Final Answer:-
Spacecrafts that do not return to Earth, such as satellite probes, do not require an aerodynamic shape because they do not need to contend with the Earth's atmosphere. This lack of aerodynamic constraints allows for the design to incorporate a large central antenna, which can be optimal for communication purposes.
Explanation:-
In contrast, spacecraft that are designed to return to Earth, such as the space shuttle and the Apollo lunar modules, must have an aerodynamic shape. This is crucial for safely handling the intense conditions of re-entry into the Earth's atmosphere, where the spacecraft must endure significant heat and aerodynamic forces.
For these returning spacecraft, the communication antenna must be positioned in a way that does not interfere with the aerodynamic profile of the spacecraft. Therefore, the antenna is commonly placed on the side of the spacecraft. Moreover, because space is at a premium in the design of such a craft, and because maintaining an aerodynamic profile during re-entry is essential, the antenna is typically designed to be retractable.
This means that when the spacecraft is in space and the aerodynamic profile is not a concern, the antenna can be extended to communicate effectively. However, during re-entry, the antenna is retracted tightly against the body of the spacecraft or is folded and stored inside it to preserve the smooth, streamlined shape that is necessary to safely pass through the atmosphere. This retraction usually occurs automatically before re-entry begins.