ABSTRACT
For 40 years, the space elevator has been a concept in science fiction and appearing occasionally in technical journals. Versions of the space elevator concept have generally been megalithic in design. However, recent advances in technology and new designs for an initial space elevator have presented a much smaller and a more realistic version that has created a renewed interest in serious technical study. There are now over a dozen entities and hundreds of engineers and scientists with active research related to the space elevator. The activity includes conferences, engineering competitions, extensive media coverage, international collaborations, publications and private investment. These activities are rapidly expanding with the number of publications in 2004 nearly ten times the total for the prior forty years.
INTRODUCTION
The space elevator concept has been around for many years (Tower of Babel, Jack and the
Beanstalk, Clarke’s Red Mars Fountains of Paradise, Robinson’s) and between 1960 and 1999 a few technical studies addressed the basics of the system (Moravec, 1977; Isaacs, 1966; Pearson, 1975; Smitherman, 2000). These studies addressed the oscillations inherit in the system, the taper requirements, and the general difficulties but did not cover most of the technical details of construction and operation. In 2000, Edwards published a unique design for the space elevator and followed this publication with an overviewengineering funded by NASA’s Institute for Advanced Concepts (NIAC). The final report from the Phase I effort and book resulting from the Phase II effort (Edwards, 2003) outline the basics of a space elevator. These publications go through the basic ribbon design, the climber design, the deployment spacecraft, the power delivery system, challenges to the system, etc. The basic design presented in the NIAC work has stressed simplicity – a single, small, static ribbon with mechanical climbers that ascend using conventional electric motors (figure 1).
The design implements conventional technology with little or no development wherever possible. The design is easy to grasp and analyze and may present a reasonable first system though may not present the optimal final design for future generations of elevators. This initial effort completed with $570,000 in funding has been the catalyst for variant designs and additional studies. The initial effort also generated a template for defining the challenges and where research and engineering were most critically needed. Some items such as the anchor station have been viewed as straightforward and understood in terms of current technology where as other components, such as the ribbon and system dynamics, are unique and considered challenges. By defining the challenges the problem has been broken down into pieces that can be investigated by individuals or groups. This accessibility of the problem has spawned growing interest in engineering and research communities. For example, in 2000, a search on the Internet for ‘space elevator’ would have produced several hundred links. The same search today will return over 150,000 links.The primary technical hurdle for construction of the space elevator is the production of the highstrength material with a tensile strength of 100 GPa. At the current time, carbon nanotubes (CNTs) have been measured with tensile strengths of 200 GPa. CNTs have been spun into yarns of pure carbon nanotubes and have been implemented in composite fibers. The spun fibers are a new development (Li, 2004) though CNT composite fibers have been made with as high as 60% CNTs, strengths comparable to steel (5% CNTs by weight) and kilometers in length. The high-strength material being the primary hurdle to construction it has also become the focus of several efforts. The ribbon design and deployment are being reexamined in terms of possibly building the ribbon by attaching full width segments end-to-end instead by of the baseline increasing the width by splicing additional ribbons onto an initial small ribbon. The system dynamics has also become an active area of study due to its ease of entry. The dynamics that are now being investigated range from the smallest scale (individual fibers) to the largest (finite element modeling of the full 62,000 mile ribbon). Small-scale dynamics revolve around the degradation of the ribbon components at the individual fiber and interconnect level. Primarily this pertains to breakage of individual fibers in the ribbon and how the ribbon responds. Large-scale dynamics involve the oscillations, profile variations and how the ribbon generally responds as a system. The climber, being a traightforward mechanical system, has also attracted interest in the form of engineering competitions and detailed design studies. The various designs now being considered include the baseline tread system, pinching rollers, and offset rollers. Few new designs for the power transmission have been presented. With the increasing interest there has also been a healthy re-examination of the baseline design.
APPLICATIONS:
NASA’s exploration program is driving toward a sustained presence in space with a station on
the moon and men on Mars. The required technology developments for this program including habitat modules will benefit the space elevator in terms of allowing rapid development of space and producing detailed estimates of cost and complexity of commercializing space. The disconnect between the NASA effort and what will be needed in applications using the
space elevator is in the much more expensive construction required for rocket based systems
Trends and Unique Aspects :
One of the unique aspects of the space elevator is the speed at which it has gone from being
considered a strictly science fiction concept or distant possibility (1999) to a concept seriously
considered for near-term construction (2004). Most of this change has occurred since completion of the NIAC study and release of the book, The Space Elevator, in early 2003. This
rapid change is a result of clarifying the engineering arguments for construction of the space elevator. However, the construction of a space elevator is a large program and will require a much larger effort than what currently exists. Estimated costs for construction are around $10 billion for the first space elevator and a fraction of this for subsequent systems. Development costs for the space elevator should then be expected to be around 5% to 10% of the final cost or $500 million to $1 billion. The other aspect of this is the schedule for development. The engineering of integrating the components and conducting the required tests will take years. The effort will need to grow considerably in the future for the space elevator to be built in the next 15 years. Future work on the space elevator could go in several directions. Private organizations are currently pushing development with the only public funding coming through a congressional appropriation (ISR/MSFC). This disparate level of interest is in spite of many more briefings to government agencies than to private organizations. Governmental briefings have included perhaps a dozen at NASA headquarters and various NASA centers, DARPA, Air Force Research Laboratory, Air Force Space Missile Center, NRO, NSA, Rayburn House Office Building and personal invitations to the space elevator conferences. In addition, proposals in response to NASA’s Exploration Systems Broad Area Announcement for examining a space elevator based exploration program were not selected for funding
CONCLUSION:
Recent developments in the design of a viable space elevator have led to a dramatic increase in the amount of activity and research conducted in this area. The number of researchers investigating the space elevator has grown froma handful in 1999 to hundreds today at many
institutions. The activity includes dedicated conferences, publications, media coverage, and
private investment.
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