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field emission electric propulsion wikipedia jump to content main menu main menu move to sidebar hide navigation main page contents current events random article about wikipedia contact us contribute help learn to edit community portal recent changes upload file special pages search search appearance donate create account log in personal tools donate create account log in contents move to sidebar hide top 1 basic concept 2 liquid metal propellants 3 slit emitter 4 other designs 5 references 6 external links toggle the table of contents field emission electric propulsion 3 languages العربية bahasa indonesia italiano edit links article talk english read edit view history tools tools move to sidebar hide actions read edit view history general what links here related changes upload file permanent link page information cite this page get shortened url switch to legacy parser print export download as pdf printable version in other projects wikidata item appearance move to sidebar hide from wikipedia the free encyclopedia type of electric spacecraft propulsion system this article needs more citations please help improve this article by adding citations to reliable sources unsourced material may be challenged and removed find sources field emission electric propulsion news newspapers books scholar jstor june 2018 learn how and when to remove this message field emission electric propulsion feep is an advanced electrostatic space propulsion concept a form of ion thruster that uses a liquid metal as a propellant usually either caesium indium or mercury 1 a feep device consists of an emitter and an accelerator electrode a potential difference of the order of 10 kv is applied between the two which generates a strong electric field at the tip of the metal surface the interplay of electric force and the liquid metal s surface tension generates surface instabilities which give rise to taylor cones on the liquid surface 2 at sufficiently high values of the applied field ions are extracted from the cone tip by field evaporation or similar mechanisms which then are electrically accelerated to high velocities typically 100 km s or more although the ion exhaust velocity is high their mass is very low resulting in very weak acceleration forces their benefit comes from sustained acceleration forces over long time periods 3 due to its very low thrust in the micronewton μn to millinewton mn range feep thrusters are primarily used for microradian micronewton attitude control on spacecraft such as in the esa nasa lisa pathfinder scientific spacecraft the feep thruster was also slated for installation on gravity field and steady state ocean circulation explorer spacecraft 4 but the gridded ion thruster was used instead 5 the first feep thruster operated in space was the ifm nano thruster successfully commissioned in low earth orbit in 2018 6 basic concept edit field emission electric propulsion feep is an electrostatic propulsion method based on field ionization of a liquid metal and subsequent acceleration of the ions by a strong electric field sharp features such as needles are used to enhance and concentrate the strength of this electric field the needle is coated in the liquid metal maximising the acceleration of the ions 7 feep is currently the object of interest in the scientific community due to its unique features sub μn to mn thrust range near instantaneous switch on switch off capability and high resolution throttleability better than one part in 10 4 which enables accurate thrust modulation in both continuous and pulsed modes 8 presently baseline for scientific missions onboard drag free satellites this propulsion system has also been proposed for attitude control and orbit maintenance on commercial small satellites and constellations a separate electron source is required to keep the spacecraft electrically neutral liquid metal propellants edit this type of thruster can accelerate a large number of different liquid metals or alloys the best performance in terms of thrust efficiency and power to thrust ratio can be obtained using high atomic weight alkali metals such as cesium cs 133 amu and rubidium rb 85 5 amu these propellants have a low ionization potential 3 87 ev for cs and 4 16 ev for rb low melting point 28 7 c for cs and 38 9 c for rb and very good wetting capabilities 9 these features lead to low power losses due to ionization and heating and the capability to use capillary forces for feeding purposes i e neither pressurised tanks nor valves are required moreover alkali metals have the lowest attitude to form ionized droplets or multiply charged ions thus leading to the best attainable mass efficiency the actual thrust is produced by exhausting a beam consisting mainly of singly ionized cesium or rubidium atoms produced by field evaporation at the tip of the emitter an accelerating electrode accelerator is placed directly in front of the emitter this electrode consists of a metal usually stainless steel plate where two sharp blades are machined when thrust is required a strong electric field is generated by the application of a high voltage difference between the emitter and the accelerator under this condition the free surface of the liquid metal enters a regime of local instability due to the combined effects of the electrostatic force and the surface tension a series of protruding cusps or taylor cones are thus created when the electric field reaches a value in the order of 10 9 v m the atoms at the tip of the cusps spontaneously ionize and an ion jet is extracted by the electric field while the electrons are rejected in the bulk of the liquid an external source of electrons neutralizer provides negative charges to maintain global electrical neutrality of the thruster assembly slit emitter edit liquid metal ion sources lmis based on field ionization or field evaporation were introduced in the late 60s and quickly became widespread as simple cheap ion sources for a number of applications and in 1972 the european space agency started development on an electric propulsion system based on the field emission principle using liquid metal ion sources 10 the use of lmis operated on gallium indium alkali metals or alloys has also been standard practice in secondary ion mass spectrometry sims since the 1970s while there exist different field emitter configurations such as the needle the capillary and slit emitter types the principle of operation is the same in all cases in the slit emitter for example a liquid metal propellant is fed by capillary forces through a narrow channel the emitter consists of two identical halves made from stainless steel and clamped or screwed together 11 a nickel layer sputter deposited onto one of the emitter halves outlines the desired channel contour and determines channel height a k a slit height typically 1 2 μm and channel width a k a slit length which ranges from 1 mm up to about 7 cm 11 the channel ends at the emitter tip formed by sharp edges that are located opposite a negative or accelerator electrode and separated by a small gap about 0 6 mm from the emitter tip an extraction voltage is applied between the two electrodes the emitter carries a positive potential while the accelerator is at negative potential the electric field being generated between the emitter and accelerator now acts on the liquid metal propellant the narrow slit width not only enables the capillary feed but when combined with the sharp channel edges directly opposite the accelerator also ensures that a high electric field strength is obtained near the slit exit the liquid metal column when subjected to this electric field begins to deform forming cusps taylor cones which protrude from the surface of the liquid as the liquid cusps form ever sharper cones due to the action of the electric field the local electric field strength near these cusps intensifies once a local electric field strength of about 10 9 v m is reached electrons are ripped off the metal atoms these electrons are collected through the liquid metal column by the channel walls and the positive ions are accelerated away from the liquid through a gap in the negative accelerator electrode by the same electric field that created them slit emitters had been developed to increase the emitting area of the thruster in order to yield higher thrust levels and to avoid the irregular behaviour observed for single emitters the substantial advantage of slit emitters over stacked needles is in the self adjusting mechanism governing the formation and redistribution of emission sites on the liquid metal surface according to the operating parameters in a stacked needle array on the contrary the taylor cones can only exist on the fixed tips which pre configure a geometrical arrangement that can only be consistent with one particular operating condition other designs edit slit emitters with a wide variety of slit widths have been fabricated currently devices with slit widths between 2 mm and 7 cm are available these devices spanning a thrust range from 0 1 μn to 2 mn are operated with cesium or rubidium the miniaturized feep module design with a crown shape emitter to fit into the standard cubesat chassis was reported in 2017 the single emitter feep design of 0 5 mn is commercially available 12 and its arrayed version development is nearing completion as in 2018 13 references edit massotti l 2021 the next generation gravity mission and the qualification of the indium fed mn feep thruster ceas space journal p 2 basu sourav 2010 an analytical review on electric propulsion system for space satellites incas p 7 defelice david 7 december 2004 nasa ion propulsion farther faster cheaper www nasa gov archived from the original on 11 november 2020 retrieved 3 february 2023 feep feasibility report pdf european space agency esa report archived from the original pdf on 14 march 2004 retrieved 26 september 2018 gravity field and steady state ocean circulation explorer goce pdf european space agency esa archived from the original pdf on 14 march 2004 retrieved 26 september 2018 krejci david demonstration of the ifm nano feep thruster in low earth orbit researchgate report retrieved 27 march 2019 massotti l 2021 the next generation gravity mission and the qualification of the indium fed mn feep thruster ceas space journal p 7 marcuccio s genovese a andrenucci m september october 1998 experimental performance of field emission microthrusters pdf journal of propulsion and power 14 5 774 781 doi 10 2514 2 5340 archived from the original pdf on 20 may 2013 kramida a ralchenko yu reader j and nist asd team 5 february 2023 nist atomic spectra database ver 5 10 online nist atomic spectra database retrieved 5 february 2023 mitterauer j 1987 liquid metal ion soutces as thrusters for electric space propulsion journal de physique colloques p 173 1 2 mitterauer j 1987 liquid metal ion soutces as thrusters for electric space propulsion journal de physique colloques p 172 ifm nano thruster for cubesats 30 000 cubesat shop ifm 350 nano thruster iod european space agency esa external links edit feep field emission electric propulsion alta spa archived from the original on 7 july 2011 feep thrusters nonequilibrium gas and plasma dynamics group university of michigan archived from the original on 21 february 2009 v t e spacecraft propulsion concepts rocket rocket engine reaction engine reaction mass thrust specific impulse delta v staging rocket equation propellantless propulsion physical propulsion cold gas thruster thermal rocket water rocket steam rocket solar sail diffractive electric sail magnetic sail solar thermal rocket photon rocket wine chemical propulsion state liquid propellant rocket solid propellant rocket hybrid propellant rocket propellants liquid propellant cryogenic hypergolic monopropellant bipropellant tripropellant power cycles staged combustion cycle expander cycle gas generator cycle tap off cycle intake mechanisms pressure fed engine pump fed engine electric pump fed engine electrical propulsion electrostatic colloid thruster ion thruster gridded hall effect thruster field emission electric propulsion electromagnetic pulsed inductive thruster magnetoplasmadynamic thruster electrodeless plasma thruster plasma magnet electrothermal pulsed plasma thruster vacuum arc thruster helicon double layer thruster arcjet rocket resistojet rocket microwave electrothermal thruster vasimr other atmosphere breathing electric propulsion high power electric propulsion magbeam mass driver nuclear propulsion closed system direct fusion drive nuclear electric rocket nuclear thermal rocket radioisotope salt water gas core lightbulb nuclear photonic rocket open system nuclear pulse propulsion antimatter catalyzed pulsed nuclear thermal rocket fusion rocket bussard ramjet fission fragment rocket fission sail external power beam powered propulsion laser propulsion tethers related concepts aerobraking aerocapture aerogravity assist alcubierre drive atmospheric entry gravity assist non rocket spacelaunch oberth effect orbital mechanics orbital maneuver reactionless drive space launch warp drive spaceflight portal retrieved from https en wikipedia org w index php title field emission_electric_propulsion oldid 1298410750 category ion engines hidden categories articles with short description short description matches wikidata articles needing additional references from june 2018 all articles needing additional references use dmy dates from august 2020 this page was last edited on 2 july 2025 at 09 25 utc page was rendered with parsoid text is available under the creative commons attribution sharealike 4 0 license additional terms may apply by using this site you agree to the terms of use and privacy policy wikipedia is a registered trademark of the wikimedia foundation inc a non profit organization privacy policy about wikipedia disclaimers contact wikipedia legal safety contacts code of conduct 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