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The engineering team at JHU/APL, lead by Karen Kirby, includ- ed Yanping Guo (mission design), Steve Vernon (launch vehicle inter- face), Gordon Maahs (structural analysis) and Jeff Kelley (mechanical design). The engineering team at ESA included Danielle Renton (Solar Orbiter Payload Engineer), Javier Marti Canales (Solar Orbiter System Engineer) and Jose Rodriguez Canabal (Solar Orbiter Mission Analyst). Jennifer Rumburg at the Goddard Space Flight Center provided edito- rial and production support. Available from: NASA Center for AeroSpace Information National Technical Information Service 7115 Standard Drive 5285 Port Royal Road Hanover, MD 21076-1320 Springfield, VA 22161 Table of Contents HELEX Joint Science and Technology Definition Team......................................................iv Executive Summary................................................................................................................1 1.0 Introduction......................................................................................................................2 1.1 Heliophysical Explorers (HELEX): Solar Orbiter and the Inner Heliospheric Sentinels...................................................................................................................3 2.0 Science Objectives...........................................................................................................3 2.1 What are the origins of the solar wind streams and the heliospheric field?.............4 2.2 What are the sources, acceleration mechanisms, and transport processes of solar energetic particles?.........................................................................................9 2.3 How do coronal mass ejections evolve in the inner heliosphere?..........................12 2.4 High-latitude-phase science...................................................................................15 3.0 Measurement Requirements and Science Implementation............................................15 3.1 Measurement Requirements...................................................................................15 3.2 Observational Strategy...........................................................................................22 3.3 Supporting Observations........................................................................................23 4.0 Theory and Modeling.....................................................................................................24 5.0 Mission Design...............................................................................................................25 6.0 References......................................................................................................................26 iii HELEX Joint Science and Ex Officio Members Joint Science Technology Definition Team and Technology Definition Team Robert P. Lin (co-chair) Madhulika Guhathakurta University of California, Berkeley, CA, USA LWS Program Scientist NASA/HQ, Washington DC, USA Eckart Marsch (co-chair) Max-Planck-Institut für Haydee M. Maldonado Sonnensystemforschung, Lindau, Germany Sentinels Project Manager NASA Goddard Space Flight Center, Greenbelt, Spiro Antiochos MD, USA Naval Research Laboratory, Washington DC, USA Adam Szabo Sentinels Study Scientist Thierry Appourchaux NASA Goddard Space Flight Center, Greenbelt, Institut d’Astrophysique MD, USA Spatiale, Orsay, France O. C. St. Cyr Joseph M. Davila LWS Project Scientist NASA Goddard Space Flight NASA Goddard Space Flight Center, Greenbelt, Center, Greenbelt, MD, USA MD, USA Silvano Fineschi Hermann Opgenoorth Osservatorio Astronomico di Torino, Italy Head of Solar System Missions Division ESA-ESTEC, Noordwijk, The Netherlands Alan Gabriel Institut d’Astrophysique Philippe Kletzkine Spatiale, Orsay, France Solar Orbiter Project Manager ESA-ESTEC, Noordwijk, The Netherlands Jean-François Hochedez Observatoire Royal de Belgique, Richard Marsden Brussels, Belgium Solar Orbiter Study Scientist ESA-ESTEC, Noordwijk, The Netherlands Timothy Horbury Imperial College, London, UK William Lewis (Technical Writing Support) Glenn Mason Southwest Research Institute, San Antonio, The Johns Hopkins University Applied TX, USA Physics Laboratory, Laurel, MD, USA Richard Mewaldt California Institute of Technology, Pasadena, CA, USA Alan Title Lockheed Martin Advanced Technology Center, Palo Alto, CA, USA Robert Wimmer-Schweingruber Christian-Albrechts-Universität, Kiel, Germany iv Heliophysical Explorers The mission design that will enable HELEX (HELEX): Executive Summary to accomplish these objectives foresees a launch of Solar Orbiter in 2015, followed two years Heliophysical Explorers (HELEX) brings later by Sentinels. A NASA-provided launch together and augments the unique capabili- vehicle will place Solar Orbiter into an inner ties of ESA’s Solar Orbiter mission (near-Sun heliospheric orbit that will bring the space- and out-of-ecliptic in-situ plus remote-sens- craft as close to the Sun as ~0.22 AU by the ing observations) with those of NASA’s Inner end of the transfer phase and, through progres- Heliospheric Sentinels (in-situ observations sive raising of the inclination employing Venus from multiple platforms arrayed at varying ra- gravity assist maneuvers, to heliolatitudes dial distances and azimuthal locations in the of 27.5° by the end of the nominal mission near-ecliptic plane) to investigate, character- phase and to ~34° by the end of the extended ize, and understand how the Sun determines mission. Four Inner Heliospheric Sentinels the environment of the inner solar system and, spacecraft will be launched together into a he- more broadly, generates the heliosphere it- liocentric orbit in the orbital plane of Venus. self. This joint ESA-NASA science program Three or four Venus gravity assist maneuvers offers a unique opportunity for coordinated, will be performed over 2.5 to 3 years to bring correlative measurements, resulting in a com- the four spacecraft into their final orbits, with bined observational capability and science re- perihelia