From: "Mark W. Bautz" Subject: ACE levels to watch To: rac@head-cfa.harvard.edu (Rob Cameron) Date: Fri, 22 Oct 1999 17:29:17 -0400 (EDT) Cc: plucinsk@nesvig.harvard.edu (Paul Plucinsky), svirani@head-cfa.harvard.edu, ybutt@space.mit.edu (Yousaf Butt), ODELL@ssl.msfc.nasa.gov (Steve Odell), martin@smoker.msfc.nasa.gov (Martin Weisskopf), ht@head-cfa.harvard.edu (Harvey Tananbaum), das@cfa.harvard.edu (Dan Schwartz) Rob, Dr. Susan Gussenhoven of Air Force Research Lab. spoke (separately) with both Steve Odell and me today, and provided the following provisional suggestion (I paraphrase): Chandra personnel should continuously monitor two ACE channels ACE Channel Energy "Danger" Level EPAM Electrons 175 keV - 315 kev 100 electrons /cm**2/s/ster/MeV EPAM Protons 112 keV - 187 keV 1e5 protons/cm**2/s/ster/MeV If either channel exceeds its danger level for a period of more than about 1 hour, then Chandra should consider taking action to protect ACIS. As you noted on the telecon today, the ACE data are available from the Space Environment Center. The URL is http://sec.noaa.gov/ace/ACErtsw_home.html (text files are available here also) Of course, these danger levels and the danger period (1 hour) are subject to discussion. How soon could we establish continuous monitoring of these channels? AFRL recommends we do so immediately. mark ------------------- From: "O'Dell, Steve" To: "'Mark W. Bautz'" , rac@head-cfa.harvard.edu Cc: plucinsk@nesvig.harvard.edu, svirani@head-cfa.harvard.edu, ybutt@space.mit.edu, martin@smoker.msfc.nasa.gov, ht@head-cfa.harvard.edu, das@cfa.harvard.edu, "Kolodziejczak, Jeffery" Subject: RE: ACE levels to watch Date: Sun, 24 Oct 1999 09:50:22 -0500 Mark - Based upon what we think we know of the ACIS degradation to date, the change in CTI is about 10^-17 per EXTERNAL 0.1-MeV proton (cm^2 sr MeV)^-1 when ACIS is at the focal position and negligible when at the next-in-line position. Assuming we want to limit any further increase in CTI to less than 1*10^-4, means that the total fluence when ACIS is at the focal position, for the rest of the mission (10 years), should not exceed 1*10^13 EXTERNAL 0.1-MeV proton (cm^2 sr MeV)^-1, corresponding to an average intensity of 3*10^4 EXTERNAL 0.1-MeV proton (cm^2 s sr MeV)^-1. Thus, we should be alert whenever the ACE EPAM P3' channel (115-195 keV) exceeds this value, begin active monitoring to look for further increases, and consider hiding the ACIS pending further increases in the proton intensity. We need to develop an allocation for the maximum acceptable fluence per event. Tentatively, I assume that this value is about 1*10^10 EXTERNAL 0.1-MeV proton (cm^2 sr MeV)^-1 per event --- i.e., 1*10^-3 of the allowed total mission fluence --- or a CTI increase of 1*10^-7. Thus, we could tolerate a flux of 1*10^5 EXTERNAL 0.1-MeV proton (cm^2 s sr MeV)^-1 for about a day, 1*10^6 EXTERNAL 0.1-MeV proton (cm^2 s sr MeV)^-1 for a couple hours, 1*10^7 EXTERNAL 0.1-MeV proton (cm^2 s sr MeV)^-1 for only about 15 minutes, etc. ACE's position at L1 gives about a 1-hour advance notice of what is headed down-wind toward the vicinity of the Earth. Rob - In addition to working with the AFRL Space Hazards Branch, we have begun working with the Sverdrup Technologies support personnel attached to MSFC's Space Environments and Effects group. They point out that NOAA SEC is eager to provide additional services. I know that the OCC is already aware of the real-time ACE EPAM data available at http://www.sec.noaa.gov. There is also a list server for space-weather alerts. The OCC may already have subscribed. If not, send the following message, with NO subject heading, to majordomo@sec.noaa.gov: "subscribe advisory-list your_userid@your_host". In addition, one of the Sverdrup SEE persons tells me that the NOAA SEC might also dispatch direct paging alerts. The contact for real-time data, given on the SEC page, is Kent A. Doggett (telephone: 303-497-3317, mailto:kdoggett@sec.noaa.gov). - Steve ------------- From: "Steve O'Dell" Date: Tue, 26 Oct 99 16:02:01 -0500 To: Yousaf Butt , gussen@plh.af.mil Subject: Re: proton alert levels Cc: Rob Cameron , sisafe@head-cfa.harvard.edu The low-energy protons are fairly isotropic --- i.e., not moving directly away from the sun. Because their Larmor radii are small compared to relevant scales, they scatter in the magnetic-field irregularities and move as a suprathermal fluid convected with the solar wind at a few-to-several hundred km/s. - Steve Sue, please correct me if I've misstated the physics. Begin forwarded message: To: Rob Cameron Subject: Re: proton alert levels cc: sisafe@head-cfa.harvard.edu Date: Tue, 26 Oct 1999 16:41:02 -0400 From: Yousaf Butt Rob, We should get some input from Space Environment experts on the directionality of these low-energy solar proton events, before setting the final limits -- are we even in danger pointing X degrees away from sun? Yousaf