Home School Questions
A couple days ago, I spoke at here: http://www.seattleastro.org/ for the monthly meeting. It was a lot of fun. About 60 people or so, and they had a lot of good questions. I started about 8pm, and was still going about 930, when my voice, knees started giving out. 
As I told them, “this is my favorite topic, and I can talk about it all night…” but it was getting late, and I didn’t want to keep people. But then, afterward, we sold a few books, and I kept chatting with folks. There are a couple tangible deliverables that might emerge from this group. Cross your fingers, and we will see what happens.
Below, is one of these things… as most of you know, we are very engaged in education – especially younger kids. So I was very happy to have these students in the crowd. We have done a few projects with home-school students and parents so far, and I expect/hope to do more. If you home school; or are a 6-12 teacher, and want to lend a hand, let us know.
______
Hi (snip),
Thanks for your interest in the project; I appreciate it. And I am especially grateful that you brought your kids along.
On May 20, 2007, at 10:59 PM, (snip) wrote:
Hello!
I would like to thank Mr. Laine for the informative presentation at the Seattle Astronomical Society meeting. I truly enjoyed the lecture; I find these sort of projects fascinating. I remember reading about space elevators, first in Kim Stanley Robinson’s “Red Mars”, and later in Ben Bova’s “Mercury”. Imagining that this can become a reality in my lifetime is exciting!
I have enjoyed both of those books. And I have been lucky enough to have had a beer with Stan, and we chatted about how his elevator caused problems for our elevator… the concept of it crashing down and encircling the planet has caused us a lot of problems. So he was kind enough to write a short essay in our book – “LiftPort: Opening Space to Everyone” about that.
And I am pretty sure that Bova was in an audience of mine… there are several similarities to his character and me. Including word choice and mannerisms. I really liked his book (many of them, actually) but I have to admit it was a little creepy being revenge-filled killer…
In addition to my “day job”, I am an amateur physics teacher for several home-schooled high-school kids; my students and I were all attending Mr. Laine’s lecture. We prepared for the talk by reviewing the physics supporting this idea, and we came up with a lot of questions. Michael answered most of them during his talk, but there were several that we didn’t get a chance to ask. Unfortunately, we had to leave before the talk was finished (in order to visit the Observatory — the public viewing was another highly anticipated part of our field trip). Perhaps you can answer a few of our remaining questions about the elevator:
My friend and teammate on this project will be very pleased when he reads this. He home schools his kids – and loves it.
I would really like to chat with you about your preparation, prior to coming to the event. Specifically, what notes, materials, equations, homework, and if applicable, tests/grading, you have regarding this project? The reason I am asking, is we would like to develop some standardized curricula regarding the project, and, frankly, I’d like your help.
I am glad I answered most of your questions. I will try to give short answers here. But I also suggest our forums, blogs, and newsletter for further information.
#1. We learned that the elevator will carry at a rate of 100 tons per week, but we didn’t know:
(a) How many lifters will be present at a time — is it constrained to 1 car? If there are more than 1, will they pass, or transfer the loads?
1 lifter, per week, one-way trip (initially, that will change later. And later than that, we will add in additional ribbons. In the long term, we plan to have 4. 2 that are dedicated to “up”, 2 that are going ‘down’; 2 that are ‘fast’, designed for people, and 2 that are ‘slow’, designed for cargo. But in the meantime, we will have a single ribbon, and will have to share out the duties. They cannot pass each other or transfer cargo.
(b) How long does an individual trip take? How fast will the cars climb? Will they climb at a steady pace, or will they accelerate as they climb out of the Earth’s gravity?
They will accelerate, but the ‘top speed’, initially, is around 200mph. Not very fast, really. So the trip will take about a week.
(c) What will an individual lifter carry?
They will be primarily configured for cargo – 80 to 90 tons or so, per trip. However, just like the early railroads that were traveling cross-country, there will be passengers. We are planning on 20 people per trip; 50 trips per year, for a total of 1000 people. We hope that these will be construction workers, to help develop and deploy the solar energy satellites to help power the planet.
#2. In class, we computed that geosynchronous orbit is at about 35,000 km, and Michael estimated in his talk that the cable will span out to 100,000 km.
(a) Does this mean that there will be no counterweight on the space-end of the cable? What influences the decision to have such a long cable instead of a counterweight to reduce the length requirement?
There will be a ‘small’ counterweight. About the size of a couple buses… these are the dead rockets, and used construction lifters that we sent up, when we were expanding the ribbon (remember the grey and yellow ribbon on the video? The lifters that carry this ribbon, will stop at the end. They become the counterweight. We will build it ourselves, one lifter at a time. So, it exists, but it is pretty small – compared to the size of the system.
One interesting idea that has come up, and likely been rejected, is not having a counterweight at all. If you make the ribbon long enough, the mass of the string becomes its own counterweight. Right?
(b) 100,000 km is 1/4 of the way to the Moon! How will the Moon’s gravity affect the cable? Will compensations have to be made in order to keep the cable in orbit, or is it stable without adjustment?
Stable without adjustment. It will always move, and the moon will pluck the ribbon like a guitar string… but that motion is designed into the system.
#3. One problem in aviation is the formation of ice upon the wings of an aircraft. Could ice form on the cable and threaten to pull it down?
We don’t know. Originally, we suspected that ice would form. And the weight of it was significant, if it were allowed to build up. So, the simple answer is to not let it build… we can do that a couple ways, robotic lifters, or our power-beaming system could do it. However, now it looks like the ribbon will be ‘warmish’, because of the span of ribbon that is deep out in space. It might keep they system a (ranged) constant temperature – but we don’t know what that temp will be…
#4. Will there be any stations along the cable? Will there be lifters of different kinds for different purposes? How will people travel on it (and where will they go)?
No stations attached to the ribbon. But several stations at GEO, nearby the ribbon. Several different types of lifters – cargo, people (usually combined in on unit) but also construction and maintenance as well. Those will likely be different types of robots.
And where will the go – anywhere they want! Moon, Mars, GEO, and L5 – would all be places I would want to go…
#5. The current elevator design calls for power to be beamed up to the lifter via laser & photovoltaic cells. Lasers have a very narrow frequency response; solar cells are receptive over a broader spectrum, and become less effective as their temperature increases.
(a) How efficient is this process? How much power will be needed to propel the lifter?
Sorry, but I really can’t answer the question. I am pretty weak on my knowledge of lasers.
(b) Are there other power-sending methods in the works?
A couple. One that I think is interesting is carrying a flywheel-based power supply, using CNT as the construction method for the flywheel. Personally, I am a little nervous about that. But so far, no system is better than the laser. I really wish there were a better solution, and we are still looking into it. I don’t like the lasers, but don’t have a better option, yet.
(c) Could one harness the voltage potential between the Earth’s surface and the upper layers of atmosphere to power the lifter?
I don’t know yet. There are people looking into this, but we could use some help in this area.
#6. Mr. Laine mentioned that there is a group working on controlling the harmonics of the cable. As someone with background in applied mathematics, this sounds like a delicious problem. With varying tension, mass, and wave velocity all along the cable, and the desire to form nodes & troughs at precise locations, I imagine working on this would be a lot of fun. Could you direct me to the people who are tackling this problem?
Not so much ‘controlling’ as ‘understanding’… but yes folks are working on this. We are about to release some important info, regarding this and other research. So, if I can ask you to be patient a couple more days, I will answer that later. Check our newsletter and blog for more info.
Again, thank you for your time. Good luck with the project!
And thank you for your interest and enthusiasm. And who knows, maybe one of your students will end up working with us…
Take care. mjl