The Korean Lift College is one of those places.  But it was an honor to attempt to inspire those just starting on their journey into their professional lives this past weekend.

Although I think it was really the director of the school who was the most interested and was the reason we got the invitation, the students were much more attentive than I originally guessed they would be.

This probably had much to do with the quality of the translator which we had.  Although it was somewhat more difficult for me to present in Japanese than in my native English, it worked out much better that way.  But I believe Ohno-san was probably the primary reason they felt somewhat inspired after the speech.  Apparently we were there on a special day where the students take off to exercise and reflect on their year.  So they were in a good mood to start with.

After the presentation, it was somewhat difficult to communicate over dinner, but they were very hospitable and appeared interested in at least investigating the possibilities of an elevator which has a drive-train instead of a pulley system.

Unfortunately at just about every meal, I could only eat about half of the dishes.  But the half I could eat was very good.  And the amount I could eat increased proportionately with the amount of alcohol I consumed.

I most enjoyed just thinking about the things that we want to accomplish with the organization in the future.  It is always good to think out loud and to bounce ideas off of people.  This doesn’t happen enough in the scientific world due to pride sometimes.  But as we are not really scientists it may be easier for us.

The simulation I talked about in my last post I believe is a good tool, and it makes me think still that the first prototype of the SE that is built should be launchable and deployable in a single mission (< 100-200 tons).  This will keep mission costs down and allow for true trial deployments.  I hope this is possible in my lifetime, although the feasibility is highly dependent on the tether strength.  I believe a very lightweight climber will be able to be built in order to climb the scaled down tether.  Depending on the situation, it will probably need to be around a 100-200 kg climber.  This is assuming we can achieve a 1300 kg/m^3 and 30-40 GPa tensile strength.  If these are the requirements, I believe this is an achievable goal in our lifetime.

You can see this at <a href=”http://jsea.oreth.com/spaceelevator/3dsim/javascript/googlekml/se.html”>this link</a>  I have updated the parameters to reflect this.

So the question remains, what prevents us from sending a single mission to automatically deploy a tether with these parameters and lift a 200 kg climber into space.

For the baseline Space elevator we will need 5 thousand tons of material if we have a 50 GPa ribbon.  This sounds like a lot, but when you compare it to something like the World Trade Center it is nothing.  The WTC weighs about 100 times that much a whopping 500 thousand tons.  In terms of material it is not that much.  But we are talking about hauling it into outer space which still runs about 10,000$/kilogram.  So we are talking about 50 billion dollars.  But then again, lets put that in perspective.  It costs a few billion dollars to build a large skyscraper like the WTC or Taipei 101 or something of that nature.  And we have already launched that much mass into space before.  If you add up all the satellites (30,000 or so) masses, I imagine it is well beyond that figure.  So for me the hard part is still the actual deployment and maintenance of the elevator than the actual lifting of the mass. With next generation heavy-lift rockets, the mass could really be launched in about 100 launches.  It is definitely a big project, but the payoff is phenomenal.

This is still the part of the simulation that I have not completed.  The effect of the moon’s gravity on the motion of the elevator is still unclear.  When making this simulation it is clear to me that breaking things down into components and essentially allowing the computer to be your integration system, it makes the math quite a bit easier to manage.  I read some of the papers about the subject many of which appear to be very well thought out, but I often get bogged down in the math.  The calculations behind the simulation that I have done are fairly simple and fairly accurate.  It gives a decent overall view of the system.

Here is the link to the simulation.  Sometimes it takes a while to load. And it works best in Firefox.  It is a little jumpy when I do the Tether gravity simulation which is what I was working on before I stopped doing anything with it a few months ago.

For the time being everything is set in the Javascript so you cant change the parameters.  But if you are interested in playing around with it yourself, here is the source at the time of writing this post.  It is not really that big, but the 3d models are what takes up the space.  It is the easiest way to get something that looks realistic on Google Earth.  Although things still appear and disappear due to the difficulty of rendering objects quickly on Google Earth.  That may improve at some point.  If you cant see an object you will have to zoom in and out.  And you will have to use your own Google Earth Key if you put it on your server.

So I previously wrote about the detection mechanisms we currently use to track some 30,000 or so pieces of debris that are greater than about 4cm in diameter, and the detection mechanism is already pretty crude (no better than about a 100m accuracy) for anything a significant distance from earth.  I imagine from statistics and tracking the path for some time this improves quite a bit, but the basic technology which would be able to detect NEW debris that we dont know about and track it until it struck something would be about this (I dont remember the mechanism for the tracking at the moment so don’t quote the 100m).  Anyway, there are some few hundred thousand pieces of debris that are smaller than this.

So the question is what do satellites do currently to avoid this stuff?  Well, they move out of the way which is expensive since the cost of launching fuel is so drastic.  1kg of weight to orbit is still on the order of thousands of dollars which goes for fuel too.

The other thing they have used for smaller objects for the past few decades is a Whipple shield which is just a light-weight shield made of Kevlar or some other high-strength material.  See a sample of one from KIBO here.  And some more info from NASA here.

This would be a potential early application for high-strength Carbon Nano-tubes.

There is a slight difference between the elevator and these Whipple shields though in the fact that only a perpendicular hit on the elevator would cause damage.  I don’t know the research that has been done on this, but basic physics I imagine would show that anything other than a close to perpendicular hit would simply push the space elevator ribbon to one side or the other.

A low impact angle which runs the length of the ribbon would also be dangerous and could be potentially more damaging than a direct perpendicular hit. Again I haven’t thought through the physics of either of these scenarios.

In any case, from just a brief review of existing debris collision shields, it becomes obvious that this would not be a feasible solution to protect the space elevator from existing debris.  It is possible that there would be some way to adapt or pick up a piece of the existing technology, but it would be a stretch I think.  Anyway protecting from a low impact angle which runs the length of the ribbon may require some thought.  I dont believe this would be deflected.  If it hit at a low impact angle in a cross-section of the ribbon, it would spin the ribbon around, but running the length I am not quite sure how it would react.  This is something for further thought.