the past that have been refered to as fatal flaws, this is not insoluble. Preliminary calculations suggest that the SOFI will deteoriate at a rate of about 0.8 grams per second for the entire ET (3). This rate is purely an order of magnitude prediction subject to change with further investigation. Outgassing may be a problem to vehicles and structures in the vicinity of the ET. Possible solutions include bagging the tank in a mylar blanket which will retard the rate, applying metals by vapor or liquid deposition to the outside of the tank on orbit, removing the SOFI from the tank, or keeping the tank based structures lower in orbital altitude than the rest of the operation by the use of tethers (14). The ramifications and the magnitude of this problem warrant further investigation as tanks are proposed for orbital applications. IV. The Aft Cargo Carrier The first actual enhancement of the STS is likely to be the Aft Cargo Carrier (ACC) (4). The ACC is detailed in the figure below. It is basically a cargo volume constructed similar to the ET components using the same tooling and bolted onto the bottom flange of the hydrogen tank. There are three basic advantages to the ACC. The first is that it provides a volume nearly equivalent to the cargo bay of the shuttle that is not constrained by a diameter of 15 feet. Its volume of 9,100 cubic feet compares well with the orbiter cargo bay of 10,600 cubic feet. The ACC dimensions of 27.5 feet in diameter and 20 feet in height allow large diameter relatively low mass payloads to be flown without the constraints imposed by the 15 feet diameter orbiter cargo bay. A typical ACC weighs near 14,000 pounds (4). It consists of a skirt which connects to the ET, a payload support structure and a shroud and is insulated for protection from the SRB plumes and blast effects. Payload penalty to orbit for an ACC is from 9,800 - 11,400 pounds (68). This is below the actual ACC weight as a result of shroud jettison after SRB separation. Center of gravity problems during flight have been addressed and do not appear to be a problem. The beauty of the ACC is that it provides another cargo volume at a minimal cost. This is important to the STS program because it helps remove a payload constraint. The orbiter imposes two constraints on payloads. These are volume and mass limitations. The mass limitation can not be changed without changing actual orbiter performance. The volume constraint can be
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