then add two more solar array wings in order to increase the user power to 75 kW for the Assembly Complete (AC) configuration. Now, however, budget cutbacks have forced a revised plan where just one array wing will be added, enabling a 56 kW user power capability at AC. Nevertheless, the consequence of using such large solar arrays to generate power at this low altitude is that the drag will be high. As a result, propellant must be ferried to Freedom every year to keep re-boosting the station and avoid it falling back into the atmosphere. Current NASA planning indicates that for the 56 kW configuration nearly 8 tonnes of propellant will have to be launched every single year. [5] To this must be added the mass of the propellant container of about 2 tonnes. [6] Thus, to keep Freedom in orbit for one year requires launching around 10 tonnes dedicated entirely to meeting the station-keeping requirement. At the 37.5 kW capability, this mass is about 8 tonnes, and at 75 kW it would be around 12 tonnes if Freedom was ever upgraded to this level of power. It is important to note that Freedom cannot be placed in a higher Earth orbit (i.e. 500-600 km) where the drag is much less because the Shuttle's payload capability falls off rapidly at higher altitudes. One way to counter this would be to launch the Shuttle more often to make up the performance shortfall. However, limitations on the Shuttle's flight rate to around 6-8 flights per year simply preclude this possibility. Battery life As Freedom is in a low altitude and inclination orbit, 30 to 40 minutes of each 90 minute orbit will be spent in the Earth’s shadow. This means that batteries (NiH^ must be used to maintain a constant level of power. When Freedom is in sunlight, the solar arrays are used to both power the station and charge the batteries. When in shadow, the batteries are discharged. As a
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