A group from Bremerton, Washington is attempting to achieve what some consider impossible: constructing a space elevator enabling humanity to not only escape Earth's orbit, but also reduce the cost of space travel, thus opening up space for everyone.
Simply known as LiftPort, this company's goal is to construct a space elevator over 100,000 kilometers into space from an oceanic floor. But while constructing a space elevator may be feasible on Earth, building one off world may not be.
In order for the space elevator cable to remain "straight" and upright, centrifugal force is needed to counteract the pull of gravity. Like a yoyo needs to be constantly spun around a hand in order to remain "afloat," so will the counter weight of the space elevator need to be in motion around a world, otherwise it will collapse to the surface below.
Although Earth provides enough momentum with its 24-hour rotation, other worlds may lack the rotational speed to make construction of a space elevator on them reasonable. Planets such as Mercury (if we could colonize it) and Venus may not be suitable since both planets have solar days that can last a couple of months (if not longer).
An object as long as the space elevator would have much of its length exposed to the hazards of space, such as meteoroids and micrometeorites. Although it may be possible to move the space elevator slightly to avoid a collision with a small asteroid near the top, protecting the base of the elevator is critical in order to prevent the entire structure from drifting off into space via destruction of the "bottom anchor."
Earth's atmosphere presents a nice shield against these rocky intruders, protecting not only life on our homeworld, but also any future space elevator project. Despite the Moon being seen as a secondary location for a space elevator, it lacks a notable shield protecting it from the numerous meteoroids that hit the lunar surface.
Article comments
1 - Marco
The Space Elevator sounds interesting, but I think there must be a bettet way. This idea sounds to simplistic. We can do better and we will.
2 - Jim
Arthur C. Clarke in his 1978 novel "The Fountains of Paradise" described much the same type of elevator. His story presaged much of the technology that is available today in constructing an elevator. Including the development of the carbon fiber nanotubes that are currently being developed. It's interesting how science fiction can so closely predict some of the technological advances that we now have. By the way, I believe it's centripetal force that holds the thing up and not centrifugal force. Good article.
-jim
3 - duane
"Centrifugal" is correct. The gravitational force is centripetal.
4 - Jim
Duane,
I'm not sure that is correct. There's a reference that states that centrifugal force is an "invented" force to explain what happens in a non-inertial frame. When we use an intertial framework, there is no need to use centrifugal force to make the equations balance.
A couple of references, here and here.
-jim
5 - duffs
Ha, South Park did it!
6 - Victor Plenty
Arthur C. Clarke was not the first to describe a space elevator. Konstantin Tsiolkovsky is generally credited with the first descriptions of the basic concept, which he wrote back in 1895. (In fact Tsiolkovsky described a number of ideas that became highly influential in space exploration, including the use of rocket propulsion as the main technology for space travel.)
The current space elevator idea, focusing on some form of cable suspension method rather than Tsiolkovsky's tower concept, dates back to 1957 and was first discussed by Yuri Artsutanov, another Russian scientist.
After 1960, space elevator concepts were widely discussed in a number of publications, both in the Soviet bloc and in the Western countries. However, most of them were relatively obscure for the mainstream reader or even the average science fiction fan. Clarke's 1978 novel may deserve the credit for bringing the idea to a much wider audience, even if it cannot be called the first publication of the idea.
7 - duane
That's right, Jim (#4). The centrifugal force, like the Coriolis force, is invented as a means to desribe the motion of objects in a non-inertial frame, i.e., a frame in which a moving particle does not follow a straight-line path.
Imagine being in a space capsule moving in a perfectly circular orbit around Earth, for example. Also imagine a "God's eye view" of the spacecraft moving around Earth. God would say "the force of gravity is bending the trajectory of the spacecraft away from its natural state of motion, which is a straight line. The only force is centripetal. There are no other forces." You, inside the spacecraft are not sensibly aware of any forces. You are weightless. If you hold a ball and release it it will float next to you. It is weightless. But you know that Earth is below you, and that Earth exerts a force on you that is directed towards Earth's center. You ask, "What gives? Why do I not perceive any forces?" You must add a term to the force equation:
vector F_net = vector F_grav + vector F_fake = 0
F_fake is called the centrifugal force and can be represented mathematically as
(vector F_cent) = - (mass of spacecraft) times (vector omega) cross [(vector omega) cross (vector R)]
where vector omega is the angular velocity vector as observed by God, vector R is the position vector with respect to Earth's center, and "cross" is the vector cross product. Since v =omega times R, where v is God's measure of the spacecraft velocity, evaluating F_cent for this case gets you
F_ cent= mv^2/R pointed exactly opposite Earth's center.
Then you have GmM/R^2 = mv^2/R,
where M is the mass of Earth, G is the gravitational constant. The gravitational force and the centrifugal force are exactly balanced. Note that you get from the previous equation
v=sqrt(GM/R), the velocity of a circular orbit at distance R from Earth's center.
So the description of motion depends on whether you are in an inertial frame (God's eye view) or a non-inertial frame (inside the spacecraft). The centrifugal force is invented, but it is not without its uses. For example, meteorologists think about the Coriolis force, another invented force, to explain the movement of air masses in Earth's atmosphere. The behavior of a Foucault pendulum also illustrates the Coriolis force.
8 - duane
Thanks, Victor (#6). I have always been dubious about crediting sci-fi authors with technologically based ideas that later see the light of day. I think Clarke is credited with the idea of communications satellites, and that may well be valid, but sometimes I think popularized technologies ar introduced by writers who are aware of "out there" ideas being batted around in various scientific circles. I dunno.
9 - Jim
Thanks Victor (#6), I was aware of the reference to Tsiolkovsky's work. I think that Clarke went further in refining the concept by including the use of a super strong carbon fiber in the tether construction. I'm sure Clarke was also inspired by Tsiolkovsky's work.
An elevator certainly makes more sense when the (present) alternative is having to make use of technology where a disproportionate amount of mass has to be discarded in order to move a much smaller mass out of Earth's gravity well.
Also thanks Duane, for the clarification on the centrifugal force question. It's one of the concepts that tends to confuse me at times.
-jim
10 - Joe Julian
Thanks for the nice article. I hope our efforts help you get that house on the moon you're looking for.
11 - Victor Plenty
Duane's explanation of centrifugal force in #7 makes me glad I refrained from any attempt to tackle that issue and left it for a real physicist to elucidate.
Now if we could just get people to stop saying "everything is relative" whenever they talk about Einstein's work... but that's probably beyond the scope of this article.
12 - Show Me
Is there any place where people are against the space elevator? I don’t like to be rude, but if there is not a single person saying anything negative, then why don’t we build it? I have run my own numbers, and yes I am in the business, and even when we assume to have every technical miracle in hand (at no expense), there still does not appear any economic justification for the space elevator. Don’t believe my numbers. Run your own. 36,000 km of anything will dominate the economics and add to that a 3 to 1 counterweight and that’s another 100,000 kms of pure material cost. You can’t make a profit if the elevator volume is filled with concrete at today’s prices (yes, I know that does not work). Why? Because it only carries one small cart at a time and you have to charge a small price per pound to use it. It is like building a highway across the US (BTW, that is less than 5,000 km). Asphalt is cheap and you only need a narrow lane, but you can only send one car at a time on the road. So even if the car is screaming at 200 mph, it takes 15 hours before the next one goes on. That is less than 2 per day and the best I can charge for each passenger is the price of a cheep airline ticket. Before all is said and done, it takes 100s of years to try to recoup the investment on the asphalt! Can someone do some really basic numbers and show how the space elevator makes any economic sense, even when you have every one of the killer technical issues solved?
13 - Ruvy in Jerusalem
In his 1978 novel, "Fountains of Paradise" Clarke credited Tsiolkovsky with the idea as well as going into the economics a bit. In addition, he noted that his novel was set in places that didn't really exist. He had moved his version of Sri Lanka south by 3 degrees, and therefore had moved his version of India south as well.
I tend to agree with Show Me that a space elvator cannot make money being bult with the off the shelf technology that is around now. But hope springs eternal...
14 - Joe Julian
Chapter 24: Return on Investment
In short, reduced price and more frequent access to a resource increases demand for that resource.
I don't think your roadway model is all that accurate. Your neglecting the fact that your pricing model competes with other modes of transportation. You've also limited your model to "passengers". Which is more cost effective, a truck load of ball bearings on a road, or several plane's full?
Think more along the lines of early railroads. When the railroad was first built across North America it created vast opportunities that weren't cost effective before. J.P. Morgan, Cornelius Vanderbilt, Charles DeGaulle, Jay Gould, and many others made fortunes in railroad.
You are right, however, that it is not cost effective if built today. Today's material strength is insufficient to build a 100,000km ribbon and launch it. Even with our required material strength, we will require more than 6 heavy rocket launches. With the strongest material around today it would take over 100.
Thank you for your interest.
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