Monday, February 27, 2023

The Missed Lesson of the Falcon Heavy

  Copyright 2023 Robert Clark

  Every time Gwen Shotwell or Elon Musk are interviewed about the Superheavy launch they are always fretting about a possible explosion on the launch pad, possibly damaging the launch tower.

 Shotwell and Musk have even said the test launch will be considered a success just clearing the tower without damaging it. Presumably then, the test launch will still be considered a success even if it does explode during the flight, as long as it first clears the tower. This hardly instills confidence in the reliability of the flight. Indeed it begins to look like the approach of the Russian N-1 engineers who tested the N-1 by launching it multiple times without sufficient ground testing first, resulting in the  rocket exploding on each test flight.

 One wonders, if the SuperHeavy does explode during flight, would SpaceX like the N-1 engineers before them do the next test launch again without full length test firing of all engines together, as long as the launch tower is undamaged? Suppose the launch tower is damaged, would they still take this same approach?

 What should have been done in regards to the SuperHeavy booster is to construct a separate test stand to test all 33 engines at the same time for the full, true flight burn time of the engines. The static test fire done so far was barely more than 5 seconds long, hardly a true shake out of the complete engine package at once. Plus, it was only at half thrust. During that short test, 2 engines failed. Without further information it can just as well be every 5 seconds or so another 2 engines would fail.

 Constructing a separate test stand will allow the engines all together to gradually be ramped up to full thrust and to full, true burn length duration. The automatic and manual shutoff of the two engines in the last test is encouraging. If might mean in a gradual testing program, flaws could be detected and the test curtailed if one or more engines failed. Then the flaws in those engines could be corrected and the tests conducted again.

 Note this was how it was done for the five F-1 engines of the Saturn V, conducting true, full duration tests of all five engines at once. The engines were not certified for flight until all five engines successfully completed true, full duration test firings all together, for multiple test firings.

 However, more importantly SpaceX missed major advantages of the Falcon Heavy approach of using three cores to form a heavy lift vehicle. They incorrectly concluded the Falcon Heavy was not a good approach because it cost something(!) The SpaceX engineers should have noted that for the Delta IV Heavy, also a triple-cored vehicle from existing cores, the development cost was in the range of $500 million. The correct conclusion they should have drawn is how much cheaper it was than building an entire new booster three times as big. The FH development cost also turned out about $500 million. This is only about 50% more than that of developing the original Falcon 9 at $300 million but at 3 times the payload of the current Falcon 9. 

 Actually the advantage may be even greater than that. The original Falcon 9 was only about 10 tons to LEO. So the Falcon Heavy is at 6 times the payload of the original Falcon 9. On the other hand the total development cost for all the Falcon 9 versions up to the current Falcon 9 FT has been estimated in the billion dollar range. So the Falcon Heavy increased the payload by a factor 3 over the current F9, but at a development cost less than half that of the current version 

 Likewise to the Falcon Heavy, a triple-cored Starship could have formed a launcher at 3 times the payload of a two-stage launcher based on the Starship being the booster with a smaller mini-Starship as the second stage.This was discussed here:

Starhopper+Starship as a heavy-lift launcher. Triple-cored Starship for super-heavy lift. 2nd UPDATE, 9/2/2019: Starhopper as a lunar lander.

 Quite importantly the two-stage to orbit vehicle, TSTO, would be able heavy lift 100+ tons to LEO. This is important because a 100 ton launcher is regarded as a requirement for a manned lunar mission in a single launch architecture. So already in 2021 with the Starship performing its test launches then we would already have had a manned lunar mission capable launcher. This is assuming the "Starhopper" as a small upper stage would also have had its development continued.

 This is for a single launch architecture, no 4 to 16 launches needed to refuel the Starship in orbit as a lunar lander. Note also the triple-cored version also could do a manned Mars mission in a single launch.

 And before the Falcon Heavy flew, there were over a 100 flights of the Falcon 9. That's over 1,000 actual full, operational burns of the Merlin engines. The equivalent of more than 30 full flights of the Falcon Heavy. 

  This brings up another major advantage of this approach, in regards to safety. Gwen Shotwell has said ideally Starship would have 100 launches before launching people. This is actually a logical disconnect to the Artemis missions with the Starship intending to carry people to the Moon as a lander by 2025:

Shotwell says SpaceX ready for Starship static-fire test
Jeff Foust
February 8, 2023
She said she expected Starship to fly at least 100 times before it carries people for the first time, a challenge as the company prepares a lunar lander version of Starship for NASA’s Artemis 3 mission, currently scheduled for as soon as 2025.

In her later conversation with reporters, she called that 100-flight milestone a “great goal” but suggested it was not a requirement. “I would love to do hundreds before. I think that would be a great goal and it’s quite possible that we could do that,” she said.

She noted the company has a goal of 100 Falcon launches this year. “If we can do 100 flights of Falcon this year, I’d love to be able to do 100 flights of Starship next year. I don’t think we will do 100 flights of Starship next year, but maybe 2025 we will do 100 flights.”

 But the Starship making 100 flights would mean the SuperHeavy making 100 flights by 2025. This is highly unlikely with the Superheavy not having made a single launch yet.

 Note the Falcon 9 made 85 unmanned flights before it launched crew to orbit. With, instead, a Starship  TSTO making its first flight in 2021 at over 5 times the payload as the Falcon 9, it very well could have already superseded Falcon 9 at that role and have been making ~25 flights per year over the 4 years from 2021 to 2025.

Single Stage to Orbit(SSTO) possibility.  

 The accepted interpretation of the SSTO as infeasible stems from the earliest days of the Space Age where ground launch engines only had ca. ~300 s vacuum Isp. Having to fire from the ground put severe limits on the engine efficiency as measured by Isp of engines. Because of that, it was argued an SSTO would need some major technical advance to be feasible, such as nuclear engines with ca. 900 s Isp.

 It is unfortunate that the paradigm for making a SSTO feasible was by assuming nuclear thermal propulsion. In point of fact for a kerosene-fueled engine only a ~330 s vacuum Isp was needed and for hydrogen fueled only ~440 s vacuum Isp for the ground-launch engines. Both of these became possible by the 1970's with the Russian RD-180 for kerosene-fueled at 338 s vacuum Isp and the American SSME at 452 s vacuum Isp. 

And now, with the SpaceX Raptor as a ground-launch capable engine reaching 370+ s vacuum Isp, quite significant payload becomes possible as an SSTO.

 With the Starship and mini-Starship as SSTO's radical increases in orbital flight especially for point-to-point transport would have been possible.

  Robert Clark


Thursday, February 16, 2023

Clamshell wings for hypersonic reentry of rocket stages. UPDATED, May 4, 2023.

 Copyright 2023 Robert Clark

(Patent pending)

 It is known that large wings can reduce the speed and therefore aerodynamic heating a stage can experience during reentry. But such wings would induce high drag on ascent in addition to their high weight.

 A proposal to solve both of these issues: wings that open up from the stage sides or from the fairing for the upper stage, clamshell wings.

An overview of research on waverider design methodology

  • August 2017
  • Acta Astronautica 140
  •    The curved shape of the wings around the cylindrical rocket when opened up would provide both high lift and drags, important for the hypersonic reentry.

     For a reusable lower stage, though it would be difficult to maintain the structural integrity of the tanks for reuse when they open up to be wings, especially for maintaining a leakproof seal for the next flight. If this is to be used for a lower stage, the clamshell wings would have to be added around the stage. This would reduce the weight efficiency of the stage. However, quite likely they would still weigh quite a bit less than the propellant that has to be kept on reserve, unused, during ascent, for use for return to launch site.

     For the SuperHeavy it’s to be 7% of the propellant mass or 250 tons being kept on reserve for return to launch site. This high amount of propellant kept on reserve is a large part of the reason why the reusable versions of the Starship/SuperHeavy, just as with the Falcon 9 lose so much on reusability, 30% for partial reusability, and 50% for full reusability. 

    The clamshell wings around the tanks likely can be designed to be well less than the mass of the tanks, which for the SuperHeavy is in the range of 80 tons. Wings in general commonly weigh in the range of 5% to 10% of the aircraft weight to be carried. This would be quite heavy if they had to support the fully fueled weight of the vehicle, as is normally the case with aircraft. Note though the wings would be closed around the tanks on ascent and would only open up to support the dry mass on return. Elon has estimated the dry mass of the SuperHeavy as less than 200 tons, so only at most 10 to 20 tons would be added to the stage weight, far less than the 250 tons of propellant needing to be carried now as “deadweight” during ascent. 

     For this to work you would want the clamshell wings to have high lift and drag at hypersonic speeds. The Space Shuttle for example has been described as a flying brick at hypersonic speeds having a hypersonic L/D at about 1, though its subsonic L/D was better at about 4.5. The clamshell wings will quite likely have high hypersonic L/D because of the prior research done on caret-wing hypersonic waveriders:

       The clamshell wings would be analogous in shape to the caret-shaped waveriders able to achieve high hypersonic L/D. During the return flight, we can also imagine achieving high levels of control by varying the angle on each side of the wing.

        Falcon 9 opened up fairing as clam-shell wings.
        Renders Credit Caspar Stanley 

      Starship fairing opened up as clam-shell wings.
      Renders Credit Caspar Stanley

           In this case though the fairings are returned, in separate halves, with the convex outer side downwards facing the airstream. We are proposing instead having the concave inner side facing the airstream. This will provide greater L/D drag ratio and also greater drag in that at high altitude hypersonic speed the clam-shell wings will be analogous to hypersonic waverider caret-shaped wings and then at low altitude, slow speed they can act as a parachute.

           This second mode is rather analogous to the Rogallo wing concept that had been proposed for capsule return from space:
      High Wing Area per Weight Gives Lower Reentry Heating.

         If you can make this extra surface be lightweight then you would get low wing loading. The importance of low wing loading for reentry for spaceplanes is discussed here:

      Wings in space.

      by James C. McLane III
      Monday, July 11, 2011

      At the end of the article there is this passage:

      Wing loading (the vehicle’s weight divided by its wing surface area) is a prime parameter affecting flight. The antique aluminum Douglas DC-3 airliner had a big wing with a low loading of about 25 psf (pounds per square foot of wing surface). At the other end of the spectrum, the Space Shuttle orbiter has a high wing loading of about 120 psf. This loading, combined with an inefficient delta-shaped wing, makes the orbiter glide like a brick. A little Cessna 152 private plane features a wing loading of about 11 psf and modern gliders operate down around 7 psf. A space plane with huge lifting surfaces and a very low wing loading might not require any external thermal insulation at all. Building a space plane with a wing loading of, say, 10 psf should not be an impossible proposition. Perhaps some day it will be done.

      {emphasis added}

      Moreover, because of their curved shape they should be even more effective at slowing down the descent during reentry at high angles of attack, like a parachute.

      I estimated the wing loading using this clamshell wing idea for the new Falcon 9 FT first stage, assuming they added a proportionally small amount to the weight. I used the specifications here:

      Falcon 9 FT (Falcon 9 v1.2).

      The dimensions given there are listed as 42.6 meters long and 3.66 meters in diameter, at a dry mass of 22,200 kg.

        Regarding the stage horizontally, you would have to put the swing points along the sides, rather than at the top, so that the clamshell wing on each side could open without blocking the opening of the clamshell wing on the other side. This means the wing area would be half that of the full surface area. So the surface area is (1/2)*Pi*3.66*42.6 = 244.9 m^2, 244.9*3.28^2 = 2634.86 ft^2.

      The dry mass is 22,200 kg, 22,200*2.2 = 48,840 lbs. So the wing loading is 48,840/ 2634.86 = 18.5 pounds per square foot(psf). This is not 10 psf, but it is significantly better than the shuttle, and with the reduction in descent due to the curved surface this might still be enough to require minimal thermal shielding.

      Also, we might be able to get additional wing area by putting clamshell wings on the upper surface, though not the same size as the lower ones so that all can open fully. This would essentially be a hypersonic biplane. It is known biplanes increase left at subsonic speeds. Recent research shows this also happens at hypersonic speeds.

      The hypersonic I Plane has a unique biplane configuration to increase its payload and reduce drag. China Science Press

       For attitude control we allow the swing points to be moved up or down.

      For making upper stages reusable.

       SpaceX has wanted to make the Falcon 9 upper stage reusable but has been unable to do so. This method can allow the upper stage to be reusable as well as providing a simpler approach to recovering the fairing.

       The upper stage dry mass of the Falcon 9 is about 4 tons. Then a 5% wing mass using the clamshell approach would only be an additional 200 kg, a small reduction in the payload mass. Note also the high wing area afforded by a clamshell wing approach would reduce the reentry heating as well.

       For the fairing we could allow the fairing itself to open up to form the clamshell wings. Unlike the case for the propellant tanks, you don’t have the need for the high degree precision and accuracy for closing up the wings for reuse for just the fairing.

       Another possibility might not detach the fairing at all. The fairing would be carried to orbit along with the upper stage. It would open up like a clamshell to release the payload. Then it would remain in the open position for fly back to the launch site, serving as the wings for the upper stage as well. This has the advantage of not having to recover and reintegrate the fairing and upper stage separately, but more importantly it's a simpler task than attaching variable clamshell wings to propellant tanks without damaging the structural integrity of the tanks. At a mass of the fairing at about 2 tons for the Falcon 9, this would subtract about 300 kg from the payload instead of just 200 kg for the case where the fairing was detached and clamshell wings applied to the upper stage. Actually, it would be a little better than this since the fairing being jettisoned so high in the flight, it subtracts nearly it’s weight from the payload anyway.

       Aerobraking is the proposal to slow down at Mars aerodynamically only, not using thrusters which would require carrying extra propellant at arrival. For several years hypersonic waveriders have been proposed to accomplish it:

      •  This would be especially important if we want to reduce the travel time to Mars to limit the health effects due to high energy cosmic rays and long exposure to zero gravity, rather than the commonly proposed 6 to 8 months.
          Interestingly the SpaceX Starship upper stage if fully refueled in orbit could achieve a 12 km/s delta-v. This would be sufficient to get a small habitat for a small exploration team to Mars in 35 days.

      Fully aerodynamic landing at Mars, aerobraking.

           Such high departure speeds would result in high arrival speeds at Mars as well, in the range of 20 km/s. I’m proposing clamshell wings emulating caret-shaped waveriders perhaps in biplane format, by approaching at low altitude, “skimming the tree-tops” so to speak, can accomplish aerobraking at Mars to land without propellant burn.
           Further modeling needs to be done to confirm this.
            Robert Clark

    Wednesday, February 15, 2023

    The mystery of SpaceX ship 26.

     Copyright 2023 Robert Clark

     Interesting article:

    SpaceX rolls naked Starship prototype to test site. 
    By Eric Ralph
    Posted on February 12, 2023

       Much web discussion is going on on space forums about the Starship version Ship 26. This surprised everyone in being a completely expendable format. It has no top or bottom flaps, heat shield, or legs. Since it is to be expendable it likely also has no ballast tanks. The most frequent speculation is its a test vehicle for orbital refueling. But it has no visible external connections for linking up to another Starship.

     The key clue is it’s moved to the suborbital launch pad. This means it can launch without the SuperHeavy booster. With 6 Raptor 2 engines it can launch fully fueled unlike the previous Starship test flights meant just to test landing.

     The key question: what is the dry mass of this expendable version without flaps, legs, heat shield, or ballast tanks? If you know that you can calculate how much payload it can lift to orbit in a single stage.

     Elon said the expendable version with only 3 engines might mass only 40 tons:

     Add another 5 tons for 3 more engines and this version might mass 45 tons. However, the increased thrust may require strengthening of the tanks which would increase the dry mass. On the other hand, this version would have to support far less payload atop it than the max 250 tons of the full two-stage so would need reduced tank strengthening.

      The argument can be made that just being moved to the suborbital launch pad does not mean it is going to be launched. It might be just used for pressure testing for example.

     However, the “Angry Astronaut” did a video from Boca Chica showing the Raptor work station being moved towards Ship 26:

     He says that’s only done if you are installing engines on the Starship. You don’t do that if you are only doing pressure testing. He notes though that it could be putting engines either on S26 or S25. Probably we’ll know by the end of today which ship is having engines installed.

           Robert Clark

    Thursday, February 2, 2023

    Creating arbitrarily long graphene and carbon nanotubes. 2nd UPDATE: 2/24/2023: additional proposals for lengthened graphene-nanotube hybrids.

     Copyright 2023 Robert Clark

    (patents pending)

    (Appended at the bottom below are additional suggestions for combining graphene/carbon nanotubes.)

     Carbon nanotubes were created in the early 1990's. Experiments on them revealed extraordinary strength in the range of 1,000 times higher tensile strength per weight than standard grade steel plate and 100 times higher tensile strength per weight than the strongest steel wires available

     Graphene which can be regarded as carbon nanotubes flattened out were discovered about a decade later. Experiments confirmed they had comparable strength to carbon nanotubes.

     The only problem towards making them common industrial materials is that they have only been available in small sizes, at microns to a few millimeters in size.

     This is a proposal for constructing larger size graphene and carbon nanotubes. 

    I.)Creating Large Graphene Sheets.

    Recent research has produced hybrids of graphene and carbon nanotubes:

    James’ bond: A graphene/nanotube hybrid

    Rice University’s James Tour Group creates single-surface material for energy storage, electronics


    Seven-atom rings (in red) at the transition from graphene to nanotube make this new hybrid material a seamless conductor. The hybrid may be the best electrode interface material possible for many energy storage and electronics applications. Image by Yang Yang/Yakobson Group


    Nanotubes are grown from graphene to create nanoscale odako, so named for the giant Japanese kites they resemble. Image courtesy of the Tour Group

     The researchers were able to attach carbon nanotubes to graphene sheets. 


    Several teams have been able to create such hybrids, [1], [2], [3], [4], [5]. Usually, these are formed by placing nanotubes onto graphene. However, one team was able to place graphene onto nanotube surfaces, [6].

     Repeating such hybrids into multiple layers, the strength and electrical properties of graphene and carbon nanotubes can be extended into 3-dimensions, [7], [8], [9], [10]:

    Hybrid Structures of Graphene and Nanotubes Exhibit Unique Mechanical Properties

    Carbon nanotube pillars between sheets of graphene may create hybrid structures with a unique balance of strength, toughness and ductility throughout all three dimensions, according to Rice University scientists. Five, seven or eight-atom rings at the junctions can force the graphene to wrinkle. Illustration by Shuo Zhao and Lei Tao

     However, other research had shown it is possible to "unzip" carbon nanotubes to turn them into graphene sheets:

    Unzipping Carbon Nanotubes: A Peeling Method for the Formation of Graphene Nanoribbons

    First published: 19 August 2009
     Graphical Abstract

    Zipper examined: Elegant unzipping procedures result in the clean opening of multiwalled carbon nanotubes, leading to graphene nanoribbons (see scheme). Since graphene exhibits outstanding electronic properties, this method may be important in the development of modern nanoelectronic applications.

    Description unavailable

     Several different methods have been found for accomplishing the unzipping, [11], [12], [13]. However, for my purposes the unzipping has to be targeted, as well as being able to cut the graphene at a targeted location in the graphene/nanotube hybrid. I therefore suggest using electron beams or x-ray beams to cut the graphene/carbon nanotubes at the specified locations:

     The idea would be to slice the graphene-nanotube along the lines shown then open up the material flat, to get a larger single sheet of graphene. Then the process would be repeated to attach further nanotubes, slice them open as well and open them up to get a larger sheet of graphene to make a graphene sheet arbitrarily large.

    II.)Creating long nanotubes.

    That's for creating arbitrarily large graphene. How about for arbitrarily long nanotubes? First the large graphene sheets would be created. Then methods for rolling up the graphene into carbon nanotubes would be used. Theoretical simulations had shown this possible, [14]:

    Graphene Nanoribbons Zip Up
    February 23, 2012• Physics 5, s29
    Nanoscale planar materials such as graphene could be twisted to fabricate tubular objects.
    O. Kit, Phys. Rev. B (2012)

    Figure caption
    O. Kit, Phys. Rev. B (2012)

       And this has been experimentally confirmed:

     2013 Oct 4; 4: 2548.
    Published online 2013 Oct 4. doi: 10.1038/ncomms3548
    Growth of carbon nanotubes via twisted graphene nanoribbons


    1.)Graphene as an atomically thin interface for growth of vertically aligned carbon nanotubes.
    Rahul Rao, Gugang Chen, Leela Mohana Reddy Arava, Kaushik Kalaga, Masahiro Ishigami, Tony F. Heinz, Pulickel M. Ajayan & Avetik R. Harutyunyan 
    Scientific Reports volume 3, Article number: 1891 (2013)

    2.)Growing Carbon Nanotubes from Both Sides of Graphene.
    Jinlong Jiang*‡§, Yilun Li‡, Caitian Gao‡#, Nam Dong Kim‡, Xiujun Fan‡, Gunuk Wang‡, Zhiwei Peng‡, Robert H. Hauge‡⊥, and James M. Tour*‡⊥||
    ACS Appl. Mater. Interfaces 2016, 8, 11, 7356–7362
    Publication Date:February 23, 2016

    3.)A Three-Dimensional Carbon Nanotube/Graphene Sandwich and Its Application as Electrode in Supercapacitors.
    Zhuangjun Fan, Jun Yan, Linjie Zhi, Qiang Zhang, Tong Wei, Jing Feng, Milin Zhang, Weizhong Qian, Fei Wei
    First published: 20 August 2010

    Open Access
    Published: 11 March 2019
    High-Electrical-Conductivity Multilayer Graphene Formed by Layer Exchange with Controlled Thickness and Interlayer.
    Hiromasa Murata, Yoshiki Nakajima, Noriyuki Saitoh, Noriko Yoshizawa, Takashi Suemasu & Kaoru Toko 
    Scientific Reports volume 9, Article number: 4068 (2019)
    5.)A seamless three-dimensional carbon nanotube graphene hybrid material
    Yu Zhu, Lei Li, Chenguang Zhang, Gilberto Casillas, Zhengzong Sun, Zheng Yan, Gedeng Ruan, Zhiwei Peng, Abdul-Rahman O. Raji, Carter Kittrell, Robert H. Hauge & James M. Tour 
    Nature Communications volume 3, Article number: 1225 (2012)

    6.)Open Access
    Published: 05 August 2013
    Self-Assembly of Graphene on Carbon Nanotube Surfaces.
    Kaiyuan Li, Gyula Eres, Jane Howe, Yen-Jun Chuang, Xufan Li, Zhanjun Gu, Litong Zhang, Sishen Xie & Zhengwei Pan 
    Scientific Reports volume 3, Article number: 2353 (2013)

    7.)AUGUST 2, 2018
    Nanotube 'rebar' makes graphene twice as tough
    by Mike Williams, Rice University
    8.)Rebar Graphene
    Zheng Yan†, Zhiwei Peng†, Gilberto Casillas∥, Jian Lin‡§, Changsheng Xiang†, Haiqing Zhou†, Yang Yang†‡, Gedeng Ruan†, Abdul-Rahman O. Raji†, Errol L. G. Samuel†, Robert H. Hauge†‡⊥, Miguel Jose Yacaman∥, and James M. Tour†‡§*
    ACS Nano 2014, 8, 5, 5061–5068
    Publication Date:April 2, 2014

    9.)Pillared graphene gains strength

    10.)Graphene and Carbon Nanotubes: Two Great Materials Even Better Together Researchers use carbon nanotubes to create a reinforced version of graphene.
    09 APR 2014

    11.)Published: 24 April 2009
    Graphene nanoribbons
    Unzipping nanotubes
    Gavin Armstrong 
    Nature Chemistry (2009)
    Two methods for producing graphene nanoribbons by unzipping carbon nanotubes have been developed.

    12.)Published: 16 April 2009
    Longitudinal unzipping of carbon nanotubes to form graphene nanoribbons
    Dmitry V. Kosynkin, Amanda L. Higginbotham, Alexander Sinitskii, Jay R. Lomeda, Ayrat Dimiev, B. Katherine Price & James M. Tour 
    Nature volume 458, pages872–876 (2009)

    13.)Unzipping of Single-Walled Carbon Nanotube for the Development of Electrocatalytically Active Hybrid Catalyst of Graphitic Carbon and Pd Nanoparticles.
    Siniya Mondal, Sourov Ghosh, and C. Retna Raj
    ACS Omega 2018, 3, 1, 622–630
    Publication Date:January 19, 2018

    14.)Twisting graphene nanoribbons into carbon nanotubes
    O. O. Kit, T. Tallinen, L. Mahadevan, J. Timonen, and P. Koskinen
    Phys. Rev. B 85, 085428 – Published 23 February 2012

    UPDATE: 2/14/2023: Squashed together carbon nanotubes and graphene sheets.

    (patents pending)  
     A recent report demonstrated producing graphene sheets from squashing carbon nanotubes under diamond anvils:

    New Research Narrows the Gap for Graphene Nanoribbon Applications
    Cvetelin Vasilev, Ph.D.

    Published: 06 September 2021
    Sub-10-nm graphene nanoribbons with atomically smooth edges from squashed carbon nanotubes.
    Changxin Chen, Yu Lin, Wu Zhou, Ming Gong, Zhuoyang He, Fangyuan Shi, Xinyue Li, Justin Zachary Wu, Kai Tak Lam, Jian Nong Wang, Fan Yang, Qiaoshi Zeng, Jing Guo, Wenpei Gao, Jian-Min Zuo, Jie Liu, Guosong Hong, Alexander L. Antaris, Meng-Chang Lin, Wendy L. Mao & Hongjie Dai 
    Nature Electronics volume 4, pages 653–663 (2021) (behind paywall)
    Free PDF: 


     Then the proposal is to use graphene sheets and/or carbon nanotubes laid one on top of another but with only for a short overlap distance compared to their lengths. The test is to see if the high pressure compression can induce the carbon-carbon bonds of graphene/nanotubes between the layers of the graphene/nanotubes. Previous work with graphene and nanotubes have been able to induce much weaker van der Waals bonds between the carbon atoms. These do not have the same strength as the carbon-carbon covalent bonds that prevail in graphene and carbon nanotubes.

     The purpose of the short overlap distance compared to their lengths is that likely there will be a combination of the stronger carbon-carbon bonds and van der Waals bonds between the layers. You might then need several layers to make the equivalent cross-sectional strength of a single graphene/nanotube layer. However, by making this portion of the composite small compared to the rest of the graphene/nanotubes the overall strength to weight ratio will be close to that of the pure graphene or carbon nanotubes.

    2nd UPDATE, 2/24/2023: Cyclic graphene growing nanotubes growing graphene.

    (patent pending)

     Above was first described methods of growing carbon nanotubes on graphene, as references, [1], [2], [3], [4], [5]. However, reference [6] described growing graphene on nanotubes:

    Open Access
    Published: 05 August 2013
    Self-Assembly of Graphene on Carbon Nanotube Surfaces.
    Kaiyuan Li, Gyula Eres, Jane Howe, Yen-Jun Chuang, Xufan Li, Zhanjun Gu, Litong Zhang, Sishen Xie & Zhengwei Pan 
    Scientific Reports volume 3, Article number: 2353 (2013)

      Then the proposal is to cycle repetitively first of growing nanotubes onto graphene and then growing graphene onto nanotubes to produce arbitrarily large graphene-nanotube hybrids.