L. S. Sollitt

A novel technique to infer ionic charge states of solar energetic particles

In some large solar energetic particle (SEP) events, the intensities of higher energy SEPs decay more rapidly than at lower energies. This energy dependence varies with particle species, as would be expected if the decay timescale depended on a rigidity-dependent diffusion mean free path. By comparing the decay timescales of carbon, nitrogen, oxygen, neon, magnesium, silicon, sulfur, and iron, mean charge states are inferred for these (and other) elements in three SEP events between 1997 and 2002 at energies between 10 and 200 MeV nucleon−1. In a fourth event, upper limits for the charge states are inferred. The charge states of many different particle species are all consistent with a single source temperature; in two events in 1997 and 2002, the best-fit temperature is much higher than that of the corona, which could imply a contribution from solar flare material. However, comparison with lower energy iron charge states for the 1997 event implies that the observed high-energy charge state could also be understood as the result of stripping during shock acceleration in the corona.

Penetrator Science - Making an Impact On Planetary Compositional Science

NASA’s return to the Moon has a pressing need to understand whether usable con centrations of ice exist in permanently shadowed cold craters. This need is only one example of a number of high value scientific measurements that can be cost effectively made using penetrators. A significant body of penetrator data, software modeling t ools, concepts, and history exist that provide a basis for penetrator missions to be defined, designed, developed and implemented. This paper examines the operational constraints for planetary missions, past and current penetrator missions , and, using lun ar ice as an example mission, defines and explores the trade space for future penetrator missions.

Inferred Ionic Charge States for Solar Energetic Particle Events from 2012-2015 with ACE and STEREO

Mean ionic charge states for SEP events can reflect source temperatures, stripping during acceleration and transport, and the composition of source material. Multi-spacecraft measurements of mean ionic charge states for single SEP events can also demonstrate longitudinal dependence depending on seed particle composition or acceleration conditions. in previous studies, we calculated inferred high-energy ionic charge states for SEP events. The analysis method fits the energy dependence of decay times for each element in SEP events, combined with charge-to-mass ratios relative to a calibration element, and derives mean charge state estimates for elements from O to Fe. Previously, we applied the method using ACE and STEREO data to SEP events through the beginning of 2012, in order to elucidate evidence on seed populations or longitudinal variations with charge state for single SEP events, with varying results. In this paper, we continue applying the method to new SEP events from 2012 to 2015 in the ACE and STEREO data. With the three spacecraft widely spread apart during this time period, there are fewer single SEP events with multi-spacecraft data, but the wide spacing allows more SEP candidate events to be considered, separately, than would be available with just a single spacecraft. Our new results for two SEP events continue to be consistent with observed correlation between Q(Fe) and Fe/O in previous events.

A Solar Path to Europa: How Solar Electric Propulsion Can Enable Missions to the Outer Solar System

The use of Solar Electric Propulsion (SEP) is evaluated in the context of a mission to Europa. It is shown that smaller missions making use of SEP can deliver a larger payload on a smaller launch vehicle than is possible with an all -ch emical mission. Large missions (over ~3700 kg) are possible on existing launch vehicles only with SEP systems. The cruise times for SEP missions are generally longer than for all -chemical missions, but depend on launch date. In examining missions to Europa , future planners would be well advised to include SEP in their trade studies. I. Introduction upiter’s moon Europa is one of the most important places in the solar system for future scientific study. Recent evidence 1-4 suggests that Europa may have beneat h its icy surface an ocean of liquid salt water that could potentially support a biosphere. The confirmation of the existence of such a subsurface ocean, and the detection of signs of life on Europa, are two of the most compelling science objectives in pla netary science. Europa has been designated as the most important destination in the outer planets by the NRC Decadal Survey for planetary science 5 . In this work, we examine mission ideas for the future exploration of Europa, and suggest how such a mission (or set of missions) could be done using proven launch vehicles and existing propulsion and other technologies. In this work, we discuss a number of possible missions to Europa. We start with concepts for small missions which would carry a reasonably limit ed payload and could include a lander. Ideas for the design of these missions are discussed in some detail; mission ideas that use solar electric propulsion (SEP) for part of the cruise to Jupiter are examined, as well as missions that use chemical propuls ion only. The point designs for the smaller missions are then scaled to larger mission ideas, with concomitantly higher payloads and capabilities. We will show that for large missions, only payloads delivered in part by a SEP system can be undertaken with a single launch using existing technology.

Feasibility studies of laser desorption to study surfaces of Jupiter's icy moons

We report the first efforts to characterize a laser desorption and thermal emission spectroscopic technique that could be used to detect and analyze the abundances of organic and inorganic compounds in the surfaces of Jupiters icy moons. Based on the literature, an infrared laser near 3.1 μm at a moderate fluence 120 mJ/cm2 may desorb the compounds in the ice surface into the gas phase through an efficient explosive phase-transition process. The desorbed compounds, which are much warmer than the ice, can be analyzed by monitoring their IR thermal emission spectra against the colder icy surface by use of an IR spectrometer. However, there appears to have some discrepancies in the literature on the exact threshold fluence for desorption. We have conducted experiments to determine the threshold fluence for the laser desorption of ice by use of a sensitive photoacoustic spectroscopy technique. Our results suggest that the threshold fluence near 3.1 μm, at the peak of optical absorption of ice, is close to 120 mJ/cm2, as compared to some other higher values being reported. In addition, our data shows a delay time of about 24 μs or longer for an explosive removal of a layer of the ice surface after the irradiation of a laser pulse. Implications for mission and instrument design are discussed.