Spacecraft propulsion system and method of operation

A spacecraft propulsion system comprising:

• at least one thruster, including (i) an ion source for creating a stream of ions to propel the spacecraft and (ii) a neutralizer comprising at least one electron source for emitting electrons from the spacecraft to neutralize the stream of ions;
• and
• a controller that applies control signals to the neutralizer to one or both of:
• ramp up from an OFF state of the electron source associated with a first voltage to an ON state of the electron source associated with a second voltage to increase a flow of electrons wherein the ramp up comprises a first plurality of voltages over a first time between the first voltage and the second voltage as specified by the control signals and wherein the first plurality of voltages and the first time are selected such that a rate of increase of the flow of electrons is slower than when the electron source is switched instantaneously from the first voltage to the second voltage;
• and
• ramp down from the ON state of the electron source associated with the second voltage to the OFF state of the electron source associated with the first voltage to decrease a flow of electrons wherein the ramp down comprises a second plurality of voltages over a second time between the first voltage and the second voltage as specified by the control signals and wherein the second plurality of voltages and the second time are selected such that a rate of decrease of the flow of electrons is slower than when the electron source is switched instantaneously from the second voltage to the first voltage.

A computer readable medium comprising instructions for implementation in a spacecraft propulsion system comprising at least one thruster, the at least one thruster comprising an ion source for creating a stream of ions to propel the spacecraft and a neutralizer comprising an electron source for emitting electrons from the spacecraft to neutralize the stream of ions, wherein when the instructions are implemented in a processor in a spacecraft propulsion system controllers the system is caused to operate at least one thruster by controlling the neutralizer, with control signals applied thereto, to constrain production of electrons to perform one or both of:

• ramping up from an OFF state of the electron source associated with a first voltage to an ON state of the electron source associated with a second voltage to increase a flow of electrons wherein the ramping up comprises a first plurality of voltages over a first time between the first voltage and the second voltage as specified by the control signals and wherein the first plurality of voltages and the first time are selected such that a rate of increase of the flow of electrons is slower than when the electron source is switched instantaneously from the first voltage to the second voltage;
• and
• ramping down from the ON state of the electron source associated with the second voltage to the OFF state of the electron source associated with the first voltage to decrease the flow of electrons
• wherein the ramping down comprises a second plurality of voltages over a second time between the first voltage and the second voltage as specified by the control signals and wherein the second plurality of voltages and the second time are selected such that a rate of decrease of the flow of electrons is slower than when the electron source is switched instantaneously from the second voltage to the first voltage.