The baseline design for an earth-based space elevator calls for a tether that is 100,000 km long. Just 40 kilometers (four one-hundredths of a percent (.0004)) of that length is within the commonly defined boundaries of the earth’s atmosphere. And yet this tiny fraction of length is “home” to many special problems which must be dealt with; wind, storms, lightning, ice, etc.
A new study has been released on Astra Astronautica entitled Design Concepts for the First 40 KM a Key Step for the space Elevator discussing these exact issues. From the reports abstract:
The Marine Node for the Space Elevator Infrastructure is the base for all activities to load and unload the cargo and climbers. As the basic design of the space elevator power system is solar power only, the first 40 km is hazardous to operations and demands enclosed packaging of fragile tether climbers. A significant question is: how do we place a full-up tether climber, driven by solar power, above the atmosphere? Two approaches, starting at the Marine Node, allow the tether climber to initiate the climb with solar energy above the atmosphere. The third viable approach is to provide a platform at altitude for initiation of tether climb. These approaches would enable solar power to be the source of energy for climbing. The three approaches are:
Option One and Two: Marine Node (MN) Starting Location.
MN – Box Protection – use boxes to protect the fragile solar panel and power the climber directly with a power extension cord to climb out of the atmosphere.
MN – Spring Forward – use the characteristics of the elastic factor of the tether material.
Option Three: High Stage One—develop a platform at altitude.
Dangers for the space elevator during the first 40 km in altitude are discussed, and the options to deploy the tether climber and its solar arrays from the ocean surface to the desired altitude are explained.
The study is very well done and well worth the time for anyone who is at least casually interested in the idea of a space elevator. The problems discussed are certainly real and were first discussed at length in the Edwards-Westling book, The Space Elevator: A Revolutionary Earth-to-Space Transportation System.
The idea of “Spring Forward” was inspired by this:
By the way, the Acta Astronautica’s study authors were Dr. John Knapman and Dr. Peter Swan. Dr. Knapman is an ISEC Board Member and the head of the ISEC Research Committee. Dr. Swan is also an ISEC Board Member and the president of ISEC.
(The awesome image of Church Bell ringers is from here)
Blaise Gassend and I tossed around what’s basically the Spring Forward approach about ten years ago, with some differences:
1. The first 40 km (actually we used 30) of the SE wouldn’t be a ribbon at all, but a cylinder about the size of a pencil. This would be almost entirely immune to wind and other atmospheric effects and relatively simple to wrap around the spool of the ground-based winch.
2. The top end of the round cable would be permanently attached to the bottom of the weather shield (the Box), as would the bottom end of the ribbon part of the SE.
3. The top of the weather shield would open at altitude to allow the climber to collect solar energy and climb out and away. As it climbed, the Box would be winched back down to the surface.
4. Since the 40 km of the SE above the box is a ribbon, the box would be kept above the atmosphere whenever the weather forecast was unfavorable.
We also talked about winches at the counterweight and at GEO to compensate for the effects of winching the first 40 km up and down.
I’m really quite dubious about the High Stage proposal with the rotors zipping up and down; it’s just too darned complicated. I’m also dubious about using nothing but sunshine to power the climber. A couple of sun-pumped lasers in GEO at maybe 30° ahead of and behind the SE could put a lot more energy on the climber’s solar panels.