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May 23rd, 2017, 01:41 AM  #1 
Newbie Joined: May 2017 From: Belgium Posts: 1 Thanks: 0  Spacecraft attitude estimation
Hi all, I'm studying aeronautical engineering and I'm making an error assessment of a star tracker (https://en.wikipedia.org/wiki/Star_tracker). I have made a simulation in matlab, this simulation generates a star image. This star image is used to estimate the attitude of the satellite after a pixel error has been added. Now I want to retrieve this added error from the attitude. I'm trying to do this with matlab by using the function fsolve. I need to create a cost function to use it in the fsolve function. This is were I'm stuck. Let me try to clarify this: 1 star image is generated 2 pixel error is added to these 2D star coordinates (error is a normal distribution) 3 these 2D star coordinates are transformed to 3D position vectors. 4 The 3D position vectors are used to calculate the estimated attitude. 5 trying to retrieve the added error from step 2, by using fsolve function in matlab. There are 2 star trackers, this means that their are 2 images generated and 2 attitudes are determined with the same error added. My plan to retrieve the error from the attitude: 1 find relative error between star trackers (done)(attitude quaternion 1 * attitude quaternion 2) 2 find the mean relative error (done) 3 find the standard deviation of the relative error (done) (this has to be used in step 4). 4 iterative approach (fsolve) a choose standard deviation for startracker (guess) b create Star tracker attitude c calculate Star tracker relative error d compare with step 3. and iterate. Step 4 is were i'm having trouble and I would like some help in creating this step and cost function. If you need extra information, please let me know. Kind regards, Sam Last edited by skipjack; May 23rd, 2017 at 10:57 AM. 
May 25th, 2017, 03:54 AM  #2  
Senior Member Joined: Feb 2016 From: Australia Posts: 1,518 Thanks: 506 Math Focus: Yet to find out.  Quote:
Likely you will need to use a couple of for loops to first populate your vectors, and then use those within your equation before working with fsolve, is this the tricky part? A snippet of code may be helpful .  

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attitude, estimation, spacecraft 
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