6.35 The ES group anticipated that the hull would also be subject to translational motions (due, for example, to forces applied while moving cargo in and out or thrust from gas leaking to vacuum). The internal controls could not cure this problem. Neither could they apply the precessive torque required or handle emergency situations. For these purposes the ES group proposed a set of thrusters. So that their exhaust would not impinge on the shield, they would be mounted on projections of the hull extending through the light beam and cargo cutouts. Since they would rotate with the hull at 2 to 3 RPM, a force applied in any direction other than along the spin axis would require timed sequential firing of the appropriate thrusters. Firing thrusters in opposite directions at each end of the hull would provide torque on the hull. Firing thrusters in the same direction would translate the hull relative to the shield. The ES group saw several advantages to this active open bearing system. It was simple, in that it left the shield alone. The hardware anticipated was all existing technology. Since the shield was not spun and had no forces applied to it, it would not require much support structure. The Fabrication and Test Group considered using the despun shield as a place to anchor cargo while it waited processing. However, there were also fundamental disadvantages to this design. First, it would not be fail-safe. If the mechanism applying precession torque failed, the hull would stop precessing but the shield would keep its rotation about the q-axis. With a rotation rate of l.99lxl07 radian/sec, the shield would take 46.5 hours to move 5 meters across the tips of the hull's endcaps. Thus, if nothing were done about the torque failure, the hull would contact the shield in approximately two days. There would be some unattractive stopgap measures to lengthen that time. For example, an emergency system could torque the hull against the shield to precess it but this would tip the shield's axis of symmetry out of the plane of the ecliptic. Similarly, slowing or stopping the shield's rotation would help but the colony's axis of symmetry would move away from the Sun. Though preferable to a disastrous contact between hull and
RkJQdWJsaXNoZXIy MTU5NjU0Mg==