Status of Pulsed Inductive Thruster Research

Abstract

Abstract. The TRW Pulsed Inductive Thruster (PIT) is an electromagnetic propulsion system that can provide high thrust efficiency over a wide range of specific impulse values. In its basic form, the PIT consists of a fiat spiral coil covered by a thin dielectric plate. A pulsed gas injection nozzle distributes a thin layer of gas propellant across the plate surface at the same time that a pulsed high current discharge is sent through the coil. The rising current creates a time varying magnetic field, which in turn induces a strong azimuthal electric field above the coil. The electric field ionizes the gas propellant and generates an azimuthal current flow in the resulting plasma. The current in the plasma and the current in the coil flow in opposite directions, providing a mutual repulsion that rapidly blows the ionized propellant away from the plate to provide thrust. The thrust and specific impulse can be tailored by adjusting the discharge power, pulse repetition rate, and propellant mass flow, and there is minimal if any erosion due to the electrodeless nature of the discharge. Prior single-shot experiments performed with a l-meter diameter version of the PIT at TRW demonstrated specific impulse values between 2,000 seconds and 8,000 seconds, with thruster efficiencies exceeding 55% for ammonia and hydrazine propellants. This paper outlines current and planned activities to transition the single shot device into a multiple repetition rate thruster capable of supporting future DOD and NASA strategic enterprise missions.

State-of-the-Art and Advancement Paths for Inductive Pulsed Plasma Thrusters

“…From Eqs. (9) and (20) it would appear that the directed energy increases with thruster size. Previous experimental work defined to some degree the boundaries for MAP.…”

“…The switch connecting the energy storage capacitor to the drive coil must be capable of holding off the nominal charging voltage, conducting currents up to several kA, and surviving extremely large transient dV/dt and dI/dt values. The PIT MK V and MK Va employed a series-parallel array of 18 spark gaps designed to switch peak currents of I peak 100 kA ( 11 kA per switch) at rise rates on the order of 270 kA/µs (≈30 kA/µs per switch) [3,9]. Nominal stand-off voltages for these switches was V bd > 15 kV.…”

“…Future work to develop the PIT MK VI identified several additional disadvantages associated with the use of spark gap switches. Hrbud et al [9] noted that the nominal erosion rate of the spark gap electrodes was too high to support the large number of pulses required for an interplanetary mission. In addition, electrode erosion would change the spark gap electrode separation over time, which would likely alter the operational characteristics of the gaps even before switch failure occurred.…”

“…Previous work has identified implementation of solid-state switching as a necessary step for long-lifetime IPPT discharge circuit operation [3,9]. Doing so is expected to require either a reduction in the discharge circuit electrical requirements (charging voltage, peak current, dI/dt and dV/dt levels), advancements in solid-state switching technology, or the use of arrays of switches to subdivide the load.…”

“…The case for using solid-state switches in the IPPT discharge circuit has been discussed in multiple publications [9,16,92] and was summarized in Section 4.1.2. While both pulsed power thyristors [18] and IGBTs [43,86] have been implemented as discharge switches, no solid-state switch has been tested extensively enough to be considered a mature technology in the context of IPPT operation.…”