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Hubble Space Telescope
South Atlantic Anomaly (SAA)

Q.: I Need to complete a log of HST observations including the durations the telescope was in the south atlantic anomaly. I also need the SAA information for days 164-165.
A.: SAA 05 is the operation contour for NICMOS. There is another deeper contour inside this, but 05 is the one we key off of. In general, all but the first and last of the set of passages on a given day go into SAA 02 as well

For all users, the easiest way to get the SAA05 ENTRY and EXIT times is to use the SAA Crossing Calculator. The elapsed time since the most recent SAA exit (in seconds) can also be found in science image headers in the keyword SAA_TIME, which can be queried using the hedit or imheader tasks in IRAF. Also, the UT time of the most recent SAA exit is contained in the header keyword SAA_EXIT.

For internal STScI users, the SAA 05 entry and exit times can be obtained from the spacecraft calendars on the web at this address:

http://www.stsci.edu/reports/spss-status.html

These are the flight calendars showing more-or-less what the spacecraft will be doing. Look down the list and find the topmost "timeline" file which occurs *before* your observations. These calendars are built weekly and the daynumber in the bulleted list is the daynumber of the *start* of the calendar. Save the file to disk as text. In this case, you will have two files since the date ranges you specified fall on 2 calendars.

In these text files there is a line for each SAA05 ENTRY and EXIT. Use the following gawk script to extract the info:


BEGIN{print "CONTOUR  ENTRY (UT day)  EXIT (UT day)    TIMEIN (minutes)"}

{CONVFMT="%.9g"}

{OFMT="%.9g"}

/SI DOWN NIC       

SAAOPER/{tdown=substr($1,1,3)+substr($1,5,2)/24.+substr($1,8,2)/24./60.+substr($1,11,2)/24./3600.}

/SAA 05     \(ENTRY\)/{


{saaenter5=substr($1,1,3)+substr($1,5,2)/24.+substr($1,8,2)/24./60.+substr($1,11,2)/24./3600.}

}

/SAA 05     \(EXIT\)/{


{saaexit5=substr($1,1,3)+substr($1,5,2)/24.+substr($1,8,2)/24./60.+substr($1,11,2)/24./3600.}

{saain5=saaexit5-saaenter5}

{printf("%6s%15.9f%15.9f%15.3f\n","SAA05",saaenter5,saaexit5,saain5*24.*60.)}

}

(PS: gawk lines end with a "}". For clarity, there is a blank line between each individual line in the above script. gawk will ignore the whitespace.)

Then, execute the script as follows, assuming you saved a calender file as "98159.sms" and the script as "saascr" (UNIX only):

         gawk  -f  saascr  98159.sms

This will print all the SAA passages to the screen, with the daynumber (and fraction of a day) of entry and exit, and the total time the spacecraft was inside contour 5 in minutes (last column). You can redirect this output to a file if you like:

         gawk  -f  saascr  98159.sms  >  98159.saa

as an example, here is the output for your data for days 164-165:

      SAA05   163.066770833  163.078680556         17.150
      SAA05   163.139039352  163.145208333          8.883
      SAA05   163.582511574  163.597847222         22.083
      SAA05   163.650254630  163.669166667         27.233
      SAA05   163.719189815  163.739664352         29.483
      SAA05   163.789467593  163.809270833         28.517
      SAA05   163.860671296  163.878692130         25.950
      SAA05   163.932557870  163.948182870         22.500
      SAA05   164.004016204  164.017743056         19.767
      SAA05   164.075486111  164.086030093         15.183
      SAA05   164.526064815  164.534618056         12.317
      SAA05   164.589131944  164.606562500         25.100
      SAA05   164.657847222  164.677627315         28.483
      SAA05   164.726990741  164.747673611         29.783
      SAA05   164.797916667  164.817129630         27.667
      SAA05   164.869594907  164.886562500         24.433
      SAA05   164.941261574  164.956099537         21.367
      SAA05   165.012673611  165.025219907         18.067
      SAA05   165.084247685  165.092627315         12.067
      SAA05   165.529571759  165.543668981         20.300
      SAA05   165.596701389  165.615138889         26.550
      SAA05   165.665578704  165.685868056         29.217
      SAA05   165.735474537  165.755567130         28.933
      SAA05   165.806400463  165.824988426         26.767
      SAA05   165.878414352  165.894479167         23.133
      SAA05   165.949918981  165.964004630         20.283