The Lacrosse satellites are interesting in that they are just big enough to
be resolved and a number of people have observed flares and strange disappearance
events of them.
The main aim of these observations is to
determine the size and shape of the satellites. My latest theory is that
the satellites have a basic central body with an Earth facing radar panel
angled at 25° to the ground and a Sun facing solar panel. The solar panel rotates
around the y-axis to
maximise power output. This model is illustrated by the screen shot from the VRML simulator at left.
For each of my observations I have used a slightly modified version of
the ISS simulator to compare this model with the image. In general the
model does pretty well.
The major panel orientation is matched by either XVV or YVV flight
mode although there is no obvious rule. The only exception is a poor
match for L3 on 29/04/05
Brightness and panel width tie up fairly well with panel
illumination
Lacrosse 2 NORAD 21147
Circular orbit at 645km and inclination 68°, launched 08/03/91
This is a single frame capture from the JVC camera at x10 zoom and 1/50
second exposure with an 18mm orthoscopic on the LX200 at f6.3. It
measures 36 pixels which suggests a size of 35m at 860km.
The small extension to the north-west of the satellite was not clearly
seen on any other image, however this frame is exceptionally sharp and it
seems unlikely that it is an artifact.
Later in the pass the whole satellite appeared brown/orange as the
south-east part does here. Also the satellite appeared smaller even though
it was closer. I can only assume part of it had gone into shadow.
A ten frame stack from Registax. The colours
resemble Envisat in which case the white is solar panel and the orange the
main body of the satellite. I have increased the colour saturation in the
left hand image
In the simulation the flight mode is XVV. Neither panel is
well lit and so the image appear to come from the cylindrical ends of the
satellite.
Simulation YVV
Lacrosse 3 NORAD 25017
Circular orbit at 657km and inclination 57°, launched 24/10/97
In the
picture the panels measure about 40 pixels which represents 32m at the
683km range. The simulation result was poor in that the panel angles were
pretty inaccurate. A match was obtained if the simulated time is 30 seconds later in XVV
mode.
Simulation YVV
Again a good match neither panel is lit and only the central body is
seen as for L2 on 08/10/04
Simulation YVV
Another image with the satellite apparently in XVV mode. However the
simulator did not match the observed panel angles until 19:33:40. The image
hints at a colour difference between the solar panel and the radar panel. On
the camcorder the radar looked distinctly blue to me and the solar panel maybe
orange. The capture process struggles to show this effect though. Captured
at 640x480.
Part of a low resolution capture from the video
camera during tracking. Based on a panel angle of 44° and YVV flight mode
the flare mis-angle was 1.1° at 20:43:47 when the satellites altitude was
63.5°. The animation appears to show the flare spreading from the panel at
the bottom to the top. So maybe there are 2 radar panels because the second
flare would certainly not come off a correctly aligned solar
panel
Lacrosse 4 NORAD 26473
Circular orbit at 680km and inclination 68°, launched 17/08/00
The image at left is clearly NOT resolved but it represents a flare of the
satellite. I back calculated the panel angle that would have caused a flare
at this time and put it in the simulator. The resulting panel is at 90° to
the main satellite body and at 25.4° to the Earth's surface. This is
encouraging because radar radar panels are often tilted at around 25°. Follow
the link at the top of this page for more on flares.
Lacrosse 5 NORAD 28646
Circular orbit at 715km and inclination 57°, launched 01/05/05
Left Lacrosse 5 at 22:07:55GMT on
01/05/05 when it had been in orbit
less than 2 days. I assume the range of 564km is as a result of the orbit
having not been finalized at this stage. The remains of its Titan
launch vehicle passed through the 2 degree finder field about 30 seconds
or less before the satellite itself. None of the images on the tape
were very good but there is a hint of a shape similar to that of Lacrosse
3 above. Simulation YVV
Lacrosse 5 only 5 seconds after closest approach
which was at an altitude of 82°. Simulation YVV
Two raw frames grabbed at 640x480
from the JVC CamCorder. Range 879km and 917km. Seemingly a good
result:
At the later time the image shows both ends of the satellite are
brighter as predicted by the VRML
The biggest difference is for the Solar panel which appears to be
correct
