Optimize the fuel tank size of the Goddard rocket to reach desired height.
Tips
Add a parameter that represents the fuel tank capacity and update the starting mass depending on the new parameter.
{ mf '==' t_0(rocket.mass-rocket.maxFuel) }
Another tip is to set the end height to be the same as the maximum height of the Goddard rocket problem, which is { 1.6141e+05 '==' t_f(rocket.height) } and then you can compare the plots and see if they are simular.
Code to be modified
%% Goddard Rocket, Maximum Ascent
% Author: Dennis Edblom
% Create the Yop system
sys = YopSystem('states', 3, 'controls', 1, ...
'model', @goddardRocketModel);
% Symbolic variables
time = sys.t;
% Rocket signals (symbolic)
rocket = sys.y.rocket;
m0 = 214.839;
mf = 67.9833;
Fm = 9.525515;
% Formulate optimal control problem
ocp = YopOcp();
ocp.max({ t_f( rocket.height ) });
ocp.st(...
'systems', sys, ...
... % initial conditions
{ 0 '==' t_0(time) }, ...
{ 0 '==' t_0(rocket.velocity) }, ...
{ 0 '==' t_0(rocket.height) }, ...
{ m0 '==' t_0(rocket.mass) }, ...
... % Constraints
{ 0 '<=' t_f( time) '<=' inf }, ...
{ 0 '<=' rocket.velocity '<=' inf }, ...
{ 0 '<=' rocket.height '<=' inf }, ...
{ mf '<=' rocket.mass '<=' m0 }, ...
{ 0 '<=' rocket.fuelMassFlow '<=' Fm } ...
);
% Solving the OCP
sol = ocp.solve('controlIntervals', 60);
%% Plot the results
figure(1)
subplot(311); hold on
sol.plot(time, rocket.velocity)
xlabel('Time')
ylabel('Velocity')
subplot(312); hold on
sol.plot(time, rocket.height)
xlabel('Time')
ylabel('Height')
subplot(313); hold on
sol.plot(time, rocket.mass)
xlabel('Time')
ylabel('Mass')
figure(2); hold on
sol.stairs(time, rocket.fuelMassFlow)
xlabel('Time')
ylabel('F (Control)')
%% Model
function [dx, y] = goddardRocketModel(t, x, u)
% States and control
v = x(1);
h = x(2);
m = x(3);
F = u;
% Parameters
D0 = 0.01227;
beta = 0.145e-3;
c = 2060;
g0 = 9.81;
r0 = 6.371e6;
% Drag and gravity
D = D0*exp(-beta*h);
F_D = sign(v)*D*v^2;
g = g0*(r0/(r0+h))^2;
% Dynamics
dv = (F*c-F_D)/m-g;
dh = v;
dm = -F;
dx = [dv;dh;dm];
% Signals y
y.rocket.velocity = v;
y.rocket.height = h;
y.rocket.mass = m;
y.rocket.fuelMassFlow = F;
y.drag.coefficient = D;
y.drag.force = F_D;
y.gravity = g;
end