|
|
|
|
|
Electrostatic Ion ThrusterThe electrostatic ion thruster is a kind of design for ion thrusters (a kind of highly-efficient low-thrust spacecraft propulsion running on electical power). These designs use high voltage electrodes in order to accelerate ions with electrostatic forces. Although electrostatic ion thrusters have been in development since the early 1960s, they were rarely used before the late 1990s. NASA has produced practical electrostatic ion thrusters, notably the NSTAR engine that was used successfully on Deep Space 1. Hughes Aircraft Company has developed the XIPS (Xenon Ion Propulsion System) for performing station keeping on geosynchronous satellites. NASA is currently working on a 20-50kw electrostatic ion thruster called HiPEP which will have higher efficiency, specific impulse, and lifetime than NSTAR. Method of operation - Fuel atoms are injected into the propulsion chamber. The fuel atoms are heated and bombarded with electrons from a hollow cathode, causing the atoms to lose electrons of their own and become ionized, thus forming ions. The thruster walls and grid absorb the lost electrons.
- The positively charged ions move towards the back of the chamber due to magnetic and ambient pressure. Ions will leak past the positively charged grid.
- Once ions are between the positive and negative grids at the very back of the chamber, they are electrostatically accelerated away from the positive grid and towards the negative one.
- The positive grid is charged more then the negative grid, thus the push on the positive ions is much greater than the pull from the negative grid, the ions shoot past the negative grid and out into space at a high speed. The main purpose of the negative grid is to focus the ions into a beam way from the ship in a specific direction (vector) to maximize efficiency in thrust.
- The expelled ions propel the ship in the opposite direction according to Newton's 3rd law.
- Electrons are shot from a cathode towards the ions behind the ship to neutralize the ions. Neutralizing is needed to prevent the ship from gaining a net negative charge.
Performance Originally there was doubt that electrostatic ion thrusters could be competitive with other ion thrusters such as the Hall effect thruster. The grid is constantly bombarded by propellant ions and erodes or wears away, thus reducing engine efficiency and life. Ion engines need to be able to run efficiently and continuously for years. Several techniques were used to reduce erosion; most notable was switching to a different fuel. Mercury or caesium atoms were used as fuels during tests in the 1960s and 1970s, these fuels would adhere to and eroded the grids; Xenon atoms on the other hand were far less corrosive, and became the fuel of choice for virtually all ion thruster types. NASA has proven continuous operation of NSTAR engines for over 16,000 hours (1.8 years), and test are still ongoing for double this lifetime. Electrostatic ion thruster have also managed Isp above most other ion thruster types, having a Isp between 3000s-10,000s. Electrostatic ion thrusters have accelerated ions to speeds reaching 100km/s! Variants The chief variable in electrostatic ion thrusters is the method of ionizing the fuel atoms. New techniques such as using microwaves to heat the fuel atoms into a plasma (thus ionizing them) are under development; the advantage of such a technique is the lack of a cathode that would wear out or erode, increasing thruster life. Other designs of ion thruster have also been developed in an effort to circumvent the problems of the electrostatic ion thruster. The chief focus of attention has been the grid, since grid wear is a major limiting factor in engine lifetime. See also External links
|
 |
|
| Copyright 2005-2009 OnPedia.com. All Rights Reserved |
|
|