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The Electric Solar Wind Sail (E-sail): Propulsion Innovation for Solar System Travel


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The electric solar wind sail (E-sail) is a novel propulsion concept that enables fast and economic space travel in the solar system. For propulsion it utilizes a continuous particle stream from the Sun (i.e., solar wind) by deploying long, electrically conductive charged tethers, which through electric force interaction are pushed by the charged solar wind particles, mainly protons (Janhunen et al. 2010). The E-sail thus provides constant thrust without fuel consumption, enabling more ambitious space missions than current technologies. In this paper we explain how the E-sail works and review some advantages and challenges of the technology. We then describe some specific possibilities that it opens for solar system travel and exploration: asteroid mining of water and metal ores, support for a manned Mars presence, and the reduction of space debris.
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Pekka Janhunen
Sini Merikallio
The E-sail will enable space travel and exploration with
higher speed, better mass economy, and at less cost.
The electric solar wind sail (E-sail) is a novel propulsion concept that
enables fast and economic space travel in the solar system. For propulsion
it utilizes a continuous particle stream from the Sun (i.e., solar wind) by
deploying long, electrically conductive charged tethers, which through elec-
tric force interaction are pushed by the charged solar wind particles, mainly
protons (Janhunen et al. 2010). The E-sail thus provides constant thrust
without fuel consumption, enabling more ambitious space missions than cur-
rent technologies.
In this paper we explain how the E-sail works and review some advantages
and challenges of the technology. We then describe some specific possibili-
ties that it opens for solar system travel and exploration: asteroid mining of
water and metal ores, support for a manned Mars presence, and the reduction
of space debris.
The Electric Solar Wind Sail: Overview
The physical principle of the E-sail was discovered in 2004 (Janhunen 2004)
and the technical concept in 2006 (Janhunen 2010a). The E-sail is currently
Sini Merikallio and
Pekka Janhunen
The Electric Solar Wind Sail (E-sail):
Propulsion Innovation for Solar System Travel
Sini Merikallio is a student at the University of Helsinki Faculty of Veterinary
Medicine; she was previously a scientist at the Finnish Meteorological Institute, Earth
Observations. Pekka Janhunen is research manager, Space Research and Observation
Technologies, Finnish Meteorological Institute.
under development by
the Finnish Meteoro-
logical Institute (https://,
NASA (the Heliopause
Electrostatic Rapid Tran-
sit System, HERTS),
and the European Space
Agency (ESA; unpub-
lished information).
The possible applica-
tions of the E-sail are
numerous and promis-
ing. It may be used to
support manned Mars
flight (Janhunen et al.
2015), tow an Earth-
threatening 3 million
ton asteroid to a more
benign track ( Merikallio
and Janhunen 2010), or
deliver a probe to Mer-
cury within a year with-
out any gravity assists
(Quarta et al. 2010).
It will be ideal for a cometary rendezvous ( Quarta et
al. 2016), fast planetary entry probe ( Janhunen et al.
2014), or asteroid investigations and sample returns
(Quarta and Mengali 2010a; Quarta et al. 2014).
Travel ling toward the edges of the Solar system, the
E-sail will make it possible to reach the heliosheath in
15 years (Quarta and Mengali 2010b), a feat that took
the Voyager spacecraft 27 and 30 years (Decker et al.
2008; Stone et al. 2005).
How It Works
Thrust for the E-sail is produced by the interaction of
charged tethers with solar wind particles: deflected by
the electric potential surrounding the tethers, the par-
ticles transfer some of their momentum to the E-sail.
Solar wind consists mainly of hydrogen and helium
nuclei, and a comparable number of electrons. All of
these contribute to the thrust of the E-sail, although
most of the wind’s momentum is a function of the more
massive positively charged particles.
Figure 1 shows an artist’s impression of an E-sail
design; the size of the solar wind particles and spacecraft
is hugely exaggerated, and the numbers of tethers, pro-
tons, and electrons are not representative. Wire tethers
are deployed from the spacecraft and their extension
maintained by centrifugal force due to rotation of the
whole system.
The produced thrust of an E-sail is inversely propor-
tional to its distance from the Sun, F α (1/r) (Janhunen
et al. 2010), in contrast to the traditional photonic solar
sail, for which F α (1/r2). The reason behind this is that,
with greater distance from the Sun and a corresponding
attenuation of the solar wind, the effective area around
the charged E-sail wires increases. In other words, the
impact of the wire potential extends farther from the
sail as the plasma density dwindles, resulting in better
performance than with photonic sails, for which the
area of the sail stays constant.
Advantages and Challenges
The E-sail requires no propellant, and discharging of
the wires by the solar wind thermal electrons can be
counter acted by an electron gun powered by solar panels
of a modest size. To enable maneuvering and trajectory
control, the E-sail thrust can be steered by controlling
the voltage of individual tethers and thus changing the
plane of the E-sail’s rotation. At 1 astronomical unit
(au) of distance from the Sun, approximately 2,000 km
FIGURE 1 Artist’s impression of an electric solar wind sail showing the spacecraft from which dozens
of tethers (green) are deployed. The whole structure rotates in a cartwheel fashion around the space-
craft to keep the tethers centrifugally stretched. Also shown are solar wind particles (protons [+] and
electrons [e−]) and their tracks affected by the electric charge of the tethers. The widths of the tethers
and the size of the spacecraft are greatly exaggerated. Image by Alexandre Szames/Antigravite.
of E-sail tether are required to produce 1 newton (N)
of thrust. This can be achieved with, for example, 100
tethers, each 20 km long, spun out centrifugally from
the spacecraft. There are no technological showstoppers
in sight for producing an E-sail like this.
Space is dense with tiny dust particles that threat-
en the integrity of the E-sail. The risk of this micro-
meteorite impact is mitigated by weaving the E-sail
tether into a 2–3 cm wide mesh-like structure of several
wires so that isolated damages in constituent wires do
not jeopardize the whole (Seppänen et al. 2011).
E-sail tethers need to be lightweight, conductive,
resistant to micrometeoroid impacts, and able to with-
stand the tension and pull created by the centrifugal
acceleration. The number and lengths of the tethers can
vary. Their diameter is restricted by the need to limit
surface area so as not to generate excessive thermal elec-
tron current. Such current would need to be cast off
by the electron gun, the use of which decreases perfor-
mance by increasing power system energy consumption.
Given mechanical (tensile strength, surface area, and
weight) and availability (workability and industrial sup-
ply) requirements, the material currently under consid-
eration for the tethers is 25–50 μm diameter aluminum
alloy wire. Each kilometer of the tether weighs 10 g
(Seppänen et al. 2013), resulting in a total tether mass
of just 20 kg for a 2,000 km E-sail. The whole propulsion
unit—including supporting structures, electron guns,
power systems, and design margins—weighs 50–200 kg
(Janhunen et al. 2013), far less than the weight of cur-
rently used propellant technologies. These features give
the E-sail a significant advantage, especially in sample
return missions and campaigns with many targets.
In the future, carbon nanotube technology might
further enhance the E-sail by allowing the manufacture
of longer, more lightweight yet durable and conduc-
tive tethers (Lee and Ramakrishna 2017; Monthioux
et al. 2017).
Asteroid Mining: Rocket Fuel from Water
The E-sail will permit very low cost freight carriage in
the solar system and thus enable affordable asteroid
mining operations. It can be used for the transporta-
tion of mining equipment to asteroids and return of the
mined products. One E-sail can make several trips to
and from asteroids during its estimated 10 years of life.
The technology can be easily multiplied and operations
could proceed on several asteroids simultaneously.
In addition to relatively rich heavy metal ores in aster-
oids, our interest was raised by another reserve: an abun-
dant number of water-bearing asteroids on near-Earth
orbits (Elvis 2014) that can be readily accessed by the
E-sail (Quarta 2014). The water can be separated from
the asteroid material by using a two-part container (fig-
ure 2) in which the water is evaporated from the asteroid
regolith in the first chamber and then pressure driven
into the other chamber to condense into ice ( Janhunen
et al. 2015). The temperatures of the containers can be
controlled by their surface albedos and infrared emis-
sivities (i.e., coating by colored metal or white paint)
or by using additional
shades, heat pumps,
or solar- powered heat
elements. Once filled,
the second con tainer
can be separated
and hauled to the
orbit of the Earth or
anywhere else.
The resulting water
can be split into
hydrogen and oxygen,
which form a potent
spacecraft fuel when
liquefied. This process
requires electricity,
which in space is read-
ily available via solar
panels. Currently all
FIGURE 2 Illustration of a two-chamber unit that can be used in situ to extract water from asteroid
regolith. Asteroid material is heated in the first chamber (left) so that water in the material vaporizes.
Pressure gradient drives the water vapor into the second chamber (right), where it cools and condenses.
+50 °C
+5 °C
into water
baking unit condensation
centrifugal force and pressure
diusion gradient
bladder cooling
by heat pump
heating of oven by solar panels or direct absorption
the fuel used by a space-
craft has to be lifted from
the surface of the Earth
and carried throughout
the mission, requiring
enormous fuel mass frac-
tions. As an example,
NASA’s Juno mission
to Jupiter, launched in
2011, had a liftoff mass of
3,625 kg, of which propel-
lant accounted for more
than 2,000 kg. We have
come up with an approach
to address this challenge,
as described in the next
EMMI: Manned Mars
Flights Facilitated by
the E-sail
In 2015 we proposed the
E-sail–facilitated Manned
Mars Initiative (EMMI;
Janhunen et al. 2015). The
idea behind EMMI is to
mine water from asteroids
and bring it to space-based
“gas stations” in the orbits of Earth and Mars where it
can be turned into rocket fuel. Such stations—with two
on the way to/from Mars (figure 3)—can significantly
facilitate manned Mars exploration in the near future.
Orbital fuel tank refills will allow for smaller tanks
and thus considerably lighter spacecraft. Moreover, the
spacecraft that lifts passengers and cargo from the sur-
face of the Earth into orbit can be different from that
which taxis between Earth and Mars. This will reduce
the design requirements of both vehicles, as the one
carrying passengers from Earth will not need to have
capabilities for long-term life support, and the traverse
shuttle will not need to survive atmospheric entry and
launch vibrations and thermal loads. In addition, the
availability of virtually free fuel on the Martian orbit
will increase mission safety and enable speedy returns
when necessary.
The asteroid-extracted water can also be used in life
support as a source of potable water and even oxygen
for breathing. Thick water layers around manned space-
craft and surface habitation modules can function as a
radiation protection shield during the long traverses
between Earth and Mars.
These spacecraft can be operated at a fraction of the
current estimated Mars colonization costs: once in place,
the EMMI is estimated to run on a budget comparable to
the maintenance costs of the International Space Station
(ISS). Moreover, launchers used for setting up EMMI can
be of the same scale as those used for building the ISS.
Plasma Brake
A spin-off from the E-sail technology, a plasma brake,
can be used to bring small satellites down from their
orbits at the end of their viable life (Janhunen 2010b,
2014; Orsini et al. 2018). It can be attached to existing
satellites and space debris with, for example, harpoons.
Advantages of the plasma brake are low weight, poten-
tially low cost, and high safety, as it can be operated
without any volatiles, explosives, or inflammables.
A plasma brake payload is currently flying on a
low Earth orbit (LEO) CubeSat mission, the Finnish
Aalto-1, and waiting to be tested using a short (100 m)
FIGURE 3 Schematic presentation of E-sail–facilitated Manned Mars Initiative (EMMI). At the
heart of EMMI are asteroid mining operations: water from an asteroid (bottom) is transported to the
planetary orbit and refined into liquid oxygen/liquid hydrogen LOX/LH2 fuel, which can be used
for transportation to and from Mars. Pictures of the planets and asteroid surface are by NASA and
not presented at scale.
Manned ights
Asteroid mining for water
Mining equipment
+50 °C
+5 °C
into water
baking unit condensation
centrifugal force and pressure
diusion gradient
bladder cooling
by heat pump
heating of oven by solar panels or direct absorption.
E-sail tether (Kestilä et al. 2013). It is important to note
that the relative speed of the spacecraft and ionosphere
(~7 km/s) is not comparable to the solar wind speed
(~400 km/s). However, as the tether voltage is varied in
sync with the rotation of the satellite, the E-sail effect
will be observable in changes in the CubeSat’s rota-
tional speed.
With Aalto-1, researchers are looking forward to
verifying, and measuring, the E-sail force in real space
Summary and Discussion
The design, production, and testing of electric solar
wind sail prototypes are making good progress. E-sail
technology could be available for solar system research
within 10 years and, if successful, may revolutionize the
way space travel and exploration missions are conceived
and executed. The E-sail will enable affordable continu-
ous manned Mars presence, considerably decrease travel
times in the solar system, make it possible to tackle space
debris, and help facilitate asteroid mining operations.
The E-sail thus holds great promise for accessing both
scientific and economical treasures of the solar system.
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... where τ ∈ {0, 1} is a switching (dimensionless) parameter that models the thruster operating mode: either on (when τ = 1) or off (i.e., τ = 0). These two modes are obtained by switching on or off the onboard electron gun powered by the solar panels [24,25]. In Equation (1), a c is the characteristic acceleration [26], which is defined as the maximum propulsive acceleration magnitude a at a solar distance r = r ⊕ , andn is the unit vector normal to the sail nominal plane (the plane that ideally contains the charged tethers) in the direction opposite to the Sun. ...
Full-text available
The aim of this paper is to investigate the performance of a robotic spacecraft, whose primary propulsion system is an electric solar wind sail (E-sail), in a mission to a heliostationary point (HP)—that is, a static equilibrium point in a heliocentric and inertial reference frame. A spacecraft placed at a given HP with zero inertial velocity maintains that heliocentric position provided the on-board thrust is able to counterbalance the Sun’s gravitational force. Due to the finite amount of storable propellant mass, a prolonged mission toward an HP may be considered as a typical application of a propellantless propulsion system. In this respect, previous research has been concentrated on the capability of high-performance (photonic) solar sails to reach and maintain such a static equilibrium condition. However, in the case of a solar-sail-based spacecraft, an HP mission requires a sail design with propulsive characteristics that are well beyond the capability of current or near-future technology. This paper shows that a medium-performance E-sail is able to offer a viable alternative to the use of photonic solar sails. To that end, we discuss a typical HP mission from an optimal viewpoint, by looking for the minimum time trajectory necessary for a spacecraft to reach a given HP. In particular, both two- and three-dimensional scenarios are considered, and the time-optimal mission performance is analyzed parametrically as a function of the HP heliocentric position. The paper also illustrates a potential mission application involving the observation of the Sun’s poles from such a static inertial position.
... The Electric Solar Wind Sail (E-sail) is a propellantless propulsion system that exploits the interaction of the charged particles in the solar wind with a spinning grid of tethers, kept at high potential by an electron gun and stretched by the centrifugal force [1,2,3]. The peculiarity of an E-sail allows innovative and exotic mission scenarios to be feasible, including non-Keplerian orbits and artificial Lagrange points maintenance [4,5,6]. ...
Full-text available
The Electric Solar Wind Sail (E-sail) is a propellantless propulsion system that generates thrust by exploiting the interaction between a grid of tethers, kept at a high electric potential, and the charged particles of the solar wind. Such an advanced propulsion system allows innovative and exotic mission scenarios to be envisaged, including non-Keplerian orbits, artificial Lagrange point maintenance, and heliostationary condition attainment. In the preliminary mission analysis of an E-sail-based spacecraft, the local physical properties of the solar wind are usually specified and kept constant, while the E-sail propulsive acceleration is assumed to vary with the heliocentric distance, the sail attitude, and the grid electric voltage. However, the solar wind physical properties are known to be characterized by a marked variability, which implies a non-negligible uncertainty as to whether or not the solutions obtained with a deterministic approach are representative of the actual E-sail trajectory. The aim of this paper is to propose an effective method to evaluate the impact of solar wind variability on the E-Sail trajectory design, by considering the solar wind dynamic pressure as a random variable with a gamma distribution. In particular, the effects of plasma property fluctuations on E-sail trajectory are calculated with an uncertainty quantification procedure based on the generalized polynomial chaos method. The paper also proposes a possible control strategy that uses suitable adjustments of grid electric voltage. Numerical simulations demonstrate the importance of such a control system for missions that require a precise modulation of the propulsive acceleration magnitude.
Full-text available
Plasma brake is an innovative propellantless propulsion system concept that exploits the Coulomb collisions between a charged tether and the ions in the surrounding environment (typically, the ionosphere) to generate an electrostatic force orthogonal to the tether direction. Previous studies on the plasma brake effect have emphasized the existence of a number of different parameters necessary to obtain an accurate description of the propulsive acceleration from a physical viewpoint. The aim of this work is to discuss an analytical model capable of estimating, with the accuracy required by a preliminary mission analysis, the performance of a spacecraft equipped with a plasma brake in a (near-circular) low Earth orbit. The simplified mathematical model is first validated through numerical simulations, and is then used to evaluate the plasma brake performance in some typical mission scenarios, in order to quantify the influence of the system parameters on the mission performance index.
Full-text available
The electric solar wind sail (E-sail) is a new type of propellantless propulsion system for Solar System transportation, which uses the natural solar wind for producing spacecraft propulsion. This paper discusses a mass breakdown and a performance model for an E-sail spacecraft that hosts a scientific payload of prescribed mass. In particular, the model is able to estimate the total spacecraft mass and its propulsive acceleration as a function of various design parameters such as the tethers number and their length. A number of subsystem masses are calculated assuming existing or near-term E-sail technology. In light of the obtained performance estimates, an E-sail represents a promising propulsion system for a variety of transportation needs in the Solar System.
Full-text available
This work presents the outline and so far completed design of the Aalto-1 science mission. Aalto-1 is a multi-payload remote sensing nanosatellite, built almost entirely by students. The satellite aims for a 500–900 km sun-synchronous orbit, and includes an accurate attitude dynamics and control unit, a UHF/VHF housekeeping and S-band data links, and a GPS unit for positioning (radio positioning and NORAD TLE's are planned to be used as backups). It has three specific payloads: a spectral imager based on piezo-actuated Fabry–Perot interferometry, designed and built by The Technical Research Center of Finland (VTT); a miniaturized radiation monitor (RADMON) jointly designed and built by Universities of Helsinki and Turku ; and an electrostatic plasma brake designed and built by the Finnish Meteorological Institute (FMI), derived from the concept of the e-sail, also originating from FMI. Two phases are important for the payloads, the technology demonstration and the science phase. Emphasis is placed on technological demonstration of the spectral imager and RADMON, and suitable targets have already been chosen to be completed during that phase, while the plasma brake will start operation in the latter part of the science phase. The technology demonstration will be over in relatively short time, while the science phase is planned to last two years. The science phase is divided into two smaller phases: the science observations phase, during which only the spectral imager and RADMON will be operated for 6–12 months, and the plasma brake demonstration phase, which is dedicated to the plasma brake experiment for at least a year. These smaller phases are necessary due to the drastically different power, communication and attitude requirements of the payloads. The spectral imager will be by far the most demanding instrument on board, as it requires most of the downlink bandwidth, has a high peak power and attitude performance. It will acquire images in a series up to at least 20 spectral bands within the 500–900 nm spectral range, forming the desired spectral data cube product. Shortly before an image is acquired, the parallel visual spectrum camera will take a broader picture for comparison. Also stereoscopic imaging is planned. The amount of data collected by the spectral imager is adjustable, and ranges anywhere from 10 to 500 MB. The RADMON will be on 80% of an orbit period in average and together with housekeeping data will gather around 2 MB of data in 24 h. An operational limitation is formed due to the S-band downlink capability of 29–49 MB per 24 h for a 500 900 km orbit altitude, as only one ground station is planned to be available to the satellite. This will limit both type and quantity of spectral imager images taken during the science phase. The plasma brake will in turn be on within an angle of 20° over the poles for efficient use of the Earth's magnetic field and ionosphere during its spin-up and operation.
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The electric solar wind sail (E-sail) is an innovative propellantless concept for interplanetary space propulsion that uses the natural solar wind as a thrust source with the help of long, artificially charged tethers. The characteristic property of an E-sail based spacecraft is that the propulsive acceleration scales as the inverse Sun-spacecraft distance, and the thrust vector can be varied within about 30 deg away from radial direction. The aim of this paper is to estimate the transfer times required to fulfill a mission toward the near-Earth asteroid 1998 KY26. In doing so the propulsive acceleration of the E-sail, at a reference distance from the Sun, is used as a performance parameter so that the numerical results are applicable to E-sails of different sizes and different payload masses. The paper shows that the flight time scales nearly linearly with the inverse of the spacecraft maximum propulsive acceleration at 1 astronomical unit from the Sun, when the acceleration is greater than 0.3 mm=s 2 . For smaller propulsive accelerations the relationship for the flight time is more involved, because the transfer trajectory is complex and more than one revolution around the Sun is necessary to accomplish the mission. The numerical analysis involves a sample return mission in which the total flight time is parametrically correlated with the starting date for a given E-sail propulsion system.
Full-text available The novel propellantless electric solar wind sail (E-sail) concept promises efficient low thrust transportation in the solar system outside Earth's magnetosphere. Combined with asteroid mining to provide water and synthetic cryogenic rocket fuel in orbits of Earth and Mars, possibilities for affordable continuous manned presence on Mars open up. Orbital fuel and water eliminate the exponential nature of the rocket equation and also enable reusable bidirectional Earth-Mars vehicles for continuous manned presence on Mars. Water can also be used as radiation shielding of the manned compartment, thus reducing the launch mass further. In addition, the presence of fuel in Mars orbit provides the option for an all-propulsive landing, thus potentially eliminating issues of heavy heat shields and augmenting the capability of pinpoint landing. With this E-sail enabled scheme, the recurrent cost of continuous bidirectional traffic between Earth and Mars might ultimately approach the recurrent cost of running the International Space Station, ISS.
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The plasma brake is a thin negatively biased tether which has been proposed as an efficient concept for deorbiting satellites and debris objects from low Earth orbit. We simulate the interaction with the ionospheric plasma ram flow with the plasma brake tether by a high performance electrostatic particle in cell code to evaluate the thrust. The tether is assumed to be perpendicular to the flow. We perform runs for different tether voltage, magnetic field orientation and plasma ion mass. We show that a simple analytical thrust formula reproduces most of the simulation results well. The interaction with the tether and the plasma flow is laminar when the magnetic field is perpendicular to the tether and the flow. If the magnetic field is parallel to the tether, the behaviour is unstable and thrust is reduced by a modest factor. The case when the magnetic field is aligned with the flow can also be unstable, but does not result in notable thrust reduction. We also fix an error in an earlier reference. According to the simulations the predicted thrust of the plasma brake is large enough to make the method promising for satellite deorbiting. As a numerical example we estimate that a 5 km long plasma brake tether weighing 0.055 kg could produce 0.43 mN breaking force which is enough to reduce the orbital altitude of a 260 kg debris mass by 100 km during one year.
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The solar wind electric sail is a novel propellantless space propulsion concept. According to numerical estimates, the electric sail can produce a large total impulse per propulsion system mass. Here we consider using a 0.5 N electric sail for boosting a 550 kg spacecraft to Uranus in less than 6 years. The spacecraft is a stack consisting of the electric sail module which is jettisoned at Saturn distance, a carrier module and a probe for Uranus atmospheric entry. The carrier module has a chemical propulsion ability for orbital corrections and it uses its antenna for picking up the probe's data transmission and later relaying it to Earth. The scientific output of the mission is similar to what the Galileo Probe did at Jupiter. Measurement of the chemical and isotope composition of the Uranian atmosphere can give key constraints for different formation theories of the solar system. A similar method could also be applied to other giant planets and Titan by using a fleet of more or less identical electric sail equipped probes.
Carbon nanotubes were once the poster child for the burgeoning field of nanotechnology, spawning a sense of optimism in the possibilities of engineering materials with unparalleled properties and embedding this excitement in the scientific zeitgeist of the early 1990s. Scientists, engineers, and the growing community of nanotechnologists were all eager to explore the potential of this wonder material in applications ranging from the very small, such as in nanoscale interconnects connecting components of integrated circuits, to the very big, as is the case in the proposed “space elevator” tethering the earth to objects in geostationary orbit. In the intervening years, much work has been published in the scientific literature on these nanomaterials, documenting the developments and prophesizing their prospective uses in all manner of industries. In the domain of energy sustainability, perhaps the most significant impact that carbon nanotubes might have is in power transmission, in the form of devices such as power transmission wires and cables. This chapter will delve into the recent progress in the fabrication techniques, upscaling these nanoscale building blocks into the macroscale where the properties can be exploited in engineering applications. Additionally, this chapter will give the reader an appreciation of the efforts to apply these wires and cables in different contexts, ranging from simple power transmission to energy conversion and storage devices such as capacitors. Finally, a broad industrial perspective on the challenges remaining to be addressed before this technology can reach maturity will be provided, and the possible routes forward will be discussed.
The electric solar wind sail (E-sail) is a space propulsion concept that uses the natural solar wind dynamic pressure for producing spacecraft thrust. In its baseline form, the E-sail consists of a number of long, thin, conducting, and centrifugally stretched tethers, which are kept in a high positive potential by an onboard electron gun. The concept gains its efficiency from the fact that the effective sail area, i.e., the potential structure of the tethers, can be millions of times larger than the physical area of the thin tethers wires, which offsets the fact that the dynamic pressure of the solar wind is very weak. Indeed, according to the most recent published estimates, an E-sail of 1 N thrust and 100 kg mass could be built in the rather near future, providing a revolutionary level of propulsive performance (specific acceleration) for travel in the solar system. Here we give a review of the ongoing technical development work of the E-sail, covering tether construction, overall mechanical design alternatives, guidance and navigation strategies, and dynamical and orbital simulations.
The recent successes of the European Rosetta mission have shown the possibility of a close observation with one of the most evasive celestial bodies in the Solar System, the comets, and the practical feasibility of a comet rendezvous to obtain detailed information and in situ measurements. This paper discusses a preliminary study of the transfer trajectory toward the comet 67P/Churyumov-Gerasimenko (the same target used by Rosetta) for a spacecraft whose primary propulsion system is an electric solar wind sail. The use of a propellantless propulsion system with a continuous thrust is theoretically able to simplify the transfer trajectory by avoiding the need of intermediate flyby maneuvers. The problem is addressed in a parametric way, by looking for the possible optimal launch windows as a function of the propulsion system performance. The study is completed by a mass breakdown analysis of the spacecraft, for some mission scenarios of practical interest, based on the actual payload mass of the spacecraft Rosetta.