Electric sail
Encyclopedia
An Electric sail is a proposed form of spacecraft propulsion
using the dynamic pressure of the solar wind
as a source of thrust. It uses an electric field
for deflecting solar wind protons and extracting momentum from them. It was invented by Pekka Janhunen from Finland in 2006 at the FMI
and creates a "virtual" sail by forming an electric field on small wires.http://www.wipo.int/pctdb/en/wo.jsp?WO=2007099201. To test the technology a new European Union
-backed electric sail study project is underway.http://www.popsci.com/technology/article/2010-12/eu-backed-electric-sail-could-be-fastest-man-made-device-ever-built The EU funding contribution is 1.7 million euros and its goal is to build the laboratory prototypes of the key components of the electric sail. The research project called E-Sail involves five European countries and will last for three years. In the EU evaluation, the ESAIL project got the highest marks in its category.http://www.electric-sailing.fi/ The electric solar wind sail could enable faster and cheaper access to the solar system and in the longer run may enable an economic utilisation of asteroid resources.http://www.physorg.com/news/2010-12-eu-electric-solar.html The working principles of the electric sail will be tested in the coming years on the Estonia
n ESTCube-1 and the Finnish Aalto-1
nanosatellites.http://en.ilmatieteenlaitos.fi/press-release/121643
which are kept in a high positive potential by an onboard electron gun
. The positively charged tethers repel solar wind protons, thus deflecting their paths and extracting momentum from them. Simultaneously they also attract electron from the solar wind plasma. The arriving electron current is compensated by the electron gun. A way to deploy the tethers is to rotate the spacecraft and have the centrifugal force
keep them stretched. By fine-tuning the potentials of individual tethers and thus the solar wind force individually, the attitude of the spacecraft can be controlled.
flows and magnetic field
s. While modest variation of the thrust direction can be achieved by inclining the sail, the thrust vector always points more or less radially outward from the Sun
. It has been estimated that maximum operational inclination would be 60°, resulting in a thrusting angle of 30° from the outward radial direction http://www.electric-sailing.fi.
around the host ship. The wires are electrically charged and thus an electric field
is created around the wires. The electric field of the wires extends a few dozen metres into the surrounding solar wind plasma.
Because the solar wind electrons react on the electric field (similarly to the photons on a traditional solar sail), the functional radius of the wires is based on the electric field that is generated around the wire rather than the actual wire itself. This fact also makes it possible to maneuver a ship with an electric solar wind sail by regulating the electric charge of the wires. A full-sized operational electric solar wind sail would have 50-100 straightened wires with a length of about 20 km each.
Spacecraft propulsion
Spacecraft propulsion is any method used to accelerate spacecraft and artificial satellites. There are many different methods. Each method has drawbacks and advantages, and spacecraft propulsion is an active area of research. However, most spacecraft today are propelled by forcing a gas from the...
using the dynamic pressure of the solar wind
Solar wind
The solar wind is a stream of charged particles ejected from the upper atmosphere of the Sun. It mostly consists of electrons and protons with energies usually between 1.5 and 10 keV. The stream of particles varies in temperature and speed over time...
as a source of thrust. It uses an electric field
Electric field
In physics, an electric field surrounds electrically charged particles and time-varying magnetic fields. The electric field depicts the force exerted on other electrically charged objects by the electrically charged particle the field is surrounding...
for deflecting solar wind protons and extracting momentum from them. It was invented by Pekka Janhunen from Finland in 2006 at the FMI
Finnish Meteorological Institute
The Finnish Meteorological Institute is the government agency responsible for gathering and reporting weather data and forecasts in Finland. It is a part of the Ministry of Transport and Communications but it operates semi-autonomously....
and creates a "virtual" sail by forming an electric field on small wires.http://www.wipo.int/pctdb/en/wo.jsp?WO=2007099201. To test the technology a new European Union
European Union
The European Union is an economic and political union of 27 independent member states which are located primarily in Europe. The EU traces its origins from the European Coal and Steel Community and the European Economic Community , formed by six countries in 1958...
-backed electric sail study project is underway.http://www.popsci.com/technology/article/2010-12/eu-backed-electric-sail-could-be-fastest-man-made-device-ever-built The EU funding contribution is 1.7 million euros and its goal is to build the laboratory prototypes of the key components of the electric sail. The research project called E-Sail involves five European countries and will last for three years. In the EU evaluation, the ESAIL project got the highest marks in its category.http://www.electric-sailing.fi/ The electric solar wind sail could enable faster and cheaper access to the solar system and in the longer run may enable an economic utilisation of asteroid resources.http://www.physorg.com/news/2010-12-eu-electric-solar.html The working principles of the electric sail will be tested in the coming years on the Estonia
Estonia
Estonia , officially the Republic of Estonia , is a state in the Baltic region of Northern Europe. It is bordered to the north by the Gulf of Finland, to the west by the Baltic Sea, to the south by Latvia , and to the east by Lake Peipsi and the Russian Federation . Across the Baltic Sea lies...
n ESTCube-1 and the Finnish Aalto-1
Aalto-1
Aalto-1 is a student-built nanosatellite, created by Aalto University, Finland. Based on the CubeSat architecture, it is scheduled to be launched in 2013, and will become Finland's first indigenous satellite. The solar-powered satellite will weigh approximately , and will carry a miniature...
nanosatellites.http://en.ilmatieteenlaitos.fi/press-release/121643
Principles of operation and design
The electric sail consists of a number of thin, long and conducting tethersElectrodynamic tether
Electrodynamic tethers are long conducting wires, such as one deployed from a tether satellite, which can operate on electromagnetic principles as generators, by converting their kinetic energy to electrical energy, or as motors, converting electrical energy to kinetic energy...
which are kept in a high positive potential by an onboard electron gun
Electron gun
An electron gun is an electrical component that produces an electron beam that has a precise kinetic energy and is most often used in television sets and computer displays which use cathode ray tube technology, as well as in other instruments, such as electron microscopes and particle...
. The positively charged tethers repel solar wind protons, thus deflecting their paths and extracting momentum from them. Simultaneously they also attract electron from the solar wind plasma. The arriving electron current is compensated by the electron gun. A way to deploy the tethers is to rotate the spacecraft and have the centrifugal force
Centrifugal force
Centrifugal force can generally be any force directed outward relative to some origin. More particularly, in classical mechanics, the centrifugal force is an outward force which arises when describing the motion of objects in a rotating reference frame...
keep them stretched. By fine-tuning the potentials of individual tethers and thus the solar wind force individually, the attitude of the spacecraft can be controlled.
Intrinsic limitations
The electric sail probably cannot be used inside planetary magnetospheres because there is no solar wind there, only slower plasmaPlasma (physics)
In physics and chemistry, plasma is a state of matter similar to gas in which a certain portion of the particles are ionized. Heating a gas may ionize its molecules or atoms , thus turning it into a plasma, which contains charged particles: positive ions and negative electrons or ions...
flows and magnetic field
Magnetic field
A magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field.Technically, a magnetic field is a pseudo vector;...
s. While modest variation of the thrust direction can be achieved by inclining the sail, the thrust vector always points more or less radially outward from the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
. It has been estimated that maximum operational inclination would be 60°, resulting in a thrusting angle of 30° from the outward radial direction http://www.electric-sailing.fi.
Electric solar wind sail
The electric solar wind sail has little in common with the traditional solar sail. First of all the E-Sail gets its momentum from the solar wind ions, whilst photonic sail is propelled by photons. In E-Sail, the part of the sails is played by straigthened conducting tethers (wires) which are placed radiallyRadius
In classical geometry, a radius of a circle or sphere is any line segment from its center to its perimeter. By extension, the radius of a circle or sphere is the length of any such segment, which is half the diameter. If the object does not have an obvious center, the term may refer to its...
around the host ship. The wires are electrically charged and thus an electric field
Electric field
In physics, an electric field surrounds electrically charged particles and time-varying magnetic fields. The electric field depicts the force exerted on other electrically charged objects by the electrically charged particle the field is surrounding...
is created around the wires. The electric field of the wires extends a few dozen metres into the surrounding solar wind plasma.
Because the solar wind electrons react on the electric field (similarly to the photons on a traditional solar sail), the functional radius of the wires is based on the electric field that is generated around the wire rather than the actual wire itself. This fact also makes it possible to maneuver a ship with an electric solar wind sail by regulating the electric charge of the wires. A full-sized operational electric solar wind sail would have 50-100 straightened wires with a length of about 20 km each.
Applications
- Fast mission (>50 km/s or 10 AUAstronomical unitAn astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....
/year) out of the Solar systemSolar SystemThe Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...
and heliosphereHeliosphereThe heliosphere is a bubble in space "blown" into the interstellar medium by the solar wind. Although electrically neutral atoms from interstellar volume can penetrate this bubble, virtually all of the material in the heliosphere emanates from the Sun itself...
for small or modest payload - As a brake for small interstellar probeInterstellar probeAn interstellar probe is a space probe that has left—or is expected to leave—the Solar System and enter interstellar space, typically defined as the region beyond the heliopause...
which has been accelerated to high speed by some other means such as laser lightsailBeam-powered propulsionBeam-powered propulsion is a class of aircraft or spacecraft propulsion mechanisms that use energy beamed to the spacecraft from a remote power plant to provide energy... - Inward-spiralling mission to study the Sun at closer distance
- Two-way mission to inner Solar System objects such as asteroids
- Off-Lagrange point solar wind monitoring spacecraft for predicting space weatherSpace weatherSpace weather is the concept of changing environmental conditions in near-Earth space or thespace from the Sun's atmosphere to the Earth's atmosphere. It is distinct from the concept ofweather within the Earth's planetary atmosphere...
with longer warning time than 1 hour