Payload fairing

A payload fairing (English payload fairing ) surrounds almost always the payload of a rocket and protects it from external influences.

Tasks of a payload fairing

The payload fairing of a launch vehicle protects the sensitive satellites or spacecraft on the launch pad before the weather (rain, wind, dust, etc.). After the engine ignition and starting, however, it still fulfills important tasks:

• After ignition of the engines and shortly after the start, it protects the payload prior to the acoustic effect of the sometimes very high noise level of the rocket motors.

• During the flight, it protects the payload before the air resistance, and after exceeding the speed of sound, they must protect the payload even before created by the supersonic flight in the dense layers of air friction heat to the air particles.

In secret military satellites, the payload fairing adds, with help to ensure that the design and the purpose of the satellite, at least until after the exposure in orbit will remain secret.

Period of use

After the rocket has left the dense layers of the atmosphere, the payload fairing is jettisoned. For this, the payload fairing is blown up along as well as at the lower end by detonating cord into at least two parts laterally during flight with most types of missiles ( there are more rare) repelled and the parts. The separation with a tension band system is possible. The pieces fall back to Earth. The Ariane 5, it is common to drop the payload fairing at an altitude of about 110 km during the burn time of the main stage when the frictional heat that has to endure the satellite, has become lower than the heat produced by solar radiation in orbit. This view for the vertical and for the horizontal separation pyrotechnic systems are used.

After a discharge test, the three parts of the Titan IV payload fairing are visible, one of the few of more than two parts.

Only partially dissolved payload fairing of ATDA during the Gemini 9 mission.

A payload fairing is jettisoned during the operation of the advanced level.

Since launching the payload fairing is performed during the flight with and at a very high speed (mostly during the rocket continues to accelerate ), the payload fairing meet in extremely rare cases, the payload or the rocket and cause serious damage. Also, the fairing can not or only partially be shed in rare cases. Both can be a cause of false starts, like Gemini 9 ( picture) or in two consecutive starts of the 3110 Taurus rocket carrying the Orbiting Carbon Observatory and the Glory satellite. Some missiles ( such as the Atlas V) throttle during this phase of flight, the engines to allow through a smaller acceleration a safer separation; a low fuel consumption you take this into account.

Materials

There are fairings which are made of metal (usually aluminum), as the standard fairing Delta II rocket payload and cladding composite material (CFRP, etc.). When Ariane rockets, for example, an aluminum honeycomb core structure is used, which is clad in CFRP sandwich panels. When soundproofing the inside is often disguised or with cork or plastic.

Size and shape

The basic form of all payload fairings is that of a cylinder, on which a cone is attached. This is a low air resistance can be achieved.

In practice, there are thereof depending on the purpose deviations. Often a payload fairing has a larger diameter than the upper rocket stage and there is a transition region in which the increases of the diameter of the upper to its actual diameter. Also, most payload fairings have rounded ogive instead of normal cone at its tip. Some payload fairings, like the Ariane 5, Vega and Atlas V 5XX have, in order to reduce the shape of a rifle bullet with no corners ( " ogive " ) drag on. The size of a payload fairing depends on the size of the transported payload. In general, it is common for a payload fairing with a standardized diameter for different lengths of payloads in different length versions, may with extension rings to offer. But there are also missiles, can use the payload fairings of different diameters and lengths.

Furthermore, in some types of rockets, the upper stage of the rocket is in addition to the payload enclosed by the fairing. Examples are the U.S. Titan III, IV and Atlas V rockets with a 5.4 -m fairing. Also located in the Russian Soyuz / Fregat rocket, the Fregat upper stage in the payload fairing.

Further requirements

Other common requirements or features may be:

• Access doors to have access to the payload shortly before the start;
• Radio -transparent areas, in order to receive radio signals from an active during the starting phase can payload;
• Thermal protection (usually a cork or plastic layer ), especially against the frictional heat during atmospheric flight;
• Electrically conductive white paint as protection against static electricity and heating by the sun;
• Measurement technique to verify the successful separation, such as a unrollable band, which measures the distance to the upper stage, or layer gyroscope for measuring the rotational speeds;
• Valve systems to relieve the internal pressure controlled during the ascent and to prevent the ingress of outside air.

Typically, the area of the payload is supplied with the fairing to the moment of lifting, and conditioned with filtered air. The safe closure of the necessary opening is also an important element.

Mission logo

On the fairing a large highly visible logo of the payload is usually attached, which is located under the cowl. If more satellites are found, several logos be placed next to or under each other. This can, for example, are often observed in Ariane 5 launches. In secret military payloads either no logo is attached to or one that says nothing or almost nothing about the payload.