The following discussion is taken from the User's Manual for JMAN, a program for determining viewing opportunities for the JET-X instrument (M. Ricketts, Rutherford Appleton Laboratory, JET-X(93)RAL-150.1). Since the Jet-X and SODART telescopes are co-aligned, it is generally applicable to the SODART instruments as well.
The orientation of the Spectrum-X-Gamma platform is constrained by
several factors. If one defines the telescope pointing direction as
the X axis and the solar panel pointing direction as the -Z axis
, then the sun must be within
10
of the XZ plane and within 40
of the YZ
plane. Further, the two star sensors, which can only use stars
brighter than about magnitude 1.0, view in planes 20
from XY
plane towards -Z, and between 70
and 140
from the
X axis. These constraints are illustrated in
Figure 3.
When the OXS instrument is operating, The X-axis is constrained to
view along an arc 90
from the OXS target and between
50
and 130
from the Sun. The precise location of
the arc depends on the Sun position, as is shown in
Figure 4. In ecliptic coordinates the Sun is in
the horizontal plane, and the OXS can view a point at ecliptic
latitude lat. when the sun is between S1 and S2, and again 6 months
later.
As the Sun direction changes from S1 to S2, the arc the telescope can
view changes ; the total accessible arc is approximately 80+ 20 Sin(lat). The OXS can view the ecliptic pole at any time, and the
telescope can view any point in the ecliptic plane if the date is
chosen appropriately.
The above is, of course, subject to a star being available for the star sensor in a suitable position.