International Space Elevator Consortium
November 2023 Newsletter

In this Issue:

Editor’s Note
President’s Corner
20th Reinventing Space Conference
ISEC Study Report Completed!
Notes from the 74th IAC 2023
ISEC published in the Journal of the British Interplanetary Society
Tether Materials
Upcoming Events
Contact Us/Support Us

Editor's Note

Dear Fellow Space Elevator Enthusiast,

Beth Barany has written four mystery novels in a series about a space station detective named Janey McCallister. Her novels include a space elevator!

Beth recently emailed me and said that our work at ISEC inspires her. She mentions us and our academic challenge in her "How to Write the Future" podcast, episode 67, called "Inspiration for the Janey McCallister Mystery series."  

I have not read any of the books yet, but I have the first one on order, and I hope to do a write-up of it in the future.

Sandee Schaeffer
Newsletter Editor

President's Corner

by Pete Swan

Building Partnerships

ISEC cannot develop the Green Road to Space without the help of partnerships around our communities of interest – financial, environmental, engineering, transportation, and government relationships. I would like to invite each of you to think about how you can help with relationships you have with individuals or organizations. The example I will use here is the National Space Society. We have an excellent relationship with them and hope to grow it even stronger. I would like you to look at this summary of one relationship and think about other organizations and how we could develop more positive co-operations moving our objective forward jointly. Here are some of the elements that are essential to success in the long run as explained within our NSS commitments.

Joint Memorandum of Understanding (MOU): This step is usually one of the first. It sets out expectations of the giving and receiving between organizations. Our joint MOU has led to a very positive relationship with many activities across the common missions. The initial agreement was signed in 2013 with the relationship strengthening each year. Here are some of our agreements for actions and commitments.

1. Involvement and support to their yearly conference: We have been involved at many levels within their International Space Development Conference and followed them around the US as they placed their activities at various locations. We have not only attended their conferences, we created and then led a technical session on Space Elevators. We usually present/support 10 to 15 talks. In addition, we have supported the annual reception on Saturday evening before the formal awards dinner.

2. This year we have co-sponsored a global student competition with sizable cash prizes to the winners in two categories: Artificial Intelligence -- applications within a space elevator architecture -- and an explanation of the impact of the Green Road to Space approach to space access. This joint venture will result in winning teams presenting at the International Space Development Conference.

3. In parallel, a small ISEC team is assisting the NSS SpacEdge Academy development leading to lesson plans for K-12 and college students. The objective of the NSS Academy is to provide support to teachers around the world with information that can be utilized inside the classroom with support from the NSS. In parallel, there is the development of tremendous information for their website. This allows students and professionals to understand and teach topics such as space elevators. We are providing them tremendous access to our modern-day Space Elevator body of knowledge so they can “translate” to the various student levels and researcher needs.

In addition, we should leverage opportunities that surface which are within the NSS and ISEC activities. This last weekend (26 Oct 2023), the NSS conducted a two-day Space Settlement Summit asking the question, “where are we?” and how do we arrive at settlements in space and on other orbiting bodies? The main focus was on Low Earth Orbits and the Artemis lunar landing program. The beauty of our relationship with the National Space Society is that we can join forces and contribute towards our common future. At this Summit, ISEC had two attending – our Director of Educational Outreach (Jason Arnold) and our President. The topics became complex when they moved towards funding of orbiting space stations (commercial replacements for our ISS) and “how to” execute the programs within the commercial imperative versus large government programs such as NASA’s movement to the Moon and then Mars.

This summary of one of our relationships is to ensure our friends know that we are here for them as we both move forward toward our common future. This would include our movement off-planet and the creation of satellite programs that can help solve Earth’s significant problems. The approach we have taken is to have great partners and support their desires and hopes. Indeed, the NSS’s favorite programs have a common vision while needing our strengths and insights into transportation and logistics.

Pete

20th Reinventing Space Conference 

by Peter Robinson and Adrian Nixon

90th Anniversary of the British Interplanetary Society
and the 20th Reinventing Space Conference – Liverpool, UK

The British Interplanetary Society (BIS) celebrated 90 years since its founding on the 13th of October 2023. They also organise the Reinventing Space Conference, which is in its 20th year, so a double celebration. The event was held in Liverpool, UK in the Spine building of the Royal College of Physicians.

The International Space Elevator Consortium (ISEC) was invited to present at the event, Peter Robinson and Adrian Nixon delivered a joint presentation. We were on the top floor, so naturally we took the elevator.

Our presentation was titled “Space Elevators – The Ultimate Architecture.”

Peter took the lead with the first part of the presentation providing a condensed history of the space elevator concept.

He covered the historical people involved all the way from Konstantin Tsiolkovsky (1895) through Yuri Artsutanov (1960), Jerome Person (1975), and Arthur C. Clarke. He then moved to the 21st-century developments with Brad Edwards's NASA/NIAC feasibility study (2003) and more recently the work by ISEC in reference books published by the International Academy of Astronautics (IAA).

Peter came right up to date with the latest work this year. In June 2023, the BIS magazine, Spaceflight, carried five articles by ISEC members about the construction and operation of the space elevator. In August 2023 ISEC had its annual conference in Chicago. In October 2023, Peter presented at the 74th International Astronautical Congress (IAC) in Baku, Azerbaijan, and this time a representative from the Chinese Academy of Launch Vehicle Technology (CALT) also presented about the space elevator. This was notable because the paper behind the talk had four out of the five authors from CALT and the work was supported by the National Natural Science Foundation of China. The lead author left the conference as soon as he finished presenting so Peter couldn’t get a chance to talk directly with him to find out more. This means that we can speculate that China has a dedicated team of at least four people working on the space elevator as part of its national space programme, but we cannot be sure.

Peter made the point that the Chinese work with the same physics as everyone else. The rocket equation applies to everyone and means that rocket lift can only deliver limited amounts of mass to Earth orbit and beyond. In the history of spaceflight (1957 to 2020) we have delivered 20,000 tonnes to space with rockets. Space elevators can deliver 30,000 tonnes per year [1].

Space elevators beat the rocket equation and can raise massive tonnage by electricity to GEO and beyond, daily, routinely, inexpensively, safely, and in an Earth-friendly manner. Small wonder the Chinese appear to have an active space elevator programme.

Adrian took over for the second part of the presentation.

Adrian delivered an overview of advances in materials science that identify the leading tether candidate materials. He reviewed all the leading materials, covering carbon nanotubes and graphene. Then moved on to the industrial manufacture of these materials, pointing out that graphene can already be made in lengths of up to one kilometre and speeds of up to two metres per minute.

The audience was not aware of the rapid advances in material science over the past few years. They were particularly impressed by the development of continuous processes to manufacture graphene at industrial scales. They understood that this was not yet tether quality, and appreciated the direction of travel of the manufacturing state of the art.

Beyond the Moon panel discussion “Humanity’s future in space”

At the end of the event, Adrian was invited to join the panel on stage.

The very first audience question to the panel was about the space elevator. Could a tether survive a direct hit in space? This was answered in two parts.

The first was the risk of collision with satellites and other large orbiting objects. A hit from large orbiting objects would be mitigated by moving the tether out of the way. This is possible because designs for the Earth port are based on the sea, not land and this means the structure is movable.

The second part of the answer was the harder problem of pieces of space junk. Objects made of aerospace alloys, tens of square centimetres in size, could travel with speeds of tens of thousands of kilometres per hour. The impact would be comparable with a 9mm high-velocity bullet fired at point-blank range. Our modelling suggests that a tether made from graphene laminate would behave like lightweight bulletproof armour. Impacting objects would bounce off the tether. We fear for the space junk more than the tether.

We sensed the audience wanted more but the panel chair had to move on to other topics. We are steadily raising awareness that space elevators need serious consideration. We will be invited back to discuss this further.

References:

1. Swan, C. (2023). Modern day space elevators. SpaceFlight, 65(6), pp.18–19.

ISEC Study Report Completed!

Leverage Dual Space Access Architecture
Advanced Rockets and Space Elevators

Jerry Eddy, Ph.D., a member of our ISEC board, and a team of experts, completed a two-year-long research project into how advanced rockets and modern-day space elevators leverage each other’s set of strengths and provide services to future customers needing massive movement of supplies and support to distant destinations. This report will be available for purchase in hard copy or downloaded in pdf (free) from our website (https://www.isec.org/studies)

The preface explains the research and the results as follows:  This study assumes Space Elevators can and must be built. “Space Elevators: The Green Road to Space,” a study completed in April 2021, emphasizes that Space Elevators will not replace rockets but would join them on parallel paths toward the stars.  This Dual Space Access Strategy will carry out currently planned missions and ensure the future we dream of becomes a reality. Space Elevators are needed to do the “heavy lifting” for movement off-planet. Their transformational characteristics will enable so many of humanity’s dreams by moving huge mass to far-away destinations. 

Space Elevators enable mass to be raised against gravity – without using rockets.  This leads to Space Elevators defeating the Rocket Equation! Our future of moving off-planet includes Space Elevators as necessary, compatible, and complementary to rocket architectures. The future needs both communities to work together. It seems obvious that cargo should be moved by a permanent transportation space access infrastructure with humans rapidly transitioning through the radiation belts on advanced rockets.

As a result of this study’s results, when you look at the question, “Why Space Elevators?”  the answer is – Space Elevators have:

• Unmatched efficiencies (70% of mass to GEO and beyond, with reusable climbers as the other 30%) vs. delivery by rockets to LEO of 4% of the mass on the pad while delivery to GEO (or trans-lunar insertion) is about 2%.

• Unmatched velocities (7.76 km/sec at Apex Anchor - release to go beyond Mars –  no fuel required) – leading to release possibilities every day of the year – no 26-month wait for a rocket launch window.

• Unmatched movement of logistics (30,000 tonnes in their first year of operations — humanity has only put up 20,000 tonnes with rockets between 1957 and 2020) 

Advanced Rockets to Open Up the Moon and Mars
Space Elevators will then supply and build up their dreams!

Notes from the 74th IAC 2023 

by Peter Robinson

The 74th International Astronautical Congress was held Monday, October 2nd through Friday, October 6th, 2023 in Baku, Azerbaijan. It was sponsored by the International Astronautical Federation (IAF) and the theme was “Global Challenges and Opportunities: Give Space a Chance.”

Excerpts from the “Final Proceedings” email sent to myself and other delegates by the IAF (23-Oct-2023) provide a good summary of the IAC2023 event:

From 2 to 6 October 2023, the 74th International Astronautical Congress held under the theme “Challenges and Opportunities: Give Space a Chance”, has brought together the global space community in Baku including astronauts, scientists, researchers, academicians, industry representatives, policy makers, investors, media, young professionals, students, and space enthusiasts who have shared together their passion for space and discussed the latest achievements and developments in the space sector.

IAC 2023 has encouraged all delegates to push boundaries and explore the limitless possibilities of space by submitting their scientific papers and session proposals. Over 5400 participants from 137 countries, some of them actively engaging in the programme for the first time…Three incredible venues: a brand-new congress centre efficiently adapted to the need of an ever-growing programme, a tailored made exhibition hall with more than 150 organizations represented, and an architectural gem. (The Heydar Aliyev Centre)

55 new member organization[s] whom have chosen to deepen their engagement with us and lay the foundation of stronger cooperation through membership. Over 50% of delegates below 35 years of age …. meetings, plenaries, GNFs, Special Sessions, more than 2000 papers presented in Technical Sessions +500 Interactive Presentations uploaded creating. an outstanding programme that covered every possible topic linked to space.

Now we invite you to browse, search, and enjoy the manuscripts of the congress:

https://iafastro.directory/iac/proceedings/IAC-23/

Username: iac-23
Password: murobiga

The Space Elevator technical session D4.3 ‘Modern Day Space Elevators Customer Design Drivers’ was part of Symposium D4 ‘21st IAA Symposium on Visions and Strategies for the Future’ and was held at 1500 AZT on Tuesday, October 3rd, 2023.

Co-chairs were myself (Peter Robinson) and Dr. Yoji Ishikawa (Obayashi Corporation, Japan), with rapporteurs Mr. Yasuhiro Fuchita and Mr. Ryuta Niinobe (both of Obayashi Corporation, Japan).

Ten papers were presented at the session, summarised as follows. 

I must apologise to the authors for summarising their detailed and thorough papers in so few words. I hope I have mentioned a few of the key points, but readers must study each paper themselves to learn all that is said.

D4.3.1: KEYNOTE, 2nd Jerome Pearson Memorial Lecture -- “Research into Characteristics of a Permanent Space Access Transportation Infrastructure”.

Lead Author: Pete Swan. 

Presenter: Peter Robinson

The presentation introduced the work of Jerome Pearson (1938-2021), describing how his 1975 article contained the first engineering description of the Space Elevator. 

It then described four aspects of the ‘Modern Day Space Elevator, starting with the Vision of several ‘Dreamers’ of the future of humanity in space, all requiring space elevators to raise the necessary mass to space. These elevators, the ‘Green Road to Space’, would join rockets as part of a ‘Dual Space Access Architecture’ to move the necessary cargo to GEO and beyond.

The second aspect is the Transformational Characteristics of the Space Elevator, with so many major advantages over alternative means of beating the rocket equation and escaping the Gravity Well (as described in previous ISEC studies and publications).

The third aspect includes the many Research Topics being studied by ISEC and others around the world, with the conclusion that space elevators are feasible.

The fourth aspect is the Engineering Status: all aspects of the project are technically feasible and ready to transition to ‘Engineering Validation’ to mature and finalise the design concepts.

In Summary, the visions of many demand that Space Elevators Start Now!

D4.3.3 : “A surveys for effect on the space elevator by electric particles in space” (sic)

Mr. Ryuta Niinobe, Obayashi Corporation (+ six co-authors).

This paper assessed the radiation environment around the Earth, and in particular the electron and proton intensities and distribution along the length of the tether and their interaction with the Earth’s magnetosphere. Calculations yielded extremely high peak induced voltages (250,000 kV) and currents (200,000 A) in the tether, with three distinct regions (below 100km, 100-20500 km and above 20500km). The paper concludes that further work in needed to enhance the results, and also to predict Lorentz forces resulting from the interaction of the induced currents with the Earth’s magnetic field.

COMMENT: One figure indicates a tether temperature in excess of 2000 K, but this is not discussed in detail. The paper does not detail the tether design dimensions, material, or material properties, although carbon nanotubes are mentioned. Further work is needed to confirm the high magnitude of predicted induced voltages and currents.

D4.3.4: “Evaluation of the effect of current through cable on temperature and dynamics of space elevator”

Lead author: Prof. Yoshiki Yamagiwa, Department of Engineering, Shizuoka University

Presenter: Dr. Yoji Ishikawa, Obayashi Corporation

This paper describes a detailed simulation of the tether system, predicting dynamic motion with and without climbers as well as induced currents in the tether from both geomagnetic and environmental plasma sources. The tether is assumed to be tapered and of CNT, with all material properties defined. The induced currents are predicted to be small (less than 5 A), resulting in a negligible change in the tether temperature (4 K). Tether oscillation east-west is predicted to be of the order of 200km, increasing by perhaps 10% due to current effects. A small north-south disturbance (<1 km) is also predicted from current effects.

COMMENT: This thorough paper contains a great deal of detail and predicts only a small effect from induced tether currents. These conclusions are very significantly different from those of the previous paper; this discrepancy is under investigation by one of the co-authors.

D4.3.5: “A Large-Scale Tether Deployment Control Scheme for Space Elevator Construction”

Lead Author & Presenter: Dr. Feng Zhang, China Academy of Launch Vehicle Technology (CALT) + four co-authors.

This paper describes the use of a dynamic model to simulate the deployment of a space elevator tether. The deployment strategy was bi-directional, starting from GEO with deployment spacecraft traveling both towards the Earth and beyond GEO to maintain system balance. Factors taken into consideration included atmospheric forces, Moon and Sun gravity perturbation, solar wind forces and gravity gradient torque. Analysis included a study of both linear and non-linear deployment strategies, concluding that non-linear required the least thruster fuel for the deploying spacecraft. Another conclusion was that deployment would be possible within a 12-month timescale and that refuelling of the deployment spacecraft would be required: one strategy included two refuellings of the GEO station, three of the ascending spacecraft and ten of the descending spacecraft.

COMMENT: This appears to be a thorough and valuable paper, confirming the feasibility of tether deployment in a useful timescale. The paper was produced by three researchers at CALT, and two academics supported by five grants from the National Natural Science Foundation of China. The eleven references include two ISEC studies from 2013 & and 2019, the Edwards deployment paper from 2000, and the Cohen/Misra tether oscillation study from 2007.

D4.3.6: “Controlled Deployment of a Partial Space Elevator”

Prof. Arun Misra, McGill Institute for Aerospace Engineering (MIAE), Canada

This paper derives a mathematical model describing the 2D deployment of a partial Kevlar tether of constant cross-section between two spacecraft (500t at GEO, 50t descending). It shows that the elasticity (Young’s Modulus) of the tether is an important factor and would increase the tendency for the system to ‘fall’: a control strategy is derived for the upper spacecraft, with results shown in detail. A control strategy for the lower craft is proposed as future work.

COMMENT: Supported by a complex mathematical model, the paper describes the deployment of what has been described by ISEC as a ‘Pathfinder’ orbital prototype tether system. Future work would include details such as the effect of fuel burn on the spacecraft’s mass.

D4.3.7: “High-precision multibody model for space elevator including torsional deformation”

Mr. Ryo Kuzuno, Tohoku University, Japan + four co-authors.

This study describes a high-precision numerical simulation model of a space elevator system. It uses a nonlinear finite element method to consider large deformations, including elongation, bending, torsion, and rigid body rotation of a tether. To reduce unnecessary computational costs the model excludes negligibly small deformations. The model includes a moving climber, torsional deformation, and includes gravitational perturbation caused by the oblateness of the Earth, with 14 degrees of freedom. The model is used to study the behaviour of nonequatorial Earth space elevators with 10deg and 20deg latitude attachment points, and in particular assesses torsional deformation and tether energy levels: elongation energy is dominant (as could be expected), but torsional energy is shown to be greater than bending energy, especially near the Earth at higher latitudes.

COMMENT: This appears to be a highly detailed model, the studies of non-equatorial elevators, torsional behaviour, and energy levels are of particular interest.

D4.3.8: “Evaluation of the counterweight type space elevator: in the case applied to the altitude upper than GEO” (sic)

Lead author: Prof. Yoshiki Yamagiwa, Department of Engineering, Shizuoka University

Presenter: Dr. Yoji Ishikawa, Obayashi Corporation

This paper describes the analysis of a counterweight-type space elevator system above GEO, consisting of a conventional tether on which unpowered ‘gondolas’ run. Pairs of gondolas are connected by a cable looped over an upper driven pulley such that the weight of one gondola (and cable section) is partially balanced by the weight on the other side. The analysis evaluated multiple sets of gondolas and cables with cable lengths ranging from 5,000km to 30,000km extending from GEO to the Apex Anchor. It was concluded that longer cables required lower overall drive energy, but that the higher mass of longer cables required more power for initial acceleration and deceleration: a maximum speed of 100 km/hr was used in the analysis. Future work is needed to optimise accelerations and investigate the interaction of the gondola cable with the guide cable.

COMMENT: This concept has similarities to one of the options described in paper D4.3.11, except for not being a steady-state system (which would require a continuous cable looped around a lower pulley).

D4.3.9: “Development of Space Elevator Climber Applied in High Vacuum Space Environment and Extraction of its Problems”

Prof. Fumihiro Inoue (Shonan Institute of Technology, Japan) + five co-authors

This paper described the design of a three-tonne climber capable of accommodating four crew for ascending from Earth from GEO. Work included design of motor and wheel configurations and an analysis of the power/speed relationship during the ascent: five fixed ascent speeds were assessed, with step speed changes at appropriate altitudes as the power requirement fell. A 1/10th scale model of the climber was built and tested in a small (300mm) vacuum chamber with a 0.8m ‘tether’ loop: one observation from the test was that roller (wheel) temperatures rose in vacuum (500 Pa) conditions, probably due to friction and the reduction in heat loss.

COMMENT: This climber design is an interesting alternative to the concept described in the recent ISEC Climber/Tether Interface study but with the bonus of the assembly and test of a scale model. The vacuum chamber observation regarding wheel temperature rise suggests that a wheel cooling system may be required for vacuum operation.

D4.3.10: “Performance Verification of Space Elevator Climber with Hybrid Drive Roller and Development of Small Manned Climber”

Lead author: Prof. Fumihiro Inoue + co-authors

Presented by: Ms. Momoe Terata, Shonan Institute of Technology, Japan

This paper broadly described a continuation of the work of the previous paper, including a 50kg climber prototype tested on a 40m tether suspended from a crane. Analysis and experimental results compare the performance with opposed (“crossed”) and offset (“confronted”) wheels (“rollers”), concluding that the offset wheels led to a lower total motor current during the ascent. Details of the tether material or dimensions are not given, although a coefficient of dynamic friction of 0.11 was estimated. Future work includes the construction and test of a climber with 300kg gross mass powered by a 3kW motor capable of carrying two passengers. It is hoped that the climber would then move on to tests on a construction site to gain operational experience.

COMMENT: This is valuable experimental work, though not yet capable of operating on a future space tether.

D4.3.11: “The Space Elevator Payload Journey beyond GEO: Climber Concept and Options”

Mr. Peter Robinson, ISEC

This paper reviews the power and other requirements of a climber on the journey from GEO to the Apex and compares the necessary concept with that of a climber ascending from Earth to GEO. The need for braking to control the ascent speed is investigated: this concludes that energy rejection is an important factor, with additional radiator systems required to allow rapid ascent at higher altitudes. The mass of additional systems required for ascent above GEO will reduce the useful payload raised from Earth: the impact of ascending climbers and Apex mass release on Anchor dynamics was also reviewed. This work prompted a review of alternatives to the concept of using a wheeled climber to carry interplanetary payloads to the Apex for high-speed release, with options including a “conveyor belt” system and payload release from GEO using future high-power electric drives.

General Comments

IAC2023 was held in three buildings: the technical sessions were held separately from the exhibition hall and the building used for the plenary and other “big name” sessions. This may have contributed to the smaller audience size for the D4.3 and other technical sessions that I attended.

In addition to the speakers, notable attendees of the Space Elevator session included Kevin Barry (Lightbridge Strategic Consulting) and Rob Coppinger (Editor, BIS Spaceflight magazine).

Peter Robinson

Additional photographs from IAC2023 can be found on the ISEC Flickr site:

We are unable to share most of the papers and presentation material on our website due to copyright reasons, but they can be accessed by ISEC members in our private Zotero library.

(Becoming a member is not the same as subscribing to this newsletter, join here: https://www.isec.org/membership)

ISEC published in the Journal of the British Interplanetary Society

ISEC is featured in a special Issue of the Journal of the British Interplanetary Society called “Future Directions for Space Elevators.” Beginning with an introduction by David Raitt putting them in their historical location as the eight distinct architectures over the last 130 years, it contains five additional articles explaining the progress accomplished inside the Space Elevator Community over the last several months. 

Please review them to keep up with our progress.  You may download them from our website under “recent publications” or go to the BIS website to purchase the magazine representing our progress.

I wish to thank the authors as it takes a “commitment” to successfully publish in this important journal, and to David Raitt for ensuring each article sailed through the TBIS processes. 

Pete

Tether Materials

by Adrian Nixon, Board Member, ISEC

How 2D Material Laminates Respond
to Temperature Changes

Regular readers will know that the material for the space elevator tether has to be incredibly strong and lightweight. Two-dimensional materials such as graphene and hexagonal boron nitride (hBN) have the necessary qualities that make them candidates for the task.  They can be made in monolayers at industrial scales and attention is now being turned to making multilayer (laminates) that will ultimately create the tether.

We already know that two-dimensional (2D) materials have excellent heat conduction properties.  Graphene and hBN also have extremely high melting points, both over 3000K.  In a previous newsletter, we explored how new materials such as graphene laminates would be structured (Newsletter archive, August 2022).  Graphene laminates are made from large area sheets of graphene stacked on top of one another.  Stacked layers of hBN can also form laminate structures.

Understanding how heating and cooling affect 2D materials, such as graphene and hBN, will become more important as they are made at larger and larger scales.

Most materials expand when heated and contract when cooled.  However, this is not the case for all materials. Graphene and hBN are contrary examples, they have negative thermal expansion coefficients, at least for their in-plane behaviour [2,3].

The thermal expansion coefficient (TEC) tells us how much a material expands and contracts with a change in temperature [1]:

∆L= αL∆T

Where:

∆L = The change in length

α = The thermal expansion coefficient

∆T = The change in temperature

The TEC can also change with temperature and it is a mistake to think the TEC has a constant value for a given material.  However, the following table uses data from peer reviewed sources where the TEC is relatively stable.  The calculations will be good enough for the purposes of this article.

The following graphic shows what is meant by planes in this context:

The data shows us that graphene and hBN have negative TEC values in the in-plane dimensions.  They both contract slightly with increasing temperature and expand slightly as they are cooled.  This difference is small, it is an order of magnitude smaller than for metals such as aluminium and steel (ten times less).

Aluminium and steel are isotropic materials.  This means their properties are the same no matter what the plane dimension.  Graphene and hBN are layers of 2D materials and this gives them anisotropic properties.  They behave differently in-plane to the cross-plane. 

The experimental data for hBN shows that the TEC is positive in the cross plane and is about ten times greater. This will probably be similar for graphene although experimental data for this was hard to find. This means that when heated, a bulk material made from layers of hBN will contract very slightly in-plane and expand slightly in the cross plane. 

These effects are interesting but for most practical purposes, in temperature ranges from absolute zero to 1000K, they are so slight that we can focus on other physical properties and consider graphene and hBN laminates as essentially thermally stable materials. 

However, the scale of a space elevator tether is such that a 0.038% length change for each 100K temp change corresponds to a length change of 38 km for a 100,000km tether.  This assumes the temperature change applies all the way along the entire length of the tether.  This might not happen if the tether is used purely mechanically as there will probably be regions of relatively hot and cold that would mitigate this overall expansion. If a graphene tether is used to conduct electricity for power distribution then this could heat the tether to the point where the contraction would need to be take in to account in the design of the structure.

References:

1. Jibson, D. and Wordeman, K. (2023). Steps for Calculating the Change in Length of an Object Due to Thermal Expansion. [online] Study.com. Available at: https://study.com/skill/learn/how-to-calculate-the-change-in-length-of-an-object-due-to-thermal-expansion-explanation.html.

2. McQuade, G.A., Plaut, A.S., Usher, A. and Martin, J. (2021). The thermal expansion coefficient of monolayer, bilayer, and trilayer graphene derived from the strain induced by cooling to cryogenic temperatures. Applied Physics Letters, 118(20), p.203101. doi: https://doi.org/10.1063/5.0035391.

3. Kriegel, M.A., Omambac, K.M., Steffen Franzka, Meyer, F.-J. and M. Horn‐von Hoegen (2023). Incommensurability and negative thermal expansion of single layer hexagonal boron nitride. Applied Surface Science, 624, pp.157156–157156. doi: https://doi.org/10.1016/j.apsusc.2023.157156.

4. Anon (2005). Thermal Expansion Coefficients. [online] hyperphysics.phy-astr.gsu.edu. Available at: http://hyperphysics.phy-astr.gsu.edu/hbase/Tables/thexp.html.

Upcoming Events

42nd International Space Development Conference
Sponsored by the National Space Society
https://isdc2024.nss.org/
Thursday, May 23rd through Sunday, May 26th, 2024
Sheraton Gateway, Los Angeles, California, USA
Theme: “No Limits”

75th International Astronautical Congress
Sponsored by the International Astronautical Federation (IAF)
https://www.iafastro.org/events/iac/international-astronautical-congress-2024/
Theme: “Responsible Space for Sustainability”
Monday, October 14th through Friday, October 18th, 2024
Milan, Italy

76th International Astronautical Congress
Sponsored by the International Astronautical Federation (IAF)
Monday, September 29th through Friday, October 3rd, 2025
Sydney, Australia

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