Space Elevator

In one of my classes I was assigned the task of writing a feasibility study of an engineering project with a team of students. My team chose to write our document on the space elevator. It was really fun, this project is ambitious, but after reading and writing on this subject for the past six weeks, I believe that we could see something like this within the next 50 years.

I asked my team for permission to post our report here, they were gracious. I worked with Aaron Seitz, Amitesh Parikh, and Sean O’Brien. We were asked to write as if we were a company within the industry, so we chose SpaceX. Our report is below.

One note of clarification, all references to SpaceX are fictitious. I have no reason to believe that they are suffering any financial difficulty, or are in need of new ideas. It was part of the assignment to presume that we were writing this report for an executive engineer within an actual company.


ABSTRACT
In an attempt to improve profitability of SpaceX, a feasibility study into space elevators was done. If space elevators are feasible, they will provide SpaceX with a product to use in order to rebound from recent revenue losses.

A space elevator has several components that allow it to function properly. The cable connects the base station to the counterweight and is the most important. This cable allows a climber to be designed to take passengers and cargo along it and place into orbit. The cable must have a very high tensile strength in order to support the weight of itself at such a long length in addition to the weight of the climber. There are materials being research which should have this strength. The space elevator design makes it significantly cheaper than traditional rockets and allows payloads to be placed into orbit at very little comparative cost. Space elevators are very safe. There is not the need for millions of gallons of explosive rocket fuel to be sitting below passengers on every lift. The speed of a space elevator may impact safety in the Van Allen Radiation belt and expose people to ionizing radiation. Special consideration must be made when using the space elevator to avoid this deadly radiation.

INTRODUCTION
SpaceX has seen a loss of revenue in the past several quarters due to growing competition in the private space sector. In order to counteract this trend, a new product is needed that will stifle competition and rejuvenate profits for SpaceX. A feasibility study was done on the space elevator to determine if it would be a worthwhile investment.

This report is the final account of all research undertaken during the feasibility study. Key portions of it were presented before the board of trustees along with our official recommendation. This report does not give any final decisions on design approaches should a space elevator project begin, it is simply meant to determine if we feel it is plausible to invest money in this potential technology. We evaluate several aspects of a space elevator and then provide a summary of our opinion on the feasibility of such a project.

The core areas that were researched during this feasibility study were the components, the materials and technologies, the economics, and the safety or ethical concerns regarding a space elevator. These areas cover all major aspects of a space elevator and will provide an assessment of feasibility in four areas and ensure that the research did not miss any key elements.

COMPONENTS by Amitesh Parikh
A space elevator has four components, they are the base station, the cable, the climber (or lift), and the counterweight.

Base Station
A base station is the part of a space elevator which is situated on land or at sea. All the power required by the space elevator is to be supplied to the base station. There can be two types of base stations: stationary and mobile. Mobile base stations are large oceangoing platforms that can be maneuvered. We did not research Mobile platforms due to a lack of resources on the subject.

Stationary base stations are typically situated on land. These base stations are required to have a reliable power supply, a controlled temperature storage facility, a fueling station, a loading station and a control room and such a base station must be easily accessible by land, water and air. The power supply, along with being used at the base station, may be used by the climber to carry the payload to the top of the space elevator. The control room will monitor the obstacles like space debris, asteroids, and high winds that may come in the way of the space elevator and will accordingly stop the transport of payloads up the space elevator. The controlled temperature storage facility is to be used for storing temperature sensitive payloads. The loading facility would where the payloads would be loaded onto the climber and the fuelling facility is to be used for fuelling a space shuttle with propellant.

Cable
The component of the space elevator that enables the climber to carry payloads to space is the cable. The cable, which connects the base station to the counterweight, is the most important part of the space elevator. The material to be used for the cable depends on the design of the space elevator. We mainly looked at the two most commonly proposed designs. The first design thought of the space elevator as a tower with a constant cross section. This was determined to be unfeasible by the following calculation:

In a cable with constant cross section, for an element of the cable at geostationary height, the weight of the element, W and centrifugal forces Fc are equal i.e. W = Fc for an element at geostationary height. This requires the tension at both ends of the cable to be equal. For an element below geostationary height, the weight force, W is greater than the centrifugal force, Fc. Therefore, for equilibrium, tension must be greater in the top end of the cable than the tension at the bottom end. Both of the facts above imply that Tension in the cable increases with height till the cable reaches geostationary height. For an element above geostationary height, the centrifugal force Fc is greater than the weight force, W. Therefore, for equilibrium, the tension in the lower end of the cable must be higher than that in the upper end.

Therefore, in a tower with constant cross section design, the tension will increase from zero to maximum at geostationary height and will decrease back to zero at the counterweight. This will lead to a lot of unnecessary internal stresses will need the material making the tower to have a tensile stress of 382 GPa which is not materially feasible at this point of time.

The second design is based on the principle of keeping the tension (force per unit area) on the cable constant by tapering the cross-section of the cable. The requirement of keeping tension constant throughout the cable implies that the cross-section of the cable will taper outwards till the cable reaches geo-stationary height and then will taper back inwards till it reaches the counterweight. This design will need a tensile stress of about 60-120 GPa. To make this feasible, we need a material that has a relatively high maximum tensile stress and that will enable us to provide a low taper ratio.

Climber
The climber is the part of the space elevator that helps transport the payload from the base station to geostationary height. This is also the most problematic part of the space elevator. We looked at various ways to transport the payload. One method we looked into was moving the cables to transfer the payload. We however found this unfeasible since the cables need to be tapered at geostationary height and if these cables are moving, the taper won’t remain at the required height. The other option is that the climber moves up autonomously. This can be achieved with the help of rollers with a traction system. The traction system will provide friction on interaction with the cable, by which the climber will move upwards.

Transmission of electricity might be a problem. The cable by itself will not be able to transmit electricity since it is made of carbon. One method to work around this is to use laser power beaming. The base station will have a beam director which will direct the beam that is ~15m wide of a free electron or solid state laser onto the photovoltaic cells on the climber. This beam will be of average intensity so that birds and planes flying by will be unharmed. Currently, Lawrence Berkeley National Laboratory is designing such a system and will soon produce it.

The climber poses additional problems. Any bending of the cable, such as around the rollers of the climber will cause the cable to wear. The cable will thus have to be replaced at regular intervals. Secondly, the heat from the laser may transfer to the climber thus causing the payload to heat up. This may damage the payload. Special care has to be taken to insulate the climber; however the insulation will increase the weight of the climber.

We have not performed sufficient research in order to determine whether the climber will be able to come back down or not. The problem with the climber coming back down into the Earth’s atmosphere is that the climber will experience a lot of friction thus causing it to heat up excessively. This may damage the climber and the solar panels and the climber may burn up. One way around this problem is that the climber be made with extremely heat resistant materials. Another solution is that the climber itself be added to the top of the tower as an addition counterweight. This will simply make the cable more stable as the tension in the cable will still remain constant.

Counterweight
The counterweight is used to keep the cable at constant tension i.e. it helps prevent the cable from slacking. This is because the centrifugal force at a height above geostationary height is much greater than the centrifugal force on the surface of the earth. Thus the tendency of counterweight to move outwards, away from the centre of earth keeps the cable taut. The counterweight, however, can disrupt normal functioning of the elevator. If there is some disturbance acting on the cable, the disturbance will travel upwards in the form of vibrations. These vibrations will then hit the counterweight and be reflected back towards the earth. In order to prevent this from disrupting regular working conditions, a disturbance, opposite in magnitude and direction to the original disturbance must be sent up the cable from the base station in order to cancel out the disturbance.

MATERIALS AND TECHNOLOGY by Aaron Seitz
There are four major components related to space elevator technology, they are the cable material, power transmission, robotic climber, and collision avoidance.

Cable Material and Design
Since it was first conceptualized, the largest technological hurdle plaguing a space elevator has been the cable design. For over half a century a suitable material, one which is strong and light enough to handle the forces acting on the cable as well as the climber necessary to lift payloads into orbit, did not exist. It wasn’t until the early 1990’s that such a material was discovered – carbon nanotubes (CNTs).

Density & Characteristic Height of Possible Cable Materials
For a long time, a “super-material” with the properties of carbon nanotubes was just a pipe dream; materials scientists had even gone so far as to refer to it as “unobtainium”. They have many impressive properties Caused by the quantum effects that dominate over bulk properties at their small size (1nm and smaller); the ones of interest in space elevator design are their remarkable strength and flexibility. Carbon nanotubes are 60 times stronger than steel and incredibly lightweight. To maintain sufficient strength throughout the length of the cable, it must taper, as previously mentioned; and since more taper poses numerous problems, the smaller the amount of taper needed, the better. This is one of the largest benefits of CNTs – a taper ratio of only 1.2, compared to 1032 or more for steel or other, more conventional materials.

Atmospheric Effects on Photonic Transmission
The main limitation on the use of carbon nanotubes as a cable material is that while they have an incredibly high theoretical strength, their actual strength is limited by the method with which they’re grown and joined – it is in these areas that research progresses. Originally, carbon nanotubes all had to be created by hand in labs, using time consuming techniques which produced nanotubes with varying levels of quality. Recent advances have been made which have greatly increased the speed and decreased the number of defects found in produced nanotubes – a process which forms a 2 inch wide continuous length of CNT ribbon at a rate of over a meter a minute has been developed at the UT Dallas nanotechnology lab. Work still remains to find a bonding method which can make a reliable connection of sufficient strength for the elevator cable at a price which will make the cable possible, but hundreds of labs the world over are working on these problems, and each of their successes compound upon each other, propelling progress at a rapid rate.

Recently, Italian scientist Nicola Pugno proposed evidence that CNTs might not have sufficient actual strength to be used as a cable material due to inherent defects created during growth; essentially, that nano-scale defects in the tiny, individual fibers will compound greatly over the many kilometers of ribbon needed for a cable, decreasing the actual strength to a small fraction of it’s theoretical strength. However, proponents of the material have stated that the Van der Waals forces between the nanotubes will hold them together, evening out individual strains and maintaining the ribbons overall strength.

Other concerns as to cable strength come in the form of wear and tear on a completed ribbon, primarily due to the atmosphere and impacts. Atmospheric oxygen quickly degrades most materials, meaning it was originally thought that the cable would have to be plated with gold or platinum, which are largely unaffected by oxidation. Recent research however, has indicated that while the outer layer of binder will be oxidized, the CNTs themselves will not, meaning that once the outer binder is gone, the cable will essentially have a protective layer of CNTs. Micrometeorites (tiny bits of orbital debris from other launched objects, such as paint flecks, bolts, and bits of other craft) pose a danger to anything passing through orbit, including the ribbon, but the properties of a CNT cable will redistribute load to nearby undamaged areas; many hits must be made before a critical failure is possible, and patches can be applied to repair the damaged sections. Also, as will be discussed later, ground-based tracking systems can be employed in conjunction with a moveable base to allow the cable to avoid most major impacts.

Analysis of carbon nanotube information and research indicates that they are a solid candidate for a space elevator cable; indeed, at this time they are the only serious contender. Work remains to be done to advance them to the point where they will work, but progress is being made rapidly, and evidence indicates that within the next few years a workable prototype ribbon can be made.

Power Transmission Systems
Due to the excessive weight of batteries and power loss due to the height of the elevator, wireless power transmission is currently accepted as the most likely method with which to power the robotic cable climbers used to deliver payloads to space. Earth-to-space power transmission has been researched for decades for its possible uses in providing extra power to satellites, as well as beaming power to Earth from large orbiting solar arrays. The two methods considered are microwave and photonic transmission systems.

While being the most likely choice for many years due to immaturity of laser technologies, microwave power transmission over extended distances has many drawbacks which have caused it to no longer be considered as a feasible option. Microwave radiation spreads out to a rather significant degree as it travels from the source, making it prohibitively inefficient and costly to use due to massive power losses, as well as losses due to atmospheric interference. Laser technology, however, has rapidly advanced due to its use in countless scientific fields, and is the primary focus for long-distance power beaming. Their beams remain tightly focused over a long distance, are continually improved upon and commercially developed, and can produce extremely specific light wavelengths, allowing receiver tuning for maximum efficiency, as well as minimizing deleterious atmospheric effects. Also, recent research has shown that laser clusters can be made with efficiencies similar to high powered free electron lasers (which are impractical at this time due to the immaturity of the technology).

Various Carbon Nanotube Atomic Structures
For the photonic power receiver, solar cells are to be used. Various advances have been made in recent years which should help boost their efficiency while significantly reducing their cost and weight. Some such improvements are nano-scale anti-reflective coatings (which decreases losses due to light reflection to under 0.01%), and silicon free solar panels using no glass which are thin, flexible, lightweight, and inexpensive ($0.30 per watt vs. $3 per watt for conventional cells).

My research has shown that the technologies necessary for a functional power transmission system already exist, with improvements mainly necessary to increase power transferred; this will only improve with time due to enormous funding and interest in both. Design, testing, and tuning on the combined system needs to be carried out, but this area of the elevator is entirely feasible.

Robotic Climber and Collision Avoidance
The climbers, used to carry payload, are the backbone of the space elevator concept. While it may seem they are of little concern, there are nonetheless several things to consider in their design. Most climber designs call for them to ascend via the cable, and descend via rockets and gravity; this allows for a speedier transit time, allowing more cargo to be carried into orbit than if the climbers were to occupy the cable during descent, while not requiring much added expense from fuel costs. Climber needs were taken into consideration when designing the cable – a flat cable was chosen as to simplify climber design and operation. Whereas a rounded cable would require a complicated drive system to ensure a steady and safe ascent, a flat cable need only be pressed between two sets of treads to provide a path to orbit.

Because the amount of profit possible depends heavily on the potential number of climbers in operation, decreasing transit time (by increasing speed of ascent) is of primary concern. To do this, more power has to be delivered to the climber; because the weight of the power receiver system scales sub-linearly with size, the amount of power it provides can be increased significantly without severely impacting the payload capacity; and because doubling drive train power halves the climb time to the 0.1g position (the position at which another climber may safely begin ascent), more climbers using this power configuration can ascend at a time, decreasing construction time and increasing the amount of payload deliverable.

The collision avoidance systems, mentioned previously, are important not just from a operations view, but also a legal one. Avoiding micrometeorite impacts will help to extend the life of the cable and decrease its maintenance costs, the ability to avoid the thousands of man-made objects (such as satellites) already in orbit is one of the requirements for clearance to build the elevator. NASA has been employing radar-tracking systems which can track objects as small as 10cm in orbit; laser tracking systems, capable of tracking objects under 1cm in size are in development and testing right now, and will be available by the time a space elevator could be built. A moveable anchor station is the most likely choice for ribbon maneuvering, but other possibilities exist.

The technology necessary to successfully implement climbing and collision avoidance systems is either already in use, or is in the final stages of testing; from a technological viewpoint, both are available and practical.

ECONOMICS by Chris Leonard
Space exploration is one of mankind’s most expensive endeavors. Currently NASA spends about $450 million per space shuttle mission. With a standard payload of 24,400 kg, this averages to a cost of $18,000/kg delivered to Low Earth Orbit (LEO). These launch expenses are in addition to the $1.7 billion required to build each shuttle. Delivering payloads to Geostationary Orbit (GEO) typically costs NASA near $80,000/kg. A number of privately funded companies are working toward mission specific rockets designed to bring these costs down to $2,800/kg for LEO and $24,000/kg for GEO, but none of these are in operation today. These figures illustrate that the cost associated with leaving Earth’s surface are limiting factors. In order for space travel or exploration to become truly accessible transportation costs will need to be reduced. Of all current and proposed technology, only the space elevator has the potential to achieve this goal.

Current space elevator construction estimates, excluding legal, regulatory and certification expenses are $6 to $10 billion in 2003 dollars, excluding legal, regulatory and certification expenses. Accounting for inflation and these additional expenses, actual construction costs are likely to be approximately twice these figures, or $20 billion. Once construction is complete, ongoing costs would include the electricity required to power the geostationary platform and the elevator climbers, atmospheric and collision avoidance monitoring equipment, and the labor required to operate and maintain the elevator. Upon completion of the first space elevator, a second one could be constructed for significantly less because the first space elevator could be used to transport construction crews and material into orbit.

When compared with other large scale engineering projects, $20 billion is a reasonable number. NASA’s cumulative International Space Station support expenses from 2005 through to its decommissioning in 2016 are forecasted to be nearly $60 billion. Boeing’s cumulative development costs for their most recent 777 aircraft are estimated to be between $10 billion and $12 billion. Massachusetts will have spent a total of $14.6 billion on their “Big Dig” 3.5 mile long tunnel through the heart of Boston. While these other projects aren’t directly related to the space elevator, they demonstrate that a final bill of $20 billion is within reach for a large scale construction project.

The main reason that a space elevator would cost so much less to operate than rockets is the escape velocity required to leave Earth. The energy required to launch a rocket is the sum of the potential energy of the orbit radius and the kinetic energy of the orbital velocity. In order for an object to leave Earth, its kinetic energy must be at least equal in magnitude to the potential energy exerted on it by the gravity field. Rockets must produce enough thrust to generate this velocity while overcoming Earth’s gravity. With the space elevator, as the payload ascends up the tether the Earth imparts angular momentum, or horizontal speed, to the climber. Because a portion of the required energy is contributed by Earth’s rotation, there is a net savings of energy required.

Additionally, rockets are built with staged engines that are discarded as the payload ascends, which improves the overall efficiency of the launch. Much work is required to build and test these rocket stages to ensure their performance and safety. The majority of these rocket stages are not recovered, which increases the net expense of the launch. With space elevators, the only consumable is electricity, which costs less per unit of energy than chemical propulsion systems.

Operational costs can be further offset by recapturing energy expended in the descent of the climber. Current rockets dispense this energy as heat, which requires expensive heat shields on the bottom surface of reentry vehicles. By converting the work of the descending climber into electrical power, similar to the way that hybrid cars use regenerative braking today, the energy can either be used to power other components of the space elevator or captured and stored in batteries.

Cost per delivered kilogram
Certainly some will consider the large sum required to build a space elevator a waste of money. The space elevator’s benefit to the average citizen may be difficult to calculate. While less tangible, the advances in technology brought about by the space elevator will definitely touch other industries. Disk brakes, seat belts and carbon fiber are examples of technology developed by aerospace engineers that have benefited other sectors. Several thousands of jobs will be created for people from every corner of the world. The carbon nanotubes that are required for the space elevator will also be useful in electrical circuits, medical advancements including cancer treatment, and construction projects that require a high tensile strength.

The space elevator’s current cost estimates are close to $20 billion. In order for such a project to make economic sense, it would need to be able to generate a 15% return, or $3 billion annual revenue. Operating costs are estimated to be $100 per kg lifted. Because this cost is so much less than any other technology, we would have the unique freedom to charge whatever is needed to make this endeavor profitable. Assuming a billable rate of $1,500 per kg lifted, which is considerably less than the costs associated with any other technology, and 2 million kg lifted per year the space elevator would generate the required revenue. Upon completion of the first space elevator, second and third units could be constructed for much less, providing significant improvements on the rate of return. Clearly there is a compelling economic interest in being the company that brings this technology to market.

SAFETY AND ETHICAL CONSIDERATIONS by Sean O’Brien
There are many safety and ethical concerns about a space elevator. An analysis of what would happen in the events of collisions, collapse, and other events is needed. This will preliminarily affect the feasibility of a space elevator. However, it is important to understand many more safety issues are likely to arise during actual design of a space elevator because of inherent unknowns with mega structures.

Collisions
There are a variety of objects that could interfere with the trajectory of a Space Elevator. Planes and other air traffic could potentially collide with the tether. Satellites in orbit could collide as well if their orbit intersected the elevator. It is also possible that meteorites may strike the cable tether damaging the elevator.

It is not a difficult process to prevent collision of a space elevator due to air traffic. Patterns of flights would have to be modified to avoid the potential range of the elevator tether. If the elevator is on a mobile platform it may be necessary to creating varying flight patterns depending on the location of the tether. The downside to this is that it is a complicated process to design efficient and safe air traffic patterns.

Satellites pose a more difficult problem. It is not always possible to modify the orbit of a satellite. Most modern satellites contain mechanisms which they could use to miss the space elevator slightly, but they would have to be constantly monitoring their location in reference to it. Many older satellites are inactive or do not have the ability to alter their orbit. In order to avoid them, they would either need to be found and removed from orbit before an elevator is built or else an alternative method would be needed. One possibility includes using lasers to slightly alter the path of satellites. It is also possible to move the space elevator if it’s is on a mobile dock.

Meteorites are the most likely object for a collision because they are not easy detected early enough to make changes. They would likely impact the tether with a high velocity and multiple times. It would be especially negative for the tether if it was a micrometeorite storm where thousands of small meteorites hit the cable in a few minutes. There is a not an easy way to avoid this except to design the tether to handle these collisions. There are tether designs that allow one strand to break and not damage the elevator while repairs are made. It is feasible to design tethers that protect this and still function, but many considerations will have to be made during the design of a space elevator.

Collapse
The most common safety question brought up during interviews was, “What would happen if the space elevator collapsed?” The exact result would depend on where in the tether the elevator collapsed. None of the collapse scenarios however would put people below on Earth in harm. In addition to people below, it is important to consider what would happen to people on the lift car of the space elevator.

If the break in the tether occurred near the anchor point of the ocean, it would cause the tether to rise upward into an unstable orbit around the earth. It would slowly over time drift further out into an elliptical orbit. If the break occurred a below 25,000 km then the lower portion of the cable would wrap itself around the planet in an eastward direction. This would not cause any problems because most of the cable would burn up in the atmosphere. The part that was too low to burn up would hit the Earth with the force about as light as a falling sheet of paper because of the low weight of carbon nanotubes. The upper portion of the cable would move into an orbit away from the Earth. If the break occurs near the counterweight, the entire cable would wrap around the planet, most likely burning up in the atmosphere. Some upper parts of the cable would get so much velocity during the wrap around process that it would break off and be flung away from the Earth.

People on the Space elevator would be potentially in danger during a collapse. It is likely this would be rectified by designing the lift car to safely return down to the Earth using a heat shield and parachute, much like the Apollo command module used for its reentry. This solution will work as long as the lift car is on the falling portion of the cable and is below 23,000 km. At this point the car will immediately reenter or will be in an elliptical orbit cause it to intersect the atmosphere and reenter within a few hours. Slightly above this, the car would be held in orbit and need a rescue ship to come and retrieve passengers. The one unfortunate scenario is above 47,000 km. At this point the lift car will have a high enough escape velocity that it will jettison away from the Earth into space and it is unlikely passengers could be rescued. In fact, if the car is near the counterweight, a velocity to escape the solar system is attained. The safest solution to this is to keep any tourist lifts below this altitude. This would restrict the risk to maintenance crews. In our opinion at SpaceX this is ethical as long as maintenance crews are voluntary and well informed of the risk.

Additional Safety Concerns
There are several other safety concerns. These include severe weather around the elevator, radiation from ionizing particles in the atmosphere, and terrorism. It is important to evaluate early considerations for these potential issues.

Weather would likely be a primary concern; it could damage the elevator if there was a severe storm. One solution involves adhering to suggestions keeping the elevator within two degrees of the equator. This would put the elevator in the Hadley Cells of the Earth. Inside this area, severe weather is very infrequent and does not occur most of the time. A mobile dock could be used to move the elevator slightly in the rare cases that weather does develop.

The Earth’s magnetic field generates a region in the atmosphere known as the “Van Allen Radiation Belt” where there are high energized electrons in a plasma state. This produces ionizing radiation, which is a deadly form of radiation to humans and can even damage electrical equipment. During traditional space travel, an astronaut spends a few seconds passing through the belt, which is not long enough to cause damage. However, at the 200 km/h rate of the lift car, people would spend roughly three days inside the Van Allen Radiation Belt. This would kill anyone on board. However, it is possible to avoid this by using a lead shield on the lift car. Lead of only a few millimeters thick will stop the radiation from penetrating the car. The downside is that lead is a heavy medal will add additional weight to the lift car. This will have to be considered when designing the tether to be sure it can support a lift car with this shielding.

Van Allen Radiation Belt
In this day and age, it should not be surprising that terrorism is a significant risk factor to a space elevator. However, its effect is less than most would think. A space elevator would inherently need security for all people near it and all cargo be placed on it. The international community would not allow just anything to be placed in orbit. This would essentially remove the risk of a bomb being launched on the lift car. The risk of a missile being fired at the elevator is very low if the dock is kept far away from shore. Most major terrorist attacks on ships have occurred when they are near shore, such as the USS Cole, this is due to terrorists not having resources to access ships that can travel a distant and they are left with small boats. It is also possible as an additional precaution or in time of war to have a missile defense system built around the outside of the dock and some radius.

FEASIBILITY
After a careful assessment was made of all four of these areas, we have now reached a conclusion on the feasibility of SpaceX designing space elevators. From the standpoint of the components and the physics calculations, a space elevator will be able to be easily built given the correct materials. These materials include the carbon nanotubes which were described in details; these have not yet reached a point where their strength is enough to build a space elevator. This portion of the materials is the only part that has yet to be developed. Economically, it would be very profitable to develop a space elevator and allow SpaceX to easily turn over design costs into making money. From a safety and ethical standpoint, there are many issues that present concern, but given an ethical engineering team and careful design considerations, these can all be avoided. Assessing all this information, we have decided it is feasible to begin design of a space elevator. The engineering work required will take several years to complete and by this time it is well expect carbon nanotubes will have reached the required strength. At this point we will be ready to begin construction and if we wait on the nanotubes we will be behind years in other areas of the engineering.

CONCLUSION
A space elevator is a device which is connected from the earth to a counterweight at geostationary orbit by a tether (cable). A climber is then used to move cargo and people up and down, allowing an easier means to put satellites into orbit. The tether is made out of carbon nanotubes which have a tensile strength far greater than steel. Economically, the space elevator would provide high profit margins for the operating company as well as significantly reducing the price to put payloads into orbit. The primary safety concerns are the Van Allen Radiation Belt and the collapse of the tether; however disaster is easily diverted from both of these with a properly designed space elevator.

Officially we feel that in the position we our economically as SpaceX, design on a space elevator should begin as soon as possible. This will allow us to begin construction seamlessly as carbon nanotube technology comes to meet the needs of the space elevator. We hope you will assess the information in this report and make the best decision with the direction we should proceed as SpaceX.

One reply on “Space Elevator”

  1. Hey, that’s really cool–I remember as a kid I had one or two “space technology in the future” type of books that mentioned just such a thing. Although it was really like an elevator, in a very long tube. And I do remember it talking about having the base site be somewhere near the equator, although I don’t recall if it was for the same reasons as cited here.

    The figure cited that passengers would spend ~3 days in the radiation belts, as opposed to a few seconds, didn’t seem to make sense to me. Would space elevator travel really be *that* much slower than conventional space flight?

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