Graphene, a new material with applications in biomedical technology, electronics, composites, energy and sensors, may soon help send rockets to space.
A new propellant formulation method to use graphene foams – material used in electronics, optics and energy devices – to power spacecraft is being developed in Purdue University’s Maurice J. Zucrow Laboratories, which is the largest academic propulsion lab in the world. The research is showing success at increasing burn rate of solid propellants that are used to fuel rockets and spacecraft.
“Our propulsion and physics researchers came together to focus on a material that has not previously been used in rocket propulsion, and it is demonstrating strong results,” said Li Qiao, an associate professor of aeronautics and astronautics in Purdue’s College of Engineering.
The research team, led by Qiao, developed methods of making and using compositions with solid fuel loaded on highly conductive, highly porous graphene foams for enhanced burn rates for the loaded solid fuel. They wanted to maximize the catalytic effect of metal oxide additives commonly used in solid propellant to enhance decomposition.
The graphene foam structures are also thermally stable, even at high temperatures, and can be reused. The developed compositions provide significantly improved burn rate and reusability.
Qiao said the graphene foam works well for solid propellants because it is super lightweight and highly porous, which means it has many holes in which scientists can pour fuel to help ignite a rocket launch.
The graphene foam has a 3-D, interconnected structure to allow a more efficient thermal transport pathway for heat to quickly spread and ignite the propellant.
“Our patented technology provides higher performance that is especially important when looking at areas such as hypersonics,” Qiao said. “Our tests showed a burn rate enhancement of nine times the normal, using functionalized graphene foam structures.”
Qiao said the Purdue graphene foam discovery has applications for energy conversion devices and missile defense systems, along with other areas where tailoring nanomaterials for specific outcomes may be useful.
In a successful collaboration between the Graphene Flagship and the European Space Agency, experiments testing graphene for two different space-related applications have shown extremely promising results. Based on these results, the Flagship are continuing to develop graphene devices for use in space.
“Graphene as we know has a lot of opportunities. One of them, recognised early on, is space applications, and this is the first time that graphene has been tested in space-like applications, worldwide,” said Prof. Andrea Ferrari (University of Cambridge, UK), Science and Technology Officer of the Graphene Flagship.
Graphene’s excellent thermal properties are promising for improving the performance of loop heat pipes, thermal management systems used in aerospace and satellite applications. Graphene could also have a use in space propulsion, due to its lightness and strong interaction with light. The Graphene Flagship tested both these applications in recent experiments in November and December 2017.
The main element of the loop heat pipe is the metallic wick, where heat is transferred from a hot object into a fluid, which cools the system. Two different types of graphene were tested in a collaboration between the Microgravity Research Centre, Université libre de Bruxelles, Belgium; the Cambridge Graphene Centre, University of Cambridge, UK; the Institute for Organic Synthesis and Photoreactivity and the Institute for Microelectronics and Microsystems, both at the National Research Council of Italy (CNR), Italy; and industry partner Leonardo Spa, Italy, a global leader in aerospace, operating in space systems and high-tech instrument manufacturing and in the management of launch and in-orbit services and satellite services.
“We are aiming at an increased lifetime and an improved autonomy of the satellites and space probes. By adding graphene, we will have a more reliable loop heat pipe, capable to operate autonomously in space,” said Dr Marco Molina, Chief Technical Officer of Leonardo’s space line of business.
After excellent results in laboratory tests, the wicks for the loop heat pipes were tested in two ESA parabolic flight campaigns in November and December. “We have good tests done on earth in the lab, and now of course because the applications will be in satellites, we needed to see how the wicks perform in low gravity conditions and also in hypergravity conditions, to simulate a satellite launch,” added Prof Ferrari.
“It was amazing, the feeling is incredible and its extremely interesting to do experiments in these kinds of conditions but also to enjoy the free-floating zone. The whole experience was really great,” said Vanja Miskovic, a student at Université libre de Bruxelles who performed the experiment in microgravity during a parabolic flight operated by Novespace.
The results of the parabolic flight confirm the improvements to the wick, and the Flagship will continue to develop the graphene-based heat pipes towards a commercial product. “I think this is a very nice example of how the Flagship is working. Bringing together three academic partners and one big industry with a clearly defined goal for an application,” said Vincenzo Palermo (CNR), Vice-Director of the Graphene Flagship. “At the moment, we have tested the principle and the core of the device. The next step will be to optimise the whole device, and have a full heat pipe that can go in a satellite.”
Testing graphene space-propulsion potential, a team of PhD students from Delft Technical University (TU Delft), Netherlands participated in ESA’s Drop Your Thesis! campaign, which offers students the chance to perform an experiment in microgravity at the ZARM Drop Tower in Bremen, Germany. To create extreme microgravity conditions, down to one millionth of the Earth’s gravitational force, a capsule containing the experiment is catapulted up and down the 146 metre tower, leading to 9.3 seconds of weightlessness. The TU Delft Space Institute, Netherlands, also provided support to the GrapheneX project.
The team – named GrapheneX – designed and built an experiment to test graphene for use in solar sails, using free-floating graphene membranes provided by Flagship partner Graphenea. The idea was to test how the graphene membranes would behave under radiation pressure from lasers. In total, the experiment ran five times over 13-17 November 2017.
“Our experiment is like a complex ‘clockwork’ where every component has to go off seamlessly at the right time” said Rocco Gaudenzi, a member of the GrapheneX team. “It does not often happen that you have to build up such a clockwork from scratch, and you cannot test it in real conditions but during the launch itself.”
The team worked hard to make the experiment successful. “Despite the initial technical difficulties, we managed to quickly figure out what was going on, fix the issues and get back on track. We are very happy with the results of the experiment as we observed laser-induced motion of a graphene light sail, and most importantly we had a great experience!” said Davide Stefani, GrapheneX team member.
Santiago J. Cartamil-Bueno, GrapheneX team leader, expressed that both the experience and the results were valuable to the team. “The most important lesson is that always something will happen, and you need to be ready to adapt or to change,” he said. “I think at the end of the day, it’s about the experience; you just need to create new challenges and learn from them, and be ready to grab more experience and go to the next level.”
Though the GrapheneX experiment is now finished, the team is considering further tests as part of a new and ambitious research project, to continue exploring the influence of radiation pressure on graphene light sails.
The results of the two projects demonstrate graphene’s versatility and are the first step towards expanding the frontiers of graphene research.
Don’t be mesmerised by cool apps and flashy new gizmos – the top technology inventions of the year are ones that will have a lasting effect.
Most are advances in fields that are already changing us. Some will have immediate impact; others are portents of transformations that may take decades to complete. In this vein, and in no particular order, here are what I consider to be ten of the best technological innovations from 2014.
1. DNA Nanobots injected into cockroaches
Nanotechnology is a growing research field that manipulates materials on a molecular scale. One prospect is to transform medicine by injecting nanobots into the body where they perform functions such as treating disease.
In February, an Israeli team described devices they made from DNA and injected into cockroaches. By performing a kind of origami, the DNA nanobots assembled themselves and were able to control a molecule that targeted specific cells, so demonstrating their potential to carry out medical functions such as attacking cancers.
2. Nanotubes in chloroplasts created super plants
Nanotubes are large carbon molecules that form tubes with unusual thermal and electrical properties. In March, a team from MIT and CalTech published a method for inserting nanotubes into plant chloroplasts. The novel combination boosted photosynthesis and plant growth by several hundred percent.
Applications are still years away, but besides increasing plant growth and production, there are extraordinary possibilities: tapping plants for electrical power, building self-repairing materials and erecting buildings from materials that generate their own power.
3. Scallop-shaped robots swam through blood
Researchers at Germany’s Max Planck Institute developed tiny robots that could swim through the bloodstream, repairing tissue damage or transporting medicine.
The challenge they faced was blood’s viscosity: it not only impeded movement but also varied according to speed. They solved the problem by designing robots in the shape of scallops powered by an external magnetic field. These robots provide a starting point for many kinds of medical devices of the future.
4. A microchip helped a paralysed man regain the use of his arm
Implants are revolutionising the treatment of many medical conditions. In April, researchers at Ohio State University reported success in using a microchip implant to help a paralysed man regain use of his arm.
Ten years in development, the device, known as Neurobridge, stimulates muscles according to brain patterns. The innovation raises hopes for many disabled people. It showed that by plugging into our brainwaves we may one day control all manner of devices by thought alone.
5. Nose cells helped repair a severed spinal cord
Biotechnology is producing new cures for medical conditions long thought to be permanent. A medical team at Wroclaw Medical University cultured nerve cells taken from a patient’s nose and surgically inserted them into his spinal cord.
The transplanted cells stimulated severed nerve fibres to grow and rejoin, thus bridging a damaged section of the spinal column and allowing the patient to walk again. This innovation showed that damage to the nervous system can be reversed.
6. Unmanned drones: the future of delivery services
Unmanned flying drones are taking on a rapidly growing number of roles, especially in surveillance and monitoring. Following Chinese experiments last year to test drones as a delivery system for parcels, 2014 saw rapid expansion of serious business interest.
Robots are already important tools in many industries, but put them into swarms and they can do so much more. In August the journal Science reported work at Harvard in which 1,000 mini-robots, the largest swarm so far, was able to assemble itself into programmed shapes.
There is still a long way to go, but it raised the potential for structures that self-assemble, which would revolutionise construction.
8. 3D printers pushed the boundaries
3D printing is now an established technology, but developments this year expanded its capabilities and applications. At the one extreme a team in Amsterdam began a project to build an entire house using 3D printing.
Meanwhile researchers at Princeton developed a 3D printer that could print with five different materials, incorporating dot-emitting diodes, and demonstrated it by making contact lenses. This raises many possibilities, from wearable video to monitoring the health of pilots.
9. The next frontier in space exploration
Events this year highlighted the international character of solar system exploration in coming decades. Following a ten-year flight, European Space Agency’s probe Rosetta went into orbit around the comet 67P/Churyumov-Gerasimenko.
On November 12, it released the probe Philae which became the first spacecraft to land on a comet.
Meanwhile, Mars exploration moved forward. India’s Mangalyaan spacecraft went into orbit around Mars in September and in December, NASA successfully launched the new Orion spacecraft, a first step in preparing for manned exploration of Mars.
10. Green power and clean water
Necessity is the mother of invention, so the greater the need, the more important the invention. A worldwide need is the 780 million peoplearound the world who lack access to clean water supplies. The challenge for inventors is to meet the World Health Organisation criteria for practical systems: accessible, simple and cheap.
What of next year? We can be sure that growing fields such as automation and nanotechnology will continue to surprise us. The US Patents Office granted more than 300,000 patents during 2013, nearly 30,000 more than 2012. If patents provide a reliable indicator, then new inventions are appearing faster than ever.
Nanotechnology will play an important role in future space missions. Nanosensors, dramatically improved high-performance materials, or highly efficient propulsion systems are but a few examples (read more: “Nanotechnology in Space“). One particularly important issue is the protection of satellites from electrostatic discharge (ESD).
In space, the external insulating surfaces accumulate electrostatic charge as a result of exposure to space plasma, including high flux of charged particles especially at geosynchronous earth orbit (GEO). If that charge accumulation suddenly discharges it may damage the electronics of the spacecraft. The space industry therefore has a strong requirement to develop a flexible ESD protection layer for the exterior cover of satellites.
A study conducted by nanotechnology researchers at Tel Aviv University together with scientists from the space environment department at Soreq NRC, explores carbon nanotube-polyimide (CNT-PI) composite materials as a flexible alternative for the currently used indium tin oxide (ITO) coating, which is brittle and suffers from severe degradation of the electrical conductance due to fracture of the coating upon bending. “We developed electrically conducting and flexible CNT-PI films specifically for space applications using polymer solution infiltration into CVD-grown entangled CNT sheets with cup-stacked nanostructure,” Yael Hanein, a professor at Tel Aviv University and Director of the university’s Center for Nanoscience and Nanotechnology, tells Nanowerk. “This fabrication process prevents CNT agglomeration and degradation of the CNT properties that are common in dispersion-based processes.
Schematic illustration of CNT-PI film fabrication process: (a) ∼9 µm thick CNT sheet is first grown by CVD on a prepatterned Si substrate. (b) PI (PMDA-ODA monomer) is then infiltrated into the CNT sheet. (i) Type 1 samples were cast by ∼9 µm thick PI layer (up to the dotted line). (ii) Type 2 samples were prepared with excess of PI layer (∼15 µm thick). (c) Finally, free-standing CNT-PI film is mechanically peeled off the substrate. (Reprinted with permission by American Chemical Society)
The team has published its findings in the November 3, 2014 online edition of ACS Applied Materials & Interfaces (“Reinforced Carbon Nanotubes as Electrically Conducting and Flexible Films for Space Applications”). “We specifically explored the electrical conducting mechanism of CNT-PI composites, given that we sought a simple method to control CNT distribution within a polymer matrix, while protecting the CNT properties,” says Nurit Atar, a PhD candidate and first author of the paper.
“We found that the conductivity of the CNT sheet was preserved in spite of the insulative PI infiltration. This implies that the electrical current was enabled through the original entangled CNT network that was not interrupted by the insulative PI. This proves that the polymer solution did not penetrate into the interface at the CNT junctions and so the original continuum of ohmic contacts between adjacent CNTs was preserved.” CNT-PI composites were produced before by dispersion of CNT powder in polymer matrices. Since CNTs are insoluble and tend to agglomerate as bundles, sonication and functionalization are commonly used to improve homogeneity. These incorporation techniques often result in severe degradation of the original CNT properties (e.g., electrical, thermal, and mechanical characteristics). The preparation method used by the Israeli team is based on PI infiltration into CVD-grown CNT sheets, enabling preservation of the original CNT sheet conductivity with no degradation related to the insulating PI matrix. Hence, higher electrical conductivity can be easily reached, e.g., by controlling the CNT growth process (CVD) to form denser CNT sheets with higher conductivities. “Another advantage of the technique presented in our recent paper is the compatibility with patterning of CNT along the composites, which is not facilitated by the dispersion technique,” Atar points out.
(a) Top view HRSEM image of an as-grown entangled CNT sheet. (b) TEM image of a typical cup-stacked CNT. (c) Optical microscope image of a patterned, free-standing CNT-PI film with area of 1 × 1.5 cm2 and 10 µm thickness. (d) AFM phase image of the top surface of a CNT-PI film. Inset: Optical microscope image of a free-standing CNT-PI nanocomposite film (17 µm thick, 0.5 × 3.5 cm2 area) wrapped around a glass tube (7 mm diameter). (Reprinted with permission by American Chemical Society)
As electrically conducting films, the CNT-PI composites can prevent electrostatic charge accumulation on the exterior of satellites. Particularly, the researchers found that their CNT-PI films are durable in space environment hazards such as high vacuum, thermal cycling, and ionizing radiation. The team’s current work focuses on improving the stability of the CNT-PI film to atomic oxygen, which is dominant at low earth orbit space environment. The challenge is to introduce inorganic nanoparticles into the polymer matrix to create a self-passivation layer when exposed to atomic oxygen.