1. HESSI Science Objective  Impulsive Energy Release in the Corona  Acceleration of Electrons, Protons, and Ions  Plasma Heating to Tens of Millions of degrees  Energy and Particle Transport and Dissipation To explore the basic physics of particle acceleration and explosive energy release in solar flares A1309.03

2. HESSI Non-Solar Science Objectives ŸThe Crab Nebula – Imaging spectroscopy with 2” resolution ŸGamma Ray Bursts and Cosmic Transient Sources – Detected over a large fraction of the sky – High resolution spectroscopy – Search for cyclotron line features ŸSteady X-ray and gamma-ray sources (point and diffuse) – Detect by Earth occultation or through the rear grids – Obtain high resolution spectra – Search for line features A1309.04

3. HESSI Primary Observations  Hard X-ray Images – Angular resolution as fine as 2 arcseconds – Temporal resolution as fine as 10 ms – Energy resolution of <1 keV to ~3 keV (FWHM)  High Resolution X-ray and Gamma-ray Spectra – ~keV energy resolution –To energies as high as 15 MeV A1309.05

4. Complementary Observations SOHOEUV images and spectra Coronagraph images Particle spectra and abundances YohkohImages from both the soft and hard X-ray telescopes GOESImages from the Soft X-ray Imager Wind & ACEEnergetic particle spectra and abundances, low-frequency radio and energetic electrons TRACEUV & XUV high resolution images Ground-based Observatories Radio and optical images and spectra Magnetograms H  polarization A1309.06

5. HESSI Firsts  Hard X-Ray Imaging Spectroscopy  High Resolution Spectroscopy of Solar Gamma-Ray Lines  Hard X-Ray and Gamma-Ray Imaging above 100 keV  Imaging of Narrow Gamma-Ray Lines  High Resolution X-ray and Gamma-Ray Spectra of Cosmic Sources  Hard X-Ray Images of the Crab Nebula with 2-arcsecond Resolution A1309.07

6. Expected Numbers of Flares MicroflaresTens of thousands Hard X-ray flares with crude imaging and spectra>1000 to >100 keV Hard X-ray flares with >10 3 counts s -1 detector -1 Hundreds above 20 keV allowing spatial scales to be followed on timescales of 0.1 s Flares sufficiently intense to allow the finestTens possible imaging spectroscopy Flares with the detection of gamma-ray linesUp to 100 Flares with detailed gamma-ray line spectroscopyTens and the location and extent of the source determined to ~40 arcseconds

7. HESSI Observational Characteristics  Energy Range3 keV to 15 MeV  Energy Resolution (FWHM)<1 keV FWHM at 3 keV increasing to 5 keV at 15 MeV  Angular Resolution2 arcseconds to 100 keV 7 arcseconds to 400 keV 36 arcseconds to 15 MeV  Temporal ResolutionTens of ms for basic image 2 s for detailed image  Field of ViewFull Sun  Effective Area - cm 2 10 -3 at 3 keV, 50 at 10 keV (with attenuators out)60 at 100 keV, 20 at 10 MeV  Numbers of flares~1000 imaged to >100 keV. ~100 with spectroscopy to ~10 MeV

8. Instrument9 germanium detectors (7.1-cm dia. x 8.5 cm) Cooled to 75 K with Sunpower cooler Grid pitches from 34 microns to 2.75 mm 1.55-m grid separation Solar Aspect System to <1 arcsecond Roll Angle System to ~1 arcminute Weight130 kg Power125 watts Telemetry12 Gbits in 2 days SpacecraftSpinning at 12 - 20 rpm Pointing to within 0.1° of Sun center Launch VehiclePegasus XL from KSC Orbit38° inclination 600 km altitude, >3-year life Launch DateMarch 2001 Operations2 years, 3 years highly desirable HESSI Summary A1309.011

9. HESSI PI and Co-Is Robert LinUniversity of California, BerkeleyPI Gordon HurfordUniversity of California, Berkeley Imaging Scientist Norman MaddenLBNL, BerkeleyGermanium Detectors Brian DennisGSFC/682Mission Scientist Carol CrannellGSFC/682Education & Outreach Gordon HolmanGSFC/682Flare Theory Reuven RamatyGSFC/661Flare Theory Tycho von RosenvingeGSFC/661ACE Collaboration Alex ZehnderPaul Scherrer Inst. SwitzerlandTelescope design and fabrication Frank van BeekDriebergen, The NetherlandsGrids and Imaging Patricia BornmannNOAAGOES Collaboration Richard CanfieldMontana State UniversityGround-based Observations Gordon EmslieUniv. of Alabama, HuntsvilleFlare Theory Hugh HudsonSolar Physics Research Corp.Imaging Arnold BenzInst. of Astronomy, Zurich, SwitzerlandRadio Observations John BrownUniv. of Glasgow, ScotlandFlare Theory Shinzo EnomeNAO, JapanRadio Observations Takeo KosugiNAO, JapanImaging Nicole VilmerObservatoire de Paris, Meudon, FranceData Analysis A1309.012

10. HESSI Associated Scientists University of California, Berkeley David Smith Spectrometer Scientist Jim McTiernanMOC/SOC Scientist Isabel HawkinsEducation & Outreach Said Slassi-SennouSpectrometer Calibration Andre CsillaghySoftware George FisherFlare Theory Chris Johns-KrullModeling GSFC Richard SchwartzData Analysis Software Larry OrwigGrid Characterization Dominic ZarroComplementary Data University of Maryland Ed SchmahlImaging Software Lockheed-Martin Markus AschwandenTiming Software A1309.012

11. HESSI Prime Responsibilities UC BerkeleyGermanium detectors, cryostat, & electronics I & T Ground station, MOC/SOC Data Analysis GSFCGrid characterization & testing Cryocooler Data analysis, distribution, and archiving PSI (Switzerland)Telescope & aspect system Thermo Electron TecometFinest grids (#1 - 4) van Beek (The Netherlands)Coarser grids (#5 - 9) & mounts Spectrum AstroSpacecraft A1309.013

12. GSFC Involvement Science Dennis (682)Mission Scientist Holman (682), Ramaty (661)Solar flare physics von Rosenvinge (661)ACE/HESSI coordination Crannell (682)Education & Public Outreach Imaging Clark (547)Imager metrology and testing Amato (544)Grid environmental testing Orwig (682)Optical & X-ray grid characterization Uribe, Berg, Bilodeau (ITSS) Spectrometer Boyle, Shirey (552)Cryostat design, cooler evaluation Banks (OSC)Provide flight-qualified Sunpower cooler Data Analysis Schwartz (Raytheon ITSS) Data analysis software Tolbert (Raytheon ITSS) Graphical user interface Schmahl (UMd)Image reconstruction Zarro (EIT)Complementary data Gurman (682)Solar Data Analysis Center A1309.014

13. HESSI Imaging Parameters

14. Tecomet Grid #1 Material:Molybdenum Pitch:34 microns Slit width:15 microns Total thickness:1.2 mm Layer thickness:15 microns No. of layers:75 Active area:9 cm diameter Aspect ratio:>50:1 Second of two identical grids fabricated by Thermo Electron Tecomet in Woburn, MA. Finest, high-aspect-ratio X-ray collimator ever made. Provides modulation to X-ray energies in excess of 100 keV. Allows imaging on HESSI with an angular resolution of 2 arcseconds. Picture shows circular active area with fiducial and mounting features in the integral rim. Direction of slits is revealed by the white bar at 45º resulting from light transmitted from below through the ~1º opening angle of each slit.

15. Tecomet Grid #1

16. HESSI Top Grid Tray

17. HESSI Rear Grid Tray

18. Germanium Detector A1309.019

19. Sunpower M77 Stirling-Cycle Cooler

20. Instrument Sensitivity

21. Angular Coverage vs. Photon Energy

22. Relative Modulation Amplitude vs. Photon Energy

23. Composite Flare Spectrum

24. Energy Resolution vs. Photon Energy D1309.001

25. Count Rates in Each Detector for One Rotation A1309.025

26. P A U L S C H E R R E R I N S T I T U T Laboratory for Astrophysics Principle of Twist Monitoring System - TMS Rear Grids: 4 Laser DiodesFront Grids: 2 Annuli 3mm dia. Interference Pattern on CCD Camera

27. Prelaunch Twist Monitoring System (TMS) A1309.026

28. Roll Angle System (RAS)