55th International Astronautical Congress 2004 - Vancouver, Canada

IAC-04-IAA.3.8.3.02

TECHNOLOGY DEVELOPMENT AND DEMONSTRATION CONCEPTS FOR THE

David V. Smitherman, Jr., Architect Technical Manager, Advanced Projects Office NASA Marshall Space Flight Center, Huntsville, Alabama, USA E-mail: David.Smitherman@.gov

ABSTRACT

In 1999, the author managed for the National Aeronautics and Space Administration (NASA), a space elevator workshop at the NASA Marshall Space Flight Center to explore the potential feasibility of space elevators in the 21st century, and to identify the critical technologies and demonstration missions needed to make the development of space elevators feasible. Since that time, a NASA Institute for Advanced Concepts (NIAC) funded study proposed a simpler concept for the first space elevator system using more near-term technologies. This paper will review some of the latest ideas for space elevator development, the critical technologies required, and some of the ideas proposed for demonstrating the feasibility for full-scale development of an Earth to Geostationary Earth Orbit (GEO) Space Elevator. In conclusion, this paper finds that the most critical technologies for an earth-based space elevator include Carbon Nano-Tube (CNT) composite materials development and object avoidance technologies; that the lack of successful development of these technologies need not preclude continued development of space elevator systems in general; and that the critical technologies required for the earth-based space elevator are not required for similar systems at the , and other locations.

BACKGROUND

In the 1990’s, advances were made by NASA Study: several researchers indicating that carbon To investigate this possibility the author, in nano-tubes might be the high strength 1999, managed for NASA a space elevator material needed for fabrication of space workshop at the NASA Marshall Space elevators from geostationary orbit down to Flight Center in Huntsville, Alabama, to the surface of the Earth. These findings explore the potential feasibility of space have led to the continued development of elevators in the 21st century, and to identify nano-tubes for structural applications and the critical technologies and demonstration serious investigations into the space missions needed to make development of elevator concept as a potential space elevators feasible.1 Specifically, this infrastructure element for space science study identified CNT composites, tether missions, human space exploration, and demonstration missions, tall tower commercial space development. construction technology, electromagnetic ————————— propulsion, and space infrastructure development in general as major technology developments required before a space elevator could be developed. The time frame for possible space elevator

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construction was assumed to be greater In light of the prior studies, and the current than 50 years—in the latter half of the 21st activities, this paper will review some of the Century. latest ideas for space elevator development, the critical technologies required, and some NIAC Study: of the ideas proposed for demonstrating Since that time, a NIAC funded study of the their feasibility. Space Elevator proposed a concept for a simpler system using more near-term technologies.2 Not required were the former findings for tall tower construction CRITICAL TECHNOLOGIES technology, electromagnetic propulsion, or extensive space infrastructure development. NASA’s approach to developing new space Instead, this simpler approach used more systems for future deployment includes the near-term technologies including CNT identification of all critical technologies by composite ribbon development, electric ranking their level of maturity on a scale propulsion, wireless power transmission, known as a Technology Readiness Level mechanical crawlers, and collision (TRL), Figure 1. This approach makes it avoidance systems. In addition, the NIAC easy for technologist to identify the study resulted in a book “The Space technologies that need to be funded for Elevator”3 that provides a good detailed continued development, as well as providing description of the concept and the an overall gauge for project managers as to economics of the space elevator from a the likelihood that the project is ready, or not business perspective. The premise of this ready, for full scale development. study was that the space elevator can be built with more near-term technologies that Technology Readiness Levels: may make construction possible in the first Basic Technology Research comprises TRL half of this century—perhaps as early as 15 1: Basic principles observed and reported; years away. and TRL 2: Technology concept and/or application formulated. The CNT composite Current Activities: ribbon development is probably in the TRL 2 As a result of these studies, serious interest category because the CNT has been in the space elevator as a potential future observed to have the required strength at space infrastructure element has grown in the nano-scale, but large-scale composite both technical, public, and private circles. In fibers have yet to be developed with the 2004, NASA and the Institute for Scientific required strength for construction of a space Research established a cooperative elevator. Since the ribbon structure is the agreement to conduct further investigations primary component of the space elevator, into the space elevator concept. Specific and there are no know substitutes, the investigations to be conducted include a entire system for Earth to GEO applications more detailed systems engineering study of is considered an advanced concept worthy the entire concept, continued development of study and technology development, but of the high strength CNT composite not far enough along to warrant major materials, ribbon dynamics analysis for a full project funding. In other words, there is no length space elevator structure including guarantee that adequate time and money control systems concepts for object will mature this technology. Note also the avoidance, ribbon design, prototype red color coding, indicating that critical climbers, and collection and production of technologies at this level should not yet be technical papers and educational materials counted on for near-term projects. on the space elevator for the technical community and the general public.

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Figure 1: Technology Readiness Level

Technology Development comprises TRL 3: environment; TRL 8: Actual system Analytical and experimental critical function completed and “flight qualified” through test and/or characteristic proof-of-concept; TRL and demonstration (Ground or Flight); and 4: Component and/or breadboard validation TRL 9: Actual system “flight proven” through in laboratory environment; and TRL 5: successful mission operations. Some of the Component and/or breadboard validation in tether deployment hardware, spacecraft relevant environment. Many of the systems, and ground stations fit into these mechanical systems for the space elevator categories because similar systems have fit into these categories, in that similar flown on previous space missions, or have mechanisms exist, but have never been put been tested in a relevant environment. into the configurations required for the When all technologies have reached this space elevator, and/or have never flown in a level of maturity, it is relatively easy to put space environment. All required together a cost and schedule for technologies in these categories are development that can be done, giving the assumed to be mature enough that they project manager a green light to successful could be developed for the project given project execution. enough time and money. Hence, the yellow color could be interpreted as proceed with TRL Evaluation: caution. Given the above categorization of critical technologies, a first cut was made at System/Subsystem Development comprises examining the space elevator elements in a TRL 6: System/subsystem model or work breakdown structure (WBS), and prototype demonstration in a relevant ranking them by TRL. The following Figures environment (Ground or Space); TRL 7: 2-4 list the space elevator WBS elements in System prototype demonstration in a space the left column, and then rank them by color

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coding indicating the kind of development identical indicating where we think the and testing likely required for maturity in the technologies are today for all the space following columns. Colors indicated are as elevator systems. The next 3 columns under described above, red for the lowest TRL 1- “Ground Tests” are designed to advance 2, (stop, we have a lot of work to do here); some technologies from a lower level TRL yellow for TRL 3-5 (send money and we will in red or yellow, to a higher TRL of yellow or make it work); and green for TRL 6-9 (we green. Note that the chart extends color know how to do this and can estimate a bands across all columns, but that not every reasonable cost and schedule for experiment uses every technology. The next development). 3 columns under “Space Flight Tests and Demonstrations” are designed to advance The columns following the WBS column are mid-range technologies in yellow into a progression of experiments and integrated systems for flight in green. Once developments that will probably be needed all, or nearly all the technologies have been to mature all the technologies and integrate advanced to an integrated systems level in them into a system that can be constructed. green then space elevator construction Beginning with the two “Current Experience” would be ready to begin as indicated in the columns, the TRL rankings are nearly last column.

Acronyms: GPS – Global Positioning System ISS – International Space Station LEO – Low Earth Orbit SEDS – Small Expendable-Tether Deployer System TSS – Tethered Satellite System

Figure 2: WBS for the Ribbon Deployment Platform at GEO that will deploy the space elevator ribbon

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Figure 3: WBS for the End Effector Spacecraft that will control the lower end of the ribbon as it is deployed to Earth, the LEO to GEO Transfer Stages, and the Earth to LEO Launch Vehicles.

The numbering systems in the color-coded be around 130 Giga-Pascals (GPa) for an columns are more specific TRL indicators earth-based space elevator. In addition, a that have been identified so far. Future work full-length ribbon, whether continuous or includes more specific identification for each spliced, is anticipated to be 60,000 to technology along with better plans for 100,000 km long, so mass production advancing the lower TRL technologies; and methods will be a consideration, too. more specifics on testing approaches, flight Durability in the space environment, wear experiments, and demonstration missions. and tear of climbers, splicing methods, and repair methods are additional Low TRL Summary: considerations for the ribbon materials and As can be seen in Figure 4, the lowest TRL design to consider. technologies are in the Space to Ground Systems, and Ground Systems. In The climbers are also shown at a low TRL particular, Ribbon Materials Development, because of the automated tasks required of and Ribbon Design are at a TRL 2 the climber for ribbon splicing, inspection, indicating that an approach to their and repair—all at high speed on the order of development has been formulated, but 100 km per hour or more if possible. These successful development has yet to occur. are tasks that individually may not be Ribbon materials and design are linked and difficult for machine operations on the will require extensive analysis and testing to ground, but incorporating these functions ensure that the total system will meet the into a lightweight ribbon climber has never overall performance requirements of the been done before. elevator for mass and strength, assumed to

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Figure 4: WBS elements for the Space to Ground Systems including the ribbon and ribbon climbers, and all Ground Systems.

Several Ground Systems also have low TRL CRITICAL PATH DEVELOPMENT ratings. At the anchor station, mechanisms will be required to help control the overall Numerous paths for technology dynamics of the system, perhaps moving development and demonstrations have the base and/or inducing waves in the been suggested utilizing ground ribbon for object avoidance. Such a system experiments, air structures, LEO missions, will need to be integrated with a more robust the Space Shuttle, the ISS, GEO orbital object tracking system that is much demonstration missions, demonstrations at more refined than the 10cm size-limit, multi- the Earth-Lunar L1 or L2 points, and other kilometer positioning range, and limited locations. The following sections provide an position prediction capabilities, of the overview of those ideas for consideration to systems in use today. Also, power beaming help formulate a critical path for advancing for the climbers has been demonstrated in the lower TRL technologies to a level ready the lab, but is at a low TRL because it has for flight demonstration and eventual space never been developed for large-scale elevator construction. systems that could beam surface generated power up to GEO altitudes.

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Technology Development:

Materials: Basic laboratory research tether materials since its primary purpose is & development is in progress on high- to develop control and robotic technologies. strength CNT composite fibers for a variety of uses including the earth-based space Ground Tests: For both ribbons, elevator. At this writing, fiber development extensive ground testing can prove the still looks promising, but has yet to obtain a technology prior to flight. In particular, it has strength exceeding other commercially been suggested that a Vertical Treadmill available carbon composites in common Test could be developed that would use today. Since the CNT fiber is only simulate the ribbon undergoing the wear required for an earth-based space elevator, and tear of extensive traffic by the robotic other high strength fibers could be used to crawlers. Incorporated into that test could develop the tethers and ribbons required for be different crawlers designed to do high- design and testing of the other parts of the speed ribbon inspections, splicing system. Goals for ribbon performance have operations, and repairs. been set at about 130 GPa for the earth- based space elevator. Intermediate goals At the same time, the Ribbon Materials are needed for use of this same material in Development and Testing in a Relevant demonstration missions and other space Environment will expose them to simulated elevator concepts. Specifically, intermediate space environments to ensure their CNT composite materials performance survivability to debris, radiation and atomic goals need to be identified for the 3 oxygen. These tests are linked to the repair “ Tests and Demonstration” tests above, in that any wear induced by the missions indicated in Figures 2-4 above. crawlers or the environment will need to be repaired or replaced without the loss of Ribbon Design: The design of the structural integrity of the entire system. ribbon for assembly, durability and maintainability in the space environment is a Once the robotic technology has matured critical technology for all space elevators and the ribbon design refined to permit including the demonstration missions. This maintenance then a Tether Balloon Test has an integral relationship with the robotic would be a logical next step for moving out climbers as well, since they will be doing the of the laboratory and preparing for flight. inspections, splicing, and repairs as needed The balloon test would consist of a high to maintain the ribbon structure. Here, altitude tethered balloon equipped with a ground testing can advance the technology ribbon deployment system similar to a for ribbon design and repair in preparation ribbon deployment spacecraft. Using a laser for future space missions. power beaming system for wireless power transmission, the deployment mechanism The first two ribbons to be designed could would demonstrate the deployment of a take separate approaches given its intended ribbon down to earth, and then demonstrate test requirements. In reference to Figure 4, all robotic functions for the crawlers, the LEO Deployment Demonstration needs including inspections, repairs, splicing, and to survive the LEO environments, which will payload transfers. Balloon tests would likely include atomic oxygen and space debris. entail development and test of many of For this test the use of CNT composites is these functions independently and then important even if the high-strength culminating in a full up integrated test using requirements have yet to be obtained. The prototype equipment that is near equivalent GEO Deployment and Traversing to the flight hardware. Demonstration could use conventional

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Flight Experiments: The baseline approach to flight experiments currently programmed for science and in developing space elevator technologies exploration missions. does not include use of our space-based laboratory, the ISS, or the Space Shuttle. But, if they were available, there are several ideas on how they could be utilized to help advance the long-term development of space elevator related technologies and systems. This includes fundamental research into the possible development in the microgravity environment of space, longer single wall carbon nano-tubes than can be created on earth due to the environment, and fiber spinning experiments that might result in improvements to the ultimate strength of CNT composites. In addition, experiments in the microgravity environment on ribbon Figure 5: The ISS, with electrodynamics splicing, coatings and repairs would tether, could offer an approach to space probably be useful in the development of elevator testing, too. the robotic climber systems. For the LEO section of the earth-based Other ideas have included using the ISS as space elevator ribbon, it will eventually be a platform for shorter tether tests in advance important to have a major flight experiment of, or as part of the LEO Deployment like the LEO Deployment Demonstration to Demonstration previously mentioned. This examine ribbon deployment, control, repair, could also be done by utilizing a modified and retraction methods, to insure that it can Sparta platform as a free-flyer from the survive this environment and be repaired or Shuttle or the ISS for ribbon deployment replaced as needed. Such a mission is experiments. The recovery capability of envisioned to be within the capabilities of a these systems would make it possible to single medium class expendable launch better examine the space environmental vehicle (ELV) with the payload including a effects on the materials planned for the deployment spacecraft, ribbon spool, an space elevator system and enable end effecter spacecraft, and robotic climber modification and reuse of the system for for ribbon splicing, inspection, and repair. additional experiments. Additional investigations would include development of collision avoidance systems Another interesting idea that would advance for this structure, along with more accurate tether technology in general is the tracking and trajectory projection systems electrodynamics tether shown in Figure 5. for active and inactive objects in LEO. This advanced concept provides re-boost of the ISS to maintain orbital altitude and could An interesting concept that could someday be used to lower the space station utilize this technology is the LEO Space inclination over several years. The point of Elevator, or “Bridge to Space” concept mentioning this here is that the ISS might envisioned by the Lockheed Martin have a useful life extension mission as part Company (LMCO), Figure 6. This concept of a plan to develop space elevator was proposed to capture payloads from a technology beyond the timeframe it is future suborbital space plane at 100 km altitude, and then lift the payload to the

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upper end of the elevator at 4000 km a Full scale Lunar Demonstration, also altitude, where when released it would enter known as a Lunar Space Elevator or Lunar a GEO transfer orbit. The LEO Deployment Towers. These demonstrations would prove Demonstration would help test the feasibility the viability of space elevators for Earth, of this concept. Mars, and the of other planetary systems. Even if the CNT composite material strengths are not obtainable in the near-term for an earth-based space elevator, the technology developed through these missions should provide significant infrastructure capabilities for access to many other planetary bodies, Figures 7 and 8.

The GEO Deployment and Traversing Demonstration is envisioned to be a major technology demonstration mission to prove that the space elevator ribbon dynamics can be controlled during deployment and during robotic traversing from end to end. This demonstration would utilize at least two heavy class ELV launches to GEO where the two spacecraft will rendezvous and deploy a 30,000 km ribbon; attach a robotic crawler vehicle to traverse the ribbon from end to end; test the spacecraft control systems given varying ribbon dynamics; and demonstrate the robotic crawlers Figure 6: “Bridge to Space” concept for a capabilities for ribbon splicing, inspection LEO Space Elevator by LMCO. and repair. In addition, these systems would be required to demonstrate power-beaming Demonstration Missions: technologies for the robotic crawlers. Power Two major demonstration missions are could come from a variety of sources envisioned as important for the earth-based including ground stations, orbital platforms, space elevator: 1) the GEO Deployment or power platforms at GEO or at the counter and Traversing Demonstration, also known balance end of the tether structure. as the LEO to GEO Space Elevator; and 2)

Figure 7: Concepts for space elevators around the Earth and Moon.

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A similar technology has been proposed The final step, referring back to Figures 2-4, before for communications satellites where is the development of an Operational the transmitter is located at the lower end of System for an Earth to GEO Space a tether only a few thousand kilometers in Elevator. Once all the proceeding altitude, and counter balanced by the power developments, tests, experiments and systems at the upper end of the tether. With demonstrations have been successfully the center of mass maintained at GEO, the accomplished then construction should be systems operates like a LEO altitude feasible. These steps are far more satellite in a geostationary orbit for fast extensive that proposed in the NIAC studies voice and data response to ground stations. previously mentioned, but all have valid missions for advancing the technology. The Full Scale Lunar Demonstration is Somewhere in between this extensive set of envisioned as a major technology testing and the simplified approach of the demonstration mission for full deployment of former study is probably the right answer. a space elevator ribbon from the earth- The intent here was to identify the full range moon L2 point in space on the far side of of possible approaches for further analysis the moon. Four or more heavy class ELV and debate. launches to L2 will likely be needed to deploy multiple spacecraft for ribbon control Also, important to all these demonstration at each end, ribbon deployment, robotic missions is their compatibility with future vehicles to traverse the ribbon from L2 to space infrastructures within the Earth-Moon the surface of the moon, and an L2 docking system. Long-range plans should consider station on the ribbon for payload transfers. these potential developments so as not to This complex infrastructure has the potential inhibit their construction in the future. In to become part of a permanent lunar particular, technology and policy plans need infrastructure providing access for ongoing to be improved now that will deter the missions to the surface of the moon. In accumulation of debris in LEO and will addition, such a system would be a begin taking steps toward removal of the precursor to similar systems at the moons of debris already in orbit. Mars, and the moons around many outer planets.

Figure 8: Concepts for space elevators at the moons of Mars to facilitate access to Mars and transportation between Mars and Earth.

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CONCLUSIONS

Key Findings: In conclusion, this paper finds that the most critical technology developments that would critical technologies for an Earth to GEO accelerate the feasibility of earth-based Space Elevator include CNT composite space elevator systems. Continued studies materials development and object and technology developments on space avoidance technologies; that lack of elevators as outlined in this paper are highly successful development of these recommended. technologies need not preclude continued development of space elevator systems in general; and that the critical technologies required for the Earth to GEO Space BIBLIOGRAPHY Elevator are not required for similar systems at the Moon, Mars, Europa, or for other 1. Smitherman, D., Space Elevators: An orbital tether systems at GEO, Luna, and Advanced Earth-Space Infrastructure for other locations. CNT Composite the New Millennium, NASA/CP-2000- development is the most critical technology 210429, NASA, Marshall Space Flight development for the earth-based space Center, Huntsville, Alabama, August elevator, without which the system may not 2000. (Web accessible at be feasible. http://flightprojects.msfc.nasa.gov/fd02_ elev.html) Recommendations for Future Activities: 2. Edwards, B., The Space Elevator, Space elevator developments in general Eureka Scientific, Phase II Final Report should be investigated for Lunar L1 & L2 to the NASA Institute for Advanced sites, Mars, and the Moons of outer planets. Concepts, Atlanta, Georgia, March 1, Many of these systems appear to be 2003. (Web accessible at feasible with current technology and could http://www.niac.usra.edu/studies/) become major permanent infrastructure 3. Edwards, B. C., E. A. Westling, The elements for space science, human space Space Elevator, Spageo Inc., San exploration, and commercial space Francisco, CA, 2002. development. In addition, they could yield

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