2. Determine the flight path
To determine the parachutes required, you need to determine the object's flight path without any parachute system. For the parachute system, the most important factor is the terminal velocity of the to be recovered object and its mass. It is assumed that for the missions here no form of thermal protection is required. For missions flying to higher altitudes, a thermal protection system might be required. As a general rule of thumb, one can say that thermal protection might be required for missions flying Mach 3 or higher for a longer period of time. However, an aerothermal analysis should be considered for all supersonic missions to be sure.
The terminal velocity determination can be done using in-house developed tools, tools such as OpenRocket (http://openrocket.info/), or tools alike. Alternatively, you can use the excel sheets provided by this website.
Keep in mind though that bad data in equals bad data out. As you can never know all inputs with absolute certainty it is recommended to perform a sensitivity analysis.
Landing velocity
To determine if a mission requires a decelerator, you need to know the terminal velocity, or landing velocity, of the object. This can be determined using the following equation.
In this equation, ρ is the density at sea level, and g is the gravitational acceleration. Furthermore, K is the ballistic coefficient. Where m is the mass of the object, Cd is the drag coefficient of the object, and A is the frontal area of the object. In this equation, the object can also be the part that is recovered, in case, not the entire object is recovered.
