Characterizing Europa’s subsurface ocean is essential for assessing Europa’s habitability. The suite of instruments on the Europa Clipper spacecraft will, among others, magnetically sound Europa’s interior by measuring the ocean’s induced magnetic field. This magnetic field is generated in response to the Jovian time-varying magnetic environment in which Europa is immersed. However, the dynamic magnetized plasma flow of the Jovian magnetosphere creates electrical currents that give rise to magnetic perturbations near Europa. These perturbations complicate the interpretation of the induction signal, and hence the characterization and inferences on potential habitability. Thus, characterization of the ocean by magnetic sounding requires an accurate characterization of the plasma as it flows across Europa. We present the Plasma Instrument for Magnetic Sounding (PIMS), the instrument for the Europa Clipper mission that will measure the plasma contribution to the magnetic field perturbations sensed by the Europa Clipper Magnetometer. PIMS is composed of four Faraday Cup plasma spectrometers that use voltage-biased gridded apertures to dissect the space plasmas that they encounter. The instrument uses sensitive preamplifiers and processing electronics to measure the current that results when charged particles strike the instrument’s metal collector plates, thus enabling a measure of the plasma characteristics near Europa to produce a more accurate magnetic sounding of Europa’s subsurface ocean. PIMS consists of two sensors: one placed near the top of the Europa Clipper spacecraft and one near the bottom. Each sensor contains two Faraday Cups with a 90° full-width field-of-view. The sensors were specifically designed to withstand the Europa environment, measure both ions and electrons, and have two separate voltage ranges intended to analyze the magnetospheric and ionospheric environments, respectively. In this paper, we describe the scientific motivation for this experiment, the design considerations for the PIMS instrument, the details of the ground calibration, and other details pertinent to understanding the scientific data retrieved by PIMS.

Recently, there has been an unmistakable trend in the space industry toward public/private partnerships for access to space. This is particularly true for suborbital space, where an unprecedented number of companies are vying to provide routine access to near-earth space. Although much has been focused on commercialization for manned tourist suborbital flights, there is a burgeoning opportunity for scientific and engineering activities on-board these spacecraft. Such opportunities are exciting because of the potential for unprecedented lower costs and frequent access to space. The Johns Hopkins University / Applied Physics Laboratory (JHU/APL) is leading an effort to focus on instrumentation for suborbital re-usable launch vehicles. NASA has awarded three flight opportunities to JHU/APL aboard commercial suborbital vehicles, with flights scheduled to be completed in 2012. This paper presents the planned approach undertaken by JHU/APL from these groundbreaking experiments to understand and characterize the environment in and around commercial suborbital spacecrafts. The empirical measurements, to be gathered through these NASA-sponsored suborbital flights, will help to baseline the environment of the host vehicle, thereby allowing a quantified platform for the scientific community to conduct future space experimentation.