Atmospheric Drag

Sounding Rockets are all subject to atmospheric drag. There are three sources of drag on a sounding rocket. First it’s fins. The fins are needed to stabilize a rocket, but they also result in drag, especially when the fins are canted to cause the rocket to rotate during its flight. Generally the more fin are, the more stability, but also the more drag. Drag is a purely atmospheric effect, and decreases with altitude. Below is a Black Grant 12 rocket. Each of its three stages has fins (each needs to be stabilized during flight.

Figure 1 A Black Grant 12 Sounding Rocket

Drag affects sounding rockets in two ways. First it limits the maximum acceleration and velocity a rocket can achieve, and second it makes the rocket subject to other forces (such as wind.) Using physics we can calculate the given drag force for [a] rocket at any point in time by knowing the rockets parameters, then using this equation:

Where p is the density of air, A is the cross sectional area of the vehicle, C is the experimentally determined drag coefficient, and v0 is the instant velocity of the vehicle. Scientists use the drag force (as a function of time) to determine the total drag force experienced by a rocket during its flight. They then can determine how drag will affect performance (such as altitude.)