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High Energy Solar Spectroscopic Imager, also called SMEX 6, later renamed RHESSI (Reuven Ramaty High-Energy Solar Spectroscopic Imager)


Designation 27370 / 02004A
Launch date 5 Feb 2002
Country of origin United States
Mission Scientific: Sun study
Perigee/Apogee 587/600 km
Inclination 38°
Launch vehicle Pegasus #32

HESSI will investigate the physics of particle acceleration and energy release in solar flares through an unprecedented combination of high resolution imaging and spectroscopy of X-rays and gamma rays from 2 keV to 20 MeV during the next solar maximum.

Project cost: $85 million (including $13 million for launch)

In Mar 2000, the satellite was damaged when during a test it was shaken 10 times harder than intended. Once on orbit, the satellite proved to work properly.

End of life

Decay 20 Apr 2023

External resources


sat-index articles

Technical data


Prime contractor Spectrum Astro Inc
Platform derived from SA-200S
Mass at launch 304 kg
Mass in orbit  
Solar array 4 panels
Stabilization spin stabilized (15 rpm)
DC power 120 W
Design lifetime 2 years

It uses Fourier-transform imaging with 12 bi-grid modulation collimators and cooled germanium and silicon detectors mounted on a Sun-pointed spin-stabilized spacecraft in a low-altitude equatorial orbit. HESSI will carry out the first imaging spectroscopy in hard X-rays with 2 arcseconds angular resolution, time resolution to tens of ms, and \sim1 keV energy resolution; the first gamma-ray line spectroscopy from a spacecraft with \sim1 keV energy resolution; and the first gamma-ray line and continuum imaging with 20 arcseconds angular resolution.

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