Patent Number: 
Section: claims

1. A pulsed plasma thruster propellant module comprising: at least one propellant rod including:  a first stage having a first propellant source having dimensions defining a first stage discharge length;  a second stage having a second propellant source having dimensions defining a second stage discharge length, wherein the first stage discharge length is less than the second stage discharge length; and  an ignition source for generating an ignition discharge across the first stage discharge length, wherein the first and second stages are designed such that said ignition discharge across the first discharge length initiates a subsequent ignition discharge across the second discharge length. 2. The propellant module as described in  claim 1 , further comprising a passive impedance source designed to transmit the ignition discharge current from the first stage propellant source to the second stage propellant source. claim 1 3. The propellant module as described in  claim 1 , wherein the ignition source includes a power supply in electrical communication with at least one ignition electrode. claim 1 4. The propellant module as described in  claim 3 , further comprising a switch for connecting or disconnecting the electrical communication between the power supply and the at least one ignition electrode. claim 3 5. The propellant module as described in  claim 1 , wherein the ignition source comprises: claim 1 a power supply;  a first ignition electrode in electrical communication with the power supply;  a second ignition electrode, wherein the first stage propellant source is disposed between the first and second ignition electrodes; and  a third ignition electrode, wherein the second stage propellant source is disposed between the second and third ignition electrodes. 6. The propellant module as described in  claim 5 , wherein the first, second and third ignition electrodes are cylindrical and arranged in a coaxial geometry. claim 5 7. The propellant module as described in  claim 5 , wherein the first and second propellant sources are made of a non-conductive material. claim 5 8. The propellant module as described in  claim 5 , wherein the electrodes are made of a conducting metal. claim 5 9. The propellant module as described in  claim 5 , further comprising at least two propellant rods. claim 5 10. The propellant module as described in  claim 5 , further comprising a passive impedance in electrical communication between the first and second stage, wherein the passive impedance transfers the ignition discharge from the first stage to the second stage. claim 5 11. The propellant module as described in  claim 5 , further comprising a switch in electrical communication between the first and second stage for triggering the ignition discharge of the second stage. claim 5 12. The propellant module as described in  claim 5 , further comprising a trigger capacitor in electrical communication with the ignition source, wherein the trigger capacitor provides an additional quantum of discharge energy to the ignition discharge across the first stage propellant source. claim 5 13. The propellant module as described in  claim 5 , further comprising an RC circuit in electrical communication with the first stage, wherein the RC circuit impedes the voltage rise on the first stage and controls the firing frequency of the propellant module. claim 5 14. A propulsion unit comprising the propellant module described in  claim 5 . claim 5 15. The propellant module as described in  claim 1 , wherein the first and second stages comprise independent cylinders arranged in an adjacent relationship. claim 1 16. The propellant module as described in  claim 15 , wherein the first stage includes: claim 15 wherein the second stage includes: a first ignition electrode in electrical communication with a power supply, and  a second ignition electrode, wherein the first stage propellant source is disposed between the first and second ignition electrodes; and  a third ignition electrode in electrical communication with the second ignition electrode, and  a fourth ignition electrode, wherein the second stage propellant source is disposed between the third and fourth ignition electrodes. 17. The propellant module as described in  claim 16 , wherein the first and second electrodes are arranged in a coaxial geometry and form a first propellant cylinder, and wherein the third and fourth electrodes are arranged in a coaxial geometry and form a second propellant cylinder. claim 16 18. The propellant module as described in  claim 15 , wherein the first and second propellant sources are made of Teflon. claim 15 19. The propellant module as described in  claim 15 , wherein the electrodes are made of a conducting metal. claim 15 20. The propellant module as described in  claim 15 , further comprising a passive impedance in electrical communication between the first and second stage, wherein the passive impedance transfers the ignition discharge from the first stage to the second stage. claim 15 21. The propellant module as described in  claim 15 , further comprising a switch in electrical communication between the first and second stage for triggering the ignition discharge of the second stage. claim 15 22. The propellant module as described in  claim 15 , further comprising a trigger capacitor in electrical communication with the ignition source, wherein the trigger capacitor provides an additional quantum of discharge energy to the ignition discharge across the first stage propellant source. claim 15 23. The propellant module as described in  claim 15 , further comprising an RC circuit in electrical communication with the first stage, wherein the RC circuit impedes the voltage rise on the first stage and controls the firing frequency of the propellant module. claim 15 24. The propellant module as described in  claim 15 , further comprising at least two second stages. claim 15 25. The propellant module as described in  claim 24 , further comprising a selector switch in electrical communication with the ignition source, wherein the selector switch determines which of the at least two second stages is ignited by the ignition discharge of the first stage. claim 24 26. A propulsion unit comprising the propellant module described in  claim 15 . claim 15 27. The propellant module as described in  claim 1 , further comprising: claim 1 a power source for generating an ignition voltage;  a bundle of at least two propellant rods in electrical communication with the power source, the at least two propellant rods each including:  a first electrode,  a second electrode, and  a propellant source disposed between the first and second electrodes having dimensions defining a discharge length; wherein the power source randomly applies the ignition voltage to one of the at least two propellant rods to generate an ignition discharge across the discharge length of said propellant rod until the propellant source within each propellant rod is exhausted. 28. The propellant module as described in  claim 27 , wherein the ignition discharge is triggered by a triggering technique selected from the group consisting of: claim 27 self-triggered, triggered, and quasi-steady. 29. The propellant module of  claim 27  wherein each of the at least two propellant rods are designed to enter an open-circuit condition such that no further ignition discharges occur across said discharge length once the propellant source has been expended. claim 27 30. The propellant module of  claim 27  wherein each of the at least two propellant rods further comprises an insulating tube surrounding one end of the first electrode such that when the propellant source has been depleted sufficiently to expose the insulating tube an open-circuit condition is entered such that no further ignition discharges occur across the discharge length. claim 27 31. The propellant module of  claim 27  wherein each of the at least two propellant rods further comprises a non-ablative material disposed between the first and second electrodes at one end of the propellant rod such that when the propellant source has been depleted sufficiently to expose the non-ablative material an open-circuit condition is entered such that no further ignition discharges occur across the discharge length. claim 27 32. The propellant module of  claim 27  wherein the discharge length between the first and second electrodes of each of the at least two propellant rods increases at one end of the propellant rod such that when the propellant source has been depleted sufficiently to reach the increased discharge length an open-circuit condition is entered such that no further ignition discharges occur across said increased discharge length. claim 27 33. The propellant module as described in  claim 27 , further comprising a propellant rod switch for directing the ignition voltage between the at least two propellant modules. claim 27 34. A propulsion unit comprising the propellant module described in  claim 27 . claim 27 35. A propulsion unit comprising the propellant module described in  claim 1 . claim 1