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The idea of using high-power electron beams to trace magnetic field lines and unambiguously connect physics phenomena occurring in the magnetosphere with their image in the ionosphere has been around since the seventies. It would help solve long standing questions in magnetospheric-ionospheric physics (such as what magnetospheric processes drive the aurora) and allow us to use the ionosphere as a ‘TV screen’ of magnetospheric activity for the first time. However, these capabilities have never been realized in practice due to the fear of catastrophic spacecraft charging problems driven by the electron beam current greatly exceeding the thermal current available from the low-density magnetospheric plasma. The importance of solving this spacecraft charging problem is such that it is listed as an open problem in the recent decadal survey for magnetospheric science.
One promising spacecraft-charging mitigation scheme used extensively in past missions and on the International Space Station is based on the plasma contactor. Essentially a plasma contactor emits a high-density, neutral plasma plume from the spacecraft to alter current to the spacecraft and reduce spacecraft potential. Plasma contactors have already been shown to ‘make contact’ with the background plasma, increasing the effective electron collection area of the spacecraft, however this is not a viable neutralizing scheme in low-density plasmas such as those found in the magnetosphere. Our recent research has shown that plasma contactors can operate efficiently in what we term the ‘ion emission’ mode. This is true even for the most difficult situation of a ‘collisionless’ or low-density plasma. Essentially, the plasma contactor reduces space-charge problems in this mode using the large surface area of its plasma plume. Substantial ion currents can be emitted from this large plasma surface in order to balance the electron beam current. This mode also represents the only known, viable option for a magnetospheric electron beam experiment involving substantial beam currents.
B-SPICE is designed specifically to address spacecraft-charging mitigation using a plasma contactor and provide the ultimate validation of our theoretical framework. The primary goals of B-SPICE are the following: 1) Identify the physics of spacecraft charging mitigation using a plasma contactor (including scaling laws of the spacecraft potential versus various important parameters) and determine to what extent the contactor acts as an electron collector vs. an ion emitter. 2) Raise the technological readiness level (TRL) of 3 critical supporting technologies, namely: a) the spacecraft-charging mitigation scheme using plasma contactors for application to active electron beam experiments in low-density space plasmas, b) a novel, highly efficient plasma contactor technology, and c) a novel spacecraft charging diagnostic with rapid potential measurement capabilities.
B-SPICE is a tethered rocket experiment equipped with a 1-keV, 150 mA electron beam, a hollow cathode plasma contactor with variable ion current production between 1 mA and 500 mA. Additional diagnostics are included to characterize spacecraft charging and different plasma contactor operating regimes. The standard experimental pulsing sequences last about 10 seconds and involve changing parameters such as the contactor ion current, expansion time, and expellant utilization to obtain important scaling laws with respect to the spacecraft potential. A nighttime launch and experimental operation over a range of altitudes 150-280 km will allow for a range of plasma density conditions to be scanned. We intend to draw upon past NASA sub-orbital rocket beam experiments (CHARGE-2 in particular). The experiments will be supported by spacecraft-charging simulations conducted with our CPIC code. Once validated with B-SPICE data, CPIC could be used to support future magnetospheric missions.
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