code just runs and never stops not sure what to do

%define input variables
qs=1400; %solar input
qe=240; %earth radiation
ar=0.3; %earth albedo
sigma=5.67*10^(-8); %boltzmann constant
R_e=6371000; %radius of earth(m)
Mu=3.986*10^14; %gravitational parameter for earth
h=1336000; %altitude
alpha=0.46; %absorbance of spacecraft
epsilon=0.77; %emittance of spacecraft
m=1000; %mass of spacecraft
P_sun=1000; %power dissipated in sunlight
P_eclipse=500; %power dissipated in eclipse
A_surf=3.35; %surface area of single face
A_total=20.1; %total surface area
cp=900; %specific heat capacity
Ti=263; %initial temperature
R_R=h/R_e;
orbit_period=2*pi*sqrt((R_e+h)^3/(Mu)); %time period of orbit
P=5*orbit_period;
%calculate time in eclipse
te=((2*pi*(h+R_e)^(3/2))/sqrt(Mu))*(asin(R_e/(R_e+h))/pi);
%calculate thermal timeconstant
tt=(m*cp)/(sigma*epsilon*alpha*A_surf);
%calculate view factor
F12=1/(1+R_R)^2;
%calculate input
Qin_sun=(qs*alpha*A_surf)+(ar*qs*alpha*F12*A_surf)+(qe*epsilon*F12*A_surf)+P_sun;
Qin_eclipse=qe*A_surf*epsilon;
%calculate equillibrium temperatures
Teq_sun=(Qin_sun/(epsilon*sigma*A_total))^(1/4);
Teq_ecl=(Qin_eclipse/(epsilon*sigma*A_total))^(1/4);
%given values
dt=1; %steps
t=0:dt:P; %time array
T=zeros(size(t)); %temperature array

counter=1;
while t(counter)<=P
    if rem(t(counter),orbit_period)<=te
        T(counter+1)=T(counter)+dt*(Teq_ecl^4-T(counter)^4)/tt;
        
    else
        T(counter+1)=T(counter)+dt*(Teq_sun^4-T(counter)^4)/tt;
        
    end
end

%Plot the results
figure;
plot(t / orbital_period, T, 'LineWidth', 2);
hold on;
plot([te / orbital_period, te / orbital_period], [min(T), max(T)], '--r', 'LineWidth', 2);
xlabel('Orbits');
ylabel('Temperature (K)');
title('Satellite Temperature Variation Over Time');
legend('Temperature', 'Eclipse Start');
grid on;
hold off;

Answer 1

[Image Analyst]

You forgot to put a failsafe in your code so most likely t(counter) never exceeds P. Try it this way

% Initialization steps.
clc;    % Clear the command window.
close all;  % Close all figures (except those of imtool.)
clear;  % Erase all existing variables. Or clearvars if you want.
workspace;  % Make sure the workspace panel is showing.
format long g;
format compact;
fontSize = 20;

%define input variables
qs=1400; %solar input
qe=240; %earth radiation
ar=0.3; %earth albedo
sigma=5.67*10^(-8); %boltzmann constant
R_e=6371000; %radius of earth(m)
Mu=3.986*10^14; %gravitational parameter for earth
h=1336000; %altitude
alpha=0.46; %absorbance of spacecraft
epsilon=0.77; %emittance of spacecraft
m=1000; %mass of spacecraft
P_sun=1000; %power dissipated in sunlight
P_eclipse=500; %power dissipated in eclipse
A_surf=3.35; %surface area of single face
A_total=20.1; %total surface area
cp=900; %specific heat capacity
Ti=263; %initial temperature
R_R=h/R_e;
orbit_period=2*pi*sqrt((R_e+h)^3/(Mu)); %time period of orbit
P=5*orbit_period
%calculate time in eclipse
te=((2*pi*(h+R_e)^(3/2))/sqrt(Mu))*(asin(R_e/(R_e+h))/pi);
%calculate thermal timeconstant
tt=(m*cp)/(sigma*epsilon*alpha*A_surf);
%calculate view factor
F12=1/(1+R_R)^2;
%calculate input
Qin_sun=(qs*alpha*A_surf)+(ar*qs*alpha*F12*A_surf)+(qe*epsilon*F12*A_surf)+P_sun;
Qin_eclipse=qe*A_surf*epsilon;
%calculate equillibrium temperatures
Teq_sun=(Qin_sun/(epsilon*sigma*A_total))^(1/4);
Teq_ecl=(Qin_eclipse/(epsilon*sigma*A_total))^(1/4);
%given values
dt=1; %steps
t=0:dt:P; %time array
T=zeros(size(t)); %temperature array

counter = 1;
% Demonstration of how to avoid an infinite loop by setting up a failsafe.
% Set up a failsafe
maxIterations = 34000; % Way more than you think it would ever need.
loopCounter = 0;
% Now loop until we obtain the required condition: t(counter) > P.
% If that never happens, the failsafe will kick us out of the loop so we do not get an infinite loop.
while (t(counter)<=P) && counter < maxIterations && counter < numel(t)
    if rem(t(counter),orbit_period)<=te
        T(counter+1) = T(counter)+dt*(Teq_ecl^4-T(counter)^4)/tt;
    else
        T(counter+1) = T(counter)+dt*(Teq_sun^4-T(counter)^4)/tt;        
    end
	counter = counter + 1;
	fprintf('Iteration #%d.  t(%d) = %f.\n', counter, counter, t(counter))
end
% Alert user if we exited normally, or if the failsafe kicked us out to avoid an infinite loop.
if counter < maxIterations
	% Then the loop found the condition and exited early, which means normally.
	fprintf('Loop exited normally after %d iterations.\n', counter);
else
	% Then the loop never found the condition and exited when the number of iterations
	% hit the maximum number of iterations allowed, which means abnormally.
	fprintf('Loop exited abnormally after iterating the maximimum number of iterations (%d) without obtaining the exit criteria.\n', maxIterations);
end
fprintf('All done after %d iterations.\n', counter)

%Plot the results
figure;
plot(t / orbit_period, T, 'LineWidth', 2);
hold on;
plot([te / orbit_period, te / orbit_period], [min(T), max(T)], '--r', 'LineWidth', 2);
xlabel('Orbits');
ylabel('Temperature (K)');
title('Satellite Temperature Variation Over Time');
legend('Temperature', 'Eclipse Start');
grid on;
hold off;

Actually since t is just a vector

t = 0 : dt : P; %time array

you should be using a for loop instead of a while loop

for counter = 1 : numel(t)

[fin]

thankyou

Answer 2

[Walter Roberson]

while t(counter)<=P
    if rem(t(counter),orbit_period)<=te
        T(counter+1)=T(counter)+dt*(Teq_ecl^4-T(counter)^4)/tt;
        
    else
        T(counter+1)=T(counter)+dt*(Teq_sun^4-T(counter)^4)/tt;
        
    end
end

Your while loop tests t(counter) compared to P. If the test fails right at the beginning, then the loop body will not be executed at all. But if the test suceeds at the beginning, the loop body will be repeated as often as needed until eventually the test fails.

In order for the test to fail once it has succeeded, if the test is determininstic, then at least one of the variables involved in the test must have the potential to change inside the loop. You are comparing against t(counter) and against P, so to have the possibility of exiting the loop, the loop body must change at least one of counter or t(counter) or P . But it does not -- it changes T(counter+1) .

Note by the way that t and T are different variables, but even if they had been the same variables, the location you are changing is offset counter+1 but the while test is at offset counter.

So, once the loop has been entered once, it is going to keep going until you terminate it (or you have a memory error, or your computer overheats...)