic fields. The electric dipole antenna was mounted at the tip of the magnetometer boom. The search coil magnetic antennas were mounted on the high-gain antenna feed. Nearly simultaneous measurements of the electric and magnetic field spectrum allowed
electrostatic waves to be distinguished from
electromagnetic waves. The PWS weighed and used an average of 9.8 watts. ==
Galileo entry probe==