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The electric solar wind sail transforms the momentum of the solar wind into an acceleration of the spacecraft. Figure courtesy of Alessandro Quarta.
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The electric solar wind sail (E-Sail) is a new propulsion method for interplanetary travel which was invented in 2006 and is currently under development. The E-Sail uses charged tethers to extract momentum from the solar wind particles to obtain propulsive thrust. According to current estimates, the E-Sail is 2-3 orders of magnitude better than tra...
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... onboard electron gun, typically of few hundred watts of power, is used to keep the spacecraft and the wires in a high (typically 20 kV) positive potential. Figure 1 illustrates the E-Sail concept. The modest amount of electric power required to operate the electron gun is typ- ically created by solar panels. ...
Citations
... By modulating the tether voltages synchronistically with the sail rotation, the sail attitude with respect to the sun can be controlled [9,10]. There are several mission analyses that have been performed based on E-sail propulsion: non-Keplerian orbits [11]; electric sail mission analysis for outer solar system exploration [12]; electric sail missions to potentially hazardous asteroids [13]; moving an asteroid with an electric solar wind sail [14]; electric sail for a near-Earth asteroid sample return mission for the case of 1998 KY26 [15]; electric sailing for cometary rendezvous [16]; and nanospacecraft fleets for multi-asteroid touring with electric solar wind sails [17]. ...
A new method of producing robust multi-wire tethers for Coulomb drag applications was developed. The multi-wire structure required for redundancy against the micrometeoroid flux of the space environment is realised through the method of wire twist bonding traditionally used for chicken wire. In the case of the Coulomb drag tether, the diameter of the individual wires is 50 μm, which introduces the main technological challenge. To manufacture the tether, a manually driven tether machine was designed and built. Two multi-wire tethers for Coulomb drag applications were produced for two in-orbit demonstrations of the FORESAIL-1 and ESTCube-2 CubeSat missions. The flight tethers were both 60 m long as produced, clearly demonstrating beyond the level of proof of concept the applicability of both the method and the manually driven tether machine. Altogether, 6480 twist bonds were produced without a single wire cut. In this paper, the requirements for the tether are listed and justified. The production method is reviewed, and the 4-wire tether produced is evaluated against the requirements. Finally, the test procedures of the tether are described, and on the basis of the results, it is concluded that the tether can tolerate a tension of 14 g without the twist bonds slipping or the tether structure collectively collapsing. Furthermore, the tether can be reeled from the production reel to the flight reel, which simplifies the final integration of the tether reeling system with the Coulomb drag propulsion device.
... Other innovative mission scenarios that could be performed by an E-sail include the maintenance of displaced non-Keplerian orbits [10], the generation of artificial equilibrium points in the restricted three-body problem [11], and the asteroid deflection by means of a kinetic impactor [12,13]. Finally, an E-sail could also be exploited for deep space transfers towards planets [14,15], comets [16], asteroids [17], or other targets in the Solar System [18]. ...
The transfer between two coplanar Keplerian orbits of a spacecraft with a continuous-thrust propulsion system is a classical problem of astrodynamics, in which a numerical procedure is usually employed to find the transfer trajectory that optimizes (i.e., maximizes or minimizes) a given performance index such as, for example, the delivered payload mass, the propellant mass, the total flight time, or a suitable combination of them. In the last decade, this class of problem has been thoroughly analyzed in the context of heliocentric mission scenarios of a spacecraft equipped with an Electric Solar Wind Sail as primary propulsion system. The aim of this paper is to further extend the existing related literature by analyzing the optimal transfer of an Electric Solar Wind Sail-based spacecraft with a Sun-facing attitude, a particular configuration in which the sail nominal plane is perpendicular to the Sun-spacecraft (i.e., radial) direction, so that the propulsion system is able to produce its maximum propulsive acceleration magnitude. The problem consists in transferring the spacecraft, which initially traces a heliocentric circular orbit, into an elliptic coplanar orbit of given eccentricity with a minimum-time trajectory. Using a classical indirect approach for trajectory optimization, the paper shows that a simplified version of the optimal control problem can be obtained by enforcing the typical transfer constraints. The numerical simulations show that the proposed approach is able to quantify the transfer performance in a parametric and general form, with a simple and efficient algorithm.
... The peculiarity of the E-sail makes it appealing for various mission scenarios [1][2][3][4][5][6][7][8][9][10][11], such as the outer solar system exploration [12], asteroid flyby [13], cometary rendezvous [14], and asteroid tug [15] since in theory it could reduce the cost of space travel. The most prominent configuration of E-sail consists of a spinning central spacecraft connected by positively charged tethers (main tethers) with remote units at their tips as shown in Fig. 1(a). ...
This paper investigates the spin rate bounds, the configuration stability subject to the solar wind fluctuations, and sail angle control of an electric solar wind sail (E-sail) by a high-fidelity tether dynamic model. This model describes the elastic deformation of tethers with inter-connected 2-noded tensile elements discretized by the nodal position finite element method. The E-sail is assumed to be an axisymmetric system spinning in the plane normal to the heliocentric ecliptic plane. The upper and lower spin rate bounds are revisited to reveal the physics that dictates these bounds and analytic expressions are provided to ensure the proper operation of E-sail. Then, the influences of the solar wind fluctuations on the configuration stability of the E-sail are investigated by parametric analysis with different E-sail configurations, sail angles, and spin rates. Finally, an alternative sail angle control strategy for the E-sail is proposed by applying control force at the remote units with a simple PD control. Numerical analysis demonstrates that the sail angle of E-sail can be controlled quickly by the control law at the remote units with a high-precision.
... An interplanetary spacecraft would require an electron emitter to keep the tether's bias positive in order to operate in the solarwind environment. While complex multi-tethered concepts have been discussed in the past [61][62][63], covering missions to non-Keplerian orbits as well as inner-and outer-Solar-system rendezvous and flybys, the latest study shows the feasibility of a fleet of autonomous nanospacecraft to reach the main asteroid belt and return to Earth's vicinity with a single 20-km tether in 3.2 years [41]. Analyses show that cubesat-esque nanospacecraft could indeed perform surface and trajectory reconstructions as well as provide spectral information on asteroids with shape reconstruction possible during a 300-km flyby [42]. ...
This paper presents two technology experiments – the plasma brake for deorbiting and the electric solar wind sail for interplanetary propulsion – on board the ESTCube-2 and FORESAIL-1 satellites. Since both technologies employ the Coulomb interaction between a charged tether and a plasma flow, they are commonly referred to as Coulomb drag propulsion. The plasma brake operates in the ionosphere, where a negatively charged tether deorbits a satellite. The electric sail operates in the solar wind, where a positively charged tether propels a spacecraft, while an electron emitter removes trapped electrons. Both satellites will be launched in low Earth orbit carrying nearly identical Coulomb drag propulsion experiments, with the main difference being that ESTCube-2 has an electron emitter and it can operate in the positive mode. While solar-wind sailing is not possible in low Earth orbit, ESTCube-2 will space-qualify the components necessary for future electric sail experiments in its authentic environment. The plasma brake can be used on a range of satellite mass classes and orbits. On nanosatellites, the plasma brake is an enabler of deorbiting – a 300-m-long tether fits within half a cubesat unit, and, when charged with 1 kV, can deorbit a 4.5-kg satellite from between a 700- and 500-km altitude in approximately 9–13 months. This paper provides the design and detailed analysis of low-Earth-orbit experiments, as well as the overall mission design of ESTCube-2 and FORESAIL-1.
... These were rendezvous to potentially hazardous asteroids [14], sample return missions from an asteroid [15], and flyby missions [16]. Even in a planetary defense field, the Esail is an attractive system for kinetic impactors [17] tractors [18] to deflect an asteroid with an unacceptable Earth collision risk. Moreover, since a feasibility study showed that the E-sail can accelerate a spacecraft effectively, the NASA Marshall Space Flight Center studied the E-sail for a rapid heliopause mission. 1 To investigate the capability of the E-sail, a solar wind force model was developed. ...
The electric solar wind sail is a propulsion system that extracts the solar wind momentum for the thrust force of a spacecraft by using an interaction between solar wind protons and the electric potential structure around charged long thin conducting tethers. The system enables a spacecraft to generate a thrust force without consuming
reaction mass. This paper investigates the capability of the electric solar wind sail as a propulsion system for deep space exploration missions. The shape of the conducting tether that is determined by the equilibrium of the solar wind force and centrifugal force is numerically calculated for formulating an advanced solar wind force
model. The conducting tethers deviate from the ideal sail spin plane, and the maximum value of the thrust direction varies from 13∘ to 19∘. To estimate the spacecraft thrust vector, which is calculated as the sum of solar wind force vectors exerted on each tether, best-fit polynomial equations are proposed. We performed numerical simulations for a two-dimensional orbital transfer mission to investigate the capability of the electric solar wind sail. Results of numerical simulations show that the electric solar wind sail enables spacecraft to perform Earth-Venus, Earth-Mars, and Earth-Itokawa transfer missions. Additionally, this paper performs three-dimensional
simulations for an Earth–Ryugu transfer mission. The electric solar wind sail achieves a more complicated orbital transfer in a reasonable mission time.
... If planetary swing-bys are planned during the mission, each solar eclipse has to be carefully considered to avoid drastic thermal contraction and expansion of the sail tethers [10]. In addition to scientific missions, the electric sail can be used for planetary defense as a gravity tractor [11] or an impactor [12] and to rendezvous with such Potentially Hazardous Objects that cannot be reached by conventional propulsion systems [13]. The electric sail has also been suggested as a key method of transportation for products of asteroid mining [14]. ...
The shape of a rotating electric solar wind sail under the centrifugal force and solar wind dynamic pressure is modeled to address the sail attitude maintenance and thrust vectoring. The sail rig assumes centrifugally stretched main tethers that extend radially outward from the spacecraft in the sail spin plane. Furthermore, the tips of the main tethers host remote units that are connected by auxiliary tethers at the sail rim. Here, we derive the equation of main tether shape and present both a numerical solution and an analytical approximation for the shape as parametrized both by the ratio of the electric sail force to the centrifugal force and the sail orientation with respect to the solar wind direction. The resulting shape is such that near the spacecraft, the roots of the main tethers form a cone, whereas towards the rim, this coning is flattened by the centrifugal force, and the sail is coplanar with the sail spin plane. Our approximation for the sail shape is parametrized only by the tether root coning angle and the main tether length. Using the approximate shape, we obtain the torque and thrust of the electric sail force applied to the sail. As a result, the amplitude of the tether voltage modulation required for the maintenance of the sail attitude is given as a torque-free solution. The amplitude is smaller than that previously obtained for a rigid single tether resembling a spherical pendulum. This implies that less thrusting margin is required for the maintenance of the sail attitude. For a given voltage modulation, the thrust vectoring is then considered in terms of the radial and transverse thrust components.
... An interplanetary spacecraft would require an electron emitter to keep the tether's bias positive in order to operate in the solarwind environment. While complex multi-tethered concepts have been discussed in the past [61][62][63], covering missions to non-Keplerian orbits as well as inner-and outer-Solar-system rendezvous and flybys, the latest study shows the feasibility of a fleet of autonomous nanospacecraft to reach the main asteroid belt and return to Earth's vicinity with a single 20-km tether in 3.2 years [41]. Analyses show that cubesat-esque nanospacecraft could indeed perform surface and trajectory reconstructions as well as provide spectral information on asteroids with shape reconstruction possible during a 300-km flyby [42]. ...
This paper is republished in Acta Astronautica as "Coulomb drag propulsion experiments of ESTCube-2 and FORESAIL-1": https://www.researchgate.net/publication/337626758_Coulomb_drag_propulsion_experiments_of_ESTCube-2_and_FORESAIL-1 // Here we present the preliminary mission design for the ESTCube-2 three-unit CubeSat. Its main mission is to test Coulomb drag propulsion. Coulomb drag can be used in Low-Earth Orbit by deploying and charging a tether that is used to brake the orbital velocity of the satellite and reduce its orbital altitude. To test this concept, ESTCube-2 will deploy and charge a 300 m tether. Such a tether could deorbit ESTCube-2 from the altitude of 700 km to 500 km in half a year.
Other payloads that are being considered for the ESTCube-2 satellite are an Earth observation camera, a C-band communications system and an experimental laser communication system.
ESTCube-2 in-orbit demonstration platform will also be designed for other electric solar wind sail experiments outside of the influence of Earth’s magnetic field. The satellite bus will be integrated into one system that could also be reused for different types of missions. The integrated system is developed to maximise the space for payloads on a nanosatellite. This paper presents the payloads and system design of ESTCube-2.
... Applications of the E-sail have been extensively researched [12], outlining for example outer planet exploration [13][14][15], asteroid flyby [16], asteroid rendezvous [17], NEO sample return [18], and hazardous asteroid deflection [19]. ...
http://www.sciencedirect.com/science/article/pii/S0094576515001290
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.
... Given the baseline of 1 N thrust of a full scale sail [8], several types of missions have been suggested and analyzed [9], [5]. These include outer solar system exploration [11], missions in non-Keplerian orbits [10], asteroid missions [12], [13], and protection from hazardous asteroids [13], [14]. Many of these missions require accurate navigation to the target in variable solar wind conditions [15]. ...
... where ν a is the angular average of the angular frequency (<φ >). Furthermore, substituting Eq. (14) in Eq. (1), averaging over the rotation phase (Λ = 0), and using Eqs. (13) and (15), we write To calculate the thrust, the spherical components of the acceleration of Eqs. ...
The electric solar wind sail produces thrust by centrifugally spanned high
voltage tethers interacting with the solar wind protons. The sail attitude can
be controlled and attitude maneuvers are possible by tether voltage modulation
synchronous with the sail rotation. Especially, the sail can be inclined with
respect to the solar wind direction to obtain transverse thrust to change the
osculating orbit angular momentum. Such an inclination has to be maintained by
a continual control voltage modulation. Consequently, the tether voltage
available for the thrust is less than the maximum voltage provided by the power
system. Using a spherical pendulum as a model for a single rotating tether, we
derive analytical estimations for the control efficiency for two separate sail
control modes. One is a continuous control modulation that corresponds to
strictly planar tether tip motion. The other is an on-off modulation with the
tether tip moving along a closed loop on a saddle surface. The novel on-off
mode is introduced here to both amplify the transverse thrust and reduce the
power consumption. During the rotation cycle, the maximum voltage is applied to
the tether only over two thrusting arcs when most of the transverse thrust is
produced. In addition to the transverse thrust, we obtain the thrusting angle
and electric power consumption for the two control modes. It is concluded that
while the thrusting angle is about half of the sail inclination for the
continuous modulation it approximately equals to the inclination angle for the
on-off modulation. The efficiency of the on-off mode is emphasized when power
consumption is considered, and the on-off mode can be used to improve the
propulsive acceleration through the reduced power system mass.
... According to numerical performance estimates [3], the E-sail has a high ratio of produced total impulse per propulsion system mass. The E-sail can be used for many solar system propulsive tasks, including inner planets [4], asteroid rendezvous and sample return missions [5,6], asteroid deflection [7], various continuous thrust non-Keplerian orbits [8] and flyby and orbiter missions to outer planets [9,10]. ...
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.
