Moon & Mars Orbiting Spinning Tether Transport - Tethers Unlimited

Commercial Tether Transport AIAA 2000-3842satellite into a low circular LEO orbit. The microsatellitewould maneuver to rendezvous with the spinningTORQUE ª tether, and the TORQUE ª system wouldcatch and then toss the payload, injecting it into a GTOtrajectory. The TORQUE ª tether system would have atotal mass of approximately 1500 kg. It might be possibleto design the mission hardware so that after theTORQUE ª experiment concludes its technology demonstrationmissions, it would then enter operationalservice, performing useful, revenue-generating operationssuch as sending service & refueling microsatellitesto GTO as well as boosting lunar/interplanetarymicrosatellites into pre-escape trajectories.First Operational System:LEO⇒GTO/LTO Tether Boost FacilityBecause the launch costs for deploying componentsof a Tether Transportation system will be a significantdriver in the overall development costs, it will be imperative to the economic viability of the tether transportation architecture that every component placed intoorbit be capable of generating revenue very soon afterdeployment. Although our ultimate goal is to developa tether transport system capable of providing low-costtravel to the Moon and Mars, we have chosen to focusour initial development efforts on designing a TetherBoost Facility optimized for servicing traffic to geostationary orbit because lunar, Mars, and even LEO trafficvolumes are currently speculative or highly uncertain,whereas GEO satellite deployment is a relatively wellunderstoodand growing market.The LEO⇒GTO Tether Boost Facility will boostpayloads from low-LEO to geostationary transfer orbits(GTO). In sizing the facility design, we have sought tobalance two somewhat competing drivers: first, thedesire to be able to have a fully-operational, revenuegeneratingtether boost facility that can be deployed in asingle launch on a rocket expected to be available in the2010 timeframe, and second, the desire for the tetherfacility to be capable of gaining as large as possible amarket share of the projected GEO traffic. Recent projectionsof GEO traffic, shown in Figure 6, indicatethat the general trend for GEO payloads is to becomemore and more massive. Over the projected timeframe,payloads in the range of 4-6 metric tons are expected toaccount for roughly 80% of the commercial market.Consequently, it would be highly desirable to designthe Tether Boost Facility to handle payloads on theorder of 5,000 kg. On the other hand, a tether facilitydesigned to toss payloads to GTO must mass roughly 9times the mass of the payloads it can handle (due primarilyto tether sizing, orbital mechanics, and conservation-of-momentumconsiderations). If the tether facilityis to provide an operational capability after one launch,the tether facility must fit within the payload capacityof an available launch vehicle. In the 2010 timeframe,the largest payload-to-LEO anticipated is that of the2520151050Projected GEO Traffic2000 2002 2004 2006 2008 2010 2012 2014COMSTAC Projections, May 1999YearBelow 2,000 kg2,000 - 4,000 kg4,000 - 5,500 kg> 5,500 kgExtended ForecastFigure 6. GEO traffic projections for 2000-20015.Delta-IV-Heavy rocket, which will be able to place20,500 kg into LEO.Consequently, we have chosen to follow a modulardevelopment approach in which the initial Tether BoostFacility 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. DependingDelta-IVfPanelsFigure 7. The LEO⇒GTO Tether Boost Facilityr/appleechanismD6