IAC 2014 - Day 4: My Presentation

Today, I give my presentation about the static deformation of the space elevator tether due to the presence of a climber.  I have decided to open the talk with a picture of the CN tower.  You see, its been a foggy week of weather in Toronto, and I have taken some time to stare up at the tower from its base.  The top of the tower disappears into the fog - no end in sight.  The sight appeals to me for obvious reasons, so I have to mention it to the other space elevator aficionados in attendance.  Imagine a time, decades from now, when there will be no end in sight to such a structure, even on the clearest day.

I present a summary of my most recent research.  One of the most surprising things is that this fundamental mechanical analysis had not been documented yet.  You station a climber at some location on the tether, and what will the new equilibrium state of the tether be?  Will it stretch more or less and in what locations?  What are the changes in stress and tension throughout the tether?

The results are as follows:

Chief Technical Editor of Climb

When I look at other fellow engineers, there is one trait that we tend to share besides the obvious ones (affinity for Star Wars, unwarranted big egos, etc): lots of extra-curricular activities.  Most engineers that I know play in a sports league and are involved in multiple projects outside of their actual profession.

I play on a soccer team, drum in bands from time to time, and manage this blog.  Well, I now do something else - this week I was asked to be the new Chief Technical Editor of Climb, the Space Elevator Journal affiliated with ISEC (the International Space Elevator Consortium).

Cover shot of Climb, Vol. 1 (courtesy of lulu.com)

I Predict a Space Elevator on Earth in my Lifetime

Most of my readers are aware of my research on and affinity for the space elevator project.  A whole page on this site is devoted to it.  Still, I try not to overload my blog with S.E. related content; spaceelevatorblog.com is the place for S.E. devotees to stay up to date with the goings on, while isec.com is where one goes to get involved in the actual project.

Still, I could not help but give a brief response to George Dvorsky's article that was posted last week on the io9 blog entitled "Why we'll probably never build a space elevator."  In it, Dvorsky lists five problems, which is a strange choice of word to describe what engineers call challenges. While the challenges he discusses are mostly relevant and the discussion mostly accurate, the conclusions he draws from them are odd - it seems as though he arrives at them in order to satisfy the title of the article.

For example, the number one 'problem' with a space elevator is, as the author correctly states, producing a material with a sufficient strength to density ratio with which to construct the tether. Though his numbers on this are not entirely correct, it is true that material science is far from producing a substance rendering S.E. construction feasible.  However, the argument that the project is a dud because construction cannot begin today is absurd.  Over the past one hundred years, the field of material science has taken many leaps, each paving the way to new technologies.  The space elevator is not the first technology that needed to patiently await a strong enough and light enough material, and it will not be the last.

Furthermore, I take issue, personally, with his 'problem #3', about climber excitation, which happens to be one area I have researched extensively.  My research found the extent to which a climber excites the tether (it is proportional to lifted mass, distance climbed, and climber speed), and proposed some reasonable methods to mitigate such effects.  With respect to all of the big challenges associated with the space elevator, this one has been shown to be minor.

The Space Elevator

There are two main reasons why, for the past sixty years, man has launched rockets from the surface of the Earth. 

The first reason is to place satellites into an orbit around our planet.  The moon is a Celestial body that orbits the Earth in an elliptical fashion at an average of about 380,000 km away from the Earth.  Other than this large body and other small space debris that orbit the Earth, all other bodies that do so were placed in their respective orbits by man to serve some purpose.  One can think of an orbit as a path that a falling object takes continuously around a larger body.  Much in the way that a baseball’s path curves to fall towards the Earth once it is thrown, an orbit is in a perpetual state of falling.  The difference is that the orbiting body is moving much faster than the baseball (think kilometres per second), and the baseball faces the resistance of air, whereas the drag forces in space are negligible. 

It boggles the mind, but we (and when I say we, I mean America and Russia) have transported thousands of satellites into space.  Most satellites are used for communication, be it internet, phone, or television, while some are used for Earth observation leading to weather prediction, the tracking of oil spills, and the marvel that is Google Earth.  Most satellites are located hundreds of kilometres above the surface of the Earth (note that an airplane’s altitude rarely exceeds 12 km) in an area known as LEO (Low Earth Orbit).  

Another popular zone is at the GEO (Geosynchronous) altitude of about 35,800 km altitude; this is a special altitude for which the orbital period of a satellite is the same as that of the Earth.  If one were to stand on the equator and stare up at an equatorial GEO satellite, one would observe no motion at all.  It would be as though the satellite were attached to the Earth by an invisible cord.  The typical operational life of a satellite is fifteen years.  As such, the majority of satellites currently in orbit are decommissioned and commonly referred to as space junk.

The other reason for which man sends payloads to space via rockets is for interplanetary travel.  Such ventures are done in the name of research, observation, exploration, and discovery.  Sometimes these payloads contain astronauts, as in some trips to the moon, but often these are unmanned missions, or probes, investigating, for example, Mars or Saturn’s moons.  The missions are very exciting, sometimes providing answers to important scientific questions, other times demonstrating what we can achieve when we put our minds to it; the 1969 moon landing was perhaps the defining moment, technologically speaking, of the twentieth century. 

An even more formidable task would be sending man on a return trip to Mars.  The greater distance to Mars as well as the greater Martian escape velocity means that the payload leaving the Earth would be much more massive than that for Apollo 11.  Also, the trip length (years instead of days) would make the challenge for the astronauts far greater.  However, it is the issue of the large mass which makes the Mars mission unrealistic today.  Transporting mass away from the Earth using rockets is prohibitively expensive.  The cost for satellite placement in GEO is in the area of $10,000 US per kilogram of payload; it is substantially greater for interplanetary travel. 

In today’s space industry, every gram is questioned.  In order for a payload to achieve the escape velocity required for interplanetary travel, over 90% of the mass leaving the Earth must consist of fuel; this is a chemical constraint associated with rocket travel.  For this reason and others, the rocket will probably not be the principal mode of travel used to escape the Earth’s gravity fifty years from now.  

The most promising upgrade from the conventional rocket appears to be the space elevator, which could reduce the cost to GEO to as low as one hundred or even ten dollars per kg (reducing satellite placement costs by at least a factor of one hundred).  An operational space elevator, which would carry no fuel, would open up space to mankind; it would bridge the gap between us and the vastness we see when we stare up at night, both figuratively and literally.