John Simpson's Legacy to Space Science

By John Cooper

Professor John A. Simpson (1916-2000) founded the Laboratory for Astrophysics and Space Research (LASR) at the University of Chicago and was a leading cosmic ray physicist and statesman of science. A memorial Web site (http://ulysses.uchicago.edu/simpson/), instituted at the University of Chicago after his untimely passing on August 31, 2000, documents the history of his life and accomplishments. During World War II in 1943-1946 he was a scientific group leader in the Metallurgical Laboratory at the University of Chicago as part of the Manhattan Project to develop the atomic bomb. One non-technical outgrowth of this work was his co-founding of the magazine Bulletin of the Atomic Scientists as a means of publicly addressing political and social impacts of nuclear weapons and advocating the peaceful use of such weapons under international control. The most important result of this advocacy in the United States was probably the McMahon Act of 1946 providing for civilian control of atomic energy. At the University of Chicago he later applied his war-time experience with radiation detector development to the nascent field of cosmic ray physics. A network of ground-level, shipboard, and airborne detectors was also used, based in part on his 1948 invention of the cosmic ray neutron monitor, to investigate the origins and properties of cosmic rays through effects of the geomagnetic field on access of these high energy particles to the Earth's atmosphere. Neutron monitor recordings from the spectacular solar proton flare of February 23, 1956 were used by Simpson (with P. Meyer and E. N. Parker) to first prove that a large-scale heliosphere of magnetic fields surrounded the solar system.

According to NSSDC Master Catalog records, Simpson and his scientific staff thereafter designed and constructed cosmic ray and dust instruments for flight on forty NASA, ESA, DoD, and Soviet satellites, from the attempted (but unsuccessful) mission of Pioneer 2 to the Moon in November 1958 to the launches of Stardust and the Advanced Research Global Observation Satellite (ARGOS) in February 1999. Thirty of these satellites achieved expected mission objectives, while others were lost due to launch or orbital insertion failures. Even the ill-fated Pioneer 2 satellite still returned valuable data on energetic particles of the inner radiation belt. Later missions achieved many firsts, including the first deep space probe (Pioneer 5), U.S. probe to Mars (Mariner 4), solar orbiting satellite (Pioneer 6), flybys of Jupiter (Pioneer 10 and 11) and Saturn (Pioneer 11), flybys (3) of Mercury (Mariner 10), in-situ dust measurements near Halley's Comet (Vega 1 and 2), and interplanetary spacecraft in polar heliocentric orbit (Ulysses). For these missions he pioneered the development of proportional counters, solid state coincidence detectors for charged particle dE/dx versus E telescopes, position-sensing solid-state detectors allowing high resolution measurements of cosmic ray isotopes, and (with A. J. Tuzzolino) polyvinylidene fluoride (PVDF) detectors for measurement of dust particles in space. Innovative instruments incorporating the PVDF technology are now flying on the Cassini Orbiter, Stardust, and ARGOS spacecraft for measurements of planetary, interplanetary, and interstellar dust particle populations. The full list of the 40 Simpson-involved spacecraft, with several attributes for each, can be found in Table 1.

John Simpson's space science legacy includes not only his innovations in instrument design but also at least 330 publications ( http://ulysses.uchicago.edu/simpson/JAS_ScientificPublications.html) with his scientific staff at LASR and co-investigators at other institutions, as well as his supervision of 34 Ph.D. students ( http://ulysses.uchicago.edu/simpson/JAS_Student_Theses.html) and numerous undergraduates and postdocs. As one small example, this author (Ph.D. Physics, 1983) published item #29 on Simpson's dissertation list concerning the origin of high energy protons, discovered by Pioneer 11, in the radiation belts of Saturn's inner magnetosphere from cosmic ray interactions with that planet's main rings. In later work (J. F. Cooper et al., J. Geophys. Res., 90, 3415, 1985) with another Simpson Ph.D., J. H. Eraker (now at Ball Aerospace in Boulder, CO), we estimated the mass of Saturn's rings from modeling in-situ Pioneer 11 observations of secondary protons, electrons, and gamma rays emanating from the rings. Simpson's ideas and support for this project arose in part from his many years of work with neutron monitors and cosmic ray interactions in the Earth's atmosphere. Many other stories of thrilling discoveries and scientific results can be told by his numerous students, postdocs, and other colleagues.

John Simpson's legacy at NSSDC for present and future generations of space scientists consists of the 92 recorded data sets in our data archive and the many well-written documents which describe the source instruments, spacecraft, and the parameters and format of the data. NASA's public archives have long been appreciative of the efforts by Simpson and his collaborators to ensure public access to information and data from over forty years of results from his satellite experiments. Listings and descriptions of these data sets are available on-line through the URL links in Table 1 and through the NSSDC Master Catalog (http://nssdc.gsfc.nasa.gov/nmc/sc-query.html). On-line data sets from his experiments on the IMP-8, Pioneer 10 and 11, CRRES, and Ulysses spacecraft can be found at the NSSDC Anonymous FTP site ftp://nssdcftp.gsfc.nasa.gov/spacecraft_data/. The fifty years of ground-level cosmic ray data from Professor Simpson's neutron monitor network are not archived at NSSDC, which mainly receives data from spacecraft. These neutron monitor data are accessible at LASR's Cosmic Ray Neutron Monitor Project site at: http://ulysses.uchicago.edu/NeutronMonitor/neutron_mon.html.