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This week's guest blogger is Waddell Robey. He has eighteen years of aerospace engineering and management experience and thirty plus years in health and human services research. He is a strong space exploration activist and maintains a steady commentary on Twitter as XiNeutrino and through direct mailings to NASA leadership. He has several blogs devoted to space exploration. His philosophy is that we are here to explore, and in exploring we discover, and in discovering we seek to explain, and in explaining we enrich that which we call science.
Introduce a topic about space elevators within a group of space travel enthusiasts and you will usually get a variety of reactions from eye-rolls, to snickers, to nods of acceptance and interest. Although there is continuing encouragement, especially from NASA, for design research into the total space elevator concept, there remains several critical areas that pose serious barriers. One of the most important and the most challenging to address is the exposure of the space elevator to intense radiation.
Anchored to an ocean platform on the equator and to a geo-synchronous space terminal 100,000 kilometers above the Earth, the space elevator, driven by high-powered lasers, rises along a carbon-nanotubular1 ribbon to its space terminal. Sounds dramatic and fascinating; and it is.
In the course of its travel, the space elevator will pass through the Van Allen Belts2. The belts are a space travel hazard. It is dangerous when systems and humans are directly exposed to their radiation. This would certainly be the case for the passengers, cargo and the space-elevator itself. Yes, Lunar bound astronauts passed through the belts, but at a speed that sharply reduced the length of time of their exposure. High-speed passage through the belts by the space-elevator is currently not an option. If it were, travel could be like this description.
Although there is no specific research into radiation shielding for a space-elevator system, there are two shielding concepts that are examples of the kind of shielding technology that may work. At MIT, researchers have developed and experimental model of a shielding system based upon superconducting magnet technology4. Research in this area began during the early start of this century and is still relatively new. In addition to creating a strong magnetic shield the MIT system is designed to require low energy input. Additionally, when under relatively stable temperature conditions the magnetic field can be maintained for long periods of time. These two latter factors, low energy requirements and sustained activation have significance for any space-elevator program.
The other potential shielding system is based upon asymmetric electrostatic shielding5. Applied research to spacecraft shielding also began in the early part of this century. Of the two, this is the least desirable application for space-elevators. This is due to the required high energy support as well as a unique balloon array. The array of balloons is differentially charged and thus provides shielding of various particle charges as well as cosmic radiation. This could be a cumbersome and actually limited shielding approach. Regardless, the research into the application of this shielding concept can be of value for eventual shield-system designs for space-elevators.
Yes, it is certain that many, who regard the idea of space elevators as unlikely space transport systems, will still regard the open radiation shielding issues as high priority for major spacecraft design. They would just consider that there would be limited or no planned application for space-elevators. This understandable position does affect funding and program support for specific shielding research as applied to potential space-elevator operations.
Returning to the topic of this article, can we presume that space-elevator systems design will progress and need serious design solutions for radiation shielding? A broad review6 of the progress in overall design efforts of this space transport system supports an affirmative response.
Long before the radiation issue is critical, the overall system must overcome other major hurdles such as safety from space junk, safety from violent Earth weather events, and the proven functional safety of the nanotube ribbon. Additionally, the power systems that support the laser propulsion technology must be powerful enough to also support some form of radiation shielding. Lastly, the entire package must be designed in a compact and weight sensitive manner if the space-elevator is to achieve its 13+ ton cargo/passenger lift capacity.
My vote would be for a dream that is rapidly approaching reality. What is yours?
1Carbon nanotubes: http://bit.ly/gL6OSX
2Van Allen Belt: http://bit.ly/dIDotu
3Space radiation research: http://bit.ly/fcnQRZ
4MIT Superconducting Magnet Technology: http://bit.ly/fnz6GV
5Asymmetric Electrostatic Radiation Shields: http://bit.ly/h5VoVy
6Space-Elevator Conference and Data: http://www.spaceelevator.com/
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Are there any estimateson when this technology might be viable?
Wow- very cool article, and easy to read.
Instead of shielding the radiation, there must be a way to cancel it our or neutralize it. Or what if you could block it by slowing down the radiation (instead of speeding the passengers up)?
Nice overview of oft-neglected issues in space elevator design.
It's worth mentioning that while a human-capable elevator is an ideal end-goal, there are other way-points that might support construction and improvement of the system until that ideal (assuming it's possible) can be reached. Low-cost transport of radiation-tolerant payloads to and from orbit still might be a viable economic application, and providing sufficient radiation protection for more sensitive (but smaller-volume) payloads may be a way of developing and proving systems that might be applied to humans.
The original reason for a space elevator was the suppression of the first stage of typical rocket systems. The first stage of a rocket system operates only up to the Karman line (+/- 100 km/70 miles). Due to its operational requirements a centrifugal CNT tether needs to be extended up to a GEO distance and along the way going through the Van Allen belt.
There is another system that can do the trick of eliminating altogether the use of a first rocket stage and is that of a SpaceShaft. Although its general appearance is that of a column this is not a space tower but an elevator system. The reason why this is not a tower is because the whole structure is constantly moving upwards due to constant accumulation of upthrust from buoyancy throughout the dense regions of the atmosphere, allowing the system to rise thousands of tonnes instead of tens of tonnes.
To see pictures of the proposed system and for a better description of the mechanism visit http://spaceshaft.org