Mir station power bus to the microwave generator input. The other is needed at the receiving side to connect the rectenna power output to the power input of the Progress spacecraft. The Mir station electrical power subsystem has the capability of supplying an external user with 27 V DC of electrical power at a maximum load of 10 kW for 1 hour periods. The experiment uses a nominal power of 5 kW. The Mir electrical power is available via the connectors that are used for supplying power to modules docked to the Mir. They are situated at the corresponding docking aggregates. The power is fed to the microwave generator via a 20 m long cable. The power cable is laid along the outside of Mir and the connection is made by a cosmonaut during EVA . Assuming a power loss of less than 50 W (1%) by the interface cable, application of Ohm's law gives us a maximum resistance of 0.0015 £2 for the cable. Considering that the resistivity for copper is 1.7 x 10'8 £2/m, a cable diameter of 17.2 mm is obtained. The mass of this cable is about 36 kg. The power system on the transmitting side has the main functions of switching and regulating power for the microwave generator. On the receiving side, the rectenna power output is connected to the power connector located at the auxiliary solar panel attachment of the Progress spacecraft. The required power connection and cabling is made on-ground. As a minimum, the following data interfaces to the Mir and Progress spacecraft would be needed: • serial telemetry/telecommand interface between the phased array control computer and the data handling equipment inside the Mir spacecraft • serial telemetry interface between the rectenna power measurement equipment and the data acquisition equipment inside the Progress vehicle • serial telemetry interfaces between the scientific experiment and the data acquisition equipment inside the Progress vehicle The Mir station provides auxiliary electrical signal interfaces via connectors which are nominally used for data transmission between the Mir and any docked modules. They are situated at the corresponding docking aggregates. The control computer of the phased array antenna could be connected to this point using a 20 m long shielded twisted pair cable. During EVA the cable is installed and the connections are made by a cosmonaut. The signal interface connections between the rectenna side equipment and the Progress vehicle are made on-ground. This also requires some minor modifications to be made to the existing Progress vehicle. An estimated data budget for the mission is given in the section “Command and data handling”. Guidance and Control The problem of guidance and control can be split into three fields: • attitude control of the Mir space station • orbit and attitude control of the Progress vehicle • beam control As described in the section “Mission Scenario”, the Mir space station will be oriented with the docking port in the local horizontal plane pointing opposite to the orbital velocity vector. The Mir attitude control loop is independent from the experiment and pointing accuracy is better than 1 degree. The attitude of Progress will be controlled by the automatic docking system so that the longitudinal axis of the Progress vehicle will be pointing to the docking port with an accuracy of better than ten arc minutes. A critical parameter will be the orbital position relative to Mir. Besides the distance requirement of 80 m the variation in orbit radius should not result in excessive shading of the beam on the antenna or the rectenna side as shown in Figure 10.2.12. Since the precise mounting positions of the antenna and the rectenna are not yet decided, this requirement could not be translated into a precise orbital position requirement. However the effect of shading on the beam control loop would be an important feature of the demonstration mission.
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