SATELLITES TRACKING
ADAPTATION OF A TAKAHASHI EM400

 

Any use of one of these images other than strictly private must be subject to prior authorization

In mid-2009 Thierry Legault contacted me to adapt his Takahashi EM400 for motorized satellite tracking (ISS, space shuttle etc.), in order to take complete video sequences of nighttime passages. The works have been carried out in two steps:
- Step 1 : visual tracking with a finder and control with wireless joysticks
- Step 2 : computerized autoguiding through Videos Sky (homemade)

Below, the EM-400 mount modified for step 1. A digital control box (hooked on the left leg of the tripod) controls the mount up to 2/s while receiving the orders from the radio double joystick (one for right ascension, the other for declination). When this box is not connected or is off, the mount behaves as a standard EM-400. Tracking is performed visually with the help of a finder with cross-hair reticle. Design and manufacturing of this electronic modification (more tricky than expected) are handmade, from drawings to electronic design and manufacturing (PCB, soldering etc.) to mechanical modification. The acquisition of the images on the Meade Schmidt-Cassegrain 10" is performed by a  Lumenera Skynyx L2-2 video camera.

 

This image of the space shuttle Discovery (orbiter) has been taken from Northern France on April 20th 2010 at 5:37UT, a few hours before its landing in Florida at the end of the STS-131 mission. What we see is the top of the orbiter with the payload bay door opened, and the sunlight comes from back left. Altitude 332 km (206 miles), distance to observer 343 km (213 miles), speed 7.6 km/s (4.7 miles/s), apparent speed at zenith 1.3/s. The length of the orbiter at zenith represents 22 arcsec. With respect to this image, the orbiter flies from left to right, in order to slow down with its main engines before entering the atmosphere (after turnaround in the normal orientation, of course!).

Numerous details are recognizable: the elevons, the  NASA  logo on the left wing (angular diameter: 1.2 arcsec), the orbital maneuvering systems, the payload bay door opened (in four segments), the articulated arm (Canadarm/SRMS), the MPLM module (inside the bay), the airlock, the cockpit windows.

 

 

Despite this performing tracking system and hours of training of Thierry on airplanes passing in the sky, keeping the space ship inside a sensor of a few millimeters at a focal length of 5000 mm and a speed over 1/s needs a lot of concentration and training. Since October 2010, the mount is autoguided, with the help of a DMK 31AF03 Firewire video camera mounted on the finder (FL 200 mm) and of the software Videos Sky made by myself and modified with the help of Thierry for fast tracking with the EM400. Autoguiding and acquisition are carried out by a HP Pavilion dv8 laptop with double hard drive (one of which is a SSD - Solid State Drive - made with flash memory), the precision of tracking being about one arc minute.

Below, a real time video sequence of the capture of the ISS by the autoguiding system (15 images/s), at a speed of 1/s (images reduced by 50%). The field of the DMK is about 1 and the small rectangle in the center represents the field of the main acquisition camera. Initially, the mount is still, it is positioned slightly ahead of the trajectory of the ISS with the help of a second finder and it is waiting for the entry of the ISS on the autoguider sensor.

The whole modification of the EM400 and the results are described on my Forum at these addresses and also on Thierry's site ( http://www.astrophoto.fr ) :

Below, a real time video sequence of the capture of the ISS by the autoguiding system (15 images/s), at a speed of 1/s (images reduced by 50%). The field of the DMK is about 1 and the small rectangle in the center represents the field of the main acquisition camera. Initially, the mount is still, it is positioned slightly ahead of the trajectory of the ISS with the help of a second finder and it is waiting for the entry of the ISS on the autoguider sensor.

Below, the real time video sequence of the same passage of the ISS, by bad seeing (the fading at the end of the sequence is caused by the entry of the ISS in the shadow of the Earth). The raw images have been registered.

Below, the same sequence accelerated 3 times, processed with stacking of images by group of 10, sharpening by wavelets and adjustment of low levels.

 

The videos in DivX format::
http://www.emmanuel-rietsch.fr/ManuAstro/ERCS_Electronique/IssSuivi/capture.avi
http://www.emmanuel-rietsch.fr/ManuAstro/ERCS_Electronique/IssSuivi/iss_101030_b_10i.avi
http://www.emmanuel-rietsch.fr/ManuAstro/ERCS_Electronique/IssSuivi/iss_101030.avi

Below, a screen copy of Videos Sky with the EM400 satellite tracking parameters:

 

Thierry has also modified his Meade optical tube to add in the rear cell:
- a very firm primary mirror blocking system, composed of 3 groups of push/pull screws going through the cell
- four 12V fans for faster thermal equilibrium

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(C) Emmanuel Rietsch 2014.