Visual
SAT-Flare Tracker 3D
1.0 SATELLITE SURFACE MODELLING - WINDOW
This window allows
the user to model the satellite's surfaces by means of specifically
oriented mirrors. The windows is composed by
several frames and a set
of Design Draw Options (at the right side) as shown in the following picture:

Fig. 1
The window contains the following frames:
- Working Satellite
- Satellite Orientation
- Satellite Surfaces
- Surfacce Parameters
- Mirror Trimming
- Selected Satellite Actions
1.1 WORKING SATELLITE - Frame
This
frame reports the working satellite, which is the satellite whose
surfaces are being modelled. The working satellite can be selected by
means of the Satellite window, which can be opened also by means of the Select Satellites button at the bottom centre of the window.
1.2 SATELLITE ORIENTATION - Frame
Operative
satellites usually employ attitude control systems to keep themselves
correctly oriented, depending on their duty. As an example, the IRIDIUM
satellites are kept oriented with the Z axis vertically (along the Earth
centre) and with the X axis along the orbit direction. However, other
orientations may be more convenient for other kind of satellites. Old
orbiting satellites or out-of-service satellities may be, however,
without any working attitude control and their orientation no more controlled.
In order to take advantage of the satellite
geometry to predict light reflections, it is necessary to know exactly
how the satellity is oriented. This program version supports the
following satellite orientations (which can be selected by means of this
frame):
- Vertical, Along Track
- Vertical, Along a Target
- V-Sun
- Rotating
- None
1.2.1 Vertical, Along Track - OrientationThis option keeps the satellite's Z axis along the Earth centre, and the X axis along the orbit (see note 1). Many LEO satellites uses this kind of orientation.1.2.2 Vertical, Along a Target - OrientationNot documented.
1.2.3 V-SUN - OrientationThis option keeps the satellite's Z axis along the Earth centre and the X axis toward the Sun (see note 1).
This kind of orientation may be useful to model mobile structures
that are oriented toward the Sun, such as the solar panels, rather than the
satellite's main body.
1.2.3 Rotating - OrientationThis
option allows the program to deal with satellites without attitude
controls and that are fast rotating around a fixed axis. Since the
satellite is fast rotating (rotation period in the
order of a few seconds or less), the knowledge of the rotation angle at
a given time is not really important for a visual observer, who can
though observe a whole rotation in just a few seconds. In this case,
the knowledge of the rotation axis is enough to compute the Earth
locations where
reflections are visible.
The direction of the rotation axis can be
entered manually or can be determined automatically if at least three
reflections have been observed coming from the same reflective surface. Please
see this section to know more details about the model of fast rotating satellites.
1.2.3 None - Orientation
This
option allows the program to deal with satellites without attitude
control that are not rotating considerably within the period of investigation. According
to this mode, the satellite orientation is kept fixed with respect
to the stars, and this means that the direction of its surfeces is
fixed as well. This allows the surface direction to be expressed
directly by means of the Right Ascension and Declination of the
celestial point toward which the surface normal is pointing.
Note 1.
Only the Z-axis is oriented along the assigned direction, while
the second axis is rotated close as much as possible to the second
target vector (in the right Z-X plane). Both the axes can not be oriented toward their
assigned directions if these ones are not perpendicular each other.
1.3 SATELLITE SURFACES - Frame
This
frame allows the user to manage all the defined surfaces and to add
new ones. The frame consists of a main list, where all the existing
surfaces are listed, and of the following buttons:
- Add Mirror: this button adds a new surface to the satellite model. The name of the surface can be assigned by means of the Mirror Name field in the Surface Parameters
frame. When a new surface is added to the model, the current program time is added to the surface data. The surface will
be shown in the list according to the following structure:
M#01 - 28/07/2009 19h27'36" - UM1
Where
M#01 is the number of the defined surface, 28/07/2009 19h27'36" is the
time of the observed flare (program time at the surface creation)
and UM1 is the surface name (which will be shown when flares are
plotted).
Note: The time can be
missing for surfaces that are automatically added when satellites are
loaded (i.e. for the Iridium satellites).
- UP: when
fast rotating satellites are being modelled, the surface order is important to
compute the rotation axis, therefore, it may be necessary to have the
possibility to change the surface order. For this reasons, the UP key
has been defined to move the selected surface at the list top. To
select a surface, simply click on its entry in the list.
- Delete Mirror: this button allows the selected surface to be deleted. To select a surface, simply click on its entry in the list.
- Update Time: when a surface is added by means of the Add Mirror
button, the current program time is added to the structure in order
to keep trace of the time at which the surface has been observed
flaring. This time can be changed by specifying a new one with the general time control and by clicking on this Update Time key.
Note:
when the surface time is defined, by cliking on the surface entry in
the list, the current program time will be automatically set to the
surface time, in order to quickly move back to the flaring event.
1.4 SURFACE PARAMETERS - Frame
This
frame contains the data fields necessary to set the surface parameters of the selected surface. These fields are: - Mirror ID: this
field is automatically defined by the system and it can not be directly
edited. The field is used to identify the satellite mirror: the
satellite NORAD number and the mirror name are composed to obtain the
identifier.
- Mirror Name: this field can be used to assign a name to the selected surface.
- Angle / RA: this field can be used to enter either the angle or the Right Ascension of the surface normal. Please see the Surface Orientation section to know how the surface normal direction is specified.
- Tilt / DEC: this field can be used to enter either the tilt or the Declination of the surface normal. Please see the Surface Orientation (section 1.4.1) to know how the surface normal direction is specified.
- Scattering Factor: this
field can be used to define how much the satellite surface will spread
the reflected ray. An ideal mirror has a scattering factor equal to 1.
More the scattering factor is high more the reflected ray can be
observed far from the Earth location where the ray centre impacts. In
the current version, this parameter is used only to plot the ray cone
size on the Earth surface, but it is planned to be used in further
releases for the magnitude estimation as well.
- Rotation Axis DEC: this
field can be used to define the Declination of the satellite's rotation
axis. This field is automatically defined when the satellite axis is
automatically computed.
- Rotation Axis RA: this
field can be used to define the Right Ascension of the satellite's
rotation axis. This field is automatically defined when the
satellite axis is automatically computed.
1.4.1 Surface Orientation
The
orientation of a satellite's surface is specified by giving the
direction of its normal vector. Such normal can be defined by
means of two different coordinate systems, depending on the satellite
orientation mode:
- For satellites that use one of the controlled orientations (Vertical Along Track, Vertical Along a Target, V-Sun) the normal vector is given by means of the Angle and Tilt
angles. These parameters indicate the direction of the normal
vector with respect to the satellite X-Y-Z coordinate system: the Tilt
angle is measured with respect its X-Y plane with positive angles when
the normal vector tilts toward the Z direction (toward the Earth),
while the Angle indicates how
much the normal vector is rotated around the Z axis. As an example, according
to this system, the Right Main Mission Antenna of the Iridium
satellites has a Tilt of -40 degrees and an Angle of -120 degrees.
- For satellites that use one of the uncontrolled orientations (None, Rotating) the normal vector is directly given with respect to the ECI coordinate frame by specifying both the Right Ascension (RA) and the Declination (DEC) of the celestial point toward which the normal vector is pointing.
1.5 MIRROR TRIMMING - Frame
This
frame contains three sliders that can be used to graphically adjust the
surface angles. As soon as one of these slider is moved, the new
configuration is employed to update the graphical Main Window. The
first two sliders can be used to adjust respectively the Angle / RA angle and the Titl / DEC
angle. The third slider, instead, can be used with fast rotating
satellites to see where the reflected ray impacts the Earth surface by
rotating the satellite around its rotation axis by a given angle. To
make this slider active, it is necessary to check the Sel option at its top.
1.6 SELECTED SATELLITE ACTIONS - Frame This
frame contains a few functions that will be performed only on the selected satellites. Please see the Satellite Window to learn how to select satellites. These functions are:
- Clear All Mirrors: the surface model will be deleted for all the selected satellites.
- Update this Mirror ID to all Sats: the selected surface will be imported by all the selected satellites that posses the same Mirror ID.
- Copy the whole Model to all Sats: the whole model of the working satellite will be imported by all the selected satellites.
1.7 DESIGN DRAW OPTIONS - Column This
column contains some additional options that can be useful to support the modelling of fast rotating satellites:
- Source Ray: checking this option, the Sun-Satellite ray will be plotted.
- Rotation Axis: checking this option, the satellite's rotation axis will be shown.
- Mirror Normal: checking
this option, the mirror normal of the rotating surfaces will be plotted
under different satellite rotation angles. If the Sel option of the third slider, in the Mirror Trimming frame, is selected, only the specified angle will be employed.
- Force Light: checking
this option, a transparent Earth model will be employed in order to
permit the surface modelling also when the satellite is in earth shadow.
1.8 BUTTONS
The window contain the following buttons:
- Auto Orient Mirror to Flare: by
clicking on this button, the current surface will be automatically
oriented in order to make it flaring on the observer location. This
action will be always performed since the Earth is supposed transparent.
- Auto Orient Beam to Hit: Preliminary - Not documented.
- Compute Rotation Axis: if at least three surfaces have been defined, by clicking on this button, the satellite rotation axis is computed. Please
see this section to know more details about the model of fast rotating satellites.
- OK: the window will be closed and the current surface model acquired.
- Apply: the current model will be acquired and the graphic updated accordingly.
- Select Satellites: the button opens the Satellite Window for the selection of satellites.
- Cancel: the window will be closed and all the changes on the surface model will be discharged.
- Export Model: the whole
surface model will be exported into a text based window. This allows
the model to be shared with other observers. Further releases will include also the model import function. An example of exported
model follows:
SATELLITE SURFACE MODEL
---------------------------------------------------
SAT ID #24840 (97030E) IRIDIUM 13 [+]
ORIENTATION TYPE #0: Vertical, Along Track
ROTAX-DEC: 0
ROTAX-RA: 0
NUMBER OF SURFACES: 3
M#01 - F >>> 0;40;5
M#02 - L >>> 120;40;5
M#03 - R >>> -120;40;5
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By
Simone Corbellini
