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Home , Counterweight, Space elevator, Specific strength

Space A New Way To Gain Adil Oubou 5/3/2014

Abstract After 56 years of great space exploration, the space flight program found itself asking an intriguing question: What’s next? Should humans constrain the space program to low orbit, revisit the , or simply go beyond anything they have done before? No matter what the next step is, there is a great need for a reliable, safe, affordable and easy method of gaining orbit. The concept discussed in this report, based on the design provided in Peter Swan’s book “Space : An Assessment of the Technological Feasibility and the Way Forward“, shines the light on an economically and technologically feasible solution within the next two decades that will lift payloads including humans from the earth’s surface into space at a greater capacity than current rockets while significantly lowering cost to $500/kg. The system design includes a tether line that extends from the Earth’s surface to an altitude of 100,000 km that utilizes electrical motor driven climbers to gain orbit. The success feasibility of this space flight system is highly dependent on the development of Nanotube (CNT) material, which will provide high strength and low mass properties for the space elevator system components to withstand environmental and operational stresses. Table of Contents 1.0 The New Way to Orbit ...... 4 2.0 Why Space Elevator? ...... 4 2.1 Purpose ...... 4 2.2 Advantages ...... 4 3.0 System Architecture ...... 5 3.1 System Overview ...... 5 3.2 Climbers ...... 6 3.2.1 Mass Budget ...... 7 3.2.2 Motor Drive Apparatus ...... 7 3.2.3 Power Requirements ...... 7 3.3 Tether ...... 8 3.3.1 Design Requirements ...... 8 3.3.2 Tether Material ...... 8 3.4 GEO Node Spacecraft ...... 10 3.5 Marine Node ...... 10 3.6 Apex Anchor ...... 11 4.0 Concept of Operation ...... 11 4.1 Pre-mission ...... 11 4.2 Flight ...... 12 5.0 Cost Estimates ...... 12 6.0 Conclusion ...... 13 References ...... 14

2 List of Figures

Figure 1. System Diagram of the Space Elevator ...... 5

Figure 2. Space Elevator Orbital Dynamics ...... 6

Figure 3. Climber Design Model ...... 6

List of Tables

Table 1. Climber Subsystem Mass Breakdown [kg] ...... 7

Table 2. Forces Experienced for the 7 Climbers Operation ...... 8

Table 3. Tether Characteristics ...... 9

Table 4. Design Requirements for the Marine Node ...... 11

Table 5. Climb Phase Breakdown ...... 12

Table 6. Initial Capital Cost for Space Elevator ...... 12

Table 7. Operational Cost of Space Elevator ...... 12

3 1.0 The New Way to Orbit The unknown drives humans. Space exploration was essentially derived from that concept. However, beyond our natural curiosity, new concepts such as energy shortage, atmospheric pollution and the chance of high impact global catastrophe are driving humans to extend our existence beyond Earth. Although we have experienced significant advancements in space flight over the last four decades, they are just not up to par for us humans to achieve our ambitious space travel goals. Current rockets are expensive, time-heavy and environmentally harmful. There is a great need for a method to gain orbit that will open up the solar system for exploration and take humans to heights never before reached, while having minimum environmental impact. Could this be a space elevator? Over the past decade, the space elevator concept has moved from a fictional Star Treck point of view, to a feasible megaproject that will lift payloads and eventually people from the Earth’s surface into space at much lower costs. This report explores the popular space elevator tether design concept and its technical feasibility within the near future. 2.0 Why Space Elevator?

2.1 Purpose The space elevator system will lift payload as well as humans from the earth’s surface into space at a greater capacity than current rockets, in a safe, reliable and routine manner for an estimated low cost of $500/kg. Achieving a method to reach the GEO altitude will open the doors for the following important missions: Ø Space transportation station Ø Assembly station for spacecrafts Ø Space tourism & colonization

2.2 Advantages § Low cost to GEO § Easy delivery to GEO within a week § Reliable and routine operations § Access to orbiting (daily launches) § Low g’s (human ) § Safe § Environmentally friendly § Permanent infrastructure § No consumption of fuel § High cargo capacity § No § Allow for space systems to be § Floating launch facility designed and constructed

4 3.0 System Architecture

3.1 System Overview The system consists of a 100,000km long tether balanced about a node in (GEO) and extending down to an anchor point on Earth, and up to an apex anchor at an altitude of 100,000km. Tether climbers, which are electrically powered spacecrafts, will serve as the elevator cabins that will travel up or down the tether from earth’s surface to the apex anchor, where their speed is sufficient enough for interplanetary travel. Figure 1 shows the space elevator system nodal layout along the tether line.

Figure 1. System Diagram of the Space Elevator

It is important to consider the system dynamics of the tether elevator from Earth’s surface to the 100,000 km altitude in space. Close to the Earth’s surface, the gravitational forces are strong, decreasing as a function of altitude as the elevator climbs to space. On the other hand, the centrifugal forces acting on the space elevator, which point away from Earth are weaker near Earth’s surface and get stronger as the elevator goes up in altitude. In order to have a balanced tether line for the elevator, the forces acting on the elevator above the GEO point, must be balanced with the forces acting below the GEO node. On the other hand, the angular momentum must also be balanced around the GEO node, to keep the elevator stable. Considering the mass below the GEO would be significantly heavy, the apex anchor will serve as a to keep the dynamics of the elevator balanced and stable. Since the GEO will be the , it will experience the highest magnitudes of , therefore requiring a thicker tether compared to near the end points, introducing a taper ratio. Figure 2 below shows a dynamics body diagram with all the forces and tensions acting on the elevator, as a function of altitude.

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Figure 2. Space Elevator Orbital Dynamics 3.2 Climbers The climber is the space system that will be travelling up and down the tether line of the space elevator. There are multiple types of climbers from the initial tether builder climber to strengthen the tether line with additional strands to repair & inspection climbers to operational climbers, which will deliver high payload masses to space from LEO to beyond geosynchronous orbit on a regular basis, then later on provide a safe ride to space for humans. Figure 3 shows a CAD model of the climber structure with its subsystem components. This is a preliminary design, and will be subject to change depending on advancements in technologies over the next couple decades.

Figure 3. Climber Design Model

6 3.2.1 Mass Budget The operational climber system is designed with a size of 20 meters in diameters and 15 meters in height, providing significant volume for payload deliveries. The climber possesses a gross of 20 MT, split into a 14 MT payload and 6 MT inert mass. Table 1 shows the subsystem breakdown of the climber along with the corresponding masses.

Table 1. Climber Subsystem Mass Breakdown [kg]

Structure 1,500 Support Equipment 555 Thermal 120 Power 2,340 Drive Motor 740 ADCS 360 TT&C 180 Propellant 205 Payload 14,000 Total Tether Climber 20,000

The climber structure mass decreases by 75% when carbon nanotubes (CNT) material is used allowing for similar strength but a reduced inert climber mass of 1.5 MT. The payload that can be carried up to space is therefore increased by 4.5 MT, significantly reducing launch cost.

3.2.2 Motor Drive Apparatus In order to accelerate the climber up and down the tether elevator line, a motor drive apparatus is required which includes an electric linear motor, driving wheels and a tether interface structure. This apparatus will be designed to a unified standard for all climbers similar to the concept of rail roads, and train drive design. This will allow for the manufacturing of one motor drive apparatus that will fit all types of climbers, and therefore reduce cost of manufacturing while providing redundancy and easy maintenance operations. The climber will utilize the roller’s friction force to elevate itself on the tether line. The Japanese Space Elevator technical and Engineering Competition in 2011, showcased a tether climber averaging a climb speed of 17m/s on a rope tether and 9m/s on a belt tether, indicating that friction drive systems are achievable and still have room to grow, when adopting more advanced materials such CNTs.

3.2.3 Power Requirements Starting at a 1g gravitational force at the surface of Earth, the initial power requirement to climb at a rate of 60 m/s is estimated to be 11.8 MW. As the climber leaves the atmosphere, the gravitational force drops by three fourths at an altitude of 6378 km and to 0g at GEO altitude. In order to provide power to the space elevator climber, large, light-weight and efficient solar panels are required.

7 3.3 Tether The tether design is one of the most important design parameters of the space elevator system, as this provides the foundation for climbers to go back and forth between space and Earth’s surface. The length of this tether structure is 100,000 km, which if built, will be the largest structure ever built by humans. The tether has to be able to withstand environmental stresses in orbit as well as operational stresses from the climbers, nodes and endpoint stations. In order to deploy the tether, a deployment spacecraft is required at the GEO altitude, for stable release of the tether line, without a sweep of complex orbital area

3.3.1 Design Requirements The design of the tether line is based on a simultaneous operation of 7 climbers, separated by a specific distance from each other along the tether. Table 2 shows the locations of the 7 climbers as a function of the orbit radius, and the resulting gravitational forces acting on each climber. As can be seen, the total equivalent weight on the tether from all 7 climbers at once is around 29 MT. Table 2. Forces Experienced for the 7 Climbers Operation

3.3.2 Tether Material The tether material must have a high value that can support its own weight and the weight of the 7 climbers discussed above of around 30 MYuri. The tether line will experience its highest stress at the GEO node and its lowest stress at the Marine node. Therefore, a taper ratio must be implemented in order to compensate for the increased stress at the GEO node, which the represents the increase ratio in mass of the tether at the GEO node compared to the Marine Node on the surface of the Earth. Basic research indicates that the most feasible material within the next decade that can deliver such high strength and low mass requirements is Carbon Nanotube (CNT). Carbon nanotube is a tubular structure made of carbon atoms, having a diameter of nanometer order but length in micrometers. It has extraordinary properties such as higher strength than steel, higher electrical conductivity than , and higher thermal conductivity than . It’s the Holy Grail to materials. Table 3 below summarizes the tether CNT characteristics required to make the space elevator design discussed feasible.

8 Table 3. Tether Carbon Nanotube Characteristics

The required operational specific strength is 27 MYuri using a 40% safety factor, leads to a rate tether specific strength of 38 MYuri, with a taper ratio of 6. The width of the tether of 1 meter aligns with the gripping mechanism of the climber drive train. Carbon Nanotubes material is the most important factor in the success of the space elevator system. Essentially without this amazing material, the space elevator concept has no chance of becoming a reality. For many years, when researchers tried to use this material as building blocks of larger structures, they had trouble getting these properties to scale up from laboratory single tubes to larger structures. One problem is the tendency for nanotubes to tangle where each point of tube-to-tube contact can compromise strength, as the strength of this material in large scales depends on how well the tubes can stay attached to each other and not so much the tube shearing in stress. But over the past few years, materials scientists have made great strides to straighten out these tangles. Currently, the carbon nanotube industry is seeing specific strengths that are exceeding 20 MYuri on a microscopic level (1 micron) from just single tunes, but is still working towards scaling up these values into a macroscopic level, that is similar to the application of the space elevator. Figure 4 below shows a plot of specific strength of carbon nanotubes for single tubes and CNT structures over time. One thing to note is that there has been a recording in 2011, of a carbon nanotube specific strength of 100 MYuri with a length of 10 cm, indicating that carbon nanotubes with 50-100 MYuri specific strengths (space elevator requirements) could be achieved as early as 2016.

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Figure 4. Strength of Single and Macro CNT Vs time

3.4 GEO Node Spacecraft The GEO node spacecraft will serve as the main operations station to off-loading hardware, assemble spacecrafts, store supplies, building components and full spacecrafts (parking). This GEO station can also be utilized for fueling of spacerafts, loading space debris collected and in the long as a space hotel or residence. It would be pretty much need to be the new Cape Canaveral of space. Based on the applications stated above, the resulting size of the GEO node spacecraft will be quite large, and therefore must be built in pieces just like the International , however construction will move a lot faster due to the weekly trips of materials up the GEO altitude using the space elevator climbers.

3.5 Marine Node The Marine node is the node on the surface of the Earth that will hold down the space elevator system to Earth. The marine node will include a floating operations platform, processing facility and a mission operations center. In the long run, the node would also include a residential area for its employees such as a military base as well as lodging for space tourists. Table 4 below list a basic set of design requirements for the marine node, which will offer the most efficient, stable and safe operations of the space elevator daily, year after year.

10 Table 4. Design Requirements for the Marine Node

3.6 Apex Anchor Without an Apex Anchor at the far endpoint of 100,000 km, the tether line would extend to a 140,000 km altitude. The purpose of it is to establish the balance of the 100,000 km tether line by acting as a counter weight, therefore balancing the dynamics between the masses above and below the GEO node. The angular momentums must be in synch, and the centripetal forces above the GEO must balance the gravitational forces near Earth. This counterweight must be 30% of the tether mass in order to keep the tether length of 100,000 km and therefore reducing manufacturing cost, and complexity of constructing the long line. This counterweight anchor would also hold an interplanetary launch site, where spacecrafts can get assembled, fueled and released for space exploration or beyond. Another use for this anchor is setting up a processing facility for mining, where missions will be launched to to mine and collect valuable metals, then processed and sent back to Earth.

4.0 Concept of Operation

4.1 Pre-mission • Contract and planning with headquarters • Delivery to base support station • Transportation on ocean cargo vessel • Delivery at floating operations platform

11 4.2 Flight The first step in the flight operations is loading the payload (customer spacecraft, fuel, and building materials) into the tether climber and securing the payload to the structure, in order to prepare for the climb. Once the tether, is ready for climb, the mission operation center will begin commanding of the drive motor to initiate acceleration. The vehicle will climb at a velocity of 60 m/s. The vehicle will operate only in the sunshine during the day and hibernate during eclipse. As it climbs, the eclipse times will get shorter and more power will be available from the sun for operations. Table 5 shows the distance travelled and radius at the sunset of each day, reaching GEO on day 8. Table 5. Climb Phase Breakdown

Day Distance Travelled (km) Radius at Sunset (km) 1 3,412 9,790 2 4,355 14,145 8 4,925 42,828 (GEO)

Depending on the desired orbit altitude, the customer payload will be delivered using the tether climber, where it will be released using a robotic off-loading system. For the spacecraft to be inserted into LEO & MEO, an altitude of at least 23,690 km must be reached. Once dropped off by the space elevator, an onboard propulsion system would be used to achieve the desired orbit inclination. On the other hand, the spacecraft can also be released by the space elevator with enough energy to sustain the equivalent orbit of GEO, at an altitude of 35,782 km. To initiate an interplanetary trajectory, the spacecraft is released at a distance above GEO based on the energy needed for the specific planet destination. The spacecraft however, will require additional energy from a rocket propulsion system in order to correct its trajectory, inclination or utilize fly-bys around other planets

5.0 Cost Estimates Table 6. Initial Capital Cost for Space Elevator

Technology advancements / risk reduction $200M Development/market confirmation $300M Construction $4B Total Costs $4.5B

Table 7. Operational Cost of Space Elevator

Mission Ops Center O&M $28M Mission Ops Center Staffing $7.5M Marine Node O&M $30.5M Marine Node Staffing $33M Miscellaneous (Marketing, PR…) $10M Total Operational Costs $109M

12 6.0 Conclusion The space elevator concept can be accomplished within the next decade’s arena. Its great advantages will improve the environment, reduce space debris and deliver payload to orbit for a much lower cost than any system today. The concept is feasible based on today’s projections of where and solar array efficiencies, as these hold the key to technological success. Carbon Nantotubes are projected to achieve the required strength to weight ratio at lengths that will enable the tether design. This mega-project will need a great amount of investors, partners and political leaders to fund the initial capital cost, sustain operations successfully within international law. When the space elevator concept is achieved, there will be a renaissance on Earth with its solutions to today’s space travel limitations.

13 References

Kumar, Mukul, and Yoshinori Ando,” Chemical Vapor Deposition of Carbon Nanotubes: A Review on Growth Mechanism and Mass Production”. Journal of Nanoscience and .2010-12-01

Swan, Peter Alfred, “Space Elevators: An Assessment of the Technological Feasibility and the Way Forward”. International Academy of Astronautics, 2013.

Nanotube Muscles Bench 50,000 Times Their Own Weight | MIT Review (MIT Technology Review) http://www.technologyreview.com/view/507576/nanotube-muscles-bench-50000-times-their- own-weight/ Scientists build the first carbon nanotube computer, change computing world forever | ExtremeTech (ExtremeTech) http://www.extremetech.com/extreme/167421-scientists-build-the-first-carbon-nanotube- computer-change-computing-world-forever

Elevator:2010 (The Spaceward Foundation) http://www.spaceward.org/elevator-feasibility

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