Moon & Mars Orbiting Spinning Tether Transport - Tethers Unlimited

Appendix L: Tether Boost Facility Design Final Report3.3.4 Recommended Follow-on studies• More detail in tether reel mechanism design.• Know that a tether guiding mechanism or system is needed. Proposeddesign solutions include (1) a fishing reel-type reel design with a structuralguide that shuttles back and forth as the tether is wound onto or off of thespool and (2) a system of pulleys guiding the tether at a specified tensionoff of the spool.• How much electrical power will it need for drum to turn and being deployingtether (with copper or aluminum wire wound into last 20 km, will tether wantto stick or jam in tether guides?)3.4 Electrical Power System (EPS)3.4.1 Design Requirements, Drivers, and AssumptionsMajor design drivers are the high power requirements of the ED Tether andreel/deployer mechanism. An assumption is made that both the ED Tether thrustmode and reel/deployer will not be utilized simultaneously. Power estimates for theTether reel vary dramatically depending on the size of the tether and rate of reel-in.While energy required for initial reel start-up can exceed that of the ED Tether, it isassumed that the reel on a per orbit average, will be equal to or less than thatrequired of the ED Tether. Thus the power system is designed for nominal worsecase ED Tether usage. Present design assumes ED Tether power of approximately300 kW.3.4.2 New Issues and Requirements IdentifiedDo to high power requirements of ED Tether and reel, several issues wereidentified. High power space DC/DC converters do not presently exist. Althoughconverters in the 100kW class and at high voltage are on the drawing boards for suchspace applications as space based radar. Also the high voltage required for the EDTether creates other issues in space. Interaction with space plasma at 20kV is asignificant design driver. The potential for discharge and corona effects will driveinsulation requirements, thus increasing system weight.Other design drivers are thermal control. In order to drive down weight and cost,the batteries selected are being utilized at a high depth of discharge. In order to getboth 10 years of life and a high depth of discharge, an active thermal control systemis required for the batteries. Optimal life is reached at approximately 25degrees C.Also due to the high power of the system, items like the DC/DC converter can createthan 10 –20 kW of waste heat in a small area. Thus an efficient thermal system isrequired for the power systems. Controlling the temperature of the DC/DC converterand power switching electronics is also critical to reliability. Reliability dropsdramatically as temperature goes up.L-60