About ACE Monitoring

ACIS Ops Response to Radiation Events

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.

    The monitor page is called Chandra Radiation Environment Summary


  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.

    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.


  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 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.


  4. Chandra RADMON trigger levels

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

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


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Last updated: 01/28/21