1. The problem statement, all variables and given/known data Hi! I just found this forum after trying to calculate something regarding a satellite's orbit. Hope that you can help me here. So, I need to calculate the matrix of a satellite's site vectors. I have found it in the ECEF form, but since the satellite is doing observations in different times, I need it in ECI for this particular problem. 2. Relevant equations See below. 3. The attempt at a solution I searched and for the ECEF position, we have the following equations to use: (see the attached file) I have, from my values and by using these equation, the site position in ECEF: r = [-7166.056 -6364.272 -3210.412 -1309.400 -186.778 824.20 669.27 -3545.190 -6467.48 ] How do I get the ECI position now? I guess that I need to consider the rotation of the Earth and the time between the observations. Is a matrix multiplication necessary? Thanks in advance!