Who’s Heard Of The Space Elevator?
The annual space elevator conference has been set for the end of August and will be held at the museum of flight in Seattle USA.
A story broke a few days ago about a large Japanese Corporation intimating that they would be building a space elevator by the year 2050.
Okay, you may be a little sceptical as you only have to imagine there will be a mammoth amount of technical issues to resolve so maybe this is just some form of visionary construction project.
Scientists and engineers, however, do believe that although it is not currently possible to construct such an equipment, it certainly is technically feasible as a construction project in the longer-term future.
Just think for a moment and you will appreciate that the main problem in exploring the space of our own solar system is actually breaking out of earth’s gravity. Our current technologies for breaking out of gravity still remains rather primitive by conceptional standards and furthermore being costly and inefficient using vast amounts of fuel in just to put an object into orbit.
However, a Space Elevator System is being proposed to function as a type of space transportation system.
This concept for a space elevator was first published in 1895 by Konstantin Tsiolkovsky, who proposed the possibility of a free standing tower reaching from the surface of the earth to the height of a geostationary Orbit. As with all buildings, Tsiolkovsky’s structure would be under compression, supporting its weight from below. Since 1959 most ideas for space elevators have been focused purely on tensile structures, with the weight of the system held up from above. In concept, a space tether would reach from a large mass or counterweight positioned beyond the geostationary orbit to the ground. The structure would be held in tension between the earth and the counterweight, something similar to an inverted plumb line. Obviously with the earth’s strong gravity even using our most sophisticated technologies we are still not capable of manufacturing a material that would be suitable as a lift rope or ‘tether’ that has adequately strong tensile properties and at the same time is sufficiently light in weight.
With this in mind, scientists have been investigating both carbon and boron nitride nano tube based materials that could be used in a “tether” design. So far they have discovered that the measured strength of the molecules in such materials is very high compared to their relative densities and therefore potentially technically feasible for such use.
Furthermore, the concept of the Space Elevator would also be applicable for use on other planets that for instance have weaker gravity than earth, such as the Moon or indeed Mars and consequently the tensile strength relative to the density properties of a “tether” would consequently not need to be as immensely strong and light that which would need to be used for such an earth based construction.
Very basically the space elevator concept would comprise a cable anchor to be fixed at the earth’s equator point base station and extending into space. A counterweight would be fixed at the opposite end beyond the orbit of earth. It is interesting to note that as the elevator cable rotates along with the rotation of the earth, any objects fastened to it will experience an upwards centrifugal force that will oppose part or possibly be even greater than the downward gravitational force exerted on it at that point. Higher up the cable the transport vehicle or ‘climber’ travels, the stronger will be the upward centrifugal force acting upon it and the greater will be the opposition to downward gravity. At a certain point this will actually exceed the gravitational force and along the length of ‘tether’, the downward actual gravity minus the upward centrifugal force would create the apparent gravitational field which can be represented as:
- The downward force (actual gravity) decreases with height; therefore g = -G.M/r2.
- The upward centrifugal force, due to the earth’s rotation increases with height; therefore a = w2.r.
- Together the apparent gravitational field is the sum of the two; g = -G.M/r2 + W2.r.
The equation symbols are as follows:
- G Gravitational constant (m3s-2 kg -1)
- M Is the mass of the earth (kilograms)
- a Centrifugal acceleration up which is positive along the vertical cable (ms2)
- r Is the distance from that point to the earth’s centre (m)
- w Is the speed of rotation of the earth (radian/s)
The main issue is that the cable ‘tether’ must be capable of supporting its own weight and the ‘climber’ transportation vehicle under tension. The vertical point with the greatest tension would be at the geostationary orbit level at approximately 22,000 miles above the earth’s equator and consequently the integral design combined with the material forming the ‘tether’ must be sufficiently strong to hold up the weight of its own mass from the surface and it has therefore been calculated that by producing a ‘tether’ of larger cross section at it’s geostationary level compared to the lower or higher lengths this will aid holding up a longer length of its own material and the cross sectional area tapering down from its maximum down to a minimum at the surface, or space station positions.
Another issue would be the powering of such ‘climbers’ which would need to run on large amounts of potential energy and in this respect scientists have been investigating the transfer of such energy to the ‘climber’ through a wireless energy transfer system whilst its climbing i.e. such as a combination of using solar power and ground based technology systems which would enable the drive / proportion cost to be a mere fraction compared to the use of fuel technology.
It is interesting to note that the large Japanese Corporation mentioned earlier have stated that in approximately 38 years it could build such a space elevator using carbon or boron nitride nano tube technology for the main ‘tether’. The ‘climber’ designed at 30 passenger capacity or so would travel at 200kph and would be capable of reaching the geostationary orbit position after approximately 6 or 7 days (could you really imagine being stuck in a 30 persons elevator car for 6 or 7 days !).
It is also interesting to note that the space positioned counterweight could be in the form of a reasonable sized space station positioned at a point beyond the geostationary orbit with a further upward extension of the ‘tether’ cable sufficient that the upward pull would be equal to the equivalent counterweight density. The advantage of having a space station as the counterweight would enable a base to assist with the future construction of extension or further “space elevators” the stations could incorporate appropriate platforms from where space vehicles can be constructed and launched that could be much smaller in size and not require the massive rockets and fuel that is required to break free of earth’s atmosphere and gravitational pull. Such vehicles would most likely be for unmanned exploration vehicles using solar or other power systems as an alternative to the heavy cost of rocket fuel based systems necessary to project from the earth’s surface. Of course dreaming on, one could imagine the potential for even manned vehicles to eventually be constructed in such a way to possibly explore and take manned landings on other planets within our own solar system.
Dream concept or serious technical viability one can only guess. However, the reality is that such systems are being discussed and technical concepts for the design of ‘tethering’ material and anchor, environmentally controlled and pressurised space ‘climber’ vehicle, counterweight and conceptual propulsion systems are in fact being investigated and may be available in 30 or 40 years time making such a concept a potential reality.
Any takers for testers and service engineers and indeed consultants to carry out witness testing, desnagging and of course maintenance auditing and Form 54 inspections !!