Payload fairing

A payload fairing is a nose cone used to protect a spacecraft payload against the impact of dynamic pressure and aerodynamic heating during launch through an atmosphere. An additional function on some flights is to maintain the cleanroom environment for precision instruments. Once outside the atmosphere the fairing is jettisoned, exposing the payload to outer space. 
The standard payload fairing is typically a cone-cylinder combination, due to aerodynamic considerations, although other specialized fairings are in use. The type of fairing which separates into two halves upon jettisoning is called a clamshell fairing by way of analogy to the bifurcating shell of a clam. In some cases the fairing may enclose both the payload and the upper stage of the rocket, such as on Atlas V and Proton M.
If the payload is attached both to the booster's core structures and to the fairing, the payload may still be affected by the fairing's bending loads, as well as inertia loads due to vibrations caused by gusts and buffeting.
Fairing retrieval and reuse.
Payload fairings have usually been either burned up in the atmosphere or destroyed upon impacting the ocean, but one company began to retrieve them after the mid-2010s. On March 30, 2017, SpaceX successfully retrieved a fairing intact for the first time in history. For a second time on June 25, 2019, SpaceX was able to catch a fairing from the Falcon Heavy STP-2 launch. After this, SpaceX began reusing its fairings, which are manufactured at a cost of per orbital launch; its CEO, Elon Musk, stated that retrieving the fairings before they touch sea water "makes refurbishment easier".
Mission failures caused by payload fairings.
In some cases, the fairing is planned to separate after cutoff of the upper stage, and in others, the separation is to occur before a cutoff, but after the vehicle has transcended the densest part of the atmosphere. Failure of the fairing to separate in these cases may cause the craft to fail to reach orbit, due to the extra mass.
The Augmented Target Docking Adapter, to be used for the Gemini 9A crewed mission, was successfully placed into orbit by an Atlas SLV-3 in June 1966. But when the Gemini crew rendezvoused with it, they discovered the fairing had failed to open and separate, making docking impossible. Two lanyards, which should have been removed before flight, were still in place. The cause was determined to be a launch crew error.
In 1999, the launch of the IKONOS-1 Earth observation satellite failed after the payload fairing of the Athena II rocket did not open properly, preventing the satellite from reaching orbit.
On February 24, 2009, NASA's Orbiting Carbon Observatory satellite failed to reach orbit after liftoff; the agency concluded that the fairing on the Taurus XL launch vehicle failed to separate, causing the vehicle to retain too much mass and subsequently fall back to Earth and land in the Indian Ocean near Antarctica.
The same happened to the Naro-1, South Korea's first carrier rocket, launched on August 25, 2009. During the launch, half of the payload's fairing failed to separate, and as a result, the rocket was thrown off course. The satellite did not reach a stable orbit.
On March 4, 2011, NASA's Glory satellite launch failed to reach orbit after liftoff due to a fairing separation failure on the Orbital Sciences Taurus XL launch vehicle, ending up in the Indian Ocean. This failure represented the second consecutive failure of a fairing on an Orbital Sciences Taurus XL vehicle. NASA subsequently decided to switch the launch vehicle for the Orbiting Carbon Observatory's replacement, OCO-2, from a Taurus to a Delta II rocket.
On August 31, 2017, ISRO's IRNSS-1H satellite failed to deploy after the payload fairing of the rocket PSLV-C39 failed to separate. As a result of extra mass, the rocket could not reach the desired orbit despite each stage's performance being nominal. The payload separated internally, but got stuck within the heat shield.