Guide Advances In Chemical Propulsion, Science To Technology

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Nevertheless, breakthrough results may be expected and the thruster efficiency may be significantly boosted. Even more sophisticated nanomaterial with the promising wear-resistance properties was also demonstrated. Specifically, the hot-filament chemical vapor deposition was used to synthesize nanocrystalline diamond-coated silicon nitride ceramics This approach may be useful for enhancing the thruster wall wear resistance and simultaneously adjusting the acceleration process parameters, such as wall conductivity, roughness, secondary emission coefficient, and others that directly influence the discharge Carbon can be also used for channel enhancement.

One more promising approach to reduce channel wall erosion is the use of carbon-based nanostructured materials and surface structures. Carbon exhibits a very low sputtering rate under the action of ion flux, as compared with the commonly used BN ceramics Along with this, the secondary electron emission yield of carbon is also lower than that of BN, and this is also a useful feature that can be a factor in Hall thruster operation We should stress that BN demonstrates one of the best performances as a wall material, so at the first stage, the aim should be the design of the material that can at least preserve the efficiency of BN state-of-the-art thrusters.

On the other hand, increase of wear resistance by the factor of 2 or 3 due to the wear-resistant carbon films 67 is attractive for enhancing the Hall thruster lifetime. Carbon nanotubes are also a promising technique to enhance channel wear resistance. It is known that the graphene and graphene-based nanostructures, such as carbon nanotubes, are very strong strongest known in nature materials The carbon nanotubes were also tested for resistance against ion flux erosion. Specifically, the multiwall carbon nanotubes were tested as the protective coating against plasma erosion in advanced space propulsion systems.

The polycrystalline diamond film was compared with multiwall nanotubes, amorphous carbon, and BN films Two types of nanotubes were investigated, including vertically aligned nanotubes and those horizontally laid on the substrate surfaces. It should be stressed that the use of carbon nanotubes in the thruster is presently at the stage of an advanced concept that requires strong efforts to check feasibility. Indeed, many properties specific to carbon nanotubes, such as a decrease of the secondary electron emission in vertically aligned structures and electrical conductivity of carbon nanotubes can degrade the thruster characteristics.

On the other hand, carbon nanotubes are very attractive due to the properties of the carbon material, and that material should obviously undergo active testing in EP devices, taking into account the above-mentioned encouraging results on wear resistance. Thus, the dense brushes of vertically aligned nanotubes demonstrate quite attractive and fascinating properties when tested for wear resistance under the action of energetic ion flux in the Hall thruster channel.

Notably, the carbon nanotubes are conductive and can change the acceleration mechanism the wall conductivity is not an inadmissible condition, but it significantly affects the process Undoubtedly, the first encouraging experiments 67 , 69 force further complex investigations to cast light on the application of carbon nanotube brushes and other graphene-containing materials in EP engineering. Graphene nanowalls is one more material potentially capable of enhancing channel wear resistance.

Along with the carbon nanotubes, graphene and graphene flakes may be attractive for enhancing the channel wall wear resistance. Graphene is the strongest material in nature and carbon and carbon nanotubes are particularly resistant to ion sputtering; this makes the surface-grown graphene flakes nanowalls extremely attractive candidates for wear-resistance testing in the Hall thruster channel. Dense patterns of carbon nanowalls can be formed directly on the ceramic surface, with or without metal catalyst particles 71 if required.

Direct growth on ceramic and metallic 72 materials is also possible The exemplary graphene patterns grown on alumina are shown in Fig. They consist of nearly vertical graphene flakes attached by one edge to the face surface of the ceramics, with the other edges being open.

Graphene nanowall patterns have not yet been subjected to extensive ion flux and wear testing in real EP devices, but positive results of the experiments with other carbon-containing, and especially graphene-like and diamond-containing nanostructures, encourage further work in this direction. Similar to other ultramodern techniques, graphene and nanotubes should find their deserved place in EP technology.

The operational tests of this material are in progress, and a flight test is planned.

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Apart from the material-related approaches, a so-called magnetic shielding technique was recently demonstrated Sophisticated selection of the shape of the magnetic field at the exit of the accelerating channel, and the proper profiling of the channel exit ensure a significant decrease in the intensity of ion bombardment to the channel walls, and hence, substantial decrease in the wear of channel walls.

As a result, the service life of the channel can be essentially increased, thus significantly prolonging the thruster lifespan without notable drop in the performance characteristics. Schematics of the magnetic shielding technique is depicted in Fig. Importantly, magnetic shielding allows to operate the thruster at higher voltage levels, i. Moreover, magnetic shielding partially precludes electrons from contacting with the walls and hence, allows changing the wall material to metals or carbonaceous materials, or cheaper ceramics without reducing the thruster characteristics.

On the other hand, this technique requires more complex magnetic topology, which could make the EP system somewhat more complicated and potentially less reliable. However, potential significant benefits of this technique call for further studies since the high-voltage operation requires new resistant materials even in the magnetic shield mode. Further, both new materials and sophisticated magnetic field topology are necessary to achieve the dual-mode operation described in more detail below Cathode is the second electrode used in any type of static thruster to apply negative potential to the discharge zone and in some cases, to supply the flux of electrons to the discharge zone where they are magnetized, as well as to compensate the space charge of non-magnetized ions; that is why the cathodes on Hall thrusters are sometimes called neutralizers.

Cathodes may also be installed well outside the thruster to ensure better thruster characteristics and thus will require strong protection Optimization of the cathode position is required to ensure the highest thruster performance characteristics The cathode in the present-day thruster see the schematic of the commonly used thermosemissive cathode in Fig. The cathode can be used as a low thrust thruster itself Cathode erosion also represents a problem reducing the service life Novel materials for cathode technology.

Gas with the flux rate of several percentage points of the total thruster propellant consumption is supplied into the central tube, which is heated by the coil. The emissive insert ensures thermoionization of the gas exiting the cathode orifice. When the thruster is working discharge is sustained in the chamber , plasma forms a narrow jet connecting the cathode orifice with the main discharge zone, and electrons pass to the discharge via the plasma jet.

The cathode includes a thermal screen to reduce the heat loss to space due to ionization. In addition, it incorporates elements and parts to attach the cathode to the thruster and the gas feed system. Copyright , ERPS. Copyright , RSC. Thus, the key challenges for the cathode and consequently possible directions for the enhancement of thruster efficiency via upgrading the cathode unit consist in the reduction or total elimination of propellant consumption via the cathode, significant boost of the cathode service life, and the reduction of heat loss from the incandescent parts.

Can nano help here? Let us examine how nanomaterials and nanotechnology can help achieve these goals. Reduced gas consumption may be ensured through the use of nanoporous materials, nanotubes, and graphene. The best solution for this problem is the total elimination of gas flux through the cathode by using high-emissive materials and surface structures. Numerous tests have demonstrated that usual solid and microporous materials cannot ensure notable enhancement of characteristics compared with the commonly used LaB 6 material.

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However, encouraging experimental results have been obtained by testing various nanostructured and surface-engineered materials, such as nanoporous metal emissive elements Fig. Carbon nanotubes were also successfully tested as field-emission electron sources operating without or at reduced gas supply 81 Fig. Moreover, multiwall carbon nanotube emitters were tested directly for the use in spacecraft cathode units; 82 the tests were conducted specifically for the operation in the Hall thruster plume environment Other nano-engineered materials also demonstrated promising electron emission properties, e.

Nano- and micro-engineered materials relevant to EP were also tested for their electron emission capabilities Vertically aligned graphene 87 has also demonstrated inspiring results in electron emission tests Investigations related to the reliability and failure mechanism of the carbon nanotube-based cathodes are also undergoing active exploration In spite of many successful experiments referenced here, more efforts are required to utilize the full potential of vertically aligned nanostructures in cathode-related applications, and newly developed nanostructures and patterns can be much more efficient than those already tested classical cathodes with a heating coil and an emissive La-B insert Fig.

An example of a novel and potentially efficient nanomaterial for cathodes is the cluster-grown carbon nanotubes and nanocrystalline graphites. These clusters could be arranged into various shapes by a simple mechanical drawing using e. Such aggregates are extremely promising for emission-related applications.

More detail about the growth process can be found elsewhere Further studies of these and other nanotube and graphene patterns and surface structures are needed to make a definitive conversion from contemporary propellant-consuming cathodes to novel, cold, propellant-free nanomaterial-based cathodes.

More examples and a detailed description can be found in Fig. When the propellant-free design is inapplicable, complex nanostructure-based surface systems metamaterials may be proposed for application in thruster cathodes, with one of the example systems shown in Fig. A dense pattern of the vertically aligned graphene flakes was grown on the nanoporous 91 alumina membrane. Propellant can be supplied directly through the nanoporous alumina, and electrons will be emitted from the acute edges of the graphene, which are emission-capable structures as was demonstrated in direct experiments Longer life of cathode could be also reached by the use of ultra-nanoporous inserts.

Emissive inserts work when electrons exit an emissive material from the surface; hence, larger surface area per volume unit of the insert could be beneficial due to the lower required heated volume and more efficient electron emission. In the example, single-crystalline MoO 3 nanowires were synthesized by a simple, environmentally friendly plasmoxy-nanotech process 92 by direct exposure of a pure Mo foil to reactive oxygen plasmas in a Pyrex glass reactor.

After synthesizing the single-crystalline MoO 3 nanowires, they were transferred to the transmission electron microscopy grid for the electron beam irradiation. This method is based on the electron beam-driven oxide-to-sub-oxide and then sub-oxide-to-metallic transition that can be controlled by the electron beam exposure. More details on the process and performed characterizations can be found elsewhere This technique can potentially be used to produce other materials, including those suitable for the emissive inserts, and very efficient inserts may be fabricated. Nanoscaled metamaterial could help to reduce the heat losses.

However, ideally, the entire heat generated in the cathode should be used within at the emissive insert and should not be released from the outer parts of the unit. Any type of currently used heat protections essentially provides passive protection. Using nanoscaled metamaterials, active heat protection physically based on heat pump principles can be designed.

Specifically, external energy should be spent to transfer the heat from colder parts to heated parts by, e. During the metamaterial operation, an electrical potential dependent on the distance between surfaces and the current density is applied between the anode and the cathode to sustain the current in the gap. As a result, heat may be transferred from the hot surface directly to the colder part by the electron current in the gap, i. As a result, heat that leaks from the hot cathode to space can be significantly reduced.

We stress that this is only a concept under active investigation Further investigations will be needed to design, test, and implement the novel heat-transferring systems in the material form factor. A schematic of the metamaterial proposed for the active heat pumps is shown in Fig. Metamaterial-based approaches. Due to strong electric field enhancement on the long nanosized structures, significant current densities could be obtained without external heating.

This structure may include a nanoporous membrane a porous insert capable of containing some amount of a highly emissive material usually working in a liquid state e. The nanoporous membrane with the emissive material in pores is placed directly onto the solid cathode, and the spacer separates this membrane and the anode with the low-emissive material. The low-emissive material e. The cathode the cold electrode in green has a temperature lower than that of the anode the hot electrode in red. Electron current emitted from the cathode flows through the inter-electrode gap to the anode.

It is evident that such metamaterials could create strong heat barriers in the systems where heating over some limit e. Curie temperature should be avoided. Copyright , Wiley. As previously mentioned, the nature of the wall material can be used to classify Hall-type thrusters as TAL featuring metallic channel walls, and thrusters with ceramic walls stationary plasma thruster, SPT. These two types exhibit slightly different characteristics and require somewhat different design approaches, and as such, these devices could occupy specific application niches and be successfully used in space exploration for various missions.

In general, the total difference in performance between ceramic-walled SPT-type thruster and metal TAL is not so significant. Nevertheless, both types are attracting attention, and among other advantages, TAL can ensure efficient operation at higher up to several kV voltage, so the specific pulse exhaust velocity will be higher. In turn, this may be advantageous for the missions requiring elevated specific impulse at somewhat lower thrust, such as orbit keeping or debris removal 96 for several years at limited onboard power and limited mass.

At present, the TAL-type thrusters are underexplored, yet numerous studies indeed demonstrate their better operability at significantly increased voltages 97 , Even within the same thruster type, the wall material characteristics may influence thrust, exhaust velocity, and thruster efficiency 99 , Evidently, TAL is not congruent to a standard SPT thruster with conducting walls, and apart from the wall material state, some other adjustments e. Is it possible to actively control processes in thrusters by nanomaterial-based techniques? Evidently, many of the present-day nanomaterials and surface-engineered systems could be tested for the active control of the thruster operation.

Undoubtedly, control of such a set of unique properties can lead to thrusters with a wide operational range, and moreover, could allow adaptive switching between the operational modes. Granted that different feedstock gases must be used to accomplish propulsion or nanosynthesis, we still find the similarities quite encouraging. Indeed, Hall thrusters have already been successfully tested for nanofabrication, and hence, desired nanostructures and nanomaterials could be in principle synthesized directly in the discharge acceleration channel.

Thus, we propose the concept of the so-called adaptive thruster, i. In more detail, the electric, magnetic, and gas supply systems of the thruster should be designed and tuned to be capable of ensuring temporary transition of the discharge from acceleration to nanosynthesis mode changing the gas composition by adding the nanomaterial precursor such as, e. Graphane can be a key material to realize this task.

The ability of switching between TAL and SPT operational modes is a possible implementation of an adaptive thruster concept. As the wall material a ceramic or a metal is the major discriminant of these modes, the thruster ability of adapting the conductivity of its own wall material would enable the realization of adaptive features. For instance, hydrogenation of the surfaces of graphene flakes on the channel walls by the thruster discharge plasma may ensure quick and reversible transition from insulating to conductive states and vice versa, thus would provide the ability to switch between TAL and SPT regimes directly in flight and possibly, without interruption of the thruster operation.

Indeed, it was already demonstrated that graphene can react with atomic hydrogen, and this reaction transforms graphene which is a perfect electrical conductor into graphane, an insulator made out of a two-dimensional compound of carbon and hydrogen i. This reaction is also reversible, and the graphene structure is maintained when graphane is formed by attaching hydrogen atoms to graphene.

Importantly, this reaction requires low-temperature plasma similar to that present in the Hall thruster discharge. The hydrogen admixture in the gas of an operating thruster could be short, since only surface hydrogenation is required. As hydrogen source, metal hydrides i. Both vertically aligned graphene flakes, as well as graphene-like inlaying films can be proposed for adaptive thruster applications.

In any case, the use of such materials should be explored due to the potential importance of the proposed in-operation and in-flight conversion of TAL to SPT. Alternatively, an insulating film could be temporarily deposited onto the metal walls to transform a TAL-type device into a SPT-type. For this purpose, a small amount of silane silicon and hydrogen containing gas, SiH 4 and oxygen or e. By tailoring the plasma properties, different nanoparticle characteristics, such as chemical composition and crystal structure, can be achieved. Oxidation can then be easily achieved with a very small amount of oxygen or even water vapor The application of a thin metal film onto the channel wall surfaces from the discharge plasma is another approach to adaptive thruster systems.

Indeed, this approach will require admixture of a metal-containing gas or evaporated metal-containing liquids capable of producing suitable metal precursors in the discharge. A metal film deposited onto the wall surface will ensure the transition from insulating to conductive states, but the wear resistance of pure metal is low and thus could be used for short-term regime switching. Deposition of such oxidized nanoparticles onto the metallic walls of the acceleration channel will create electrically insulating layer and thus transform the TAL device into SPT.

Notably, Hall thrusters with a significant addition of silica on the channel walls is quite functional, albeit with somewhat lower efficiency. Is it possible in a real thrusters? Yes, provided that an efficient control over the processes in plasma-wall sheath is ensured, e. Proper control of the plasma configuration could make it possible to temporarily separate the main discharge zone from the nanoparticle nucleation and deposition area, thus ensuring direct growth of the nanostructures in the discharge and the following deposition onto walls.

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Extended experimental and theoretical studies will be required to bring these concepts to life. Using similar design solutions, it is possible to fabricate electrodes with, for instance, thin layers of carbon mixed with layers of traditional BN. Such sophisticated structures enable active control over the near-wall conductivity , and hence, enhance the discharge and ion acceleration. Furthermore, the replacement of thin carbon layers with the graphene and possibly, multi-walled graphene flakes could potentially enhance the characteristics due to higher mechanical strength, as well as electrical and heat conductivities, intrinsic to graphene Self-healing is the ability of a material, part, or system to restore its original integrity and functionality after damage without any direct external effect or in response to a small change in the operating regime that does not affect the working capacity of the entire system.

Self-healing process may occur uninterruptedly during normal operation of the system, or periodically during specially organized sessions when the operation cyclogram permits. Was it already demonstrated in conditions similar to those found in plasma thrusters? Yes, it has already been successfully demonstrated! We have designed and conducted a series of dedicated conceptual experiments to demonstrate that the discharge system can restore its functionality during the normal operation. A thin carbon layer about 0.

Adapted with permission from Teel et al Copyright , AIP. Yes, this was demonstrated in the experiments — SEM image below sows the carbon nanoparticles synthesized in plasma and deposited to plasma-exposed surfaces adapted from Hundt et al Direct synthesis and deposition of complex nanostructures such as carbon nanotubes and graphene nanoflakes is also possible in plasmas similar to that present in Hall thrusters Moreover, the morphology of the graphene patterns on the surface can be efficiently controlled by the applied electric field, as it was already demonstrated in the experiments where the flakes were aligned by the electric field Nevertheless, this is a very complex task that requires sophisticated control of the plasma parameters and plasma fluxes in the channel.

Self-organization is a process that leads elements to order and, eventually, it results in the establishment of a system of a higher order. In simpler words, self-organization is the process of origination of larger, more complex system out of smaller and simpler parts, due to the internal driving forces. Formation of a thin layer from small particles is an example we are interested in. A pattern of material fluxes on surfaces is the main reason for self-organizing behavior in an array of nanoparticles. Since these fluxes are mainly governed by the adatom density and electric field patterns near the surface, the surface diffusion and electric field may be considered as the main driving forces for the self-organization.

Calculated distribution of the electric field in the simulated pattern of nanoscaled irregularities on a plasma-exposed surface, and b three-dimensional visualization of the nanoscaled irregularity pattern and adatom density profile on the surface. Levchenko et al Copyright , American Chemical Society. Boron nitride nanotubes have structure similar to that of well-known extra-strong carbon nanotubes and thus feature similar properties Golberg et al The nanotube fractured by the action of an external force undergoes self-healing, with no trace of kink found at the affected area Golberg et al With very high tensile strength similar to that of carbon nanotubes, and excellent electrical characteristics ensuring efficient plasma acceleration in Hall thrusters, BN nanotube can find many applications in the future thrusters.

This covers several mainlines, in particular self-cleaning surfaces, self-healing repair mechanisms, and self-repairing surfaces and materials. Initial research efforts by NASA and associated research institutions have demonstrated self-healing materials that were capable of repairing the punctures in several seconds Moreover, other possible self-healing approaches for EP systems were explored; at the thruster level, self-healing field-emission neutralizers cathodes for EP devices were developed by NASA in collaboration with Aerophysics, Inc.

The implementation of self-healing and self-restoring materials and systems to the entire spacecraft makes the self-healing approaches compulsory for subsystems such as thrusters that are the critical elements of the propulsion system. Furthermore, just the wear-affected acceleration channel walls that actually limit the thruster life are the ultimate elements to be examined in terms of incorporation of self-healing materials and techniques.

Specifically, we are proposing the self-healing approach plasma-enabled healing similar to that suggested for modification of the acceleration channel material and in-flight switching mode of thruster operation between the TAL and SPT regimes; specifically, self-healing should be enabled by plasma nucleation and deposition of various nanostructures and nanomaterials.

The difference is that in the case of self-healing, the deposition of plasma-nucleated nanomaterials most probably, as small as possible or appropriate ions e. Importantly, the first experiments have demonstrated this mode in the thruster-like conditions In any of the above modes, several key processes should be activated and controlled, such as nucleation of the appropriate nanoscaled particles most probable for the sessional self-healing or appropriate ions for concurrent self-healing ; delivery of thus-formed particles to the most appropriate locations i.

Detailed examination of all these processes is obviously outside the scope of our work, the aim of which is to set the general directions, suggest potential approaches, and stimulate discussion within this highly promising area of research. Nevertheless, we would like to take this opportunity to point out and briefly characterize the physical mechanisms at the heart of the above process.

We should highlight that surface self-healing is essentially a manifestation of self-organization and self-assembly; moreover, self-healing is a surface-based self-organizational process and plasma exposure can effectively produce strong driving forces to drive self-organization on surfaces Nucleation of the appropriate nanoscaled particles was in short discussed in the above subsections, and it was shown that the nucleation of various nanostructures and nanocrystals is possible in the plasma environment similar to that of the present-day Hall thrusters The delivery of plasma-nucleated charged nanostructures to the most appropriate locations, as well as surface processes such as diffusion and material incorporation, could be achieved via non-uniform electric fields that develop at the plasma-solid interface and in particular enhanced by rough surface.

It was already demonstrated that electric field could control movement of ions and nanoparticles near surfaces, and eventually ensure material deposition onto preferred locations within the nano-textured surface pattern Briefly, strong peaks of the near-surface electric field and adatom density causes rapid, intense material redistribution resulting in healing of worn traces by filling them with the repairing material. Importantly, the efficient incorporation of the repairing material into the worn traces requires plasma and electron irradiation for degasing of the surface and for the creation of dangling bonds In general, surface-based processes are relatively well described and numerous studies were conducted to show how the plasma composition, surface temperature, and other parameters influence surface restructuring.

Ultimately, special arrangements should be designed to fully control the entire process, e. Apparently, significant stumbling blocks and constraints should be expected during implementation of adaptive and self-healing thruster strategies. Indeed, the adaptive and self-healing strategies for boosting mission efficiency and significant extension of the thruster lifetime would clearly complicate the entire system and hence, disadvantages should be carefully considered and taken into account.

Moreover, not every thruster system could be suitable for such an upgrade, and it is quite possible that the drawbacks related to the increase in weight and complexity, and consequent lower weight efficiency and lower reliability could make some systems not appropriate for the adaptive and self-healing technologies. In general, the alternative approach could include redundancy installation of additional thrusters to prolong the life of the entire system and change the operation mode by switching the thrusters , which is commonly used in similar complex technical systems.

Evidently, a detailed systematic analysis will be required in each specific case to determine the applicability and practicability of the adaptability and self-healing strategies, based on a spectrum of parameters. Indeed, compromise between mass increase due to additional thrusters, connections, frames, and so on, in the case of the redundancy approach, and mass increase due to additional gases, gas tanks, valves, power supply units, control systems, and so on, will be required to maintain adaptability and self-healing processes.

Moreover, compromise between life increase due to self-healing and life decrease due to lower reliability of the whole system after introduction of additional self-healing subsystems should also be considered. Detailed systematic analysis should be performed in each specific case and specific mission, and possible stumbling blocks and constraints should be detected, analyzed, and assessed to consider the applicability of the adaptability and self-healing techniques and their benefit against the increased complexity.

Indeed, the self-healing and self-adjusting space system will represent a next level of complexity, in fact being in part a biomimetic system. Moreover, the study of the critical processes within an adaptive and self-healing space thruster system presents a considerable experimental challenge, with significantly more effort required to first demonstrate some self-healing functions at the system level.

However, given the potential benefits, this is a worthwhile effort since it could potentially revolutionize the entire approach to designing and building the spacecraft systems and other space-based platforms.

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Furthermore, while creation of the flight-ready self-healing thruster is a scientific and engineering challenge of immense complexity, the state-of-the-art techniques make it conceptually possible. Publisher's note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. National Center for Biotechnology Information , U. Nat Commun. Published online Feb Levchenko , 1, 2 S. Teel , 3 D. Mariotti , 4 M. Walker , 5 and M. Keidar 3. Author information Article notes Copyright and License information Disclaimer.

Levchenko, Email: gs. Corresponding author. Received Mar 23; Accepted Nov This article has been corrected. See Nat Commun. Abstract Drastic miniaturization of electronics and ingression of next-generation nanomaterials into space technology have provoked a renaissance in interplanetary flights and near-Earth space exploration using small unmanned satellites and systems. Introduction Major progress in robotics and microelectronics, as well as significant advances in nanoelectronics, make it possible to efficiently explore both near Earth and deep space with small spacecraft 1.

Electric propulsion systems as the first choice Wide application of nanoapproach in space technology could be a possible way to realize smart, nanoscale spacecraft. Open in a separate window. Box 1: Publications on thrusters and satellites Growth in the number of publications on electric propulsion and satellites. Box 2: plasma thruster as a unique propulsor Electric propulsion—why is it the first choice? Box 3: structure and operation of Hall and ion thrusters Hall thruster—what are the main parts?

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Hall-type and ion thrusters as the two main candidates Hall-type and gridded ion thrusters are among the most advanced, mature EP technologies with space-proven, relatively long flight heritage; some prominent EP-driven missions are described in more detail below. Nanomaterials in thrusters Let us now examine how to boost the properties and characteristics of the thruster itself, which is the primary and critical sub-subsystem of the entire EP platform. Table 1 Currently used and proposed materials for thrusters. Material Tested Ref. Boron nitride, BN Tested, in use, high efficiency, low erosion 0.

Longer life and higher cathode current via advanced materials Cathode is the second electrode used in any type of static thruster to apply negative potential to the discharge zone and in some cases, to supply the flux of electrons to the discharge zone where they are magnetized, as well as to compensate the space charge of non-magnetized ions; that is why the cathodes on Hall thrusters are sometimes called neutralizers. Adaptive and self-healing thruster via nanomaterials As previously mentioned, the nature of the wall material can be used to classify Hall-type thrusters as TAL featuring metallic channel walls, and thrusters with ceramic walls stationary plasma thruster, SPT.

Box 4: successful conceptual experiments toward self-healing What is self-healing? Notes Competing interests The authors declare no competing financial interests. References 1. LoKeidarng, K. Deep Space Propulsion. Dankanich, J. Fast transits to Mars using electric propulsion. ESA Bull. A survey of propulsion options for cargo and piloted missions to Mars.

N Y Acad. Takahata, Y. Research and development of high-power, high-specific-impulse magnetic-layer-type Hall thrusters for manned Mars exploration. Kuninaka, H. Hayabusa asteroid explorer powered by ion engines on the way to Earth. In 31st International Electric Propulsion Conf. Lessons learned from round trip of Hayabusa asteroid explorer in deep space. Big Sky MT, 5 March , Darnon, F.

Overview of electric propulsion activities in France. In 29th Int. Delgado, J. Space systems Loral electric propulsion subsystem: 10 years of on-orbit operation. TA Nanotechnology. Sutton GP, Biblarz O. Rocket Propulsion Elements. New York: Wiley; Mazouffre S. Electric propulsion for satellites and spacecraft: established technologies and novel approaches.

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Boeuf JP. Tutorial: physics and modeling of Hall thrusters. Choueiri EY. A critical history of electric propulsion: the first 50 years J. Hoskins, W. In 33rd Int. Electric Prop. Paper IEPC Kim, V. Electric propulsion activity in Russia. In 27th Int. Electric Propul. Brophy JR.

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Efficient electric plasma engines are propelling the next generation of space probes to the outer solar system. Dawn: a mission in development for exploration of main belt asteroids Vesta and Ceres. Acta Astronaut. Cubesat Design Specification. Keidar, M. Electric propulsion for small satellites. Wood, D.

Paper AIAA Habl, L. Design of a CubeSat propulsion system using a cylindrical Hall thruster. In Joint Conf. Staehle R, et al. Interplanetary CubeSats: opening the solar systems to a broad community at lower cost. Small Sat.

Bell, I. The potential of miniature electrodynamic tethers to enhance capabilities of femtosatellites. In 32nd Int. Barnhart, D. IEEE Proc. IEEE Aerosp. Parametric investigations of miniaturized cylindrical and annular Hall thrusters. Kagota, T. However, if we could compact and expand the fabric of spacetime ahead of and behind us, respectively, we could technically be moving faster than the speed of light. Recent tests demonstrated that the X3 thruster can operate at over kW of power, generating 5. It also broke records for maximum power output and operating current. The technology is apparently on track to take humans to Mars sometime in the next twenty years.

Compared to chemical rockets, the ionic alternative is capable of a very small amount of thrust. However, engineers are attempting to mitigate these issues with the X3 design. While most Hall thrusters can be picked up and carried around a lab with relative ease, the X3 needs to be moved with a crane. In , the team will continue to put the X3 through its paces with a test that will see it run continuously for hours.

resenephpaitha.cf A shielding system is also being developed that would prevent plasma from damaging the walls of the thruster, allowing it to operate for even longer, perhaps even several years at a time. Share to Facebook. Tweet This. Share via Email. Off World. Capable of record-breaking speeds and highly efficient, the X3 Hall thruster is our best bet yet for a trip to the red planet. Brad Jones October 13th Click to View Full Infographic. Keep up. Subscribe to our daily newsletter.