Payload fairing
A payload fairing ( English payload fairing ) always surrounds most of the payload of a rocket and protects them from external influences.
Duties of a payload fairing
The payload fairing of a launcher protects the sensitive satellites or space probes on the launch pad from the weather (rain, wind, dust, etc.). After ignition and take-off, on the other hand, it fulfills even more important tasks:
- After the engines have been ignited and shortly after take-off, it protects the payload from the acoustic effects of the sometimes very high noise level of the rocket motors.
- During the flight it protects the payload from air resistance, and after exceeding the speed of sound, it must also protect the payload from the frictional heat on the air particles caused by the supersonic flight in the dense layers of air.
In the case of secret military satellites, the payload fairing also helps to ensure that the type and purpose of the satellite remains secret, at least until after it has been deployed in orbit.
Duration of use
After the rocket has left the dense layers of the atmosphere, the payload fairing is thrown off. For this purpose, the payload fairing of most types of rocket is detonated in at least two parts laterally as well as at the lower end by detonating cord (in rare cases in more than two parts) and these are pushed off. Separation with a tensioning strap system is also possible. The parts fall back to earth. In the case of Ariane 5 , it is customary to throw off the payload fairing at an altitude of approx. 110 km during the burning time of the main stage, when the frictional heat that the satellite has to withstand has become less than the heat generated by solar radiation in orbit. Pyrotechnic systems are used for both vertical and horizontal separation. In the Falcon series rockets from the US space company SpaceX , a pneumatic system is used to release the payload fairing , which is intended to reduce the formation of debris and can be checked for correct function before take-off.
Long payload fairing of the Ariane 5 with visible separating seams.
After a drop test, the three parts of the Titan IV payload fairing are visible, one of the few made up of more than two parts.
A payload fairing is thrown off during the operation of the upper stage.
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Since the payload fairing is thrown off during flight at a very high speed (mostly while the rocket continues to accelerate), the payload fairing can in extremely rare cases hit the payload or the rocket and cause serious damage. In rare cases, the payload fairing cannot be thrown off at all or only partially. Both can be a reason for false starts, as with Gemini 9 (picture) or with two successive launches of the Taurus 3110 rocket with the Orbiting Carbon Observatory or the Glory satellite. Some rockets (such as the Atlas V ) throttle the engines during this phase of flight in order to allow a more secure separation through a smaller acceleration; a small additional fuel consumption is accepted.
materials
There are payload fairings made of metal (mostly aluminum ), such as the standard payload fairing of the Delta II rocket and payload fairings made of composite material ( CFRP etc.). In Ariane missiles, for example, an aluminum honeycomb core structure is used that is clad with CFRP sandwich elements. The inside is often clad with cork or plastics to protect against noise.
Size and shape
The basic shape of all payload fairings is that of a cylinder on which a cone is placed. This is intended to achieve the lowest possible air resistance.
In practice there are deviations from this, depending on the intended use. Often times, a payload fairing is larger in diameter than the top stage rocket and there is a transition area where its diameter increases from that of the top stage to its actual diameter. Also, most payload fairings have rounded cones rather than normal cones at their tips. Some payload fairings , such as those of the Ariane 5, Vega and Atlas V 5XX, have the shape of a rifle bullet without corners (" ogive ") to further reduce air resistance. The size of a payload fairing depends on the size of the payload to be transported. As a rule, it is common to use a payload fairing with a standardized diameter for payloads of different lengths in different lengths, u. U. also to offer with extension rings. But there are also rockets that can use payload fairings with different diameters and lengths.
In addition to the payload of some rocket types, the upper stage of the rocket is also enclosed by the payload fairing. Examples of this are the US Titan III, IV and Atlas V missiles with a 5.4 m fairing. The Russian Soyuz / Fregat rocket also has the Fregat upper stage in the payload fairing.
further requirements
Other common requirements or equipment features can be:
- Access doors to have access to the payload shortly before take-off;
- radio-transparent areas in order to be able to receive radio signals from a payload active during the start-up phase;
- Thermal protection (usually a cork or plastic layer), especially against frictional heat during atmospheric flight;
- electrically conductive white paint as protection against static charge and heating by the sun;
- Measurement technology to verify the successful separation, such as B. a rollable tape that measures the distance to the rocket stage, or gyroscope to measure the rotational speeds;
- Flap systems to release the internal pressure during the ascent and to prevent outside air from entering.
Typically, the area of the payload under the payload fairing is supplied with filtered and conditioned air until the moment of take-off. The secure closure of the opening required for this is also an important element.
reuse
Since the beginning of space travel, payload fairings have been designed as light as possible to maximize the performance of the rocket. During the launch, they were dropped as soon as possible to save weight. Then the panels fell to the ground or into the sea. They were destroyed or irreparably damaged in the process. A targeted landing was not planned. In addition to the additional weight for other opening mechanisms and landing aids, the risk of damage from impact or salt water was rated as too high for reuse to appear profitable.
The subject came back into focus when SpaceX announced it was aiming to reuse the fairings to reduce the cost / launch of the multi-million dollar fairings. Developments and tests were carried out - partly while the Falcon 9 was in operation - to bring the fairings to the ground safely. For example, both halves were provided with “ control nozzles ”, which keep the flight position stable when re-entering, as well as with controllable wing parachutes , on which they could then water in the ocean. The landing and recovery of a half of the payload fairing succeeded for the first time during the launch of the SES-10 satellite on March 31, 2017. SpaceX then equipped the “capture ship” Mr. Steven (later called GO Ms. Tree ) with a large, horizontally stretched net. On March 25, 2019, after a few unsuccessful attempts, a half of the fairing was caught directly from the air for the first time.
On November 11, 2019, a payload fairing was reused for the first time. The Falcon 9 of the Starlink 1 (v1.0) mission started with a disguise that had already been launched on a Falcon Heavy when the Arabsat 6A was launched and then fished from the sea.
Mission logos
A large, clearly visible logo of the payload is usually affixed to the payload fairing, which is located under the fairing. If there are several satellites, several logos are placed next to or one below the other. This can e.g. B. often observed during Ariane 5 launches. For secret military payloads, either no logo is attached or one that says nothing or almost nothing about the payload.
Web links
- Arianespace e-space Newsletter April 2000 ( Memento from March 11, 2006 in the Internet Archive ) (Contains a description of the various payload fairings and double launch devices, PDF; 708 kB)
Individual evidence
- ↑ Falcon User's Guide - 2.4 Retention, Release and Separation Systems. Space Exploration Technologies, January 2019, accessed May 20, 2019 .
- ↑ Caleb Henry: SpaceX demonstrates rocket reusability with SES-10 launch and booster landing. In: spacenews.com. March 30, 2017. Retrieved February 22, 2018 .