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Дата изменения: Tue Aug 16 05:51:10 2005
Дата индексирования: Tue Oct 2 03:24:57 2012
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XMM-Newton Science Analysis System Page: 1
newsiam
August 16, 2005
Abstract
Generate new SIAM from the current SIAM and a set of oset pointing angles
1 Instruments/Modes
Not applicable
2 Use
Not applicable.
3 Description
The SIAM is used to point the satellite such that a nominal on-axis source position is imaged onto a
specic point on the detectors. Due to the development of bad pixels in the imaging instruments, it
will likely be necessary in future to slightly modify this prime pointing. The purpose of this task is to
calculate new SIAM elements from existing SIAM and requested angular rotations about the space-craft
axis.
New angles for the SIAM are calculated from shifts of the pointing of the instrument given in parameter
Instrument relative to the pointing obtained by using the SIAM that is specied by parameter siamset.
The star-tracker attitude is calculated for a given bore-sight of the chosen instrument of Ra=0, Dec=0,
APos=0 (similar to strbs/ccftools). Using this, the positions of 5 test sources in the FOV of the instru-
ment are calculated. The test sources have celestial positions of
Source Number Ra (arcmin) Dec (arcmin)
1 0 0
2 15 0
3 15 0
4 0 15
5 0 15
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This establishes the position of a set of sources in the FOV of the instrument (similar to srcinfov/ccftools).
The FOV angles for these test sources are shifted by the intended osets (parameters ry and rz). These
values are used as further reference.
The angles of the SIAM are iteratively modied and the calculations of strbs and srcinfov are repeated,
until the spatial distances of these newly calculated FOV angles to those of the reference FOV angles is
minimal.
Test sources close to the limit of the FOV are necessary to also constrain the rotation of the third
angle of the SIAM (rotation around X). Obviously some redundant is included at marginal extra cost on
computing time.
The output can directly pasted into the SIAM.
4 Parameters
This section documents the parameters recognized by this task (if any).
Parameter Mand Type Default Constraints
siamset yes string /data/cerd/CCF/ccfdev/packages/xmm-
siam/XMM BORESIGHT for siam.matrix0005.CCF
DataSet containing the SIAM angles in BoreSight CCF format. (see comments)
ry yes oat 0 3600{3600
shift of source in the FOV of the instrument corresponding to a rotation of the space-craft around the
Y-axis in arcsec
rz yes oat 0 3600{3600
shift of source in the FOV of the instrument corresponding to a rotation of the space-craft around the
Z-axis in arcsec
5 Errors
This section documents warnings and errors generated by this task (if any). Note that warnings and
errors can also be generated in the SAS infrastructure libraries, in which case they would not be docu-
mented here. Refer to the index of all errors and warnings available in the HTML version of the SAS
documentation.
InstrNotFound (error)
The SIAM-set does not contain a set of angles for the given instrument. Probably this
SIAM-set is incomplete.
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6 Input Files
1. SIAM matrix, but formatted as a BoreSight constituent.
7 Output Files
None
8 Algorithm
read input parameters
find angles of the SIAM corresponding to current instrument
STATT:
calculate pointing of the star-tracker for ref attitude
SRCinFOV:
calculate FOV positions of 5 test sources
intended FOV positions:
add offsets (ry,rz) to FOV positions of 5 test sources
minimize distance of "intended FOV positions" from SRCinFOV positions
by of iteration SIAM angles and re-calculating STATT and SRCinFOV.
print resulting angles
9 Comments
Example: The SIAM should be changed such that the RGS angle of incidence onto the
gratings is increased by 10 arcsec. Due to the focusing of the XRT, thus amounts to an
o-axis angle of
L
F
=
67
75 10 = 8:9333
The dispersion of the RGS is along the Z-axis, and the gratings are arranged such that an
increase of is achieved by a rotation of the spacecraft around the Y-axis in positive sense.
Hence the task is called with
newsiam ry=8.9333
occasionally the minimization fails at the SLATEC level (SLATEC error from DNLS1E). This
cannot be circumvented, but slightly dierent values of one of the input parameters remedy
this.
9.1 Procedure for Generating a new SIAM
This is the procedure to be used:
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1. execute newsiam to obtain the rotation angles
2. store these angles into the CCF package xmm-siam, le siam.dat
3. make creates the SIAM CCF, that has to be sent to VILSPA
4. in siam.desc you need to change the type from siam to boresight
5. in siam.dct change the name of the table from SIAM to BORESIGHT
6. execute make, which generates a CCF with the structure of a BORESIGHT le
7. execute ccfextseq/ccftools --sets=boresightfile, where boresightfile is the name of
the le you just generated in the previous step
8. execute siamgen --ccffiles=boresightfile > siam.matrixnnnn; this is the SIAM ma-
trix that needs to be sent to ight-dynamics
References
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