About ACE Monitoring



ACIS Ops Response to Radiation Events

The Science Operations Team has two 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.

    Details of operation: see /proj/rac/ops/ACE/README on the HEAD LAN.
  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 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 ANY of the following three EPHIN channels exceeds the on-board threshold for 10 consecutive samples. EPHIN samples are sent to the OBC each 65.6 seconds. 

    AS OF DEC 09, 2008:

- No discrimination among electrons, protons, and nuclei will be made
  - All four proton channels will show 0 counts
  - All four electron channels will become combinations of electrons, protons 
    and nuclei (e.g. the new E150 will be E150 + P4GM + H4GM)
- The overall geometric factor will be change but will be constant (i.e. it 
   will not toggle between large and small)
- The safing channels will be E150, E1300, HRC MCP Total Rate with the 
  following thresholds:

E150      800000 counts/sample
E1300       1000 counts/sample
MCP Total     30 counts/sample (the relevant MSID is 2DETART)


The previous thresholds (now obsolete) were:
                                                   THRESHOLDS

                                                   LARGE Geom   SMALL Geom
                                    cts/cm^2-s-sr  cts/sample   cts/sample
                                    -------------  ----------   ----------
E1300 (electrons, 2.64 - 6.18 MeV):      10.0        1318.56        78.72
P4GM (protons, 5.0 - 8.3 MeV):          300.0         3542.4       3542.4
P41GM (protons, 41 - 53 MeV):            8.47          100.0        100.0
    Other links:
    1. Travel Time of CME vs. Initial Speed.- this is a link to a plot which proports to be able to calculate the travel time of a CME

    2. Costello Geomagnetic Activity Index - The Costello home page withe full details about this predictive index

    3. Magnetospheric Specification Model Latest MSM Output

    4. 3-day archive of the latest ACE data.

    5. Latest orbital fluence when CHANDRA is above 70kkm.

    6. History of fluence when CHANDRA has been above 70kkm.

    7. Fluence on ACIS per orbit (current.dat) - This is the fluence only when ACIS is in the Focal plane, corrected for grating blockage. A combination of ACE/ACIS fluence files with the data presented in scientific notation so that it is easier to read.

    8. Archival fluence in the ACE P3 channel (proton.dat) - this feeds off my archive file and produces a file that is again easier to read. Moreover, it tallies the fluence in the ACE P3 channel to date to the extent of my archive. I intend to have my fluence scripts backtrap and determine the fluence for each orbit since SSD-opening. Once that is done, this file will provide us with the observed ACE proton fluence for each orbit and for the mission to date (which we can compare against our budget of 2E10).

    9. Archival fluence of all ACE channels (all.dat) - same as 2 but does it for all ACE channels that we monitor.

    10. About our ACE Monitoring and Alerts.

    Last updated: 04/19/04