Payload fairing
Payload fairing is one of the main components of a launch vehicle
Launch vehicle
In spaceflight, a launch vehicle or carrier rocket is a rocket used to carry a payload from the Earth's surface into outer space. A launch system includes the launch vehicle, the launch pad and other infrastructure....

. The fairing protects the payload during the ascent against the impact of the atmosphere
An atmosphere is a layer of gases that may surround a material body of sufficient mass, and that is held in place by the gravity of the body. An atmosphere may be retained for a longer duration, if the gravity is high and the atmosphere's temperature is low...

 (aerodynamic pressure
Pressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...

 and aerodynamic heating
Aerodynamic heating
Aerodynamic heating is the heating of a solid body produced by the passage of fluid over a body such as a meteor, missile, or airplane. It is a form of forced convection in that the flow field is created by forces beyond those associated with the thermal processes...

). More recently, an additional function is to maintain the cleanroom
A cleanroom is an environment, typically used in manufacturing or scientific research, that has a low level of environmental pollutants such as dust, airborne microbes, aerosol particles and chemical vapors. More accurately, a cleanroom has a controlled level of contamination that is specified by...

 environment for precision instruments.

Outside the atmosphere the fairing is jettisoned, exposing the payload. At this moment mechanical shocks and a spike in acceleration might be observed.

The standard payload fairing is typically a cone-cylinder combination, due to aerodynamic considerations, however specialized fairings are in use as well.