Space Elevators Craig Borchard Scott Shjefte 13 April 2004 Reference:

Towers In early 1962 the Convair Division of General Dynamics carried out a feasibility study, to see if very high towers would be of value for astronomy, high altitude research, communications and rocket launching platforms – steel towers could be built up to 6 km high –aluminium ones up to almost 10 km high Calculations show that a tower built of graphite composite struts could reach the very respectable height of 40 km, tapering from a 6 km-wide base.

What is a Space Elevator? A space elevator is a physical connection from the surface of the Earth, or another planetary body such as Mars, to a geostationary orbit - for the Earth at roughly 35,786 km in altitude. Video clip at

Carbon Nanotube (CNT) Bundles

Fullerene Nanotubes 1997: Yakobson, B. I., Smalley, R. E., Fullerene Nanotubes: C1,000,000 and Beyond, American Scientist, 85, pp , July- August 1997 Carbon Nanotubes (CNT) Single-Wall Nanotubes (SWNT) –Strength ( ~ 100 x steel, 10 x kevlar) –Electrical conductivity (~ copper) –Thermal conductivity (~ diamond) –Manufacturing is difficult (now) Its future in manufactured products… –High tensile strength –Ultimate laminate –Low mass –Forms strong fibers –Good electrical conductor –Excellent thermal conductor

Ribbon

Deployment

Small ribbon (10 to 20 cm wide and microns thick) deployed from geosynchronous orbit using four rockets and a magnetoplasmadynamic upper stage –Supports 990 kg payloads 230 Climbers (one every 3 to 4 days) add small ribbons alongside the first for 2.3 years –Supports 20,000 kg cargo climbers –These add to counterweight Power (100kW to 2.4 MW) is beamed up –Free-electron laser (840 nm) and 13 m diameter segmented dish with adaptive optics –Received by GaAs photocells (80% overall efficiency at this wavelength) on the climber's underside –conventional, niobium-magnet DC electric motors and a set of rollers to pull the climbers up the ribbon at speeds up to 200 km/hr. Spacecraft and construction climbers would become counterweights –Space end of the 100,000 km long ribbon An ocean-going platform would be used for the Earth anchor and located in the equatorial Pacific

Deployment of Ribbon 2 Job 1 for Ribbon 1 Capacity doubles with new ribbon Cost for future ribbons declines exponentially –First one costs ~$6B –Second one costs ~$2B

Overview of Hazards Lightning –Placement of base Meteors –Large – Maneuvering of base –Small – Ribbon design Wind Loading –Placement of base Atomic Oxygen –Ribbon design Radiation –Ribbon design Induced Oscillations –Tension adjustment in Active Vibration Control (AVC) system

Magnetospheric Hazards Extreme electromagnetic disturbances can move the cable, perhaps by 10s of kms. The cable itself is not very vulnerable despite passing through most intense radiation belts. Radiation effects on electronics (cargo and crawler) can be solved at a cost. Extremely severe radiation effects on humans have never been faced before (200x Apollo dosage, due to low speed). If not solved, humans cannot travel on the Space Elevator.

Base Location Initially targeted off the western coast of South America, near the equator, as shown in clips –Lightning strikes minimal –Wind minimal –Floating base can be moved to avoid storms and large debris

Planet Accessibility Flung off the end of the cable Initial payload (to Mars) could be self-deploying elevator

Space Elevators CNT or SWNT shows promising capability –Some manufacturing challenges remain –Health hazards completely unknown –Robustness to micrometeorites important –Orbit Cleanup Day Atomic oxygen needs coating development Robotic manufacture of ribbons in situ –Including bonding, coating, QA, repair Active control of oscillations and avoidance maneuvers Easier hazards –Lightning –Wind –Radiation (except to humans) "The Space Elevator: 3rd Annual International Conference" –June 28-30, 2004 in Washington, D.C. –