approaches the space station from a slightly lower orbit and some distance behind. It moves up to the same orbit and remains behind the station until the final phase of rendezvous. Then the shuttle moves to a lower orbit, passes below the station, matches orbit and docks with the station. Thus any tethered satellite below or behind the station could be an obstacle to the shuttle during rendezvous. Coorbiting Satellites (Free-Flyers) Free-flying satellites, such as those with scientific experiments or commercial material processing, require long-range coorbital formations in order to conserve re-boost fuel. These free-flyers are largely autonomous, with only occasional servicing by the space station. A typical formation-flying orbit in front of the space station is shown in Fig. 4. These co-orbiting satellites in front of or behind the space station should not put significant constraints on the nuclear satellite’s location. Thus the satellite’s location should be determined principally from the traffic pattern zones and the radiation characteristics of the reactor/shield system. Shielding Mass Versus Separation Distance The mass of the nuclear satellite is mainly dependent upon the amount of shielding protection required. Previous concepts of a nuclear satellite in close proximity to a manned station had a shield shaped to provide maximum radiation protection towards the station. In order to conserve weight, very little shielding was placed along directions away from the station. Specifically, for a 40 kW reactor at tne end of a boom 60 meters from the station, a 8710 kg shaped shield yielded 5 mRem/hour radiation flux at the station and 100 Rem/hour in the opposite direction (a factor of 2 x 104 difference). If the projected traffic patterns for the space station are considered, a shaped shield is definitely inadequate; rather a full 4 tt shield is required to protect rendezvousing vehicles. The mass of a 4 tt shield at the station may be prohibitive or exceed the shuttle cargo capacity. A tethered nuclear satellite has two advantages over a reactor on a boom: (1) separation distance helps to reduce the station radiation flux level by a 1/R2 falloff factor, and (2) the satellite can be moved well away from rendezvous traffic zones. By substituting distance for shielding thickness, the satellite mass can be greatly
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