Editing Gridded ion thruster (section)

=== 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.