Help with using arrays to create variables

I'm trying to use arrays to create variables related to 32 different satellites (which I currently have fully written out it's awful making changes) orbiting a planet and am getting stuck quite early on. As a small example I'm trying to get working, I've got two angles for each satellite (being done in blocks of 8), th0(i) and th(i). The angle th0 works fine, however th relies upon th0 and a parameter, also an angle, called M, which relies on time. As I have 148 timesteps, M is a 148x1 array. When I input my code below, I get an error about the element numbers not matching up. I tried using the transverse of th and th0 but no joy. Can anyone suggest my next move?

%%Relevant parameters
timestep = 600;
G = 6.67408*10^-11;                  %[m^3kg^-1s^-2]
%   Mars data
    Mars.m  = 6.39*10^23;            %[kg]
    Mars.mu = Mars.m*G;              %[m^3s^-2]
    Mars.r  = 3389.5*10^3;           %[m]
    Mars.v  = 241.17;                %[ms^-1]
    Mars.T  = (2*pi*Mars.r)/Mars.v;  %[s]
    Mars.o  = Mars.v/Mars.r;         %[rads^-1]
    Mars.th = Mars.o*timestep;       %[rad] for every second
t = (0:timestep:Mars.T)';        %Mars.T, Length of martian day in seconds
H1 = 9610.5*10^3;               %[m]
a1 = Mars.r + H1;               %[m]
T1 = 2*pi*sqrt(a1^3/Mars.mu);   %[s]
n1 = (2*pi)/T1;                 %[kms^-1]
M1 = n1*t;                      %[rad]

%%Test Section
th0 = zeros(1,length(t));
th = zeros(1,length(t));

for i = 1:8
    th0(i) = deg2rad(45*(i-1));
    th(i) = th0(i) + 2*atan(tan(M1/2));
end

[Stephan]

G is missing

[Scott Hunter]

ah sorry I'll edit it in thank you

[Scott Hunter]

Update;

If I change the test section to

th0 = zeros(1,length(t));
th = zeros(1,length(t));

for i = 1:8
    th0(1,i) = deg2rad(45*(i-1));
    th(1,i) = th0(1,i) + 2*atan(tan(M1/2));
end

I end up with "Unable to perform assignment because the size of the left side is 1-by-1 and the size of the right side is 148-by-1."

Can't figure out what the 1 by 1 is?

[Stephan]

Die you try the code from my answer?

Answer 1

[Stephan]

Hi,

try:

%%Relevant parameters
timestep = 600;
G = 6.67408*10^-11;
%   Mars data
    Mars.m  = 6.39*10^23;            %[kg]
    Mars.mu = Mars.m*G;              %[m^3s^-2]
    Mars.r  = 3389.5*10^3;           %[m]
    Mars.v  = 241.17;                %[ms^-1]
    Mars.T  = (2*pi*Mars.r)/Mars.v;  %[s]
    Mars.o  = Mars.v/Mars.r;         %[rads^-1]
    Mars.th = Mars.o*timestep;       %[rad] for every second
t = (0:timestep:Mars.T)';        %Mars.T, Length of martian day in seconds
H1 = 9610.5*10^3;               %[m]
a1 = Mars.r + H1;               %[m]
T1 = 2*pi*sqrt(a1^3/Mars.mu);   %[s]
n1 = (2*pi)/T1;                 %[kms^-1]
M1 = n1*t;                      %[rad]
%%Test Section
th0 = zeros(1,length(t));
th = zeros(1,length(t));
for i = 1:148
    th0(i) = deg2rad(45*(i-1));
end
th = th0'+ 2*atan(tan(M1/2));

Best regards

Stephan

[Scott Hunter]

Hi Stephan,

Thank you very much for the response. Unfortunately I need th1 through to th32 also, as well as many other variables which will rely on the different th's. I'm not sure how I would manage this with the th outside the loop?

[Stephan]

th has a size of 148 in this code

[Scott Hunter]

Sorry yes I thought I had to do that to get it to work, here's my most recent attempt;

th0 = zeros(1,32);
th = zeros(1,32);

for i = 1:8
    th0(i) = deg2rad(45*(i-1));
end   
th = th0 + 2*atan(tan(M1/2));

This gives me a 148x32 which is progress! Not sure where to go next but I'll keep bashing on! Thanks for your help!

[Stephan]

If my answer was useful for you please accept it. I wish you success.