International Space Elevator Consortium
April 2024 Newsletter

In this Issue:

In Remembrance of Michael “Fitzer” Fitzgerald
Editor’s Note
President’s Corner
SEC 2024 and Call for Papers
Next Floor: Outer Space
Tether Materials
Creation Node
Upcoming Events
Contact Us/Support Us

In Remembrance of Michael “Fitzer” Fitzgerald

Michael “Fitzer” Fitzgerald, Lt.Col. (USAF ret) of Rancho Palos Verdes, California, passed away on his birthday, March 28th, 2024, after 77 years of a full life. We will miss him as a friend and member of the International Space Elevator Consortium Board of Directors. He was instrumental in establishing the architectural approach for our future within space elevators, contributing over 40 Architectural Notes to the newsletter. We celebrate his life and I will remember so much – especially from my 49 years of friendship. A memorial mass will be celebrated on Thursday, April 25, 2024, at the Fort MacArthur chapel in San Pedro, California.

Pete Swan

Editor’s Note

This issue of the ISEC newsletter is dedicated to Michael “Fitzer” Fitzgerald and his commitment to our organization. I want to share a short remembrance of him. This story gives insight into his character as a retired military officer who saw the need to guide a former enlisted person who he felt was “slacking off” in her role at ISEC.

During the Space Elevator Conference one year, Fitzer saw that whenever I wanted to know something, I merely asked questions of my fellow ISEC members. So, he challenged me to do more research on my own. He suggested I start with Bradley C. Edwards’ book, The Space Elevator. [See reference #2 in the Tether Materials article!] And, while we may not build the SE exactly how Edwards describes it in his book, it strengthened my vocabulary (including a plethora of acronyms) and gave me a broader scope of how big this project could be. Now, when someone in the space elevator community refers to the Edwards model, I have Fitzer to thank for this basic framework of what at least one visionary had of the future!

If anyone else would like to share a story about Fitzer, send it to me at newsletters@isec.org.

We will miss you, Fitzer!

Sandee Schaeffer
Newsletter Editor

President's Corner

by Pete Swan

Super Laminate Graphene
is the Leading Tether Material of Choice!

“The manufacture of tether-quality material for a space elevator still needs more development, but the trajectory to a high-quality industrial product is clear. It is not unreasonable to think that, as this graphene process continues apace, space elevator tether production could begin in five to 10 years using graphene as its material.” “The Right Stuff,” Spaceflight, June 2023 article by Adrian Nixon, John Knapman, and Dennis Wright.

Whenever we get information from outside our ISEC circle, they always (greater than 90%) lead with carbon nanotubes (CNT) for Space Elevator tethers -- rarely mentioning anything else. I am concerned about the lack of distribution of our (ISEC’s) findings on two-dimensional materials. It is almost like denial of the physics and development that many have achieved. We will start a full court press on placing the information and conclusions that we have formed over the last three years that lead to the above statement. I am enthused and excited about where we are going. As far as I can tell, no one is listening to us. Here are a few samples of our statements that are impactful but, in my opinion, not heard by the space community. One of our tasks as an organization is to have our results spread within the space community -- beyond ISEC and the Space Elevator community. Here are a few more great research conclusions:

• “A suitable material for the construction of the space elevator tether appears to be near at hand. There are three materials to choose from, each of which has seen rapid development since their discoveries. It is essential that the sample size of these materials be increased so that detailed mechanical, electrical and thermal testing can be done. Given what is known now, graphene super-laminate seems the best choice, with hexagonal boron nitride as an alternative.” [Wright, D. “Building the Space Elevator Tether,” Special Issue: Future Directions for Space Elevators,” Journal of the British Interplanetary Society Volume 76 No.7 July 2023]

• “Industrial scale manufacturing methods are likely to produce polycrystalline rather than perfect single crystal graphene at the scales and speeds needed to manufacture space elevator tether. This work shows that provided the material has crystal grain boundaries that are well-stitched and have few defects, the current manufacturing methods can make graphene that is strong enough to make a space elevator tether.” [Nixon, Adrian, Graphene update in ISEC Newsletter, Mar 2024.]

We need to spread the word that Graphene [or other 2-D materials] is leading the challenge to provide a tether that is long enough and strong enough. This leads to the following conclusions that must also be discussed and presented to the world beyond ISEC:

• Graphene Super Laminate is leading the tether material field of choices.

• Hexagonal boron nitride [and other 2-D materials] are not far behind with many supplemental strengths

• Poly-crystalline has all of a sudden shown up as being a front runner as it is –- both further into development and it should have sufficient strength [> 80GPa]

• CNTs are not living up to their “hype” from the early 2000’s [as to length and strength combined]

Remember, outreach is the responsibility of all ISEC team members. Expansion of these statements is given at https://www.isec.org/space-elevator-tether-materials  and at https://www.isec.org/recent-publications.

Pete

SEC Announcement and Call for Papers

Space Elevator Conference 2024

The upcoming Space Elevator Conference will be held September 7th-8th, in the Aon Center Building, Chicago, Illinois, USA. The theme is, "Space Elevators as a Permanent Transformational Transportation Infrastructure."

The latest information will be promptly posted on the ISEC website under News and Events https://www.isec.org/events/isec2024

Call for Papers

The International Space Elevator Consortium invites the submission of abstracts for papers to be presented at its 2024 conference in Chicago, Saturday, September 7th, and Sunday, September 8th. Papers should cover space elevator topics including design, dynamics, applications, scientific value, and economic impact.

Abstracts should be between 200 and 400 words in length and briefly describe the contents of the proposed paper and its importance to the development of space elevators. Abstracts must be in PDF format and submitted before 31 May 2024 to the review board chairman:

Dennis Wright (dennis.wright@isec.org)

Authors will be notified of abstract acceptance by 15 June, at which point they will be invited to submit a paper on the topic and make a 20-minute oral presentation at the conference. Authors may opt for a 10-minute oral presentation which does not require an accompanying paper. All oral presentation materials, such as ppt or PDF slides must be submitted before the conference.

Technical papers should be a minimum of 2,000 words in length, including supporting figures, and will be considered for publication either in the ISEC conference proceedings or other journal.

Important Dates

Please send questions or requests for details to the e-mail address above.

Next Floor: Outer Space

Can you image a Green Road to Space that feels like a permanent transportation infrastructure elevator? We can! The Modern-Day Space Elevator is becoming real with the current status of “ready to start developmental testing.” Recently, there were eleven articles published within British Interplanetary magazines that expand upon those themes. They are all located and available at https://www.isec.org/recent-publications where you can download free PDFs.

This advertisement is in the current National Space Society’s Ad Astra magazine, reflecting our participation in the International Space Development Conference. We are actively working with them to have an exciting and challenging four days at the end of May. Please join us there.

Tether Materials

by Adrian Nixon and Peter Robinson, ISEC

How Strong Must
a Graphene Tether Material Be?

In the previous newsletter article [1], we explored the strength of polycrystalline graphene. We found that, provided the material is "well stitched together," it has a much higher tensile strength than would be expected: between 90 and 99 GPa.

The current assumption is that a tether material must be incredibly strong over vast distances with a consistent tensile strength with a target of 100 GPa. This strength value is based on the work by Dr. Bradley Edwards for the NASA feasibility study that reported in 2003 [2].

Single crystal graphene is the term for graphene with no defects. It has a tensile strength of 130 GPa and has been made at metre scale in the laboratory [3]. However, we must assume that industrial scale manufacturing processes could make polycrystalline graphene that has a slightly lower tensile strength.

I asked my colleague Peter Robinson, “How critical is the 100GPa value for tensile strength?”

Peter replied…

The tensile strength of the tether material directly impacts the mass of the tether, and there are practical limits to how great that mass can be for early space elevators. Very simply, establishing the overall mass (and thus strength) needed by a tether depends on the answers to just two questions:

(a) how much weight does the tether need to support?

(b) how strong is the tether material?

Neither of these questions can be answered definitively yet and will require detailed knowledge of several technical design solutions.

Addressing question (a), the “supported weight,” the tether must of course support its own weight, but it must additionally support the weight of whatever climbers are climbing it. There will also be an additional force (or weight) at the Earth Port required to combat atmospheric wind loading.

It is important to recognise the difference between ‘weight’ and ‘mass’: a climber might be 20 tonnes in mass (say), but its “weight” that must be supported on the tether will reduce with altitude as the gravity force reduces and is increasingly offset by centrifugal forces, falling eventually to zero weight at geostationary orbit (GEO), as shown in the plot below.

This is not the whole story: the tether must be designed to support the weight of multiple climbers, so the distribution of the climbers along the tether must be known, as well.

The climber positioning along the tether will depend on parameters such as departure frequency from Earth, maximum drive power and maximum speed. The histogram below shows the worse-case weight that must be supported by the tether for 20 tonne climbers departing daily with 4 MW maximum drive power and maximum speeds of 100 kph and 200 kph.

Thus, slower climbers mean more weight must be supported by the tether, so the tether must be stronger. The discussion of climber design is outside the scope of this article, but this highlights how any necessary tether strength estimate must use assumptions for climber performance and operational factors.

Question (b), the required tether material strength, can be addressed once a tether loading is assumed.

The reader should first understand the concept of “tether taper.” Any part of the tether (below GEO) must support the weight of the tether below it, and this weight will increase with altitude. Thus, the necessary tether strength, or cross-sectional area, will increase with altitude. The “taper ratio” is the ratio of the area at GEO to the area at the Earth, the equation for which was first derived by Jerome Pearson in 1975 (Ref 5).

Material strength: The Yuri

The measure of material strength that determines the taper ratio is the specific strength (or specific stress), defined as a material stress divided by the material density: Pearson’s equation shows that the taper ratio will be lower for tether materials with higher specific strengths (Ref 6).

The next question is: what material stress should be used to determine the taper ratio, and hence the tether mass and overall strength? The material yield or ultimate tensile stress will be known from laboratory tests and must be confirmed on material mass-produced using the intended large-scale manufacturing process, but the tether should not be designed to operate close to either its yield or failure stress. Some safety margin is needed to prevent failures under operational and feasible extreme conditions (such as debris damage.) Margins in the range of 40-50% or more have been assumed in some work but must be confirmed by detailed safety studies.

Numerical analysis based on the techniques described in Ref 4 can derive the total required tether mass based on several (arbitrary) design parameters, including tether length (100,000km), climber mass (20t), climber departure frequency (1/day), climber max drive power (4MW) and climber max speed (235 kph, chosen to yield 7-day ascent time to GEO). The plot below shows the total Tether and Anchor masses for a range of working specific strengths.

This analysis shows that a working stress of 38.9 MYuri (89.4 GPa with 2298.5 kg/m3 density) would result in a tether mass of 4,492 tonnes, with a cross-sectional area rising from 7 mm2 at the Earth to 23.7 mm2 at GEO. This refers to the vertical grey line in Fig 3. Lower specific strengths will require a greater material mass, soon rising to excessive levels. For example, with a 50% reduction to 19.5 MYuri the mass would be 26,608 tonnes, with a cross-sectional area rising from 14.1 mm2 at the Earth to 163 mm2 at GEO.

Until macro-scale material samples are fully tested we cannot be certain what specific operating strength can be used, but a value in excess of 30 MYuri may be needed to limit the tether mass to levels that practically could be launched from the Earth. If the tether could be manufactured in space using ISRU (perhaps using lunar or asteroid material) then it may be possible to use a lower specific strength, but that’s for another newsletter.

The thickness of the tether will of course depend on the cross-sectional area and the width. Earlier work has assumed a width of 1m, which means a thickness of 7 microns for an area of 7 mm2, corresponding in turn to 20,000 layers, rising by several times at GEO.

There has been much debate on the optimum tether dimensional profile: whether it becomes wider or thicker with altitude will depend on many factors, including manufacturing and climber design issues, but that discussion must also be postponed for a later newsletter.

See the 2023 JBIS paper by Dennis Wright (Ref 6) for a more thorough and scholarly explanation of some of the above.

…Quite a comprehensive reply from Peter

To summarise: The answer to the question posed at the beginning shows that the 100 GPa tensile strength value is not a fixed cut off point for a tether material. The actual tensile strength needed depends on an interaction between various engineering design parameters. In essence, the stronger the material is, the less of it we will need.

It should be possible to design and manufacture a tether using graphene with a tensile strength in excess of 90 GPa. This means that imperfect, polycrystalline multilayer graphene should be more than capable of being used as an operating space elevator tether material.

References:

1. Nixon, A. and Wright, D. (2024). International Space Elevator Consortium Newsletter 2024 March. [online] International Space Elevator Consortium. Available at: https://www.isec.org/space-elevator-newsletter-2024-march/#tether [Accessed 18 Mar. 2024].

2. B. Edwards, 2003. The Space Elevator NIAC Phase II Final Report. [online] Atlanta, GA: NASA Institute of Advanced Concepts (NIAC). Available at: http://www.niac.usra.edu/files/studies/final_report/521Edwards.pdf [Accessed 25 February 2024].

3. Xu, X., Zhang, Z., Dong, J., Yi, D., Niu, J., Wu, M., Lin, L., Yin, R., Li, M., Zhou, J., Wang, S., Sun, J., Duan, X., Feng, Y., Jiang, Y., Wu, X., Peng, L.-M., Ruoff, R.S., Liu, Z. and Yu, D. (2017). Ultrafast epitaxial growth of metre-sized single-crystal graphene on industrial Cu foil. Science Bulletin, 62(15), pp.1074–1080. doi: https://doi.org/10.1016/j.scib.2017.07.005.

4. Robinson, P. (2023). Space elevator climber dynamics analysis and climb frequency optimisation. Acta Astronautica, 210, pp.518–528. doi: https://doi.org/10.1016/j.actaastro.2023.04.021.

5. Pearson, J. (1975). The orbital tower: A spacecraft launcher using the Earth’s rotational energy. Acta Astronautica, [online] 2(9-10), pp.785–799. doi: https://doi.org/10.1016/0094-5765(75)90021-1.

6. Wright, D (2023). Building the Space Elevator Tether. JBIS Volume 76 Issue 7 Pages 225-231 https://www.isec.org/s/JBIS-2-Building-the-Space-Elevator-Tether.pdf

Editor’s Note: The Yuri

In the above article Peter uses the unit ‘Yuri’ for Specific Strength (or Specific Stress). This unit name was coined over ten years ago by Ben Shelef in tribute to Space Elevator co-inventor Yuri Artsutanov (1929-2019) and is now extensively used in Space Elevator circles. MYuri is said as “mega Yuri.”

Specific Stress is defined as Stress/Density, meaning that 1 Yuri = 1 Pa/(kg/m3) = 1 Pa.m3/kg. Values are usually quoted in MYuri (= 106 Yuris), so for material values with typical orders of magnitude, 1 MYuri = 1 GPa / (1000 kg.m3).

DIMENSIONAL ANALYSIS FUN FACT: Specific Strength can also be thought of the Energy per unit mass, or E/m.

As 1 Pa = 1 N/m2 and 1 N = 1 kg.m/s2 the units simplify to 1 Yuri = 1 m2/s2, which is a velocity squared. Thus E/m=v2, or E=mv2 … does that look familiar?

Book Review

by Peter Robinson

Creation Node
by Stephen Baxter

Several years ago, John Knapman (ISEC Director of Research) and I spoke at a ‘Future Histories’ Symposium in London at the BIS, and another speaker was British SF author Stephen Baxter.  We discussed Space Elevators during a break, and Baxter may have heard some of what we said to him as I discovered a page about an Earth Space Elevator in his latest (2023) book Creation Node.

The Elevator isn’t a key aspect of the plot, it’s just part of his description of the solar system space infrastructure in the year 2255, so I feel I can share some of his words here without giving too many spoilers…

This orbital hub had been created as the core of the elevator's construction, suspended ... above that artificial island on the Pacific equator.  At this height a satellite would orbit Earth in twenty-four hours, matching Earth's rotation, so that the hub, itself built in space, seemed to hover over that oceanic location.

From here a tether cable had been dropped down to the island, and fixed there, so that the hub was like an enormous kite on a string but held far above the planet's kilometres-deep layer of air. At the same time a counterweight, another complex space-borne machine in itself, had been slowly lifted further outwards from the position of this main hub, on another tether itself fully eighteen thousand kilometres long. This arrangement kept the cable, as a whole, under tension.

The elevator had, since its opening a century ago, become the key space-transportation node for the newly united planet ... achieved with a minimum of energy expended, a minimum of waste heat: no more vapour-spewing rocket launches from Earth's surface, no more atmosphere-burning high-speed re- entries.  People nowadays took care of their planet - 'what's left of it' being the qualifying slogan of a group of planetary protection organisations.

You can see that this closely describes the concept that ISEC is proposing ... except we believe there will be more than one, and that it will be built well before the mid-22nd century.

But back to the book: I’m reluctant to give spoilers to what is a complex and far-reaching storyline, but readers of Baxter’s earlier book will know that he has a massive vision on the cosmological scale. There is another Space Elevator described, not on Earth, but further out in the solar system, but I won’t give more details.

Here are words that I believe I can share, given that they are the sleeve notes on the book and published on Amazon:

In the year 2255, a woman named Salma, twenty years old, is the first fully to see - with her own eyes, albeit moderated by her ship's instruments - the object called Planet Nine.  See, but not recognise what it was.  Not yet.

Planet Nine wasn't a planet, or the 'ninth' of anything.  Briefly thought to be a black hole, it suddenly changes, expands and sends a message. There is something waiting on its surface. Something not quite human.

As the ramifications of this event spread across the elements of a fractured humanity, it is clear that the small crew on the spot are at the centre of the most dramatic discovery in history. But this is not the only inexplicable event - impossibly, at exactly the same moment, a galaxy-centre quasar has appeared twenty-five thousand light years away, pouring heat into the solar system.

If the enigma of the creation node is not solved quickly, there may be no one left to investigate it...”

All I can add is that the book ends with darkness and with hope.

Publisher: Gollancz (21 Sept. 2023)
Language: English
Hardcover: 448 pages
ISBN-10: 1473228956
ISBN-13: 978-1473228955

Visit Stephen Baxter's website at www.stephen-baxter.com.

Upcoming Events

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

7th International Conference on Tethers in Space
Sponsored by Lassonde School of Engineering, York University
and the International Academy of Astronautics
https://lassonde.yorku.ca/conf/tis2024/
Sunday, June 2nd, through Wednesday, June 5th, 2024
Toronto, Canada

8th Annual Nanotechnology Conference
Sponsored by the Royal Society of Chemistry
https://www.rsc.org/events/detail/77700/8th-annual-nanotechnology-conference-nanomat2024
Sunday, August 25th, through Wednesday, August 28th, 2024
Hotel Arcotel Wimberger, Vienna, Austria

Space Elevator Conference
Sponsored by the International Space Elevator Consortium and Slalom, Inc.
https://www.isec.org/events/isec2024
Saturday, September 7th, through Sunday, September 8th, 2024 
Downtown Chicago, Illinois, USA

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
International Convention Centre, Sydney, Australia

77th International Astronautical Congress
Sponsored by the International Astronautical Federation (IAF)
https://iac2026antalya.com/
Theme: “The World Needs More Space”
Proposed Dates: October 5th through October 9th, 2026
Antalya, Turkey

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