My main long-term interest has been to understand the interaction of galactic cosmic rays and other high energy charged particles with the solar wind and interplanetary magnetic field as a function of radius and latitude in the heliosphere, and also as a function of changing levels of solar activity. Working mainly with the late John Simpson's group I have been using observations from cosmic ray experiments on the earth satellite IMP-8 and on the deep space probes Pioneer 10 and 11, and Ulysses to pursue these studies. The Pioneer are now ended as a result of the degradation of the RTG power supplies. Ulysses is providing the first scan of solar latitude. Ulysses reached maximum heliographic latitudes of ~80 degrees for the first time south in September, 1994 and ~80 degrees north in July, 1995 when solar activity was near minimum levels. It returned to the Polar Regions in 2000-2001 completing a second scan of solar latitude near the time of solar activity maximum. Now embarked on its third orbit of the sun following a distant Jupiter flyby in 2004, it will return to the polar regions of the heliosphere in 2007-2008.
A secondary interest is study of the energetic electrons and nuclei accelerated and confined in or escaping to interplanetary space from Jupiter's magnetosphere. The Ulysses flyby in 1992 provided the first-ever traversal of Jupiter's dusk-side magnetosphere and revealed an unexpectedly complex and dynamic region which poses many challenging questions concerning the interaction of the rapidly rotating magnetospheric plasmas, magnetic fields, and energetic particles with the confining solar wind plasma. The 2004 flyby revealed "jets" of Jovian electrons, apparently propagating directly along interplanetary magnetic field lines from Jupiter's magnetosphere to distances as great a 2 AU from the planet, and in directions at times almost perpendicular to the expected Parker spiral field lines.
I have also participated in development of three experiments to measure microscopic dust in space. The Space Dust (SPADUS) experiment, on the ARGOS P91-1 spacecraft, in a sun- synchronous orbit around the Earth, measured the intensity and mass spectrum of natural particles and orbital debris near Earth. On the Stardust spacecraft, the Dust Flux Monitor Instrument measured dust in the coma of Comet Wild-2 during the spacecraft's encounter with that comet in 2004. On the Cassini mission, the High Rate Detector, a component of the Cosmic Dust Analyzer, is measuring the density profiles of dust particles near the ring plane and satellites of Saturn as the spacecraft makes multiple crossings of Saturn's ring plane and close flybys of Saturn's satellites during its tour of the Saturnian system
Recently, I have been participating in development of energetic charged particle telescopes for space weather applications on Earth environmental satellites such as NPOESS and GOES. Development of the High Energy Particle Sensor (HEPS), selected for the NPOESS satellites, was terminated in 2006 as a result of severe budget difficulties of the overall NPOESS project. However later in 2006 a similar instrument, the Energetic Heavy Ion Sensor (EHIS), was selected as part of the Space Environmenal In-situ Sensor Suite on the GOES-R satellites, and I am participating in that development effort.
Finally, I am leading development of a very simple and compact phoswich based detector for fast (~1-10 MeV) neutrons from the Sun, which may be suitable for inclusion on proposed missions to the innermost heliosphere such as Solar Orbiter or the Solar Sentinels. .
Last modified November 19, 2006