Moon & Mars Orbiting Spinning Tether Transport - Tethers Unlimited

Appendix F: Tether Boost Facility Design Final Report2.2 Overview of System Requirements for Tether Boost FacilitySystem requirements are derived from mission requirements. At the top level, manysystem requirements for the MMOSTT boost facility are identical to missionrequirements. Not all are, however. Table 2 summarizes the current top-level systemrequirements. Some requirements, e.g. payload mass, are key design drivers and hada strong influence on Phase Two work. Some others, such as control of atomic oxygenerosion, are less critical as design drivers but are included in our technologydevelopment plans. Still other requirements, e.g. payload release orbit error, were notbelieved to be key design drivers or technical feasibility challenges and therefore werenot addressed in Phase Two work. Table 2 summarizes the impact of each requirementon the current design and how each will be addressed in the follow-on technologyvalidation program. Below we describe system requirements that were not describedearlier as mission requirements. These are marked with asterisks in Table 2.Payload interfaces must be compatible with satellites designed to fly on Delta 4 andAriane 5. This completes the compatibility criterion that allows customers to avoiddependence on a single launch vendor. Not only must the mission be compatible withpayloads for those vehicles, but the interfaces to the payload must also be compatible.(Interfacing to the payload will be the primary function of the payload accommodationassembly, but some payload interfaces might touch the tether boost facility.)The requirement for a ten-plus year design life means a single tether boost facility willoperate for at least ten years. An alternative we considered was to deploy multipleshort-lived facilities over the ten-year required mission life; but the high cost of hardwareprocurement and launch makes a long-life facility preferable. The requirement thatmaximum lifetime should not be limited by consumables and expendables means thesystem must permit any consumables or expendables to be resupplied in orbit. It led toa design goal of avoiding all consumables and expendables. Our current designsatisfies that goal, though further analysis is needed to see whether the facility canmaintain adequate attitude control without thrusters. Like the lifetime requirements, therequirements for evolvability and one-failure operation also support the financial goal ofletting the system earn revenues for as long as possible. Disposal and two-failuresafety requirements address political and legal feasibility.Automatic production of mission profiles increases startup costs, but is likely to be agood investment in the long run due to reduced operating costs. The requirement forlaunch on existing vehicles also supports financial feasibility by avoiding the cost ofdeveloping a new launcher. The requirement for some capability after the first launchallows the system to begin earning revenues sooner, which improves the financialfeasibility. Our payload requirement of 2500 kg to GTO for the first-launch system doesnot mean the system can handle only payloads of 2500 kg or less. A system of thatsize can handle the more common and lucrative 5000 kg payloads, though it cannottransfer one all the way to GTO from a 300 km circular orbit every 30 days. Someadditional propulsion would be needed until the second launch increases GTO capacityto 5000 kg.F-7