(Note: During the 2013 Space Elevator Conference, several workshops were held, delving more deeply, with audience participation, into specific Space Elevator related topics. This is a summary of one workshop, Space Elevator Tether Climber.)
Champions: Pete Swan, Skip Penny
Initial Presentation: “ISEC Report Major Points” – Pete Swan
Goal: To stimulate thoughts and inputs from the conference attendees on tether climbers — involve the attendees…
Outputs: Draft ISEC Report to be available by 15 December – review upon request from attendee or interested party.
- 30 minute major talk on topic
- 5 minutes of discussion on handout sheet [stimulation of ideas and areas to discuss]
- 10 minutes of brainstorming on topics to discuss
- 45 minutes of brainstorming in small groups [breakups along the lines of the topics to be discussed]
- 20 minutes of discussions by small groups to large audience on results of brainstorming
- 10 minute summary
- Champion and helper will summarize the results and put on web
Issues: The design of tether climbers in the next twenty years will leverage the phenomenal growth in materials sciences to enable lighter/stronger structures, lighter/more capable batteries, lighter deployable solar arrays, and more energy efficient laser energy devices. The question is what should the preliminary design look like? The 2013 ISEC theme and study will be focusing on these topics and looks forward to the inputs at the conference.
Major Points: Eight different types of climbers described:
- Atmospheric [up and down – dock on stratoballoons?]
- First 7,500 kms [high gravity]
- 7,500 to GEO [1 MW power standard]
- Beyond GEO
- Personnel Climbers
- Cargo Climbers
- Micro- to Macro small climbers using the tether [transparent to other climbers]
- No such thing as extra power
- Anything brought up is valuable
- Separation of 3 and 4 above is based upon power needed [from gravitational fall off], but should happen someplace between the major radiation belt altitudes.
- Mate climbers to pass payload
Topic: Evolution of Climbers
Team: Michael Schaeffer, Sandee Schaerffer, Bryan Laubscher, Peter Stewart
- Construction climber needs to build bigger tether capacity [20 MT to 40 to 60 etc]
- Second tether prior to commercial operations
- Repair climbers are important, from LEO to GEO for monitoring tether health, as well as monitoring debris fields.
- Payload climbers should also be able to de-orbit
- Astronaut driven climbers must be able to be rescued [detachable, re-enterable]
- Low orbit options to include family trips and altitude freefall records
- GEO tourist climbers will be much bigger, have plenty of food and be able to reenter
- Logical answer would be GEO solar power to climbers
- Climbers dedicated to launches to Mars and beyond, with Mars elevators + power projection to surface
- Much future is Mag-Lev option with large Apex Anchor [asteroid]
- Ring World is reasonable for GEO stations connected
- Outer planet moon trips reasonable in the future
Topic: Getting On-Off the Tether
Team: Canaan Skye Martin, Bill Rossington, Intchested Amature, David Schilling, Jose Fuentes, Hal Rhodes, Michael Laine
- Circular orbits will probably need extra thrust once released
- Ellipitical orbits will be from almost any height
- One question is how much does the motion of the tether effect the release velocity [vector, direction and magnitude]
- Figure out how to coordinate up/down climbers on same tether
- On a single strand, to go around another tether, someone must disconnect/re-connect
- Below GEO, Stop, then disconnect, then thrusters to enable mission orbit
- Most situations are very dynamic, release of climber affects mass on tether
- Chaos in launch from dynamics of tether? Could be perturbations due to debris avoidance, releasing and attaching cargo, varying climber speeds and any unpredictable movements.
Topic: Climbers Specialized for Different Altitudes
Team: Ben Sibelman, Max Braun, Dennis Wright, Jun Kikuchi, Peter Robinson
- There are strong reasons for varying designs of Climbers
- Low level climber will probably be driven by laser
- Higher speed will come from solar at higher altitudes
- Four separate and distinct phases with handoffs between climbers
- Each climber goes up, hands off payload, goes back to lower range, picks up next payload
- About half the payload throughput of original design
- Only four climbers required on tether at any one time… payloads are passed along
- To repair of changeout climbers, three high ones come down to lower climber which then loads them as payload and decends to surface.
- After proof test of concept, larger advanced climbers can replace original concept and could go from LEO to GEO.
Workshop discussion concluded that four separate optimized Climber designs would be required, but this must be confirmed by a more detailed design and operational study.
- Climber 1 for days 1 & 2 would be slow for operation in the high low-altitude gravity field : low speed, high power, laser powered.
- Climber 2 for days 3 & 4 would use large solar arrays, with shielding as required for transit through the upper Van Allen belts : medium speed and power.
- Climber 3 for days 5 & 6 would use smaller solar arrays : higher speed, lower power.
- Climber 4 for days 7 & 8 would be used to finish journey to GEO and beyond : optimized for high speed operation, with lowest-power motors and smallest solar arrays. ( Transit times may mean a 5th Climber would be needed beyond GEO, but this could be identical to the 4th Climber.)
Topic: Alternate Climbing Approach
Team: Dalong An [Samuel], Peter Glaskowsky, David Horn, Paul Wieland
- New motive approach
- Similar to rock climbers in grip
- Approaches the tether with gripping motion vs. wheel interactions
- Easier to grasp vs. pull oneself up by wheels
- Inspired by watching monkeys climb
- Hybrid loop
- Less damage to the tether from gripping [brake mechanism] vs. friction from moving wheels.
Idea: A vertical tether is approached from the side by a long loop of strong material.
- The goal Sam proposed was to find a way around the need for a wide, thin ribbon tether.
- That requirement follows from the usual assumption that the climber must use multiple drive wheels with a high normal force against a wide tether to overcome the disadvantages of a small contact patch and a low coefficient of friction.
- Sam had the idea of using some kind of hand-over-hand motion to climb the tether the way a monkey would, by gripping the tether with some kind of clamp and pulling the climber up to the clamp.
- We didn’t like the idea of reciprocating grippers repetitively passing each other on the tether for the obvious reasons. It seemed to me that we could get similar results without one “hand” passing the other by using a method like mountain climbers use to ascend a rope, with prussik knots (or mechanical equivalents such as the Petzl Ascension) that don’t bypass each other.
- My suggested solution is to have two “shuttles” above the climber.
- A rope (or multiple ropes for redundancy and balance) is looped through all three units, each of which has a tether clamp and a rope clamp.
- Each shuttle has a small electric motor and a drive system that can pull it up the tether, carrying only the load of its own weight plus the weight of the rope.
- The climber has a motor-driven capstan that can pull the rope, but it doesn’t necessarily need any way to pull on the tether.
- The rope can potentially be a COTS product; a 2″ Dyneema rope is rated at 155 metric tons and weighs less than one pound per foot.
The climbing process works this way:
- To start, imagine the Climber is on the ground and the two Shuttles are immediately above it. At this point, there will be considerable slack in the rope.
- Shuttle 1 (on top) engages its drive motor and begins pulling itself up the tether at speed 2V (where V is the target speed of the Climber) until the loop of rope is nearly tight.
- Shuttle 1 clamps the tether and the rope.
- Shuttle 2 unclamps the tether and the rope.
- Shuttle 2 begins pulling itself up the tether at speed 2V.
- The Climber engages its drive motor to pull itself up the rope at speed V, which cause it to ascend the tether but without applying any force directly to the tether. (That force is carried from the rope to the tether through a Shuttle.) As the Climber comes closer to Shuttle 1, it generates slack in the rope, which hangs below the climber.
- Shuttle 2 stops just short of Shuttle 1.
- Shuttle 2 clamps the tether and the rope.
- Shuttle 1 unclamps the tether and the rope.
- Shuttle 1 begins pulling itself up the tether again at speed 2V and stops when the rope is nearly tight.
- We repeat steps 3 to 9 to the top of the rope.
- Note that the Climber is constantly pulling itself up the rope, stops ascending the tether. Meanwhile, the two Shuttles alternate in pulling themselves up the tether, which is why they have to average twice the speed of the Climber while they’re moving. (For practical reasons they will need to travel at somewhat more than twice the speed.)
- The side of the rope loop nearest the tether (the “tight” side) remains stationary relative to the tether because at least one Shuttle is always clamped to both the tether and the rope.
- The other side of the rope loop (the “loose” side) moves intermittently upward. When moving (when Shuttle 1 is climbing) it moves upward at four times the speed of the Climber, and so will probably need to be managed carefully to keep it from whipping around. When Shuttle 1 is clamped and Shuttle 2 is moving, the loose rope just hangs in place.
- So there are some obvious challenges in this system, but perhaps it’s still a better solution than trying to drive the Climber directly against the tether. Or perhaps it’s only a better solution at lower altitudes where the direct friction drive solution is most difficult to implement.
- First, the upper gripper ascends the ribbon with almost no mass and feeds the loop rope[pulls the upper portion of the loop with it] with it as it moves up.
- Second, it grasps the tether at a much higher location than the last grasp [length of loop] and holds on
- Third, the climber pulls itself up on the rope loop without touching the tether until it approaches the upper grasping mechanism.
- Fourth, the lower grasping mechanism moves up with the climber and grasps the tether below the climber to hold it stationary at that point.
- Then repeat.