BURAN Orbital

Spaceship Airframe

Creation

System of Electric Power Distribution and Commutation OBCN-MDC

Kornilov V.S.
The procedure of choosing the structure of the system of distribution and commutation is considered, taking into account the requirements and constraints. The substantiation of accepted engineering solutions is given. The directions of improvement are indicated.

One of the systems of the airframe ensuring Orbiter’s reliable operation as a whole is OBCN-MDC (onboard cable network-means of distribution and communication) system. It executes electric power supply under the set program from onboard and ground-based electric power supplies to the onboard systems of the airframe and Orbiter.

The determining role in choosing the principles of OBCN-MDC building, as well as other systems of the Orbiter, three main requirements played:

• the Orbiter creation as a reusable space vehicle;
• ability of its operation both crew-guided and without crew (in automatic mode);
• provision of Orbiter multi-purpose usage.

Besides, the structure and composition of OBCN-MDC in many respects depended, on the one hand, on the electrical power system, on the other hand, on the number and specific features of the airframe and Orbiter onboard systems’ electric power consumers operation. As the space vehicle of an aircraft type was under construction for the first time, at designing OBCN-MDC, it was necessary to take into account the engineering solutions, which were already tested in the process of space vehicles and airplanes maintenance. This quite often caused difficulties in reaching the necessary compromises.

These reasons, and also high requirements to reliability and survivability, mass minimization, saturation Orbiter with electronic equipment and high power of consumed electric energy have created a set of problems at OBCN-MDC development. The most important were:

• choice of OBCN-MDC structure on the basis of combination of experience of development both of space vehicles and airplanes distribution and commutation systems;
• choice of principles of reliability maintenance guaranteeing task execution at one fault, at two – return and landing;
• provision of short circuit protection and prevention of occurrence of Orbiter airframe metal details connection to ‘plus’ or ‘minus’ electric circuits of OBCN-MDC;
• organization of auto-mode of monitoring and control.

The schemes of multi-channel distribution systems of airplanes and those of distribution systems of space vehicles were considered at solving these problems. As a result, the version was accepted, in which for satisfaction of the above mentioned requirements and premises a number of non-conventional solutions was used including:

• use of two-channel OBCN-MDC scheme in two-wire arrangement;
• use of a ‘split’ scheme in power electrical connections;
• application of controllable ‘design’ wire protection;
• application of reusable remotely controlled current protection;
• automatic mode of OBCN-MDC monitoring and control from the control system;
• separate arrangement of plus and minus circuits of bundles, electric connectors and lines.

Brief explanation and substantiation of the mentioned solutions is given below. The devices and bundles of OBCN-MDC are connected in such a way that form two independent electric power transmission channels each of which is arranged on one of Orbiter sides (see Figure). Thus, the normal power supply of the onboard systems is provided even at fault in one of the channels.

In the long term, at application of nonmetallic materials in the design of Orbiter body, the system of distribution and commutation can be made only two-wire. At two-wire arrangement, whereas Orbiter metallic body is not used as one of the wires for electric power supply, the following will be achieved:

• considerable reduction of short circuit probability;
• more reliable protection against internal and external atmospheric (for example, lightning) or specially organized electromagnetic disturbances.

Besides, it was necessary for usage of schematic design, which had been already implemented in some systems of Orbiter and tested on other flight vehicles. In these schemes, the presence of ‘body’ is not allowed in minus circuits. These reasons were decisive at choice of the two-wire scheme, despite of some loss in the total mass.

The so-called ‘split scheme’ of electric power connections was used for the selected scheme OBCN-MDC to comply with the high requirements to reliability (including returning and landing at two faults) and in view of mass limitations. In this case the required cross-section of an electric circuit is composed by a number of wires, one or two of which are stand-by. Thus, one or two wires break does not result in a loss of onboard systems power supply.

The indicated way of attaining reliability of power supply, in comparison with the alternate one, does not require over-commutation of power lines at failure and consequently has more simple scheme, with smaller number of elements.

The controllable ‘design protection’ is made for detection of bundles contacts with sharp edges of the airframe construction and for protection of wires against mechanical damages, which stipulates that the wires of bundles are placed inside the metal braiding with a fabric electric insulation.

The electrical insulation is checked up for damage (occurrence of the braid contact with metal details of the airframe) at Orbiter preparation to flight which allows timely to reveal and eliminate possible damage of wires.

The reusable remotely controlled current protection is applied for provision of its repeated actuation at functioning. It concerns the current protection arranged in distribution devices, the access to which is hindered. The purpose of repeated actuation is to eliminate an unauthorized operation. In addition, it gives opportunity to block the current protection for increase of reliability of electric power supply at the injection stage of Orbiter flight. The mentioned above operations are executed under the commands coming from control system.

The automatic mode of control and monitoring is implemented in OBCN-MDC. In the process of Orbiter preparation for flight and during the flight, the conditions of power contacts of remote switches, current protection of voltage on the trunks of devices are monitored automatically. The conditions of current relay assemblies of ‘design’ bundles protection, conjunction of electric connectors, serviceability of power diodes, separation of plus and minus power busses are also monitored automatically. These operations, as well as the control of power switches pursuant to the program of functioning, are made under the commands coming from the control system.

The reliable and authorized commands transmission is provided with a voter circuit ‘two of three’. To decrease the probability of short circuits, plus and minus circuits are arranged with different bundles and electric connectors, and the laying of these bundles is made along separate lines at a definite distance one from another.

To increase the reliability, quality and mass saving, the following measures are taken:

• the most advanced electric connectors such as SNT, which wires are connected to the contacts by the method of compression, are applied more widely, than on other flight vehicles;
• heat-resistant comprehensively checked advanced wires are applied;
• OBCN-MDC and the components are tested for the effect of external loads and the operation in a volume of complex program of experimental working-out is checked including:
  - in normal and emergency modes on OBCN-MDC stand with simulation of power sources and electric power consumers,
  - together with onboard systems-consumers of electric power on FSSE stand,
  - in Analogue 0002 plane and flying laboratory.

Block diagram of OBCN-MDC (right side):

CDU – central distribution unit; CDB – central distribution box; DU – distribution unit; SCAPS – socket connector of airfield power supply; PSS – power supply system; EPSS – emergency power supply system; DC – detachable connector; APSS-T – autonomous power supply system, tail; FU – filters unit; DA – distributive adapter

As a result of the tests, the indices of reliability and service life necessary for Orbiter flight tests accomplishment were confirmed.

Development and creation of OBCN-MDC are carried out under the direction and with direct participation of Mr. Kornilov V.A. the main works were accomplished by Mr.: Strelnikov V.V. and Ruzavin N.A. or under their direction, and the tests on stands – by Mr. Kovalev V.I. The design of distribution devices was developed under the direction of Mr. Soloviev A.M. (MAZ DZERZHINETZ).

The OBCN-MDC scheme is selected for the particular spaceship in view of features of the electric power system, onboard systems - electric power consumers, power consumption and at the alteration of these conditions can be transformed. The experience of OBCN-MDC development and working-out can be undoubtedly used at designing the system of distribution for other flying vehicles including the perspective aerospace ones.

In the future, technical performances can be improved due to:

• application of non-contact units in the circuit of control and monitoring, advanced lightweight wires (mass by 10…20% less), electric lightweight connectors with compressed contacts, non-contact current protection with wide functions;
• limitation of the output current of signals on the network condition, automatic repeated actuation of the network;
• replacements of braiding used in bundles design protection for metallic film;
• introduction of the controller into the system structure for solution of autonomous tasks of control and monitoring;
• consolidation of command-information connections.

A part of these innovations is intended for implementation in the system of distribution and commutation for orbital planes of reusable aerospace system of MAKS type.

References

1. E.V. Besedin, A.D. Vlasov. Qualitative Estimation of Methods Insulation Resistance Control of Double-Wire Systems of Power Supply of Direct Current // Collection of Works of NPO MOLNIYA. 1985. No. 6.
2. V.I. Kovalev. Galvanic Connections in Double-Wire Systems of Power Supply // Collection of Works of NPO MOLNIYA. 1985. No. 3.
3. O.M. Mironov. Transient Inductance of a Two-Wire Line of the Onboard Cable Network of Direct Current // Collection of works of NPO MOLNIYA. 1985. No. 3.
5. Ratclille. System Approach to Development of Power Supply on Modern Airplanes. British Aircraft Corporation Ltd, September 1977.