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Facts

Link to Overview of Solar Flares

RHESSI

Science Facts

Technical Facts

Link to the HESSI Mission Concept

Science Facts

Primary Mission Objective:

Explore the basic physics of particle acceleration and energy release in solar flares

Science Objectives

Solar:
bullet Determine the frequency, location, and evolution of impulsive energy release in the corona
bullet Study the acceleration of electrons, protons, and heavier ions in flares
bullet Study the heating of plasma to tens of millions of degrees and determine its relationship to particle acceleration
bullet Study the propagation and evolution of energetic particles in flares
bullet Determine the relative abundances of accelerated and ambient ions in flares

Non-Solar:
bullet Obtain images and spectra of the Crab Nebula with 2 arcsecond spatial resolution and ~1 keV spectral resolution
bullet Detect and obtain high resolution spectra of gamma-ray bursts and cosmic and terrestrial transient sources over a large fraction of the sky
bullet Search for cyclotron line features in gamma-ray bursts and cosmic transient sources
bullet Obtain high resolution spectra and search for line features in steady X-ray and gamma-ray sources

Primary Observations:

Simultaneous, high resolution imaging and spectroscopy of solar flares from 3 keV X-rays to 17 MeV gamma rays with high time resolution

Expected Numbers of Flares:
bullet Tens of thousands of microflares
bullet Over a thousand X-ray flares with crude imaging and spectra to >100 keV
bullet Hundreds of flares with >1000 counts per second above 20 keV, allowing spatial changes to be followed on timescales of 0.1 seconds.
bullet Tens of flares sufficiently intense to allow the finest possible imaging spectroscopy
bullet Up to 100 flares with the detection of gamma-ray lines
bullet Tens of flares with detailed gamma-ray line spectroscopy and the location and extent of the source determined to ~40 arcseconds

HESSI "Firsts":
bullet Hard X-ray imaging spectroscopy
bullet Hard X-ray and gamma-ray imaging above 100 keV
bullet Imaging in narrow gamma-ray lines
bullet Determination of solar gamma-ray line shapes
bullet Combination of spatial, spectral, and time resolution that is commensurate with physically relevant scales for energy loss and transport of >10 keV electrons
bullet Dynamic range to both detect microflares and make quantitative spectral measurements of the largest flares
bullet High resolution X-ray and gamma-ray spectra of cosmic sources
bullet Hard X-ray images of the Crab Nebula with 2 arcsecond resolution

Complementary Observations:
bullet

SOHO
bullet

EUV images and spectra

bullet

Coronagraph images

bullet

Interplanetary particle spectra and abundances

bullet

Photospheric magnetograms

bullet

TRACE
bullet

UV and XUV high resolution images

bullet

GOES
bullet

Images from the Soft X-Ray Imager

bullet

ACE
bullet

Interplanetary particle spectra and abundances

bullet

Ground-Based Observatories
bullet

Radio and optical images and spectra

bullet

Photospheric magnetograms

Technical Facts

Mission Class

Small Explorer (SMEX)

Launch

Date: February 5, 2002
Time: 3:58 PM EDT
Vehicle: Orbital Sciences Corporation (OSC) Pegasus XL  
Site: L1011 aircraft takes off from Kennedy Space Center

Orbit

Circular
Altitude: 600 km (373 miles)
Inclination to the equator: 38 degrees

Spacecraft Pointing

Spin stabilized
Spin axis within 0.2 degrees of Sun center
Spin rate:15 revolutions per minute

Ground Stations

Primary
University of California, Berkeley

Backup
Wallops Flight Facility, Virginia
Santiago, Chile
Weilheim, Germany

Operations Lifetime

2 years (3 years desirable)

Spectroscopy

Detectors

Nine segmented, hyperpure germanium crystals
Cooled to ~75 K (-198 degrees Celsius)

Energy Range

~3 keV - ~17 MeV

Spectral Resolution

~1 keV (FWHM) in the front segment up to ~100 keV
~3 keV in the rear segment up to ~1 MeV increasing to ~5 keV at 20 MeV

Imaging

Technique

Fourier-transform imaging
9 rotating modulation collimators (grid pairs)

Field of View

Full Sun (~1 degree)

Angular Resolution

2 arcseconds to 100 keV
7 arcseconds to 400 keV
36 arcseconds above 1 MeV

Source sizes that can be imaged

~2 arcseconds to ~180 arcseconds

Temporal Resolution

Tens of milliseconds for a basic image
2 seconds (half a rotation of the spacecraft) for a detailed image

Aspect System

Solar Aspect System (SAS) determines the direction to Sun-center to better than 1.5 arcseconds
Roll Angle System (RAS) determines the roll angle to better than 3 arcminutes

Spacecraft Dimensions

Height: 2.16 m (85 in)
Width: 5.76 m (227 in) after solar panel deployment, 1.1 m (43.3 in) before solar panel deployment

Total Weight: 293 kg (645 lb)

Total Power Consumption: 414 watts   

Onboard Memory: 4 Gbytes

Telemetry: Up to 11 Gbits/day (3.5 Mbits/second) 

 

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This site last updated November 10, 2008.