Cosmic ray hit frequencies in critical sites in the central nervous system.

One outstanding question to be addressed in assessing the risk of exposure to space travelers from galactic cosmic rays (GCR) outside the geomagnetosphere is to ascertain the effects of single heavy-ion hits on cells in critical regions of the central nervous system (CNS). As a first step toward this end, it is important to determine how many "hits" might be received by a neural cell in several critical CNS areas during an extended mission outside the confines of the earth's magnetic field. Critical sites in the CNS: the macula, and an interior brain point (typical of the genu, thalamus, hippocampus and nucleus basalis of Meynert) were chosen for the calculation of hit frequencies from galactic cosmic rays for a mission to Mars during solar minimum (i.e., at maximum cosmic-ray intensity). The shielding at a given position inside the body was obtained using the Computerized Anatomical Man (CAM) model, and a radiation transport code which includes nuclear fragmentation was used to calculate yearly fluences at the point of interest. Since the final Mars spacecraft shielding configuration has not yet been determined, we considered the minimum amount of aluminum required for pressure vessel-wall requirements in the living quarters of a spacecraft, and a typical duty area as a pressure vessel plus necessary equipment. The conclusions are: (1) variation of the position of the "target site" within the head plays only a small role in varying hit frequencies; (2) the average number of hits depends linearly on the cross section of the critical portion of the cell assumed in the calculation; (3) for a three-year mission to Mars at solar minimum (i.e., assuming the 1977 spectrum of galactic cosmic rays), 2% or 13% of the "critical sites" of cells in the CNS would be directly hit at least once by iron ions, depending on whether 60 micrometers2 or 471 micrometers2 is assumed as the critical cross sectional area; and (4) roughly 6 million out of some 43 million hippocampal cells and 55 thousand out of 1.8 million thalamus cell nuclei would be directly hit by iron ions at least once on such a mission for space travelers inside a simple pressure vessel. Also, roughly 20 million out of 43 million hippocampal cells and 230 thousand out of 1.8 million thalamus cell nuclei would be directly hit by one or more particles with z > or = 15 on such a mission.     

Observation of Plasma Instability on the Dayside Region between Magnetosheath and Ionosphere of Mars

Cosmic Research - The interaction of the solar wind with the plasma envelope of planets without their own global magnetic field has a different character than does the corresponding process near...     

Evaluation of a Geiger-mode imaging flash lidar in the approach phase for autonomous safe landing on the Moon

The imaging flash lidar has been considered as a promising sensor for the future space missions such as autonomous safe landing, spacecraft rendezvous and docking due to its ability to provide a full 3D scene with a single or multiple laser pulses. The linear-mode flash lidar has been developed and demonstrated for an autonomous safe landing on the Moon in order to provide an accurate distance measurement to the landing site and its 3D image. Yet, the Geiger-mode flash lidar has also been recognized as an emerging technology for the space missions because it is highly sensitive even to a single photon and provides the very accurate timing of photon arrival. In this study, the performance of the Geiger-mode flash lidar is simulated in the approach phase and evaluated for the autonomous landing on the Moon. Furthermore, a new statistical signal processing algorithm is proposed to remove the noise counts in order to obtain the 3D image from a sequence of laser pulses in the situation of the fast moving spacecraft. The algorithm is shown to be effective for the autonomous landing due to its ability to remove noise events under the condition of low signal-to-noise ratio and improve ranging accuracy.     

East–West Station-Keeping maneuver strategy for COMS satellite using iterative process

The first Korean multi-mission geostationary satellite, Communication, Ocean, and Meteorological Satellite (COMS) will be launched in 2010. The missions of this satellite will be Ka-band communications, ocean color monitoring, and meteorological imaging. The satellite was designed with only one solar array on the south panel. This novel configuration will keep imaging instruments on the north side from heating up. Asymmetry of the spacecraft configuration requires twice-a-day thruster-based Wheel Off-Loading (WOL) operations to keep the satellite attitude for imaging and communication. Thruster firings during the WOL operations cause the satellite orbit to change two times a day. Weekly East–West Station-Keeping (EWSK) and North–South Station-Keeping (NSSK) maneuver operations are planned for the COMS satellite in order to maintain the satellite in ±0.05° box at 128.2°E longitude.     

Effects of solar activity variations on the low latitude topside nighttime ionosphere

We have studied the topside nighttime ionosphere of the low latitude region using data obtained from DMSP F15, ROCSAT-1, KOMPSAT-1, and GUVI on the TIMED satellite for the period of 2000–2004, during which solar activity decreased from its maximum. As these satellites operated at different altitudes, we were able to discriminate altitude dependence of several key ionospheric parameters on the level of solar activity. For example, with intensifying solar activity, electron density was seen to increase more rapidly at higher altitudes than at lower altitudes, implying that the corresponding scale height also increased. The density increased without saturation at all observed altitudes when plotted against solar EUV flux instead of F10.7. The results of the present study, as compared with those of previous studies for lower altitudes, indicate that topside vertical scale height increases with altitude and that, when solar activity increases, topside vertical scale height increases more rapidly at higher altitudes than at lower altitudes. Temperature also increased more rapidly at higher altitudes than at lower altitudes as solar activity increased. In addition, the height of the F2 peak was seen to increase with increasing solar activity, along with the oxygen ion fraction measured above the F2 peak. These results confirm that the topside ionosphere rises and expands with increasing solar activity.     

A study on Nighttime Winter Anomaly (NWA) and other related Mid-latitude Summer Nighttime Anomaly (MSNA) in the light of International Reference Ionosphere (IRI) – Model

The ionospheric Nighttime Winter Anomaly (NWA) is a feature observed in the Northern Hemisphere at the American and in the Southern Hemisphere at the Asian longitude sector under low solar activity conditions. Jakowski et al. (2015) analyzed ground-based GPS derived TEC and peak electron density data from radio occultation measurements on Formosat-3/COSMIC satellites and confirmed the persistence of the phenomenon. Further, they assumed that Mid-latitude Summer Nighttime Anomaly (MSNA) and related special anomalies such as the Weddell Sea Anomaly (WSA) and the Okhotsk Sea Anomaly (OSA) are closely related to the NWA via enhanced wind-induced uplifting of the ionosphere. The aim of this paper is to study the factors causing these anomalies and also to investigate if these anomalies are re-produced by IRI. The results show that IRI model does include the NWA effect, though at a different longitude and could be improved for better predictions. The IRI-2016 model does show WSA in TEC but not in NmF2. Further, the IRI-2016 model could clearly predict the OSA both in NmF2 and TEC.     

Probabilistic assessment of radiation risk for astronauts in space missions

Accurate estimations of the health risks to astronauts due to space radiation exposure are necessary for future lunar and Mars missions. Space radiation consists of solar particle events (SPEs), comprised largely of medium energy protons (less than several hundred MeV); and galactic cosmic rays (GCR), which include high-energy protons and heavy ions. While the frequency distribution of SPEs depends strongly upon the phase within the solar activity cycle, the individual SPE occurrences themselves are random in nature. A solar modulation model has been developed for the temporal characterization of the GCR environment, which is represented by the deceleration potential, ?. The risk of radiation exposure to astronauts as well as to hardware from SPEs during extra-vehicular activities (EVAs) or in lightly shielded vehicles is a major concern for radiation protection. To support the probabilistic risk assessment for EVAs, which could be up to 15% of crew time² on lunar missions, we estimated the probability of SPE occurrence as a function of solar cycle phase using a non-homogeneous Poisson model [1] to fit the historical database of measurements of protons with energy>30 MeV, Φ₃₀. The resultant organ doses and dose equivalents, as well as effective whole body doses, for acute and cancer risk estimations are analyzed for a conceptual habitat module and for a lunar rover during space missions of defined durations. This probabilistic approach to radiation risk assessment from SPE and GCR is in support of mission design and operational planning for future manned space exploration missions.     

Analytical and numerical approaches of a solar array thermal analysis in a low-earth orbit satellite

This paper researches the thermal analysis of a fixed-type solar array in a low-earth orbit satellite through both an analytical method with a simplified thermal model and a numerical method with a detailed thermal model.     

The Pluto Energetic Particle Spectrometer Science Investigation (PEPSSI) on the New Horizons Mission

The Pluto Energetic Particle Spectrometer Science Investigation (PEPSSI) comprises the hardware and accompanying science investigation on the New Horizons spacecraft to measure pick-up ions from Pluto’s outgassing atmosphere. To the extent that Pluto retains its characteristics similar to those of a “heavy comet” as detected in stellar occultations since the early 1980s, these measurements will characterize the neutral atmosphere of Pluto while providing a consistency check on the atmospheric escape rate at the encounter epoch with that deduced from the atmospheric structure at lower altitudes by the ALICE, REX, and SWAP experiments on New Horizons. In addition, PEPSSI will characterize any extended ionosphere and solar wind interaction while also characterizing the energetic particle environment of Pluto, Charon, and their associated system. First proposed for development for the Pluto Express mission in September 1993, what became the PEPSSI instrument went through a number of development stages to meet the requirements of such an instrument for a mission to Pluto while minimizing the required spacecraft resources. The PEPSSI instrument provides for measurements of ions (with compositional information) and electrons from 10 s of keV to ～1 MeV in a 160°×12° fan-shaped beam in six sectors for 1.5 kg and ～2.5 W.