The status of the nine RHESSI detectors changed throughout the mission. If you are trying to determine the best detectors to use for a particular event, please take a look at these separate-detector plots available on Browser:

  • Minute-by-minute spectrum plots (click Time-Based Quicklook, magnifier, and Per-min.det. spectra)
  • Spectrograms for each orbit (click Time-Based Quicklook, magnifier, and Spectrograms)
  • Flare peak time spectrum plots (click Flare-Based Quicklook, magnifier, and Peak det. spectra)

An explanation of how to use those plots is in the RHESSI Science Nugget 'Which detectors can I use to analyze this flare?'

For more specific guidance, please contact a RHESSI expert (e.g. Brian Dennis, Richard Schwartz, Albert Shih).

16 August 2018 - END OF RHESSI MISSION. The RHESSI spacecraft was decommissioned.

11 April 2018 - Last day of RHESSI science observations. Due to difficulties in communicating with RHESSI, the detectors were never turned back on after the sixth anneal.

12 April - ~12 June 2018 - Sixth RHESSI Anneal. After over 16 years of successful operation, RHESSI is currently undergoing its sixth anneal to rejuvenate the detectors. This procedure is expected to take about two months to complete. During this time, no science observations will be made.

23 February - 29 April 2016 - Fifth RHESSI Anneal. After over 14 years of successful operation, RHESSI completed its fifth detector anneal. From February 23, 02:19 UTC to April 29, 03:48 UTC, the detectors were heated up to repair accumulated radiation damage and then cooled back down to operating temperatures. During that time, no science observations were made. RHESSI is again obtaining science data, but with a reduced number of operating detectors (usually 2 out of 9) in order to maintain optimal detector temperatures. See the RHESSI has resumed operations Nugget and the RHESSI 5th Anneal Nugget for more information.

26 June - 13 August 2014 - Fourth RHESSI Anneal.  During the anneal, RHESSI's germanium detectors are heated up from their operating temperature of ~115 K to ~100 deg C (373 K), held at that temperature for ten days, and then cooled back down.  The detectors degrade steadily over time due to radiation damage from charged particles, and heating up the germanium restores lost sensitivity and resolution. During the anneal, RHESSI does not collect X-ray or gamma-ray data.

After this fourth anneal, five of the nine detectors (1, 3, 6, 8, and 9) have electronically separate front and rear segments, and the other four detectors are currently operating unsegmented and have thresholds of ~20 keV.  Thus, hard X-ray (>~20 keV) observations have the nominal angular resolution (~2 arcsec) and spectral resolution (~1 keV), but soft X-ray (~3-20 keV) observations have a reduction in image quality.

17 January - 22 February 2012 - Third RHESSI Anneal.  On 22 February, RHESSI resumed collecting solar X-ray and gamma-ray  data, following the successful completion of the "anneal" procedure to rejuvenate the RHESSI detectors from the effects of radiation damage. The detectors were heated up from their operating temperature of ~100 K to ~100 deg C (373 K), held at that temperature for ten days, and then cooled back down.  The entire procedure took five weeks.  Among the result of the anneal:

  • All 9 detectors recovered energy resolution and sensitivity.
  • Detectors #2 and #4 have higher background because they have not divided into two segments.
  • Cryocooler efficiency improved.

16-March - 1 May 2010 - Second RHESSI Anneal.  As of 1 May, RHESSI is fully operational after the second anneal.  This anneal was performed somewhat ahead of schedule, triggered by an anomaly in the RHESSI power system that occurred on 16 March 2010.  The anomaly turned off all nonessential components including the cryocooler needed to keep the germanium detectors at their <100K operating temperature.  Since the detectors were already warming up, the anneal was performed, heating the detectors to 100 degrees C for ten days.  Read more about RHESSI's Anneal Adventure.

5-27 November 2007 -  First RHESSI Anneal.  The RHESSI germanium detectors were annealed starting ~07:00 UT on 5 Nov.  At ~20:00 Ut on 27 Nov, RHESSI resumed taking science data.

The performance of the nine RHESSI germanium detectors has been gradually degrading as expected since launch in 2002 because of radiation damage inflicted by the charged particles of the Earths radiation belts. To correct this problem, the detectors were annealed by heating them to over 90 degrees C for a week during November.

Upon cooling them back down to their operating temperature of ~90 K and turning on the high voltages, all but one of the detectors showed considerable improvement in performance with approximately half the accumulated radiation damage being removed. The detector performance has been returned to what it was in mid to late 2005. All front segments have nearly their full effective area again, and most rear segments are now capable of observing nuclear lines effectively. Neither was the case before the anneal. This will allow high- resolution X-ray and gamma-ray observations of solar flares to be continued. One detector that had been anomalous since soon after launch is currently not operational.

Although the cryocooler has lost some efficiency, it is keeping the detectors at ~94 K, about 4 K above their pre-anneal temperature with only a slight increase in power. Detector performance will be fully evaluated in the coming weeks as the occasional flare occurs during this period of very low solar activity near the minimum in the 11- year cycle.

28 August 2006 - At 18:07:47 UT the lower-level threshold on detector G8 was raised to around 6 keV to eliminate excessive low-energy noise. Do not use this detector for imaging or spectroscopy below 10 keV until after the next anneal (28 August 2006 to 27 November 2007).

9-24 June 2006 - From 05:00 UT on 9 June through 22:00 UT on 24 June, RHESSI was pointing off the Sun for Crab Nebula observations. This includes the re-pointing periods on either end. If you are interested in analyzing Crab or solar data in this interval, please contact the instrument team.

RHESSI Major Events, 2002 - 2007

Table of Anneal and Offpoint Times