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ROSAT Status 116

 		ROSAT Status Report #116
			Feb 6 1995

=                                                                       =
=              ROSAT NEWS No. 35   ---      1-Feb-1995                  =
=                                                                       =
=                 ROSAT Scientific Data Center at the                   =
=       Max-Planck-Institut fuer Extraterrestrische Physik (MPE)        =
=               Postfach 1603, D-85740 Garching, Germany                =
=  e-mail addresses (Uli Zimmermann):                                   =
=   rosat_svc@mpe-garching.mpg.de (Internet) or  MPE::ROSAT_SVC (SPAN)  =
=  ROSAT Service Area (including ROSAT Data Archive):                   =
=   ftp rosat_svc.mpe-garching.mpg.de      user: anonymous              =
=   WWW address:  http://rosat_svc.mpe-garching.mpg.de/                 =
=   interactive account (including ROSAT Result Archive):               =
=     telnet xray.mpe-garching.mpg.de  user: xray  no password          =
=   WFC Archive access via telnet/ftp ait.physik.uni-tuebingen.de       =
=                                user: xuv  (password: xuv_archive)     =

An imperfection in the mission planning procedure was identified which 
led to the scheduling of 'impossible' observing slots implying a loss 
on the order of 5 % of the total and 13 % of the time critical observing 
time. This imperfection is related to the constrained mobility of the 
satellite which requires sun sensor information for any slew or target 
acquisition procedure. While in general the mission planning accounts 
for this constraint, and does not foresee any target changes on the 
night side of the satellite orbit, there is still one particular case 
in which 'impossible' observing slots were scheduled. This case can be 
characterized as follows:

1) a target was previously acquired on the day side;
2) it then underwent a temporary earth block after which its observation 
   was to be continued (with no target changes inbetween);
3) the earth block either ended after the night began or so shortly 
   before the beginning of the night that no re-acquisition was possible 
   on the day side.

In such cases observing slots after the end of the earth block 
erroneously appeared in the mission timeline, but the targets could not be 
acquired, and the slots were not used. This situation affects time-
critical observations more strongly than non-time critical ones for which 
the optimized mission planning procedure is likely to avoid earth blocks 

In the forthcoming mission timeline for the second part of AO5 (beginning 
in April 1995) this special case will be treated properly, and we expect 
an overall increase in observing efficiency. However, we stress that 
these 'impossible' slots are a result of the degraded attitude control 
system and will remain unavailable. This is especially important for 
time-critical observations which have become more difficult to carry out. 
If in the future you will find other observations scheduled at the 
time-critical period you asked for in your proposal, it will be because 
there were 'impossible' slots for your target which were used otherwise.

Release 95JAN of the EXSAS software has been tested within the MIDAS 
94NOV environment for the UNIX systems on AXP (OSF), HP, IBM, SUN, 
SUN Solaris, and DECstations (ULTRIX). The software may be copied from 
the ROSAT Service Area. Tests on the VMS and the LINUX systems are 

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