So I did some quick research. The formula for drag/mass ratio seems to be: sum of (drag * mass of chute) / (sum of mass of all parts) An empty BACC SRB has a mass of 1.5 t. A Mk-2R Radial Parachutes has 0.15 t mass and 500 drag deployed. One parachute: 500 * 0.15 = 75 / (1.5 + 0.15) = 45.45.. Would be a failure. Two Parachutes: 500 * 0.15 * 2 = 150 / (1.5 + 0.15 * 2) = 83.33.. Some damage. Three Parachutes: 500 * 0.15 * 3 = 225 / (1.5 + 0.15 * 3) = 115.38.. Safe recovery. As a rule of thumb I would say 1 parachute per 1 t mass makes a reasonably recovery. I am not sure why I have to multiply the drag with the mass of the parachute, maybe someone could shed some light there?
