Sounding Rocket

Joachim Köppen Strasbourg/Kiel 2004/2013


About the Applet and what it does

The Applet simulates the flight of a sounding rocket through the Earth atmosphere, and permits to plot any variable of the flight (range, speed, acceleration, ...) as a function of time, or as a function of any of the other variables.

The rocket is composed of the rocket case and motor (the "dry mass"), the fuel, and the payload. It is launched into a certain angle into the air, the fuel is consumed at a constant rate for a certain time, after which the rocket continues to rise on a ballistic trajectory. During all that time, the resistance due to the air acts on the rocket, described by an effective cross section of the rocket. This will be smaller than the geometrical cross section, due to the aerodynamic shape. After some time, the payload is separated from the rocket, and descends to the ground while slowed down by the main parachute (whose braking is described by its effective cross section).

All parameters have simply been adjusted until a satisfactory match with the flight data of a Zuni mission was achieved. No claim for accuracy is made, and no warranty is given!

This software is designed as a graphical visualization only of typical missions.

The simulator solves the equation of motion, including thrust, gravity, and air friction, with a simple method using an adaptive time step width between 0.1 and 100 msec.

Let's take first steps

When you start up the applet, you shall see the plot of height versus range of a typical flight of a Zuni sounding rocket.

The red part shows the flight before separation, the blue one the flight of the payload under parachute. Change the x and y axes with the Choices in the upper right, to display the new plot. Use drag & Zoom to see more details. Change any of the parameters on the left hand side panels, and then hit the enter key or click compute to make and show the new simulation.

For instance, here we see that around the time of peak altitude there is a 30 second stretch of low acceleration (perhaps less than 0.1 G). Then the drogue chute opens and limits the acceleration to -4 G (my arbitrary assumption). When the payload is falling under the main parachute, the air drag on the chute amounts to 1 G.

The controls:

Rocket shows the parameters of the rocket:

dry mass
is the mass of the rocket without fuel and payload
fuel mass
is the mass of the propellant
burn time
is the time during which all the propellant is burned with a constant rate
specific impulse
is the thrust (in kp) per kg of propellant. The speed of the expelled gases is simply this value multiplied with 9.806 m/secē
eff. cross section
is the effective cross section of the rocket
chute cross section
is the effective cross section of the parachute
distance of observer
is the distance of an observer looking at right angles to the plane into which the rocket is launched

Flight shows the parameters of the flight:

payload mass
is the mass of all the payload (including parachute)
launch angle
is the angle (against the horizontal) into which the rocket is launched
separation time
is the time after launch when the payload is separated from the rest of the rocket and descends below the parachute

compute computes a new flight model based on the current parameters of rocket and flight, and displays the results in the current type of plot

drag & Zoom drag the mouse from the upper left to the lower right over that area in the plot which you want to zoom into

full view shows the full plot of the data

These variables can be plotted against each other:

is the time after launch
is the horizontal distance of the rocket
is the height above ground
is the angle above the horizontal under which the rocket is seen from the launch pad
is the angle (with respect to the horizontal) into which the tip of the rocket is pointing (the real thing will be tumbling!)
is the total acceleration, measured in terms of the gravitational acceleration on the Earth's surface (9.806 m/sē)
is the total speed im m/s
Mach number
is the total speed measured in speed of sound (330 m/s)
elev.from observer
is the elevation angle of the rocket, as seen from an observer at the distance specified

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