To: plucinsk cc: das, ybutt, rac, martin@smoker.msfc.nasa.gov, rjb Subject: Rad belt start/end Date: Thu, 21 Oct 1999 01:49:30 -0400 From: Shanil Virani Hi Paul, From Roger's email from earlier this evening he stated that: > (Note that rad zone entry is taken as 30 minutes after the > RADZONE_ENTRY ATS call in the DOT, and exit is taken as 30 minutes > before RADZONE_EXIT). If you or Peter or Dan or whomever can provide me with a simple file that just contains the tstart and tstop for each call, I easily overlay those time spans on the data for the various EPHIN channels I have. This will then definitely demonstrate whether we have a problem with the OFLS in predicting radiation belt transits. Of course, I will also take Harvey's suggestion and overlay SIM translations as well. To that end, I've created another really neat plot. In /data/acis0/svirani/ephin/radhist (also available at http://asc.harvard.edu/acis/radbelt/) you will find a file called "chandra-alt.ps". It is a single page plot so you all can print it out! Anyway, that file is a series of Radius vs time plots (by radius, I mean geocentric radius). Superimposed on the plots again are the E1,E2,P1,P2 time spans (horizontal lines at 5e4, 6e4, 7e4, and 8e4 km, respectively). However, from Day 261.5 and onwards, what I've also plotted is the SIM translations time. That is, I went through the time chronology at http://hea-www.harvard.edu/SOT/chron and stripped out all the times where the SIM was translated to HRC-S prior to belt passage and the corresponding SIM translation after we come out. I determined the following times: 1999:261:14:06:42.000 SIM Translation POS=-99616 (HRC-S) 1999:263:04:56:36.000 SIM Translation POS=92905 (ACIS-I) 1999:265:04:31:17.000 SIM Translation POS=-99616 (HRC-S) 1999:265:21:56:31.000 SIM Translation POS=92905 (ACIS-I) 1999:267:18:18:47.000 SIM Translation POS=-99616 (HRC-S) 1999:268:13:20:30.958 SIM Translation POS=75620 (ACIS-S) 1999:270:10:28:04.000 SIM Translation POS=-99608 (HRC-S) 1999:271:22:24:00.000 SIM Translation POS=75623 (ACIS-S) 1999:272:23:30:00.792 SIM Translation POS=-99612 (HRC-S) 1999:273:20:36:05.792 SIM Translation POS=92905 (ACIS-I) 1999:275:14:38:00.000 SIM Translation POS=-99612 (HRC-S) 1999:276:13:13:57.441 SIM Translation POS=-50505 (HRC-I) 1999:278:05:45:00.000 SIM Translation POS=-99616 (HRC-S) 1999:279:03:52:06.000 SIM Translation POS=75623 (ACIS-S) 1999:280:13:45:10.000 SIM Translation POS=-99608 (HRC-S) 1999:281:20:46:34.000 SIM Translation POS=75623 (ACIS-S) 1999:283:19:28:46.000 SIM Translation POS=-99616 (HRC-S) 1999:284:11:31:27.000 SIM Translation POS=75623 (ACIS-S) 1999:285:10:22:49.994 SIM Translation POS=92905 (ACIS-I) 1999:287:01:40:58.422 SIM Translation POS=75620 (ACIS-S) 1999:289:03:04:07.103 SIM Translation POS=-99612 (HRC-S) 1999:289:18:11:43.027 SIM Translation POS=74074 (ACIS-S) Note that according to that chronology file at the above web site, we did NOT do a SIM translation to HRC-S prior to belt entry on Day 286.5. Clearly, this is an indication that this file is incorrect since you or Royce or Yousaf have always been on hand to ensure that we've put ACIS in the next-in-line position prior to entry. At any rate, this is just another indication that I think I would be more comfortable using a file that either you or Peter has created that has "trustworthy" tstarts/tstops of each rad belt transit before we go to CXC at large and announce there is a problem with the OFLS's model of the radiation belts. Anyway, using the above SIM translations time spans, I also superimposed those values on the plots (it is the horizontal line at 1e4). The resulting plot is neat but I don't think it has much explanatory power. I mean the only observation one can make is that we're protected at perigee but I've never disputed that. Another way of stating that is this plot will not demonstrate whether the OFLS has timed the belts correctly; once you provide me with the above file, I can answer that question within minutes. However, Martin asked "at what altitude are we moving ACIS to the safe position?" and this plot can answer that nicely with a ruler and pencil! My presentation does not easily show that but clearly by joining sim translation times with the Chandra orbit, you can determine the altitude. For instance, let's answer Martin's question for perigee crossing just after Day 265. According to my list above, we translated prior to belt entry and proceeding belt entry at: 1999:265:04:31:17.000 SIM Translation POS=-99616 (HRC-S) 1999:265:21:56:31.000 SIM Translation POS=92905 (ACIS-I) Well, at 1999:265:04:31, Chandra had an altitude of approximately 8.1e4 km. Similarly, at 1999:265:21:56:31, Chandra had an altitude of approximately 9.2e4 km. Repeating this procedure for a couple of passages shows there is a lot of variability in the entrance altitude and exit altitude. At any rate, if you could add "get RADZONE_ENTRY/RAD_ZONE_EXIT times" to your action item from today's meeting, we can at least resolve the question of whether we have a problem with OFLS or not. Cheers, Shanil ------------------------------------------------------------------------ Shanil N. Virani svirani@head-cfa.harvard.edu Chandra X-ray Observatory Center Harvard-Smithsonian Center for Astrophysics http://hea-www.harvard.edu/~svirani 60 Garden Street, MS-70 FAX: 617-495-7356 Cambridge, MA 02138 USA PHONE: 617-496-7855 "It is not in the stars to hold our destiny but in ourselves." -- William Shakespeare ------------------------------------------------------------------------