====== FAQ ====== Frequently Asked Questions ===== What Can I Do To Get Involved ===== ==== I'm not in the United States, can I still get involved? ==== === LiftPort Group Policy of International Public Inclusion === Liftport has had an International Public Inclusion policy since it's inception, and has had this [[international public inclusion|written policy]] since August 2004. ===== Space Elevator Physics ===== ==== Couldn't a space elevator be built using current materials? ==== Yes. The space elevator could be built using existing stronger/lighter-than-steel materials such as Spectra or Dyneema or even Kevlar. The problem is the excessive mass of material that would be needed to support it's own weight. Even with 60 [[Giga-Pascal|GPa]] material strength an initial starter ribbon will require multiple heavy lift rocket launches to get started. These rocket launches will be very expensive. Any decrease in strength results in an exponential increase in required mass. Spectra would take well over 100 shuttle sized launches. The problem at this point becomes financial. ==== What about conservation of angular momentum? ==== When an elevator ascends the ribbon, it must be accelerated eastward because the Earth's rotation represents a larger eastward velocity the higher you go. The required eastward force on the ascending elevator would have to be provided by a corresponding westward force on the ribbon. This westward force comes from the rotation of the earth. Picture yourself on an old merry-go-round. Spin it up really fast and lay on it face down with your legs bent at a 90 degree angle. Accelerate your feet by extending them quickly straight out. The merry-go-round slows down. This happens because as the radius of the circle that your feet are travelling increases, the distance per rotation also increases. As velocity is distance/time and the time is based on the period of rotation, your feet must accelerate for them to travel the additional distance. The energy required to accelerate them can only come from the mass that is holding that potential energy - the merry-go-round. ===== Threats To The Space Elevator ===== ==== Don't all existing satellites cross the Equator, where they could hit the ribbon? ==== Each and every satellite in Earth orbit (except for those in an exact geostationary orbit) crosses the equator twice during each and every orbit. Unless that elevator is really good at dodging, one of these satellites is going to run into it. We are good at dodging, and we will avoid the satellites. We are tracking them and will have weeks to months warning. We will move the anchor about a kilometer each day to avoid the debris. ==== The Leonids and the LiftPort Space Elevator ==== The Leonids are a trail of dust and debris left by the Tempel-Tuttle comet as it traverses our solar system each 33 years. The last passage was in 1998 and the next is expected in 2031. The dust and debris left by the comet passage disperses and leaves the neighborhood of Earth on a timescale of years though some debris always remains. The flux density of the debris can fluctuate by 10,000 from year to year. The Leonid debris also has a distribution of debris that includes dust particles and objects up to 10 cm in diameter. An article published by McNeil, Lai and Murad, Charge Production due to Leonid Meteor Shower Impact on Spacecraft Surfaces, discusses the impact probability on spacecraft and the details of the Leonid debris. The flux density is for a Leonid shower with a peak visual flux of 1000 meteors per hour. The standard peak is 10 to 20 and the largest in 1966 was 160,000. We can calculate the probability of impact on the elevator ribbon based on the 1000 peak number and then scale from there. Objects larger than about 10 cm have a finite possibility of destroying the ribbon. Objects as large as 5 cm in diameter has a small chance of destroying the ribbon. If we consider a weighted probability function we might approximate the likelihood of destruction with the likelihood of impact by a 10 cm or larger object. In our baseline, with densities of 3 gm/cm3 (estimate for the Leonid debris), this relates roughly to a mass of about 1500 gm (4/3*3.141*5^3*3) or a flux density of 10-17/m2 s. A typical Leonid shower lasts roughly 2 hours or 7200 s and the total area of the proposed elevator ribbon is 108m2. This gives us a probability of damage leading to destruction for each annual passage through the Leonid debris of roughly 1/100,000 for the showers with peak visual rates of 1000/hour. For a more standard shower the probability would be 50 to 100 times less. For the largest likely event (possibly in 2031) the probability would go up by 160 to a 1/625 possibility of severe damage. These are rough estimates and more accurate calculations are required. However, these estimates indicate that until 2031 the danger is probably minimal. By 2031, modifications and mitigation techniques could be implemented to improve survivability. ==== What if lightning strikes the ribbon? ==== The best way to deal with lightning is to avoid it hence the proposed location of the ribbon is in an area that receives little to no lightning. ==== Will an oscillation bring the ribbon down? ==== There will be a 7 hour natural frequency which can be actively damped with the anchor station. ==== Will high winds pose a problem? ==== Analysis shows that the proposed ribbon (of 1cm width below 10km altitude) would break at 71.5 m/s (159 mph) or a Category 5 hurricane. The proposed location of the ribbon is not in a hurricane or high wind area. ==== Will radiation degrade the components? ==== The carbon fiber composites are good for 1,000 years in orbit. ==== Will the ribbon produce an electrical current? ==== The last space shuttle-tether experiment, which unspooled about 12 miles of cable, generated thousands of volts of electrical potential and kilowatts of power, burned through the insulation of the cable, and generated a tremendous explosive arc of electricity, that snapped the tether. Now imagine a 60,000-mile-long cable and its electrical-generating capacity and you begin to see the disastrous potential. There are several aspects to this question. An electrical current might be produced in several ways: 1) due to the electrical properties of Earth's atmosphere, 2) collection of the space plasma and 3) due to the movement of the ribbon relative to the natural magnetic fields near Earth. - Earth's atmosphere consists of voltage differentials and charge build-up in association with storm activity, in the ionosphere and even on a clear blue-sky day. The last is easiest, the voltage potential set up there can be many volts but is over a large distance and based on the resistance of the ribbon would produce little current or difficulty. Storms produce high voltage differences, enough to produce lightning which can damage the ribbon. We have selected an anchor location in an area that has essentially no lightning and very little storm activity. With our mobile anchor we will be able to avoid the rare storm. In the upper atmosphere there can also be charge and voltage potential build up. In the upper atmosphere (ionosphere) the density of plasma is low and there will be poor coupling between the plamsa and our ribbon. We will have some charge build up and small current flow but it will be comparable to a small household battery. One area we need to investigate further is sprites or breakdown events in the extreme upper atmosphere. - In space there are plasmas that can deposit charge on satellites and our ribbon. As above, the density of this plasma is very low and a small amount of charge will be collected on our ribbon. We also expect both positive and negative charge to be deposited on the ribbon which would reduce the net charge build-up. If one charge preferentially builds up this will raise the potential of the ribbon, pushing away more of this charge and attracting the opposite charge which will limit the net voltage build-up. The total charge and voltage we expect and the length and resistance of the ribbon again make the currents much smaller than what you could get from common small batteries. - The third place where currents can be produced is when a wire is dragged through a magnetic field. This is how commercial electric generators work. To produce electricity you need a strong magnetic field and a high velocity. This has been demonstrated on orbital tethers traveling at 11,000mph through Earth's magnetic field, high voltages have been produced (1000's of volts). (3a) In our case our ribbon is essentially stationary relative to Earth's magnetic field so again very little current will be produced. (3b) The upper end of the ribbon will be in space and be moving relative to the interplanetary magnetic field but since this magnetic field is very weak little current is produced here as well. If you add up all of these currents and voltages you end up with nothing that will be problematic with the exception of the lightning. So as long as we avoid lightning and the storms associated with it we will get very little current flow or trouble from this area. You can think of most of this in terms of a conventional TV tower. Related to most of the topics discussed above (1 and 3a) we will experience the same voltages and millions times less (due to the relative sizes) current as a TV tower. Several colleagues had hoped that we might produce electric power from the ribbon but from what we have found power generation from the ribbon will take a lot of work and design modifications to produce much of anything. ==== Won't a huge ribbon into space be a prime target for terrorists? ==== The LiftPort Space Elevator would indeed be a target that would interest terrorists, like any major infrastructure project would. Fortunately for us, we're going to be 2000 miles out to sea. The object of their attention would be a ribbon three feet wide if you happen to be at just the right angle or thinner than a piece of paper at the wrong angle. That's hard to find in an ocean. We're also 400 miles from any flight or shipping lanes. A divergence of that magnatude would certainly catch the attention of the international militaries. We're also quite defensable. 1500 square miles of open sea give us a long warning that someone's coming. A piece of equipment dropped from the ribbon would make quite a hole in a boat. ===== Environmental Impact of the Space Elevator ===== ==== Is the ribbon in the path of any existing flight paths or shipping lanes? ==== One of the nice things about our anchor site is that it is in the middle of nowhere, approximately 400 miles from shipping or air traffic routes. ==== What if the space elevator breaks? ==== Depending on where the break is, the ribbon will either fly away into deep space, or fall. Any portion of the ribbon sufficiently high enough to fall with any energy, will burn up in the atmosphere. The small amount that may fall to the surface will fall with all the energy of a piece of tissue, fluttering in the air as it falls. Cargo that didn't fly off into deep space, however, would fall into the ocean.