The CIA wants your help identifying individual terrorists in a photo of a training camp taken from a spy satellite at 150-km altitude. You ask for

The CIA wants your help identifying individual terrorists in a photo of a training camp taken from a spy satellite at 150-km altitude. You ask for details of the optical system used, but they’re classified. However, they do tell you that the optics are diffraction limited and can resolve facial features as small as 5 cm. Assuming a typical optical wavelength of 550 nm, what do you conclude about the size of the mirror or lens in the satellite camera?