Meet the Fields and Particles Science Group

"What is unique about science representation on flight projects such as Galileo," said Group Lead Kim Spelts, "is that operations are performed by a mixture of systems engineers and scientists." The 11-member Fields and Particles Science Group (FPSG) (see photo) possesses a diverse set of skills. Group members come from backgrounds in computer science/aerospace engineering or are scientists with backgrounds such as astrophysics, physics, or astronomy. The purpose of the group is to design the spacecraft command sequences that carry out the magnetospheric science objectives of the Project Science Group (PSG). The FPSG accomplishes this by interacting with the experiment investigators to develop a set of science observations and measurements that fit within the resource constraints of the mission and then developing corresponding command sequences for the instruments.

The FPSG is responsible for the successful operation of six instruments onboard Galileo. These instruments are the magnetometer (MAG), dust detector (DDS), energetic particle detector (EPD), heavy ion counter (HIC), plasma science instrument (PLS), and plasma wave subsystem (PWS). Together, these instruments will provide the most complete picture ever of the interaction of dust and charged particles between Jupiter, its satellites, and the Sun. "Jupiter has arguably the most complex magnetosphere in the solar system," said Magnetospheric Working Group (MWG) representative Scott Bolton. "Jupiter's magnetosphere is also the largest object in the solar system-at times, its tail reaches all the way back to Saturn's orbit."

Three JPL teams are responsible for the instruments. Bolton heads up the PLS/PWS team, assisted by Claudia Alexander, LeRoy Larry, and Steve Levin. The MAG/DDS team Science Coordinator is Carol Polanskey, who is assisted by Duane Bindschadler and Yi Mei. Neil Murphy is the Science Coordinator for the EPD/HIC team, assisted by B-G Andersson and Leo Cheng.

The primary science objective of the fields and particles experiments is to perform a near- continuous survey of the magnetosphere-mapping its structure, studying the dynamics, and gaining a general understanding of the motion of particles within it. "The magnetosphere is full of charged particles called a plasma," explained Bolton. "Plasma makes up about 99 percent of the universe and completely fills interplanetary space as well as planetary magnetospheres. Galileo's complete magnetospheric instrument package will measure the magnetic field, both low- and high-energy particles, and the electromagnetic waves that can distribute energy between particles."

Understanding the dust environment at Jupiter is an important objective. Of particular interest are charged dust particles (dust with extra or missing electrons). While neutral dust is primarily influenced by gravity, charged dust behaves quite differently--corotating with Jupiter and spinning around the planet much faster than the speed of their neutral cousins. The Io torus is a primary feature of Jupiter and will be studied in depth by Galileo. The torus, a product of volcanic eruptions on Io and Jupiter's fast rotating magnetosphere, is made up of charged particles and dust whipping around at the speed of Jupiter's rotation (about every 10 hours). The torus particles bombard Io's trailing side as Io orbits at a much slower pace, knocking off particles from Io's surface in the process.

In addition to characterizing the magnetic environment surrounding Jupiter and its satellites, the fields and particles instruments will provide information about the chemical composition of the satellites themselves. By making in situ measurements of the particles that have escaped the planet and its moons or entered into the magnetosphere from the solar wind, an understanding will be gained of what makes up the atmospheres of Jupiter and its satellites. This will complement other measurements taken by remote-sensing science instruments and by Galileo's Probe. "Unlike the remote-sensing science instruments, we are making in situ measurements, which means we are actually getting particles into the instruments to measure them," said Bolton.

The FPSG will have a unique opportunity to collect data about Jupiter's environment, since the instruments onboard Galileo that measure Jupiter's magnetosphere will be the most comprehensive of any mission flown yet. In addition to being in orbit around Jupiter for 2 years, giving the group an opportunity to measure both spatial and temporal changes, the experiments onboard Galileo are far more advanced than Voyager's. The particle instruments are specifically designed to expand on what we learned from Voyager, and the plasma wave instrument senses both electric and magnetic waves. Galileo also added a dust instrument, which the twin Voyagers didn't have. The last major objective of the FPSG will involve the passage through the distant magnetotail of Jupiter during the ninth orbit.

To achieve the magnetospheric science objectives, the fields and particles instruments are required to operate in two modes: by collecting and downlinking data in real time and by recording data on the tape recorder and playing it back later in the orbit. There are a host of challenges the FPSG faces when implementing these operating modes: most of the magnetospheric data is collected in real time and must be integrated with other demands on the downlink signal. The engineering data, playback of recorded data, and the downlink of real-time science data must all be interleaved into the available telemetry. "It's fairly straightforward to integrate our own science tasks," said Spelts, "but there is a significant amount of interaction with other Project teams who also utilize real-time downlink resources. With the failure of Galileo's high-gain antenna, every downlink bit available becomes meaningful to all teams. It can be challenging to implement crucial science objectives while also staying within allocated spacecraft resources," Spelts continued. "Along with the ultraviolet spectrometers, we are the primary set of instruments on Galileo to routinely use both methods of data collection." A key function Spelts and other group members perform is to model the real-time data collection to ensure that the science data buffer on the spacecraft won't overflow. "If that happens," she warned, "data gets overwritten and we lose it."

Kim Spelts, FPSG Lead, began her career here at JPL in 1992, shortly after completing her BS in aerospace at the University of Colorado, Boulder. She can't remember when her lifelong interest in math and science began to focus on space, but the Viking landing on Mars and the first shuttle launches certainly made their contributions. Spelts came on Lab to work for the current EPD/HIC Team Chief, Neil Murphy--so it was fields and particles right from the start. In July 1994, when Project Galileo's reorganization took place, Spelts was assigned to the FPSG Lead position. An avid sportswoman with a special love of all things out-of-doors, Spelts completed the Sierra Club's rigorous Wilderness Travel Course last winter. The culmination of the course was a weekend snow camp in the Sierras, a real challenge. After hours, you'll find her on the softball field with JPL or Pasadena league teams. For a native Coloradoan, who departed the beautiful, green high-country wilderness at home for the brown chapparal of the San Gabriels, it's been a bit of a change (sigh!).

The FPSG has been together for over a year. Despite their differing backgrounds and responsibilities, Spelts described them as a tight-knit clan. "One thing we have in common is that we all like pizza and beer," Spelts noted. "Preferably between 9 and 11 in the morning," joked Bolton.