The aerodynamic payload fairing (PLF) of a launch vehicle (LV) is intended to protect a spacecraft (SC) from external effects, including heat and aerodynamic loads during transportation of completely assembled LV, on the launch pad and in the LV atmospheric flight. Zh 4000 mm PLF is designed for use as a part of Cyclone-4 LV head module and Zh 3000 mm PLF is designed for Dnepr-M LV. The PLF design allows to adapt it for use in any operated and developed LV of this class. In this case, the requirements to comfort for the majority of SCs planned for launch will be met.

THE PLF GENERAL-ARRANGEMENT DIAGRAM

The PLF general-arrangement diagram is shown in Fig. 1, 2.

The PLF includes the following main assemblies and systems:
- a welded wafer casing made of Amg-6M aluminum alloy according to the technology used in the manufacture of rocket tanks and dividing into two doors during PLF jettison;
- a system of separation of the doors longitudinal joint made on the basis of lever-cam mechanical locks (analogous to Cyclone-3 LV locks) united into lashes and attachment joints made with the use of Zenit-2 LV sealed pyro locks;
- sealed pyro locks of the lateral joint separation system made on the basis of Zenit-2 LV pyro locks;
- a pneumatic system of PLF doors jettison, analogous to Zenit-2 LV, including the pneumatic pushers, bottles, pipelines, and valves (two pneumatic units, one on each door);
- four hinge joints of doors turn, analogous to Zenit-2 LV PLF hinge joints;
- internal heat insulation;
- a cable network of the control system (CS) and telemetry system (TMS) and the board of umbilical connectors;
- sensors of telemetry system;
- a collector of the low pressure thermostatic control system;
- low pressure thermostatic control system air inlet filler and pipeline;
- a pneumatic connector, pipelines and gas inlets of the high pressure thermostatic control system;
- valves of the system of air venting from under the PLF in the injection flight portion.

Fig. 1 - Zh 4000 mm PLF General-Arrangement Diagram

If required, the PLF may be equipped with avionics during head module assembly. The PLF may be of different length. The length of PLF cylindrical part may vary with the step of 1…1.4 m. The basis for selecting the PLF design solutions is the necessity of ensuring maximal reliability and comfortable conditions for a SC at minimal cost. High reliability and low cost of PLF casing assemblies are ensured due to the use of well-developed materials and technologies brought to a commercial level.

Fig. 2 - Zh 3000 mm PLF General-Arrangement Diagram

The applied simple and low-cost system of separation of PLF doors longitudinal joint has high reliability, low mass and allows, if required, to perform demonstration and checking actuation. The PLF is sealed, dust - and - moisture proof and meets the highest requirements to SC comfort. The PLF is not radio transparent, but if required, radio transparent windows may be made.

PLF INTERFACES

The PLF has the following mechanical and electrical interfaces with LV:
- a PLF/LV joint (the system of longitudinal joint separation);
- low-impulse sealed pyro locks and pins;
- stops of pneumatic pushers for PLF jettison (two pushers on each door);
- hinge joints for fairing opening (two joints on each door each of them works in flight in tension as a bolt);
- bonding contacts to protect from static electricity;
- HPTCS pneumatic connector;
- two CS electric connectors (50 contacts each) and two MS umbilical electric connectors and one MS electric connector on each door).
The PLF has the following mechanical interfaces with ground equipment:
- bushings for eye-bolts for PLF transfer by crane;
- platforms for PLF putting on supports;
- a sealed connector for the PLF doors jettison pneumatic system connection with the ground pneumatic equipment of the technical complex;
- a pneumatic connector for the LPTCS filler connection with the ground pneumatic equipment of the technical and launching complexes.

CLEAULINESS UNDER THE FAIRING

During the LV head module assembly, a payload is isolated in the volume limited by PLF and adapter. The air cleanliness in the clean room where the operations with PLF are performed and under the PLF in all phases of operation comply with the class not worse than M6.5 (100000) of FED-STD 209E. The PLF structural elements, as well as parts and assemblies installed in the PLF internal cavity, including the cable network, meet the following cleanliness requirements:
- fatty contamination (surface non-volatile sediments, fat, detergent residues, etc.) - not more than 2 mg/m²;
- surface particles contamination (mechanical contamination) - not more than 10 mg/m² and comply with the level of 500 MIL-STD-124G.
- non-metal materials used in the structure of PLF internal contour, as well as parts and assemblies installed on its surface meet the requirements to the total loss of mass of less than 1 % and the content of volatile condensing substances of less than 0.1%. This level of fairing cleanliness ensures after SC placement under the fairing and till its separation sedimentation on their surface of not more than 4 mg/m² of depositions, out of them: due to gaseous emissions - not more than 2 mg/m²;
- from other sources - not more than 2 mg/m².

PLF THERMOSTATIC CONTROL

For the PLF thermostatic control, three thermostatic control systems operating by the principle of active ventilation are used. The system of transport thermostatic control is intended to maintain the temperature and humidity conditions under the fairing during LV transportation from the Assembly - and Test Building (ATB) to the launching pad till the moment of switching on the low pressure thermostatic control system and during LV transportation from the launching pad to ATB in case of launch cancellation.
The low pressure thermostatic control system is intended to supply the thermostatic air under PLF in the period of transport thermostatic system switching off till the beginning of the transporter-erector removal. The high pressure thermostatic control system is intended to supply the thermostatic air under the fairing in the period from low pressure thermostatic system switch off till LV launch and also in case of launch cancellation till the moment of low pressure thermostatic system switch on. To prevent payload temperature from coming out of allowable limits if the low pressure thermostatic system fails, provision is made for the use of high pressure thermostatic system as a back - up. To purge the PLF, the air and technological gas complying with cleanliness class M 5.5 (10000) according to FED-STD-209E are used. The thermostatic control systems ensure in PLF cavity the air temperature within the range of 13…25 °C and the gas velocity on payload surface of not more than 2 m/s. The environmental conditions during the transportation of completely assembled LV and on the launching pad are as follows:
- outside air temperature, °C: -30 to +40;
- solar radiation, W/m² J: 1125;
- air humidity at 25 °C, % J: 98;
- wind velocity, m/s J: 25.
When designing the PLF, the environmental conditions for LV atmospheric flight were taken the same as for Cyclone-4 LV for Zh 4000 mm PLF and the same as for Dnepr-M for Zh 3000 mm PLF.

PLF DYNAMIC AREA. ALLOWABLE PAYLOAD AREA

The PLF dynamic area was determined taking into account maximal possible technological deviations of actual internal contour from theoretical and elastic displacements under load in the phases of ground operation of assembled head module and in LV flight, including the process of PLF jettison. To determine allowable payload area, the guaranteed clearance of 50 mm between the PLF dynamic area and payload was adopted. The configuration of allowable payload area is shown in Fig. 3. The payload area volume is 65 m³ for Zh 4000 mm PLF and 48 m³ for Zh 3000 mm PLF.

Fig. 3 Allowable Payload Area

PLF SEPARATION

The PLF separation occurs after passing the dense atmosphere when free-molecular thermal flow on SC surface will not exceed 1135 W/m². The design range of longitudinal acceleration during PLF jettison is 0 to 6.5, lateral acceleration is 0.15. By CS command, the longitudinal joint of PLF doors is separated, the lateral joint of PLF with LV is separated and pressure is supplied to the pneumatic pushers. Under the action of pneumatic pushers, the doors turn by the angle of ~15 deg about the hinge joints. Then the doors rotate under the action of acceleration till the angle of 60±3 deg when the hinge joints disintegrate and the doors continue free motion.

- high reliability, including the casing, separation systems;
- cleanliness class M 6.5 (100000) of FED-STD-209E;
- low level of acoustic and vibration effect on SC;
- comfortable temperature and humidity conditions for SC;
- optimal aerodynamic shape;
- low mass;
- low cost.

*Note: The length of PLF cylindrical part may vary with the interval of 1…1.4 m.

The design of aluminum wafer welded PLF is proposed ensuring compliance with the highest requirements to SC comfort. According to the design and manufacturing technology brought to a commercial level, within 12…16 mouths, PLFs Zh from 1500 mm to 5500 mm can be developed, manufactured, and tested. The cost of PLF development (non-recurrent) depending on dimensions is 3…6 mil. dol. (the cost of Zh 4000 mm PLF development is 4 mil. dol.). A Yuzhnoye developed and PO YMZ - manufactured up-to-date PLF is second in mass as compared to the best PLF samples made of polymer composite materials but is first in:
- low cost;
- higher reliability of casing;
- easy adaptation of design to customer's requirements.