About ACE Monitoring

The Science Operations Team has four proton monitoring systems.

1. Orbit Monitor:

   The fluence of ACE protons in the 115-195 keV energy range is integrated over each Chandra orbit, while Chandra is above 70,000 km geocentric distance. The fluence measurement is reset to 0 while Chandra is below 70,000 km.

   If the fluence exceeds a threshold, SOT and FOT members are alerted via pagers and via email. The alert message provides the measured fluence and the integrated time.

   The latest ACE proton flux, and the integrated fluence, are on the top line of the Chandra snapshot display (f_ACE and F_CRM respectively), and on the SOT's ACE page.

   ACE proton energy range: 130 - 214 keV

   An open-ended series of thresholds, at 1E9, 3E9, 9E9, 27E9, 81E9, 243E9 etc. For each threshold, issue 3 alerts at 30 minute intervals, then increase threshold to next level. Reset orbit fluence to zero, and reset threshold to 1E9 at the end of each orbit.

   • Alert list:
     • ACIS team

   The monitor page is called Chandra Radiation Environment Summary

   • Alert list:
     • Sot_yellow alert at 1e9 (attenuated)

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2. Two Hour Monitor:

   A violation of this limit is more serious than the orbital limit since it implies a similar flux in a shorter time scale.

   The fluence of ACE protons in the 115-195 keV energy range is integrated as a runing average over each 2 hour period. This is 24 measurments during each period. Bad measurments are dropped and the average Flux particles/cm2-s-ster-MeV is calculated.

   If the fluence exceeds a threshold, SOT and FOT members are alerted via pagers and via email. The alert message provides the measured fluence and the integrated time.

   ACE proton energy range: 130 - 214 keV

   Fluence threshold = 50,000 protons/cm2-s-ster-MeV average over a 2 hour window (3.6e8 protons/cm2-ster-MeV).

   An ACE instrument swap occurred in February 2004. The FP6p (761-1220 keV) channel stayed the same but the P3 channel (112-187 keV) changed somewhat. Therefore we now alert first if the fluence derived from FP6p*36.0 is greater than 1.2e8 p/cm2-ster-MeV. An alert is also sent if the new P3 channel (115-195 keV) exceeds 3.6e8 p/cm2-ster-MeV and P3/FP6f < 36.

   • Alert list:
     • sot_ace_alert

   if the alert is actionable (i.e. not in the middle of the night and SCS107 has not been otherwise run) any recipiant may call a sot_red_alert. Alert scheme: 1 alert. Once this alert triggers it is disabled for 24-48 hours or until manually rearmed by the MTA scientist.

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3. Kp Monitor:

   A violation of this limit indicate the general radiation state near the Earth is high.

   If the value of Kp (projected) exceeds the threshold a yellow alert is generated, SOT and FOT members are alerted via email and pager. The alert message provides the measured Kp, current S/C configuration and comm schedule. The threshold is variable on a matrix of time (by month) and configuration (grating and sim position).

   • Alert list: none -- This has never been actionable,

   Alert scheme: 1 alerts, Once this alert triggers it is disabled in 24 hours.
   

   The latest ACE proton flux, the integrated fluence, and Kp are on the top line of the Chandra snapshot display (f_ACE, F_CRM and Kp respectively), and on the SOT's ACE page.

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4. Chandra RADMON trigger levels

   RADMON will trigger SCS 107 (SI safing) if EITHER of the following two conditions occur:

   HRC shield rate is above 250 From Mike Juda's 2006 memo: The RADMON process uses data for the MCP total rate that is telemetered as MSID 2DETART (or 2DETBRT if we switch to the HRC B-side CEA). This MSID only reflects the high-order byte of the rate and so a rate of 5000 counts/s would correspond to a 2DETART value of 19. There have been four instances during the entire mission to date when the telemetry shows 2DETART exceeding a value of 19. There have been no cases of MSID 2DETART with a value of 30 (corresponding to ~7900 counts/s) or higher. We are using a "2DETBRT" threshold value 29.5, the OBC runs SCS-107 once we have ten consecutive samples (one sample every 65.6 s) of 2DETART within the RADMON process with a value of 30 or higher). The HRAC Antico shield rate B similarly has a limit of 250.

   Shield Rate B       250 counts/sample (the relevant MSID is 2SHLDBRT)
   MCP Total            80 counts/sample (the relevant MSID is 2DETBRT)
   
   

   ACIS TXINGs ACIS on-board TXINGs are used as a secodary radiation monitor and can also be used to trigger autonomous radiation shutdowns. This monitor, backs up the HRC anticoincidence shield, but it should be noted that threshold crossings are far from ideal as a radiation damage indicator, and also that this monitor is only active when ACIS is running. Thresholds crossings reveal significant elevation in particle background, which is not a direct indicator of the presence of CTI-inducing particles. More details are available in these SPIE publications led by Peter Ford and Catherine Grant: paper I and paper II. As of Jan. 2021, TXINGs has twice autonomously safed Chandra.

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• The OCC Solar Monitoring and Space Weather Page
• Stanford Solar Center
• Rob's newsletter article from March 2002.
• Latest ACE orbital fluence when CHANDRA is above 70kkm.
• CCMC Community coordinated Modeling Center
• ISWA iNTEGRATED SPACE WEATHER ANALYSIS SYSTEM
• STEREO (home page)
• Solar images at SDAC
• Spot maps (both sides of the Sun)
• SOHO (home page)
  • SOHO Proton Monitor
  • SOHO images
• Trieste Coronal Radio Surveillance
• Cluster overview data