Moon & Mars Orbiting Spinning Tether Transport - Tethers Unlimited

Appendix F Tether Boost Facility Design Final Report2 Tether Boost Facility System Requirements2.1 Overview of Mission RequirementsThe MMOSTT system is intended to become part of a commercially viable enterprise totransfer payloads between various pairs of orbits. Requirements for the MMOSTTsystem are focused on making the system commercially viable. Commercial viabilitymeans the system must meet customer needs and must be financially, politically,legally, and technically feasible. Customer needs drive mission requirements forpayload mass, destination orbit, release orbit precision, and reliability, as well as systemrequirements for payload interfaces and payload environment. We chose to focus oncustomers whose need is to deliver commercial comsats to GTO. Initial requirementsfor GTO delivery missions were defined in "Tether Boost Facility Mission RequirementsSpecification" by Dr. Rob Hoyt on November 17, 1999. Mission requirements wererefined and the initial system requirements were defined during a meeting of theMMOSTT team and NASA MSFC personnel in March 2000. The system requirementswere further refined during a MMOSTT technical interchange meeting in May 2000.Table 1 summarizes the current top-level mission requirements for the tether boostfacility. For the near future, comsat GTO packages will have about 5000 kg mass.Comsat launch customers usually wish to avoid dependence on a single launch vendor,so we require MMOSTT to easily accommodate satellites designed to fly on otherlaunch vehicles, Delta 4 and Ariane 5. That is, a payload designed to fly on either ofthose launchers should be able to fly on MMOSTT with no modification and no loss ofcapability. This appears as two mission requirements: one that the orbit insertion errorfor the release payload should be no greater than the insertion error for other commonlaunch vehicles, and another that the payload's environment, e.g. acceleration levels,should not be more stressing than the environment aboard those vehicles. (Note thatresponsibility for the release orbit error may be shared among the tether boost facilityand the payload accommodation assembly. Allocating error budget to these elementswill be accomplished in later work.) Customer need drives the requirement for payloadpickup reliability of at least 99%.Financial feasibility drives requirements for turnaround time and mission lifetime. Afinancially successful project must earn enough revenue to recover startup costs andoperating costs plus a healthy annualized return on investment. The missionrequirement for 30-day turnaround time matches the rate of GTO launches in theaddressable market. This permits MMOSTT to earn revenues as fast as the market willbear. The ten-year minimum life requirement means the system will operate longenough to recover startup costs and earn a profit. The unconstrained maximum lifetimeand the requirement for growth to larger payloads make the system likely to have anextended life as a cash cow, responding to changing customer needs and earningrevenues after startup costs are fully paid off.F-5