SPACECRAFT POINTING MODE AND DESCRIPTIONS

This document describes the values for the SPACECRAFT_POINTING_MODE keyword.

First, the definition of the SPACECRAFT_POINTING_MODE keyword is:
"The spacecraft_pointing_mode element provides the pointing mode of the
spacecraft.  The definition of the modes and the standard values are given
via the SPACECRAFT_POINTING_MODE_DESC element, which shall always accompany
this keyword."

Reference: VEX-ESF-IF-5005, Issue 2.2, 2005-05-20

1) Nadir Pointing

SPACECRAFT_POINTING_MODE="NADIR"
SPACECRAFT_POINTING_MODE_DESC="This pointing mode is used for science
observations normally around pericentre. The Z axis of the sc points towards
the Venus centre. The X axis of the s/c is perpendicular to the ground track."

2) Earth Pointing

[ Not present in MEX label. Do we need to create a
SPACECRAFT_POINTING_MODE="EARTH"
Apparently concerned : Radio Science]

SPACECRAFT_POINTING_MODE="EARTH"
SPACECRAFT_POINTING_MODE_DESC="HGA boresight axis pointing to the Earth
(either HGA 1 or 2),
 - Y axis of the S/C (SA axis), is either closest to the ecliptic plane
normal or perpendicular to the plane defined by the earth and sun directions.
 - In addition, in case of the Y axis ecliptic option, the direction of the Y
axis (north/south), can be selected."

3) Inertial Pointing

SPACECRAFT_POINTING_MODE="INERT"
SPACECRAFT_POINTING_MODE_DESC="Inertial attitude is used to point a payload
towards a fix direction. The direction is given in right ascension and
declination. The rotational degree of freedom around this direction can be
used to optimise power/thermal conditions."

4) Off Nadir
    a) Along track

SPACECRAFT_POINTING_MODE="ALONGTRACK"
SPACECRAFT_POINTING_MODE_DESC="the ALONGTRACK pointing mode is a derivative
of the NADIR pointing mode. It is computed by applying a rotation around the
s/c X axis. The rotational angle shall be computed such that the projection
of the s/c Z axis onto the Venus surface is separated by a constant
predefined angle from the sub-satellite point as seen from the Venus centre.
The angle is measured in degrees and shall be specified in the data product
label."

    b) Across track

SPACECRAFT_POINTING_MODE="ACROSSTRACK"
SPACECRAFT_POINTING_MODE_DESC="the ACROSSTRACK pointing mode is a derivative
of the NADIR pointing mode. It is computed by applying a rotation around the
s/c Y axis. The rotational angle shall be computed such that the projection
of the s/c Z axis onto the Venus surface is separated by a constant
predefined angle from the sub-satellite point as seen from the Venus centre.
The angle is measured in degrees and shall be specified in the data product
label."

7) Nadir with yaw steering

SPACECRAFT_POINTING_MODE="NADIR_POW"
SPACECRAFT_POINTING_MODE_DESC="The LoS axis is pointing towards the Venus
centre. The Y axis is perpendicular to the Sun. The LoS is either the Z axis
or the HGA axis. The position of X axis is selected such that no sun
illumination of the -X face occurs."

8) User custom attitude profile

SPACECRAFT_POINTING_MODE="CUSTOM"
SPACECRAFT_POINTING_MODE=" The SPEC mode pointing is a user custom pointing.
It aimed at the implementation of user specific pointing requirements which
cannot be accommodated via a specific interface."

9) Mosaic

SPACECRAFT_POINTING_MODE="MOSAIC"
SPACECRAFT_POINTING_MODE_DESC="The aim of mosaic pointing is to cover the
full Venus disc from apocenter by performing a raster motion.
For each of the raster points the attitude is computed based on the nadir
pointing with yaw steering for power optimisation and applying one rotation
along the S/C Y axis and one rotation along the S/C X axis (in this order). "