Dust observations with antenna measurements and its prospects for observations with Parker Solar Probe and Solar Orbiter

The electric and magnetic field instrument suite FIELDS on board the NASA Parker Solar Probe and the radio and plasma waves instrument RPW on the ESA Solar Orbiter mission that explore the inner heliosphere are sensitive to signals generated by dust impacts. Dust impacts have been observed using electric field antennas on spacecraft since the 1980s and the method was recently used with a number of space missions to derive dust fluxes. Here, we consider the details of dust impacts, subsequent development of the impact generated plasma and how it produces the measured signals. We describe empirical approaches to characterise the signals and compare these in a qualitative discussion of laboratory simulations to predict signal shapes for spacecraft measurements in the inner solar system. While the amount of charge production from a dust impact will be higher near the Sun than observed in the interplanetary medium before, the amplitude of pulses is determined by the recovery behaviour that is different near the Sun since it varies with the plasma environment

CHARGING AND DETECTION OF MESOSPHERIC DUST WITH INSTRUMENT SPID ON G-CHASER ROCKET

The Smoke Particle Impact Detector (SPID) was flown on the G-Chaser student rocket that was launched from Andøya on 13 January 2019. SPID is a Faraday cup instrument with applied bias voltages to deflect the ambient plasma and a target area inside the probe designed to measure the dust particles by charge detection. The charging process of the dust particles in the detector is important for interpretation of the measurements and the influence of the charging models is discussed. Preliminary analysis of the SPID observations shows that ambient plasma and sunlight had an influence on the signals; further analysis is needed to retrieve information on impacting dust from the data

In-situ Measurements of Mesospheric Aerosols - On the observable characteristics of nanoscale ice and meteoric smoke particles

Two sounding rocket payloads were launched from Andøya Space Centre (69.29 N, 16.02 E) during the summer of 2016 within the MAXIDUSTY campaign. Their payloads contained instrumentation aimed at investigating the characteristics of nanoscale aerosols in the upper summer mesosphere, and the role of these particles in phenomena like noctilucent clouds and polar mesospheric summer echoes (PMSE). The mesopause region, situated between $\sim 80$ and 90 km, contain a variety of different particle types such as ice particles, meteoric smoke particles (MSPs) and hybrids of these. The role of such particles in a number of processes in the mesopause and further down in the atmosphere is not well understood. This work aims to close some of the gaps in our current understanding mainly by using aerosol detectors of the Faraday cup type. For this purpose, we have developed new observational techniques using such probes, which makes it possible to obtain information on intrinsic particle properties such as charge state, size and number density of both ice and MSPs. The configuration and technical capabilities of the probes on MAXIDUSTY also allows for observation of spatial structures in the dusty plasma down to scales of $\sim 10$ cm. Notably, we are able to calculate the size distribution and charge state of ice particles on scales well below 1 metre. With the impact probe MUDD, we are able to infer the size distribution and volume content of MSPs embedded in larger ice particles. We moreover present the first observations of mesospheric clouds situated well below the summer mesopause, at altitudes between $66$ and 78 km, which implies a significant updraft in this region. From a thorough investigation into spatial fluctuations on different length scales, we find that the aerosol-electron coupling is changing throughout a cloud system and not strictly anti-correlated. We also find that a simple relationship between PMSE and dusty plasma parameters is not possible to obtain from MAXIDUSTY measurements

On the internal physical conditions in dust probes: transport, heating and evaporation of fragmented dust particles

We study the conditions within, and dynamics of fragmented mesospheric dust particles inside, the Faraday-cup type dust probe MUDD using numerical simulations with a dedicated model. The transport of singly charged fragments from impacting NLC particles on the main grid in MUDD, have been calculated on the basis of supplementary models of the neutral gas conditions and electric field structure within the probe. The theoretical model includes the effects of drag from neutral molecules, electric forces, as well as heating of -- and evaporation from -- the fragments. The model equations have been improved to be valid for nanoscale particles with a broad range of intrinsic properties, in the molecular flow regime. We find that the size range for unambiguous detection of pure MSP fragments of mass density rho_s=3000 kgm^(-3), is limited to fragments of radii between 1.5 nm and 2.1 nm with a 0.3 nm resolution; i.e. for the two existing detection modes of retarding potentials 10 V and 20 V. In the zero potential reference mode, fragments with radii smaller than 0.8 nm are stopped completely by neutrals. Fragments of pure ice content are found to evaporate rapidly, and will not contribute significantly to the measured currents at the bottom plate. Ice particles which contribute to the currents have to be larger than 3 nm, which renders the common assumption that ice particles smaller than 3 nm in radius must stick to probe surfaces [Tomsic, 2001; Havnes and Næsheim, 2007] redundant. From the study of alternative potential modes in MUDD, it is found that is is possible to improve the detectable size distribution of MUDD significantly by using lower retarding or accelerating potentials than the modes which already exist. Results from the E-field modeling suggest that the production of secondary charges have been somewhat underestimated due to very strong field anomalies near the edges of the probe. We also find plausibly large uncertainty factors from the investigations of initial fragment velocity, dynamic shape and heating of fragments during collisions with G2

On the Relationship between PMSE Strength and Particle Precipitation

We have studied the relationship between particle precipitation and PMSE strength on days where we observe PMSE layers both with the EISCAT VHF and UHF radars. The UHF observations of the ionization and its variation, above the PMSE layer, is used as a measure of precipitation. Variations of the precipitation is compared with variations of the PMSE strengths observed with both radars. Although many cases apparently show a clear connection between precipitation and PMSE, where an increased precipitation leads to a strengthening of the PMSE, our findings confirm that there is no general and simple proportionality between the two. For the weakest PMSE there appears to be no correlation between precipitation and PMSE strength. For PMSEs around average strength of our observations there appears to be a weak positive correlation, which can be predicted by a timedependent dust cloud charge model. On some occasions an increased precipitation can, apparently, initially lead to an increase of PMSE strength which at some point starts to decline even if the precipitation continue to increase. This feature can also be seen in the results from the statistical analysis, however the number of occurrences is too low to conclude with significance and the time-dependent charge model described here does not reproduce such features. We have studied to what degree models for the PMSE scattering can explain the various cases of reaction of PMSE to changes in precipitatio

A comparison of contact charging and impact ionization in low-velocity impacts: implications for dust detection in space

We investigate the generation of charge due to collision between projectiles with sizes below ∼1 µm and metal surfaces at speeds ∼0.1 to 10 km s−1. This corresponds to speeds above the elastic limit and well below speeds where volume ionization can occur. Impact charge production at these low to intermediate speeds has traditionally been described by invoking the theory of shock wave ionization. By looking at the thermodynamics of the low-velocity solution of shock wave ionization, we find that such a mechanism alone is not sufficient to account for the recorded charge production in a number of scenarios in the laboratory and in space. We propose a model of capacitive contact charging that involves no direct ionization, in which we allow for projectile fragmentation upon impact. Furthermore, we show that this model describes measurements of metal–metal impacts in the laboratory well. We also address contact charging in the context of ice-on-metal collisions and apply our results to rocket observations of mesospheric dust. In general, we find that contact charging dominates at speeds of up to a few kilometres per second and complements shock wave ionization up to speeds where direct ionization can take place. The conditions that we consider can be applied to dust particles naturally occurring in space and in Earth's upper atmosphere and their direct impacts on rockets, spacecraft, and impacts of secondary ejecta

Ion Cloud Expansion after Hypervelocity Dust Impacts Detected by the MMS Electric Probes in the Dipole Configuration

Dust impact detection by electric field instruments is a well-established technique. On the other hand, not all aspects of signal generation by dust impacts are completely understood. We present a study of events related to dust impacts on the spacecraft body detected by electric field probes operating simultaneously in the monopole (probe-to-spacecraft potential measurement) and dipole (probe-to-probe potential measurement) configurations by the Earth-orbiting Magnetospheric Multiscale mission spacecraft. This unique measurement allows us to investigate connections between monopole and dipole data. Our analysis shows that the signal detected by the electric field instrument in a dipole configuration is generated by an ion cloud expanding along the electric probes. In this case, expanding ions affect not only the potential of the spacecraft body but also one or more electric probes at the end of antenna booms. Electric probes located far from the spacecraft body can be influenced by an ion cloud only when the spacecraft is located in tenuous ambient plasma inside of the Earth's magnetosphere. Derived velocities of the expanding ions on the order of tens of kilometers per second are in the range of values measured experimentally in the laboratory

CHARGING AND DETECTION OF MESOSPHERIC DUST WITH INSTRUMENT SPID ON G-CHASER ROCKET

The Smoke Particle Impact Detector (SPID) was flown on the G-Chaser student rocket that was launched from Andøya on 13 January 2019. SPID is a Faraday cup instrument with applied bias voltages to deflect the ambient plasma and a target area inside the probe designed to measure the dust particles by charge detection. The charging process of the dust particles in the detector is important for interpretation of the measurements and the influence of the charging models is discussed. Preliminary analysis of the SPID observations shows that ambient plasma and sunlight had an influence on the signals; further analysis is needed to retrieve information on impacting dust from the data

Observation of mesospheric dust and ionospheric conditions during the G-chaser rocket campaign

Paper at 24th ESA Symposium on European Rocket and Balloon Programmes and Related Research, Essen, Germany, 16-20 June 2019. Conference home page.SPID, Smoke Particle Impact Detector, is a Faraday cup detector designed to measure nanometer-sized meteoric smoke particles during rocket flights. We report measurements made with SPID during the G-Chaser student rocket campaign 13 January 2019 and describe the design of the SPID instruments. Model calculations of dust trajectories within the detector result in an effective crosssection of 0.97 for particles larger than 0.5 nm at 60 km. Data analysis indicates that in order to generate the measured current, the number densities must be ∼ 1010m−3 or higher at 60 km. During the campaign the ground systems MAARSY and EISCAT were operating. These ground measurements showed smooth ionospheric conditions with weak precipitation down to 90 km. As a secondary goal of the campaign we wanted to investigate the possible connection between PMWE and MSPs. On the day of the launch there was no sign of PMWE and no conclusions can be drawn at this point

Observation of mesospheric dust and ionospheric conditions during the G-chaser rocket campaign

SPID, Smoke Particle Impact Detector, is a Faraday cup detector designed to measure nanometer-sized meteoric smoke particles during rocket flights. We report measurements made with SPID during the G-Chaser student rocket campaign 13 January 2019 and describe the design of the SPID instruments. Model calculations of dust trajectories within the detector result in an effective crosssection of 0.97 for particles larger than 0.5 nm at 60 km. Data analysis indicates that in order to generate the measured current, the number densities must be ∼ 1010m−3 or higher at 60 km. During the campaign the ground systems MAARSY and EISCAT were operating. These ground measurements showed smooth ionospheric conditions with weak precipitation down to 90 km. As a secondary goal of the campaign we wanted to investigate the possible connection between PMWE and MSPs. On the day of the launch there was no sign of PMWE and no conclusions can be drawn at this point