We have developed a very small sheet beam gun that employs a 0.001-inch diameter tensioned tungsten wire cataphoretically coated with barium-strontium-calcium carbonate and capable of greater than 1 mA of emission current, see Fig. 1. The device includes a negative voltage hemi-cylindrical repeller electrode behind the cathode and a negative slit in front for suppression. Beyond the suppressor is a focus slit at cathode potential and, finally, an anode slit just beyond it. The repeller and slit electrodes provide effective collimation of the beam, which can be subsequently focused at narrow thickness either magnetically or electrostatically. A large number of these devices have been built and tested in sealed test vehicles. A common use is as ionizers for mass spectrometers in space. They have the advantage that they dissipate only 0.1 watt. The device construction will be described and performance presented. An alternative embodiment is the substitution of a 0.002-inch diameter thoriated tungsten wire. The emitting surface is actually smaller than the 0.001-inch wire with 0.001-thick barium oxide coating. The thoriated tungsten version allows multiple excursions to atmospheric pressures without loss of emission performance. However, it uses more power, about 0.6 watt vs. 0.1 watt. It easily produces a collimated beam of 5 mA at only 1450 degrees Cb. Its output can be raised to 10 A per centimeter squared at temperatures below 1700 degrees Cb.

In the present decade and beyond, now 51 years after the last Apollo landing, the NASA Artemis human exploration program will offer abundant opportunities for heliophysics investigations from, by, and of the Moon from the vantage points of the lunar orbit and the surface. The Lunar Solar Occultation Explorer (LunaSOX) concept uses the lunar limb to occult the solar disk for high-resolution coronal observations at hourly, daily, to biweekly cadences from spacecraft either in the lunar orbit or at the surface. A 0.2 m diameter solar telescope in orbit with white light and narrow-band visible filters would provide arcsecond spectroscopic imaging of the low-to-high corona (1–10 R☉) with an upper limit of 10 –12 B☉ on the local scattered light background from lunar atmospheric dust, as compared to 10 –9 B☉ for Earth ground-based solar eclipse observations looking up through the atmosphere at totality. For eclipse observations from and by the Moon, there would be no significant atmospheric disturbances that otherwise limit seeing to arcsec resolution from Earth’s surface. The present eccentric orbits of the ARTEMIS P1 and P2 spacecraft are used as models for a 1 × 10 Rm orbit of LunaSOX to compute the times of solar eclipse intervals, up to 2 hours in duration between the east and west solar hemispheres at a daily cadence for coronal observations at 1–16 R☉ when the orbital aposelene is in anti-sunward directions. In a low-altitude circular orbit and from the surface, the observational cadences would, respectively, be hourly and biweekly. LunaSOX satellites also carrying in situ space environment instruments could integrate into a network of orbital platforms for space weather monitoring and communications relay to far-side surface lander and permanent base sites, e.g., for low-frequency radio cosmology and detection of exoplanet magnetospheres.

When incorporated into a top-hat electrostatic analyzer, a gate electrode enables the separation of ions by their mass-per-charge with modest mass resolution (M/∆M ∼ 10). Gated-time-of-flight (TOF) instruments avoid the energy straggling and angular scattering effects prevalent in foil-based detection systems, providing more pristine measurements of three-dimensional distribution functions of incident ions. Gated-TOF implementations are ideal for measuring the properties of low-energy (i.e., <100 eV) thermal ions in various space environments. We present an instrument prototype capable of separating H+, He+, O+, and O2+ in Earth's ionosphere and demonstrate that in addition to providing species determination, precise operation of the gate electrode provides an electronically adjustable geometric factor that can extend a single instrument's dynamic range by several orders of magnitude.

The interaction of our protective heliosphere and the Very Local Interstellar Medium (VLISM) is the least explored and most rewarding frontier of space physics.New evidence amplifies the central role of the heliosphere in the evolution of the solar system along its 4.6billion-year journey around the galaxy.In addition to the dense clouds of plasma, gas and dust seeding the early proto solar nebula, recent supernovae have left the entire solar system exposed to extreme fluxes of interstellar material and cosmic radiation with far-reaching implications.Our current knowledge lacks the direct measurements necessary to understand how our star upholds its vast heliosphere and its potentially game-changing role in the evolution of our galactic home.Interstellar Probe provides new, required measurements over more than a solar cycle to uncover the physical processes starting near the Sun responsible for creating our dynamic heliosphere.In April 2022, the pragmatic Interstellar Probe Mission Concept Study was completed after four years, detailing a Large Strategic heliophysics mission that would transect the heliosphere from 1 au to the VLISM.Its journey provides rich science for generations across heliophysics and presents an opportunity to push the frontier of space exploration farther than ever done before.Modest crossdivisional investments enable high-value planetary science and astrophysics, deepening our understanding of the emergence of our habitable planetary system.A trajectory through the forward hemisphere of the heliosphere would be accomplished by a launch in the 2036-2042 timeframe using conventional chemical propulsion and a heavy-lift launch vehicle, such as the Space Launch System (SLS).A Jupiter Gravity Assist could propel an 860-kg spacecraft with an 87-kg payload of ten instruments delivering a unified view of the global heliosphere, reaching the VLISM after 16 years.The spacecraft is designed to a 50-year nominal lifetime using modern-day technology based on successful missions like New Horizons.Two next-generation Radioisotope Thermal Generators (RTGs) would ensure 300 We at end of nominal mission at 375 au and could enable exploration even beyond 500 au.

Abstract Photoelectrons are crucial to atmospheric physics. They heat the atmosphere, strengthen planetary ambipolar electric fields, and enhance the outflow of ions to space. However, there exist only a handful of measurements of their energy spectrum near the peak of photoproduction. We present calibrated energy spectra of pristine photoelectrons at their source by a prototype Dual Electrostatic Analyzer (DESA) instrument flown on 11 July 2021 aboard the Dynamo‐2 sounding rocket (NASA № 36.357). Photopeaks arising from 30.4 nm He‐II spectral line were observed throughout the flight above 120 km. DESA also successfully resolved the rarely observed N2 absorption feature. Below 10 eV observations were in good agreement with the GLOW suprathermal electron. Above 10 eV fluxes substantially deviated from the model by as much as an order of magnitude.

Mercury’s southern inner magnetosphere is an unexplored region as it was not observed by earlier space missions. In October 2021, BepiColombo mission has passed through this region during its first Mercury flyby. Here, we describe the observations of SERENA ion sensors nearby and inside Mercury’s magnetosphere. An intermittent high-energy signal, possibly due to an interplanetary magnetic flux rope, has been observed downstream Mercury, together with low energy solar wind. Low energy ions, possibly due to satellite outgassing, were detected outside the magnetosphere. The dayside magnetopause and bow-shock crossing were much closer to the planet than expected, signature of a highly eroded magnetosphere. Different ion populations have been observed inside the magnetosphere, like low latitude boundary layer at magnetopause inbound and partial ring current at dawn close to the planet. These observations are important for understanding the weak magnetosphere behavior so close to the Sun, revealing details never reached before.

The ESA-JAXA BepiColombo mission to Mercury will provide simultaneous measurements from two spacecraft, offering an unprecedented opportunity to investigate magnetospheric and exospheric particle dynamics at Mercury as well as their interactions with solar wind, solar radiation, and interplanetary dust. The particle instrument suite SERENA (Search for Exospheric Refilling and Emitted Natural Abundances) is flying in space on-board the BepiColombo Mercury Planetary Orbiter (MPO) and is the only instrument for ion and neutral particle detection aboard the MPO. It comprises four independent sensors: ELENA for neutral particle flow detection, Strofio for neutral gas detection, PICAM for planetary ions observations, and MIPA, mostly for solar wind ion measurements. SERENA is managed by a System Control Unit located inside the ELENA box. In the present paper the scientific goals of this suite are described, and then the four units are detailed, as well as their major features and calibration results. Finally, the SERENA operational activities are shown during the orbital path around Mercury, with also some reference to the activities planned during the long cruise phase.

The Daedalus mission has been proposed to the European Space Agency (ESA) in response to the call for ideas for the Earth Observation program's 10th Earth Explorer. It was selected in 2018 as one of three candidates for a phase-0 feasibility study. The goal of the mission is to quantify the key electrodynamic processes that determine the structure and composition of the upper atmosphere, the gateway between the Earth's atmosphere and space. An innovative preliminary mission design allows Daedalus to access electrodynamics processes down to altitudes of 150 km and below. Daedalus will perform in situ measurements of plasma density and temperature, ion drift, neutral density and wind, ion and neutral composition, electric and magnetic fields, and precipitating particles. These measurements will unambiguously quantify the amount of energy deposited in the upper atmosphere during active and quiet geomagnetic times via Joule heating and energetic particle precipitation, estimates of which currently vary by orders of magnitude between models and observation methods. An innovation of the Daedalus preliminary mission concept is that it includes the release of subsatellites at low altitudes: combined with the main spacecraft, these subsatellites will provide multipoint measurements throughout the lower thermosphere–ionosphere (LTI) region, down to altitudes below 120 km, in the heart of the most under-explored region in the Earth's atmosphere. This paper describes Daedalus as originally proposed to the ESA.

The Miniaturized Electron pRoton Telescope, MERiT, is a low-mass, low-power, compact instrument using an innovative combination of particle detectors, sensor electronics, and onboard processing. MERiT is flying on the Compact Radiation belt Explorer, CeREs, a 3U CubeSat launched into a low earth orbit of 500-km altitude and inclination of 85 degrees on 16 December 2018. The primary and secondary science goals of CeREs are to investigate electron microbursts and to study solar particles. MERiT comprises a stack of solid state detectors (SSD) behind space facing avalanche photo diodes (APDs) surrounded by W-Al shielding to reduce side-penetrating particle background. The APD-SSD combination enables measurement of electrons from 5 to 200 keV and 1 to 8 MeV; protons from 200-400 keV and 7-100 MeV in differential channels with energy resolution Delta E/E approximate to 30% for both electrons and protons. MERiT measures microbursts with a high time resolution ranging from 4 to 16 ms and solar particles with a cadence of 1 s. MERiT energy channels and cadences are software configurable via algorithms and lookup tables residing on a field-programmable gate array. The lookup tables can be changed via ground commands. MERiT geometry factor is 31 cm(2)-sr and optimized to measure microbursts with the instrument viewing the local zenith in orbit. MERiT enables investigation of dynamical processes of radiation belt electron energization and loss, solar electron and proton transport, and their access to the Earth's polar caps. We describe the MERiT sensor design, calibration, operational modes, data products, and science goals.

The mid- and low-latitude ionosphere is home to a variety of plasma density irregularities, including depletions (bubbles), enhancements (blobs), and small-scale scintillation. Previous studies of plasma density enhancements observed using ROCSAT data have posited that these structures are the direct result of the formation of bubbles near the geomagnetic equator. However, more recent observations from the C/NOFS satellite suggest that multiple mechanisms are responsible for forming plasma enhancements, with wave action in the ionosphere and thermosphere as a significant driver of the enhanced densities. Indeed, statistical analysis of enhancements observed from satellites resembles the statistics of Medium-Scale Traveling Ionosphere Disturbances (MSTIDs) with respect to seasonal variability and solar activity. petitSat is a CubeSat mission designed to examine the link between MSTIDs and plasma enhancements. The mission will provide in situ measurements of the plasma density, 3D ion drift, as well as ion and neutral composition. The instrument suite includes a combined retarding potential analyzer and cross-track drift meter and an ion-neutral mass spectrometer. This instrument suite will provide comprehensive information about the fluctuations in plasma, as well as changes in the neutral profile. petitSat will launch into a 51 deg inclination orbit at 400 km (consistent with an International Space Station deployment), allowing for numerous conjunctions with the Boston University All-Sky Imager network over the mission lifetime. Published by Elsevier Ltd on behalf of COSPAR.

In this study, we analyze the directional distribution of the secondary interstellar neutral (ISN) O population observed by the IBEX-Lo neutral atom camera on the Interstellar Boundary EXplorer (IBEX) via the comparison with simulated ISN O intensity maps produced by an analytical model. In the analytical model, we assume that there are primary and secondary ISN populations at the heliopause. We further assume that each population is represented by a Maxwellian velocity distribution function with its own flow parameters. For the viewing directions of IBEX-Lo, we compute the incoming atom speeds at the heliopause with a Keplerian equation of motion in the solar gravity field. Then, we calculate analytically the distribution function to obtain the ISN intensities at Earth's orbit. We compare the simulated O intensity maps with the IBEX-Lo O sky map to determine the most likely flow parameters of the secondary ISN O population. Using this method, we find the most likely flow parameters of the secondary ISN O population: V-SecISNO = 11 +/- 2.2 km s(-1), lambda(SecISNO) = 67 degrees +/- 1 degrees.5, beta(SecISNO) = -12 degrees +/- 1 degrees.6, and T-SecISNO = 10,000 +/- 1500 K. The results indicate that the secondary ISN O flow direction is deflected toward lower ecliptic longitude and higher negative ecliptic latitude from the ISN gas flow direction at the heliopause. The secondary ISN O flow direction is more deflected from the ISN gas flow direction than the secondary ISN He flow direction.

Microchannel plate (MCP) detectors provide a mechanism to produce a measureable current pulse (∼0.1 mA over several nanoseconds) when stimulated by a single incident particle or photon. Reductions of the device's amplification factor (i.e., gain) due to high incident particle flux can lead to significant degradation of detection system performance. Here we develop a parameterized model for the variation of MCP gain with incident flux. This model provides a framework with which to quantify the limits of high-flux MCP operation. We then compare the predictions of this model to laboratory measurements of an MCP's response to a pulsed charged particle beam. Finally, we demonstrate that through integration of the MCP output current in pulsed operation, effective count rates up to ∼1 GHz can be achieved, more than an order of magnitude increase over conventional counting techniques used for spaceflight applications.

The Compact Radiation belt Explorer, CeREs, a 3U CubeSat, is expected to be launched July 2018. The primary science goal of CeREs will be to study the physics of the acceleration and loss of radiation belt electrons, in particular electron microbursts, an important process that contributes to loss of electrons. A secondary science objective of CeREs is to characterize solar energetic particles (SEP), specifically electrons and protons, accessing the near Earth environment via the open field lines over the poles. Solar electron observations will advance our understanding of electron acceleration mechanisms in solar flares and their transport in interplanetary and solar regions. The CeREs CubeSat will be in a low earth, high inclination orbit with a year-long prime-science phase. CeREs measurements complement and extend the science goals of the Van Allen Probes, a NASA flagship mission in a near-equatorial orbit. The MERiT instrument aboard CeREs will detect electrons (protons) at energy levels from ~5(100) keV to ~10 (100) MeV using a stack of 8 silicon solid-state detectors (SSDs) and four avalanche photo diodes (APDs), which are provided by Southwest Research Institute (SwRI), the co-I institute. The front-end electronics use an innovative Energy-4 ASIC developed at Goddard Space Flight Center. The onboard CHREC Space Processor card is multi-institutional effort funded by the NSF Center for High-Performance Reconfigurable Computing (CHREC). This paper will describe the CeREs spacecraft and its mission in detail and highlight advancements made in the development of the MERiT instrument and supporting hardware.