The Spin-plane double probe instrument (SDP) is part of the FIELDS instrument suite of the Magnetospheric Multiscale mission (MMS). Together with the Axial double probe instrument (ADP) and the Electron Drift Instrument (EDI), SDP will measure the 3-D electric field with an accuracy of 0.5 mV/m over the frequency range from DC to 100 kHz. SDP consists of 4 biased spherical probes extended on 60 m long wire booms 90• apart in the spin plane, giving a 120 m baseline for each of the two spin-plane electric field components. The mechanical and electrical design of SDP is described, together with results from ground tests and calibration of the instrument.Keywords Magnetospheric Multiscale Mission · MMS · Electric field instrument · Spin-plane double probe · SDP

Optical lenses with tunable focus are needed in several fields of application, such as consumer electronics, medical diagnostics and optical communications. To address this need, lenses made of smart materials able to respond to mechanical, magnetic, optical, thermal, chemical, electrical or electrochemical stimuli are intensively studied. Here, we report on an electrically tunable lens made of dielectric elastomers, an emerging class of “artificial muscle” materials for actuation. The optical device is inspired by the architecture of the crystalline lens and ciliary muscle of the human eye. It consists of a fluid‐filled elastomeric lens integrated with an annular elastomeric actuator working as an artificial muscle. Upon electrical activation, the artificial muscle deforms the lens, so that a relative variation of focal length comparable to that of the human lens is demonstrated. The device combined optical performance with compact size, low weight, fast and silent operation, shock tolerance, no overheating, low power consumption, and possibility of implementation with inexpensive off‐the‐shelf elastomers. Results show that combing bioinspired design with the unique properties of dielectric elastomers as artificial muscle transducers has the potential to open new perspectives on tunable optics.

The Plasma and Suprathermal Ion Composition (PLASTIC) investigation provides the in situ solar wind and low energy heliospheric ion measurements for the NASA Solar Terrestrial Relations Observatory Mission, which consists of two spacecraft (STEREO-A, STEREO-B). PLASTIC-A and PLASTIC-B are identical. Each PLASTIC is a timeof-flight/energy mass spectrometer designed to determine the elemental composition, ionic charge states, and bulk flow parameters of major solar wind ions in the mass range from hydrogen to iron. PLASTIC has nearly complete angular coverage in the ecliptic plane and an energy range from ∼0.3 to 80 keV/e, from which the distribution functions of suprathermal ions, including those ions created in pick-up and local shock acceleration processes, are also provided.

The IBEX-Lo sensor covers the low-energy heliospheric neutral atom spectrum from 0.01 to 2 keV. It shares significant energy overlap and an overall design philosophy with the IBEX-Hi sensor. Both sensors are large geometric factor, single pixel cameras that maximize the relatively weak heliospheric neutral signal while effectively eliminating ion, electron, and UV background sources. The IBEX-Lo sensor is divided into four major subsystems. The entrance subsystem includes an annular collimator that collimates neutrals to approximately 7°× 7°in three 90°sectors and approximately 3.5°× 3.5°in the fourth 90°sector (called the high angular resolution sector). A fraction of the interstellar neutrals and heliospheric neutrals that pass through the collimator are converted to negative ions in the ENA to ion conversion subsystem. The neutrals are converted on a high yield, inert, diamond-like carbon conversion surface. Negative ions from the conversion surface are accelerated into an electrostatic analyzer (ESA), which sets the energy passband for the sensor. Finally, negative ions exit the ESA, are post-accelerated to 16 kV, and then are analyzed in a time-of-flight (TOF) mass spectrometer. This triple-coincidence, TOF subsystem effectively rejects random background while maintaining high detection efficiency for negative ions. Mass analysis distinguishes heliospheric hydrogen from interstellar helium and oxygen. In normal sensor operations, eight energy steps are sampled on a 2-spin per energyThe IBEX-Lo Sensor 119 step cadence so that the full energy range is covered in 16 spacecraft spins. Each year in the spring and fall, the sensor is operated in a special interstellar oxygen and helium mode during part of the spacecraft spin. In the spring, this mode includes electrostatic shutoff of the low resolution (7°× 7°) quadrants of the collimator so that the interstellar neutrals are detected with 3.5°× 3.5°angular resolution. These high angular resolution data are combined with star positions determined from a dedicated star sensor to measure the relative flow difference between filtered and unfiltered interstellar oxygen. At the end of 6 months of operation, full sky maps of heliospheric neutral hydrogen from 0.01 to 2 keV in 8 energy steps are accumulated. These data, similar sky maps from IBEX-Hi, and the first observations of interstellar neutral oxygen will answer the four key science questions of the IBEX mission.

The tri-axial search-coil magnetometer (SCM) belongs to the FIELDS instrumentation suite on the Magnetospheric Multiscale (MMS) mission (Torbert et al. in Space Sci. Rev. (2014), this issue). It provides the three magnetic components of the waves from 1 Hz to 6 kHz in particular in the key regions of the Earth's magnetosphere namely the subsolar region and the magnetotail. Magnetospheric plasmas being collisionless, such a measurement is crucial as the electromagnetic waves are thought to provide a way to ensure the conver-

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The IBEX-Hi Neutral Atom Imager of the Interstellar Boundary Explorer (IBEX) mission is designed to measure energetic neutral atoms (ENAs) originating from the interaction region between the heliosphere and the local interstellar medium (LISM). These ENAs are plasma ions that have been heated in the interaction region and neutralized by charge exchange with the cold neutral atoms of the LISM that freely flow through the interaction region. IBEX-Hi is a single pixel ENA imager that covers the ENA spectral range from 0.38 H.O. Funsten et al. to 6 keV and shares significant energy overlap and overall design philosophy with the IBEXLo sensor. Because of the anticipated low flux of these ENAs at 1 AU, the sensor has a large geometric factor and incorporates numerous techniques to minimize noise and backgrounds. The IBEX-Hi sensor has a field-of-view (FOV) of 6.5°× 6.5°FWHM, and a 6.5°× 360°s wath of the sky is imaged over each spacecraft spin. IBEX-Hi utilizes an ultrathin carbon foil to ionize ENAs in order to measure their energy by subsequent electrostatic analysis. A multiple coincidence detection scheme using channel electron multiplier (CEM) detectors enables reliable detection of ENAs in the presence of substantial noise. During normal operation, the sensor steps through six energy steps every 12 spacecraft spins. Over a single IBEX orbit of about 8 days, a single 6.5°× 360°swath of the sky is viewed, and re-pointing of the spin axis toward the Sun near perigee of each IBEX orbit moves the ecliptic longitude by about 8°every orbit such that a full sky map is acquired every six months. These global maps, covering the spectral range of IBEX-Hi and coupled to the IBEX-Lo maps at lower and overlapping energies, will answer fundamental questions about the structure and dynamics of the interaction region between the heliosphere and the LISM.Keywords Interstellar boundary · Termination shock · Heliopause · Energetic neutral atom · ENA · LISM PACS 96.50.-e · 96.50.Ek · 96.50.Xy · 96.50.Zc