Lacrosse

 

Flares Flares 2 Disappearences L4 Oscillations 

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. 

In this video a flare is seen at 17:24:11 and is predicted for 17:24:13 if the panels are as detailed. 

Pass number 1
Orbit Number 72.2285195286303
Rise at (all times local) 29/01/2011 17:21:04
Rise Alt 9.99103247570373
Rise Az 294.564929732024
Max Alt 85.2891222092069
Max Alt at 29/01/2011 17:25:48
Min range km 660.948764112607
Sun Altitude -6.16303168499917
Sun Azimuth 248.12789426801
Set Time 29/01/2011 17:30:32
Set Alt 9.98919050556608
Set Az 119.391183524469
Sun 00:00:00
Flare 29/01/2011 17:24:13 flight mode YVV panel angle -42.3

 

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

   
   
 

 

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