A Thought Experiment: LIFEBOATS

CONTENT
REVIEW UP AND DOWN
STRANDED ON DOWN
LIFEBOAT RIDES THE BEAM
STRANDED ON UP
SUMMARY

Since Space Elevator (SE) tether ribbons will inevitably rip, it makes excellent good sense to plan emergency return capabilities.

For some scenarios, consider a "lifeboat", Thought Experiment's brainstorm. TE proposes a new type of vehicle to safely return payload back to Earth's surface. Preferably, it will land precisely at the "base station" at the bottom of the tether.
ASSUMPTION: Tether remains intact. This chapter assumes tether sustains damage but remains intact. Thus, tether is still taut, but vehicles cannot safely traverse damaged area (i.e. "rip"). In another chapter, TE proposes tether will host numerous nanobots to expeditiously repair any rips; however, practicality compels us to assume that such repairs will take a while and will need testing prior to subsequent climber traffic.

Wikipedia Article: Bussard Ramjet Magnetic Sail

Pertinent Paper by Professor Pugno

REVIEW UP-LINK AND DOWN-LINK
	ASSUME ALL GOES WELL... Once each day, a climbing vehicle begins its climb on Up-link strand; 7.5 days later, the lifter reaches GEO. Lifter cannot use same strand to return because 6 other lifters are also ascending to GEO. Thus, lifter discharges its payload at GEO platform and is ferried over to Down-link strand dedicated for downward travel and starts its descent. 7.5 days later, it arrives at Earth surface to start another 15 day cycle. WHAT HAPPENS IF THE TETHER MALFUNCTIONS? PERHAPS A RIP DEVELOPS TO PREVENT FUTHER CLIMBER TRAFFIC.
STRANDED ON DOWN-LINK.
If rip is above climber , it might continue a tenuous descent to surface if the ribbon maintains sufficient tension. The option to dismount the ribbon and free fall to the surface would be very useful.	If rip is beneath, operators might direct passengers to transfer from climber to lifeboat to safely continue to surface. Perhaps a combination of jet packs and chutes might safely cushion impact at surface.gohere
If far from Earth's surface, a vehicle configured only for tether attached travel cannot safely free fall to Earth's surface; thus, it must return to GEO Node. HOWEVER, passengers and payloads may need to evacuate while tether is still in disrepair; thus, GEO Platform will need to deploy a space borne lifeboat Replace Down-Link Tether with Particle Beam. ① As vehicle transitions LEO, gravitation force grows from .05 g to 1g at surface. ② Earth bound particle accelerator sends high speed, particle beam upward to slow vehicle down during final portion of descent.	Upon departing GEO Node, TE assumes free falling lifeboat's linear velocity toward Earth increases from 0 to about 15 kps just before impacting surface. Since 15 kps is way too fast, the lifeboat will need a reliable method to slow down for a safe impact.
	Virtual Tether: High Speed, Particle Beam.To decelerate lifeboat for safe landing at Earth's surface, TE proposes high speed, particle beam to impart collective momentum against lifeboat's magnetic field extending from bottom. Perhaps start decelerating at midway (about 20,000 km above surface) for about 30 minutes deceleration time with resultant deceleration force of -1G.
FROM LEO, LIFEBOAT RIDES THE BEAM TO SAFETY.
	Compared to Space Elevator's "climber", TE's brainstorm lifeboat will greatly reduce: travel time, radiation risk, boredom. TE brainstorms ion beam from base station particle accelerator to decelerate lifeboat from LEO, about 700 km above Earth. To minimize vehicle damage from high speed particles, combine electromagnetic fields with on-board tokamak to store/release plasma as needed.

STRANDED ON UP-LINK
If rip is above climber, climber reverses direction to return to base station.	If rip is below climber, it might continue up if GEO Node offers safe haven.
Occupants of Up-Link's GEO Node might need to return to Earth before the ribbon repair is complete. The traditional return route involves the Cross-Link shuttle to Down-Link's GEO Node to take Down-Link climber on 7 day tether trip back to Earth.	Instead of Down-Link climber, the lifeboat provides a much quicker trip back to Earth. Lifeboat would accelerate via increasing Earth gravity back to lower LEO; then, 1G decelerate via a particle beam for a zero velocity return at Earth surface. Definitely quicker, the lifeboat is likely much safer.