Power plants – Reaction motor – Ion motor
Reexamination Certificate
1999-07-27
2001-03-06
Freay, Charles G. (Department: 3746)
Power plants
Reaction motor
Ion motor
Reexamination Certificate
active
06195980
ABSTRACT:
PRIORITY CLAIM
This application is based on and claims the priority under 35 U.S.C. §119 of German Patent Application 198 35 512.2, filed on Aug. 6, 1998, the entire disclosure of which is incorporated herein by reference.
FIELD OF THE INVENTION
The invention relates to an electrostatic propulsion engine and particularly an ion engine for use in satellites and spacecraft, including an apparatus for ionizing a propellant gas, an apparatus for accelerating the propellant gas ions, and an electron source of which the output electrons are coupled or directed into the propellant ion jet for the purpose of neutralizing the same.
BACKGROUND INFORMATION
In conventional electrostatic propulsion engines of the above mentioned general type, atoms of a propellant gas expelled from a supply container or tank are first ionized to form positively charged propellant ions, and then these ions are accelerated in an electrostatic high voltage field to form a high-energy beam or jet of the ions which in turn provides a propulsive thrust. In order to maintain a constant drive thrust output, in this context, it is absolutely necessary to provide suitable measures for neutralizing the positively charged propellant ion beam or jet emitted from the engine. Preferably, a gas discharge arrangement serves as a neutralizer, in that it is used as an electron source providing electrons that neutralize the positively charged ions.
Along these lines, it is already known to provide a cathode tube having a gas flowing therethrough and an anode that is referred to as a keeper electrode, and to generate a hollow cathode gas discharge therebetween. Then, free electrons are extracted from this hollow cathode gas discharge and are then coupled into the beam or jet of the emitted propellant ions in a suitable manner so as to neutralize the positive ions.
In an arrangement of the above described type, in order to initiate the gas discharge between the anode and the cathode it is necessary to heat up the cathode relatively strongly, so that the emitted electrons have a tendency to ionize the gas flowing through the cathode tube, due to the applied anode voltage, and thereby initiate the discharge process. Such a cathode is generally made of a material having a high electron emission capacity, such as impregnated tungsten for example, and it is typically necessary to heat such a cathode to a temperature of approximately 1200° C. Not only does this heating require a considerable expenditure of energy, but the required high cathode temperature leads to high loads and demands being placed on the material, which in turn leads to accelerated and early material fatigue. Moreover, it is necessary to provide a relatively complex and costly arrangement of the entire apparatus, to ensure that it will be thermally and mechanically stable under the high temperature loading conditions and the resulting great temperature gradient and variation. Also, this known apparatus requires a high throughput or flow rate of the gas in order to initiate and maintain the ignition.
SUMMARY OF THE INVENTION
In view of the above, it is an object of the invention to provide an electrostatic propulsion engine and particularly an ionic engine which is improved so as to achieve the lowest possible material loading of the components, and thereby achieve a high reliability. It is a further object of the invention to provide such an engine that has a simple design and construction, yet is directed toward achieving a nearly steady state or equilibrium operating condition after ignition has been achieved. The invention further aims to avoid or overcome the disadvantages of the prior art, and to achieve additional advantages, as apparent from the present specification.
The above objects have been achieved according to the invention in an electrostatic engine having an improved electron source for neutralizing the positively charged ions of the propellant ion stream or jet. Particularly, the electron source comprises an anode, a hollow cathode tube, and an auxiliary electrode arranged within the interior space of the cathode tube. A pulsed discharge can be initiated between the auxiliary electrode and the cathode in order to ignite the gas discharge between the anode and the cathode.
In a preferred embodiment of the engine according to the invention, the auxiliary electrode comprises a cylindrical rod or pin that is arranged along the lengthwise axis of the hollow cathode tube. The initiating or triggering effect of the pulsed discharge between the auxiliary electrode and the cathode in turn ignites the gas discharge between the anode and the cathode. As a result, the cathode temperature required for the ignition is considerably less than the cathode temperature needed in conventional engines of this type, due to the substantially lower electron current that is required. In addition to this primary advantage according to the invention, another advantage is the reduced heating energy that must be expended for achieving the ignition, due to the lower heating temperature simultaneously, the quantity or rate of gas flowing through the hollow cathode for this process can be substantially reduced.
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patent: 4719355 (1988-01-01), Meyers et al.
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patent: 4838021 (1989-06-01), Beattie
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patent: 5947421 (1999-09-01), Beattie et al.
patent: 6121569 (2000-09-01), Miley et al.
DaimlerChrysler Aerospace AG
Evora Robert Z.
Fasse W. F.
Fasse W. G.
Freay Charles G.
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