The field of engineering which focuses on the development of spacecraft and aircraft is known as aerospace engineering. This field is closely related to the fields of aeronautical engineering and astronautical engineering. There are a number of areas which are studied under aerospace engineering such as radar cross-section, astrodynamics, avionics and aeroelasticity. Radar-cross-section measures the detectability of objects by radars. The practical problems regarding the motion of spacecraft are handled by astrodynamics through the use of ballistics and celestial mechanics. Avionics deals with the designing and programming of the computer systems in a spacecraft