Editing Gridded ion thruster

{{Short description|Space propulsion system}}
{{redirect|XIPS|the singular of XIPs|XIP (disambiguation)}}
[[Image:Electrostatic ion thruster-en.svg|thumb|right]]

The '''gridded ion thruster''' is a common design for [[ion thruster]]s, a highly efficient low-thrust [[spacecraft propulsion]] method running on electrical power by using high-voltage grid [[electrode]]s to accelerate [[ion]]s with [[electrostatic]] forces.

==History==
The ion engine was first demonstrated by German-born [[NASA]]  scientist [[Ernst Stuhlinger]],<ref>Ernst Stuhlinger, ''Ion Propulsion for Space Flight'' (McGraw-Hill, New York, 1964).</ref> and developed in practical form by [[Harold R. Kaufman]] at [[NASA Glenn Research Center|NASA Lewis]] (now Glenn) Research Center  from 1957 to the early 1960s.

The use of ion propulsion systems were first demonstrated in space by the NASA Lewis [[SERT-1|Space Electric Rocket Test (SERT)]] I and II.<ref name="Sovey">J. S. Sovey,  V. K. Rawlin, and M. J. Patterson, "Ion Propulsion Development Projects in U. S.: Space Electric Rocket Test 1 to Deep Space 1", ''Journal of Propulsion and Power, Vol. 17'', No. 3, May–June 2001, pp. 517–526.</ref>  These thrusters used mercury as the reaction mass.  The first was [[SERT-1]], launched July 20, 1964, which successfully proved that the technology operated as predicted in space.  The second test, SERT-II, launched on February 3, 1970,<ref>NASA Glenn, "[http://www.grc.nasa.gov/WWW/ion/past/70s/sert2.htm SPACE ELECTRIC ROCKET TEST II (SERT II)] {{Webarchive|url=https://web.archive.org/web/20110927004353/http://www.grc.nasa.gov/WWW/ion/past/70s/sert2.htm |date=2011-09-27 }} (Accessed July 1, 2010)</ref><ref>[http://www.astronautix.com/craft/sert.htm SERT] {{webarchive|url=https://web.archive.org/web/20101025005136/http://www.astronautix.com/craft/sert.htm |date=2010-10-25 }} page at Astronautix (Accessed July 1, 2010)</ref> verified the operation of two mercury ion engines for thousands of running hours.<ref>{{Cite web |url=http://www.grc.nasa.gov/WWW/ion/past/70s/sert2.htm |title=Space Electric Rocket Test |access-date=2010-07-01 |archive-url=https://web.archive.org/web/20110927004353/http://www.grc.nasa.gov/WWW/ion/past/70s/sert2.htm |archive-date=2011-09-27 |url-status=dead }}</ref>  Despite the demonstration in the 1960s and 70s, though, they were rarely used before the late 1990s.''

NASA Glenn continued to develop electrostatic gridded ion thrusters through the 1980s, developing the [[NASA Solar Technology Application Readiness]] (NSTAR) engine, that was used successfully on the [[Deep Space 1]] probe, the first mission to fly an interplanetary trajectory using electric propulsion as the primary propulsion.  It later flew on the [[Dawn (spacecraft)|Dawn]] asteroid mission.

[[Hughes Aircraft|Hughes Aircraft Company]] (now L-3 ETI) has developed the XIPS ([[Xenon Ion Propulsion System]]) for performing station keeping on its geosynchronous satellites (more than 100 engines flying).{{citation needed|date=November 2021}} 
NASA is currently{{clarify|date=November 2021}} working on a 20–50 [[Kilowatt|kW]] electrostatic ion thruster called [[HiPEP]] which will have higher efficiency, [[specific impulse]], and a longer lifetime than NSTAR.{{citation needed|date=November 2021}}

In 2006, [[Aerojet]] completed testing of a prototype [[NEXT (ion thruster)|NEXT]] ion thruster.<ref name=NEXT>[http://www.aerojet.com/program/news/nr_090903_aerojet_successfully_completes_next_milestones.htm?program_ID=45 Aerojet Successfully Completes Manufacturing and System Integration Milestones for NASA's NEXT Ion Engine Development Program<!-- Bot generated title -->] {{webarchive |url=https://web.archive.org/web/20060530182031/http://www.aerojet.com/program/news/nr_090903_aerojet_successfully_completes_next_milestones.htm?program_ID=45 |date=May 30, 2006 }}</ref>

Beginning in the 1970s, radio-frequency ion thrusters were developed at Giessen University and [[ArianeGroup]]. [[RIT-10]] engines are flying on the [[European Retrievable Carrier|EURECA]] and [[ARTEMIS]]. Qinetiq (UK) has developed the T5 and T6 engines (Kaufman type), used on the [[GOCE]] mission (T5) and the [[BepiColombo]] mission (T6). From Japan, the μ10, using microwaves, flew on the [[Hayabusa]] mission.{{citation needed|date=November 2021}}

In 2021, [[Double Asteroid Redirection Test|DART]] launched carrying a [[NEXT (ion thruster)|NEXT-C]] xenon ion thruster.

In 2021, [[ThrustMe]] reported satellite orbit changes using their [[NPT30 iodine|NPT30-I2]] iodine ion thruster.<ref>{{Cite web|url=https://www.cnet.com/news/in-a-space-first-scientists-test-ion-thrusters-powered-by-iodine/|title = In a space first, scientists test ion thrusters powered by iodine}}</ref><ref name=ThrustMe1 >{{cite journal |last1=Rafalskyi |first1=Dmytro |last2=Martínez Martínez |first2=Javier |last3=Habl |first3=Lui |last4=Zorzoli Rossi |first4=Elena |last5=Proynov |first5=Plamen |last6=Boré |first6=Antoine |last7=Baret |first7=Thomas |last8=Poyet |first8=Antoine |last9=Lafleur |first9=Trevor |last10=Dudin |first10=Stanislav |last11=Aanesland |first11=Ane |date=17 November 2021 |title=In-orbit demonstration of an iodine electric propulsion system |journal=Nature |volume=599 |issue= 7885|pages=411–415 |doi=10.1038/s41586-021-04015-y |pmid=34789903 |pmc=8599014 |bibcode=2021Natur.599..411R |quote=''Both atomic and molecular iodine ions are accelerated by high-voltage grids to generate thrust, and a highly collimated beam can be produced with substantial iodine dissociation.''}}</ref><ref name=ThrustMe2 >{{cite web |url=https://www.esa.int/ESA_Multimedia/Images/2021/01/Iodine_thruster_used_to_change_the_orbit_of_a_small_satellite_for_the_first_time_ever#.YaUuCq-kYyQ.link |title=Iodine thruster used to change the orbit of a small satellite for the first time ever |author=<!--Not stated--> |date=22 January 2021 |website=www.esa.int |publisher=The European Space Agency |access-date=2021-11-29 |quote=''For the first time ever, a telecommunications satellite has used an iodine propellant to change its orbit around Earth. The small but potentially disruptive innovation could help to clear the skies of space junk, by enabling tiny satellites to self-destruct cheaply and easily at the end of their missions, by steering themselves into the atmosphere where they would burn up.''}}</ref>

== Method of operation ==
Propellant atoms are injected into the discharge chamber and are ionized, forming a plasma. 

There are several ways of producing the electrostatic ions for the discharge chamber:

* electron bombardment (Kaufman type) by a potential difference between a [[Electron gun|hollow cathode]] and anode ([[NSTAR ion engine|NSTAR]], [[NEXT (ion thruster)|NEXT]], T5, T6 thrusters)
* [[radio frequency]] (RF) oscillation of an electric field induced by an alternating electromagnet, which results in a self-sustaining discharge and omits any cathode (RIT 10, RIT 22, μN-RIT thrusters)
* microwave heating (μ10, μ20)

Related to the electrostatic ion production method is the need for a cathode and power supply requirements. Electron bombardment thrusters require at the least, power supplies to the cathode, anode and chamber. RF and microwave types require an additional power supply to the rf generator, but no anode or cathode power supplies.

The positively charged ions diffuse towards the chamber's extraction system (2 or more multi-aperture grids). After ions enter the plasma sheath at a grid hole, they are accelerated by the potential difference between the first and second grids (called the screen and accelerator grids, respectively). The ions are guided through the extraction holes by the powerful electric field. The final ion energy is determined by the potential of the plasma, which generally is slightly greater than the screen grids' voltage.

The negative voltage of the accelerator grid prevents electrons of the beam plasma outside the thruster from streaming back to the discharge plasma. This can fail due to insufficient negative potential in the grid, which is a common ending for ion thrusters' operational life. The expelled ions propel the spacecraft in the opposite direction, according to [[Newton's third law|Newton's 3rd law]].
Lower-energy electrons are emitted from a separate cathode, called the neutralizer, into the ion beam to ensure that equal amounts of positive and negative charge are ejected. Neutralizing is needed to prevent the spacecraft from gaining a net negative charge, which would attract ions back toward the spacecraft and cancel the thrust.

== Performance ==
=== Longevity ===
The ion optics are constantly bombarded by a small amount of secondary ions and erode or wear away, thus reducing engine efficiency and life. Several techniques were used to reduce erosion; most notable was switching to a different propellant. [[Mercury (element)|Mercury]] or [[caesium]] atoms were used as propellants during tests in the 1960s and 1970s, but these propellants adhered to, and eroded the grids.  [[Xenon]] atoms, on the other hand, are far less corrosive, and became the propellant of choice for virtually all ion thruster types. NASA has demonstrated continuous operation of [[NASA Solar Technology Application Readiness|NSTAR]] thruster for over 16,000 hours (1.8 years) and [[NEXT (ion thruster)|NEXT]] thruster for over 48,000 hours (5.5 years).<ref>{{Cite web |last=Administrator |first=NASA |date=2013-06-27 |title=NASA Thruster Achieves World-Record 5+ Years of Operation |url=http://www.nasa.gov/home/hqnews/2013/jun/HQ_13-193_Ion_Thruster_Record.html |access-date=2022-10-29 |website=NASA |language=en}}</ref><ref>{{Cite web |date=2013-06-27 |title=NASA's NEXT ion thruster runs five and a half years nonstop to set new record |url=https://newatlas.com/next-ion-thruster-duration-record/28067/ |access-date=2022-10-29 |website=New Atlas |language=en-US}}</ref>

In the extraction grid systems, minor differences occur in the grid geometry and the materials used. This may have implications for the grid system operational lifetime.

===Specific impulse===
Electrostatic ion thrusters have also achieved a [[specific impulse]] of 30–100&nbsp;kN·s/kg, or 3,000 to 10,000 s, better than most other ion thruster types. Electrostatic ion thrusters have accelerated ions to speeds reaching 100 [[Kilometre per second|km/s]].

===Benefits of four grids===
In January 2006, the [[European Space Agency]], together with the [[Australian National University]], announced successful testing of an improved electrostatic ion engine, the [[Dual-Stage 4-Grid]] (DS4G), that showed exhaust speeds of 210 [[Kilometre per second|km/s]], reportedly four times higher than previously achieved, allowing for a specific impulse which is four times higher. Conventional electrostatic ion thrusters possess only two grids, one high voltage and one low voltage, which perform both the ion extraction and acceleration functions. However, when the charge differential between these grids reaches around 5 kV, some of the particles extracted from the chamber collide with the low voltage grid, eroding it and compromising the engine's longevity. This limitation is successfully bypassed when two pairs of grids are used. The first pair operates at high voltage, possessing a voltage differential of around 3 kV between them; this grid pair is responsible for extracting the charged propellant particles from the gas chamber. The second pair, operating at low voltage, provides the electrical field that accelerates the particles outwards, creating thrust. Other advantages to the new engine include a more compact design, allowing it to be scaled up to higher thrusts, and a narrower, less divergent exhaust plume of 3 degrees, which is reportedly five times narrower than previously achieved. This reduces the propellant needed to correct the orientation of the spacecraft due to small uncertainties in the thrust vector direction.<ref>[http://www.esa.int/esaCP/SEMOSTG23IE_index_0.html ESA Portal – ESA and ANU make space propulsion breakthrough<!-- Bot generated title -->]</ref>  

==See also==
*[[Electrically powered spacecraft propulsion]]
**[[Hall-effect thruster]]
*[[Ion thruster]], has comparison table with HET etc
**[[Dual-Stage 4-Grid]]

== Further reading ==
* {{Cite journal |last=Rafalskyi |first=D. |last2=Martínez |first2=J. M. |last3=Habl |first3=L. |last4=Zorzoli Rossi |first4=Elena |last5=Proynov |first5=Plamen |last6=Boré |first6=Antoine |last7=Baret |first7=Thomas |last8=Poyet |first8=Antoine |last9=Lafleur |first9=Trevor |last10=Dudin |first10=Stanislav |last11=Aanesland |first11=Ane |display-authors=3 |date=2021 |title=In-orbit demonstration of an iodine electric propulsion system |url=https://www.nature.com/articles/s41586-021-04015-y |journal=Nature |volume=599 |issue=7885 |pages=411–415 |doi=10.1038/s41586-021-04015-y |issn=1476-4687 |doi-access=free|pmc=8599014 }} Covers design detail that affect performance

== References ==
{{reflist}}

==External links==
*[https://web.archive.org/web/20090928054803/http://www.aerojet.com/capabilities/spacecraft.php Aerojet (Redmond, Washington USA) – Gridded Ion Thruster Vendor]
*[https://web.archive.org/web/20050307013441/http://www.boeing.com/defense-space/space/bss/factsheets/xips/nstar/ionengine.html NSTAR ion engine]
*[https://web.archive.org/web/20100529001855/http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/6428/1/03-0273.pdf Technologies to Improve Ion Propulsion System (PDF)]
*[https://web.archive.org/web/20050330130012/http://www.cpia.jhu.edu/pdfs/cptrs/CPTR_96-65.pdf Electric Thruster Systems (PDF)] 
*[https://web.archive.org/web/20021227094444/http://www.grc.nasa.gov/WWW/ion/present/hipep.htm HiPEP]
*[http://www.spacedaily.com/news/ESA_And_ANU_Make_Space_Propulsion_Breakthrough.html ESA And ANU Make Space Propulsion Breakthrough]

{{spacecraft propulsion}}

[[Category:Electrostatic motors]]
[[Category:Plasma technology and applications]]
[[Category:Ion engines]]