Moon & Mars Orbiting Spinning Tether Transport - Tethers Unlimited

IAF-00-S.6.04Facility launched will be sized to fit on a Delta-IV-H.This facility will be capable of boosting 2,500 kg payloadsto GTO as well as 1,000 kg payloads to lunartransfer orbit (LTO). This facility could potentiallyservice approximately one-quarter of the ~400 payloadsexpected to be launched to GEO in the next 40 years.The facility hardware is designed in a modular fashion,so that after the initial facility has proven its capabilityand reliability, a second set of essentially identicalhardware could be launched and combined with the firstset to create a Tether Boost Facility capable of tossing5,000 kg to GTO and 2,000 kg to LTO. Additionalmodules can increase the system capacity further.To obtain a first-order estimate of the potential costsavings of the Tether Boost Facility, consider a missionto boost a 5 metric ton class payload into GTO.To do so using currently-available rocket launch systemswould require a vehicle such as a Delta IVM+ (4,2),a Proton M, or a SeaLaunch Zenit 3SL. Dependingupon the launch service chosen and other business factors,current costs for this launch will be approximately$90M. If, however, a Tether Boost Facility is availablethat is capable of boosting the 5 metric ton payloadfrom a LEO holding orbit to GTO, the customer coulduse a smaller launch vehicle, such as a Delta-II 7920,with an estimated launch cost of $45M, or a vehiclecomparable to the Dnepr 1 (RS-20), with an estimatedsticker price of $13M. While exact comparisons at thislevel are difficult due to differing payload capacities ofeach vehicle and the dependence of launch pricing uponother business factors, these estimates indicate that areusable Tether Boost Facility could enable commercialand governmental customers to reduce their launchcosts by 50% to 85%.The design of this LEO⇒GTO Tether Boost Facilityis discussed in more detail in a previous paper. 17Thefacility is designed to boost one 2,500 kg payload toGTO once every month. Although the facility design isoptimized for boosting 2,500 kg payloads to GTO, itcan also boost different-sized payloads to different orbits;the payload capacity depends upon the total ÆVto be given to the payload.As a result, in addition to boosting payloads to GTOand LTO, this Tether Boost Facility could also serve asa component of a transportation architecture for deliveringpayloads to other orbits and other destinations. Forexample, the initial (2,500 kg to GTO) Facility couldboost 5,000 kg payloads to the 20,335 km altitudeused by the GPS system. As a component in thetransportation system for Mars-bound payloads, thefacility could be used to inject a 5,000 kg spacecraftinto a highly elliptical equatorial orbit. At the apogeeof this holding orbit, the payload could then perform asmall ÆV maneuver to torque its orbit to the properinclination for a Mars trajectory, then perform its Trans-Mars-Injection burn at perigee. The tether facility thuscould reduce the ÆV requirements for a Mars missionby over 2 km/s.Cislunar Tether Transport SystemThis heavy-lift Boost Facility could then be used todeploy a second tether facility in polar lunar orbit.This facility, called a ÒLunavator ª Ó would be capable ofcatching payloads sent from Earth on minimum-energytransfer trajectories and delivering them to the surface ofthe Earth. The Lunavator facility could also be builtincrementally. The first system would be sized to catchpayloads from minimum-energy lunar transfers anddrop them into low lunar orbit (LLO) or suborbitaltrajectories, and to pick-up return payloads from LLOand send them down to LEO. The Lunavator masscould be built up using lunar resources, until it is capable of catching payloads sent from Earth and depositingthem directly on the lunar surface, with zero velocityrelative to the surface.The deployment of a tether in lunar orbit would enablethe tether system to begin servicing round-triptraffic, creating a ÒCislunar Tether Transport SystemÓ,illustrated in Figure 12, that could deliver payloadsfrom LEO to the surface of the Moon with little or nopropellant expenditure. 8Figure 12. The Cislunar Tether Transport System.SummaryTether systems have strong potential for providinglow-cost propulsion capabilities for a number of applications.Tethers Unlimited, Inc. is currently developingseveral small electrodynamic tether propulsionproducts, including the Terminator Tether ª for satellitedeorbit and the µPET ª Propulsion System for microsatellitepropulsion. These products will provide costeffectivepropulsion for satellite orbit raising, stationkeeping,and end-of-life deorbit for LEO spacecraft.TUI is also developing designs for momentumexchangetether systems capable of transporting manypayloads from LEO to GTO and beyond with minimalpropellant requirements.8