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Published April 2008 | Published
Journal Article Open

The Low-Energy Telescope (LET) and SEP Central Electronics for the STEREO Mission


The Low-Energy Telescope (LET) is one of four sensors that make up the Solar Energetic Particle (SEP) instrument of the IMPACT investigation for NASA's STEREO mission. The LET is designed to measure the elemental composition, energy spectra, angular distributions, and arrival times of H to Ni ions over the energy range from ∼3 to ∼30 MeV/nucleon. It will also identify the rare isotope ^(3)He and trans-iron nuclei with 30≤Z≤83. The SEP measurements from the two STEREO spacecraft will be combined with data from ACE and other 1-AU spacecraft to provide multipoint investigations of the energetic particles that result from interplanetary shocks driven by coronal mass ejections (CMEs) and from solar flare events. The multipoint in situ observations of SEPs and solar-wind plasma will complement STEREO images of CMEs in order to investigate their role in space weather. Each LET instrument includes a sensor system made up of an array of 14 solid-state detectors composed of 54 segments that are individually analyzed by custom Pulse Height Analysis System Integrated Circuits (PHASICs). The signals from four PHASIC chips in each LET are used by a Minimal Instruction Set Computer (MISC) to provide onboard particle identification of a dozen species in ∼12 energy intervals at event rates of ∼1,000 events/sec. An additional control unit, called SEP Central, gathers data from the four SEP sensors, controls the SEP bias supply, and manages the interfaces to the sensors and the SEP interface to the Instrument Data Processing Unit (IDPU). This article outlines the scientific objectives that LET will address, describes the design and operation of LET and the SEP Central electronics, and discusses the data products that will result.

Additional Information

© 2007 Springer Science + Business Media B.V. Received: 5 January 2007; Accepted: 15 October 2007; Published online: 12 December 2007. This research was supported by the National Aeronautics and Space Administration (NASA) at the Space Radiation Laboratory (SRL) of the California Institute of Technology (under Subcontract SA2715-26309 from the University of California at Berkeley (UCB) under NASA contract NAS5- 03131), the Jet Propulsion Laboratory (JPL), and the Goddard Space Flight Center (GSFC). The authors thank the many individuals and organizations that contributed to the successful development of LET and SEP Central. Within SRL at Caltech we thank Janet Valenzuela, who procured and kitted electronics parts and was responsible for our documentation control; Norman Lee, who assisted the cognizant engineer in a variety of tasks; Jill Burnham, who laid out the PHASIC chip and provided engineering assistance; Minerva Calderon, who supported us in the computer and IT networks area; and Stacia Rutherford, Caprece Anderson, Pamela Nickson, Christina Davezan, Marjorie Miller, Cherylinn Rangel, and Donna Jones, who provided administrative assistance. André Jefferson of the Caltech Safety Office assisted us in moving radiation sources around the country. We wish to thank Richard Seligman, Nancy Daneau, and Gaylene Ursua of Caltech's Office of Sponsored Research for assisting us with contract issues. We thank Ray Yuen, Jose Lopez-Tiana, and Rudy Arvizu for procurement help. Rebekah Sims assisted in developing our Small Business Plan. Richard Paniagua and Joe Haggerty of Caltech's Physics shop assisted in making a variety of parts used in the lab and at accelerator calibrations. We thank Chris Martin and Peter Friedman of the GALEX team for the use of their excellent clean room facility. Caltech's JPL was instrumental in many areas of the development of LET and SEP Central. Toshiro Hatake and Amin Mottiwala were responsible for the fabrication of the Caltech PHASIC hybrid; Patrick Martin, Terry Fisher, and Andy Rose supplied environmental test facilities which were superbly run by technicians Doug Perry, Geoff Laugen, Mike Sachse, Bruce Woodward, and Sandro Torres; Tom Hill provided a bake-out chamber; Dennis Kern, Wan B. Tsoi, Michael O'Connell, and Tim Werner helped with environmental test plans and reports; Charles Cruzan, Chuck Derksen, Don Schatzel, and Reza Ghaffarian assisted with failure analysis and L1 detector rework; James Arnett, David Guarino, Peyton Bates, and Guy Prichard provided management and financial accounting assistance; Pat Dillon, Glenn Anderson, Angel Garnica, Mark Hetzel, and Pat Rodriguez helped us with connector selection and harness fabrication; Gary Bivins provided expert advice for PHASIC hybrid screening; Ed Powell and Kristan Ellis helped with parts; Mark Duran helped with thermal blankets; and Brian Blakkolb assisted with contamination control. Special thanks to the engineers and technicians in the Electronics & Packaging Section: Atul Mehta, Anarosa Arreola, Tran Ngo Lu,Martha Cortez, YolandaWalters, Hung Truong, and Gerald Gaughen; as well as the people in Instruments & Measurements Lab working under Lothar Kirk. Providing advice on ITAR issues were Edmond Momjian, Ann Bussone, Stephanie Lear, and Kerry Dolan. Dean Aalami of Space Instruments was responsible for the design of the Analog Post-regulator board and the detector bias supplies. Colin Wilburn and his staff at Micron Semiconductor Ltd. fabricated the silicon detectors. Robert Kopp of Dynacs Inc. assisted with quality assurance at Caltech. C. H. Ting consulted on the design of the P24 MISC and provided the Forth operating system used in the LET and SEP Central microprocessors. We have many to thank at UCB. Janet Luhmann is the IMPACT Principal Investigator and we thank her for her support and encouragement throughout the development period. David Curtis was the IMPACT project manager and provided expert assistance and advice to us on many levels. Peter Berg and Selda Heavner designed and fabricated the low voltage power supplies. Ron Jackson assisted us in the quality assurance area and Trish Dobson and David Weldon provided financial assistance. The support of many individuals at GSFC was critical in the development process. Russell Harrison assisted us with the thermal vacuum testing. Bert Nahory and Traci Pluchak-Rosnack provided technician assistance. Therese Errigo was responsible for contamination control and was assisted by Kelly Henderson of Swales Aerospace. Also helping us in a variety of areas were Fred Gross, Antonio Reyes, Leslie Cusick, Jong Kadesch, Richard Katz, Mario Martins, Brian Rice, and Haydar Teymourlouei. We are grateful to the individuals and institutions that provided facilities and assistance during our accelerator calibrations and part irradiation testing. Rocky Koga, Jeff George, and Mark Looper of Aerospace Corp. helped in both areas, providing assistance with the use of their chamber at the 88-in cyclotron at UCB and with 60Co radiation testing at Aerospace. Raman Anantaraman facilitated our accelerator calibration at the Michigan State National Superconducting Cyclotron Lab. We are grateful to the STEREO Project Office at GSFC for their support. Nick Chrissotimos was the STEREO Project Manager and Mike Delmont was the Deputy Project Manager. We thank them for their guidance. We are especially indebted to the IMPACT Instrument Manager, Lillian Reichenthal, who became a dedicated team member, helping us in every aspect of the development and testing of LET and SEP Central. Also assisting us were Harry Culver, Larry Gibb, Jerry Hengemihle, Shane Hynes, Mike Jones, Michael Kaiser, Diane Kolos, Alexia Lyons, Tabitha Merchant, Kevin Milligan, Robert Palfrey, James Rogers, James Thurber and Steve Wasserzug. Finally, we thank Eric Christian of NASA Headquarters who not only provided encouragement but also took shifts in monitoring our instrument during thermal vacuum testing.

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