# How to get a column vector for all the considered time instants?

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Loren99 on 11 Oct 2021
Commented: Walter Roberson on 12 Oct 2021
Hi everyone. I have a problem with this code. At the end I would like to obtain the r_ORF column vector for all the time instants (41) but I don't understand why this does not happen in this code. Thanks in advance.
clc;clear all; close all;
% Components determination in ORF
% ECI (GEOC) to ORF matrix determination
times = A(:,1);
for i = 1: length(times)
r_inertial(1,i)= A(i,8);
r_inertial(2,i)= A(i,9);
r_inertial(3,i)= A(i,10);
v_inertial(1,i)= A(i,11);
v_inertial(2,i)= A(i,12);
v_inertial(3,i)= A(i,13);
kORF_ECI=-r_inertial/norm(r_inertial);
jORF_ECI=-cross(r_inertial,v_inertial)/norm(cross(r_inertial,v_inertial));
iORF_ECI=cross(jORF_ECI,kORF_ECI);
M_ECItoORF(1,1)=iORF_ECI(1,1);
M_ECItoORF(1,2)=iORF_ECI(2,1);
M_ECItoORF(1,3)=iORF_ECI(3,1);
M_ECItoORF(2,1)=jORF_ECI(1,1);
M_ECItoORF(2,2)=jORF_ECI(2,1);
M_ECItoORF(2,3)=jORF_ECI(3,1);
M_ECItoORF(3,1)=kORF_ECI(1,1);
M_ECItoORF(3,2)=kORF_ECI(2,1);
M_ECItoORF(3,3)=kORF_ECI(3,1);
r_ECI = r_inertial;
r_ORF = M_ECItoORF*r_ECI;
display(r_ORF)
end

Walter Roberson on 11 Oct 2021
% Components determination in ORF
% ECI (GEOC) to ORF matrix determination
times = A(:,1);
num_times = size(times,1);
r_ORDF = cell(num_times,1);
for i = 1: num_times
r_inertial(1,i)= A(i,8);
r_inertial(2,i)= A(i,9);
r_inertial(3,i)= A(i,10);
v_inertial(1,i)= A(i,11);
v_inertial(2,i)= A(i,12);
v_inertial(3,i)= A(i,13);
kORF_ECI=-r_inertial/norm(r_inertial);
jORF_ECI=-cross(r_inertial,v_inertial)/norm(cross(r_inertial,v_inertial));
iORF_ECI=cross(jORF_ECI,kORF_ECI);
M_ECItoORF(1,1)=iORF_ECI(1,1);
M_ECItoORF(1,2)=iORF_ECI(2,1);
M_ECItoORF(1,3)=iORF_ECI(3,1);
M_ECItoORF(2,1)=jORF_ECI(1,1);
M_ECItoORF(2,2)=jORF_ECI(2,1);
M_ECItoORF(2,3)=jORF_ECI(3,1);
M_ECItoORF(3,1)=kORF_ECI(1,1);
M_ECItoORF(3,2)=kORF_ECI(2,1);
M_ECItoORF(3,3)=kORF_ECI(3,1);
r_ECI = r_inertial;
r_ORF{i} = M_ECItoORF*r_ECI;
end
I think you should reconsider your code a bit.
The first iteration, you write to the first column of r_inertial, so r_intertial is 3 x 1. M_ECItoORF is 3 x 3. In the calculation of r_ORF you use the * operator between the 3 x 3 M_ECItoORF and the 3 x 1 R_ECI to get a 3 x 1 result the first iteration.
The second iteration, you write to the second column of r_interial, so r_inertial is 3 x 2. And for kORF_ECI and jORF_ECI you use that entire 3 x 2 r_intertial . Are you certain that you want to be using the cumulative r_intertial in the calculation, not just the "current" column of r_intertial ?
Then you get down to the r_ORF, M_ECI is still 3 x 3, r_ECI is now 3 x 2 because it is is the 3 x 2 r_inertial, so r_ORF becomes 3 x 2, not 3 x 1.
And so on, until you get to the end, and the last r_ORF is 3 x number_of_times .
Does this make sense to do ???
Walter Roberson on 12 Oct 2021
% Components determination in ORF
% ECI (GEOC) to ORF matrix determination
times = A(:,1);
num_times = size(times,1);
r_ORDF = zeros(3, num_times);
for i = 1: num_times
r_inertial(1,1)= A(i,8);
r_inertial(2,1)= A(i,9);
r_inertial(3,1)= A(i,10);
v_inertial(1,1)= A(i,11);
v_inertial(2,1)= A(i,12);
v_inertial(3,1)= A(i,13);
kORF_ECI=-r_inertial/norm(r_inertial);
jORF_ECI=-cross(r_inertial,v_inertial)/norm(cross(r_inertial,v_inertial));
iORF_ECI=cross(jORF_ECI,kORF_ECI);
M_ECItoORF(1,1)=iORF_ECI(1,1);
M_ECItoORF(1,2)=iORF_ECI(2,1);
M_ECItoORF(1,3)=iORF_ECI(3,1);
M_ECItoORF(2,1)=jORF_ECI(1,1);
M_ECItoORF(2,2)=jORF_ECI(2,1);
M_ECItoORF(2,3)=jORF_ECI(3,1);
M_ECItoORF(3,1)=kORF_ECI(1,1);
M_ECItoORF(3,2)=kORF_ECI(2,1);
M_ECItoORF(3,3)=kORF_ECI(3,1);
r_ECI = r_inertial;
r_ORF(:,i) = M_ECItoORF*r_ECI;
end
I believe that should give you a 3 x (number of times) array

R2021b

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