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.     

关于直升机旋翼挥舞问题的探讨

本文研究直升机旋翼挥舞运动的变化规律和操纵规律,以桨叶挥舞运动的微分方程为模型,分析研究桨叶挥舞运动中旋翼拉力保持不变,且旋翼保持的挥舞状态,以及影响旋翼挥舞状态的因素。同时,直升机在悬停的基础上以前推杆为例,找出旋翼挥舞角的变化规律和旋翼锥体的倾斜方向变化规律,为分析旋翼挥舞中的实际飞行问题提供理论依据。     

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.     

Observations of ionospheric irregularities and its correspondence with sporadic e occurrence over South Korea and Japan

This study analyzed the occurrence of ionospheric irregularities over South Korea and Japan (mid-latitudes) during the years 2010–2015. The irregularities were quantified using the rate of change of total electron content (TEC) index (ROTI), which detects irregularities with scale sizes in the range of 400 m–2.5 km. The ROTI threshold for an ionospheric irregularity to have occurred was set as 0.1 TECU/min. Results showed that ionospheric irregularities mostly occur during night-time and around local noon-time in the seasons of spring and summer. In addition, the percentage of ionospheric irregularities had a high positive correlation with solar flux (F10.7) (r > 0.72). For the first time, we showed good correspondence between ionospheric irregularities measured by the ROTI index and sporadic E (Es). The median ROTI associated with ionospheric irregularities over a South Korea station (DAEJ) and a Japan station (KGNI) were 0.131 and 0.125 TECU/min, respectively. However, in severe cases of ionospheric irregularities, the ROTI values over DAEJ (KGNI) can reach 0.246 (0.217) and 0.314 (0.339) TECU/min during day and night, respectively. These critical ROTI values can be important in interpreting and monitoring ionospheric irregularity occurrence over South Korea and Japan.     

Hardware-In-the-Loop Simulations of spacecraft attitude synchronization using the State-Dependent Riccati Equation technique

A nonlinear control technique pertaining to attitude synchronization problems is presented for formation flying spacecraft by utilizing the State-Dependent Riccati Equation (SDRE) technique. An attitude controller consisting of relative control and absolute control is designed using a reaction wheel assembly for regulator and tracking problems. To achieve effective relative control, the selective state-dependent connectivity is also adopted. The global asymptotic stability of the controller is confirmed using the Lyapunov theorem and is verified by Monte-Carlo simulations. An air-bearing-based Hardware-In-the-Loop Simulator (HILS) is also developed to validate the proposed control laws in real-time environments. The SDRE controller is discretized for implementation of a real-time processor in the HILS. The pointing errors are about 0.2° in the numerical simulations and about 1° in the HILS simulations, and experimental simulations confirm the effectiveness of the control algorithm for attitude synchronization in a spacecraft formation flying mission. Consequently, experiments using the HILS in a real-time environment can appropriately perform spacecraft attitude synchronization algorithms for formation flying spacecraft.     

Design of tracking mount and controller for mobile satellite laser ranging system

In this study, we have proposed and implemented a design for the tracking mount and controller of the ARGO-M (Accurate Ranging system for Geodetic Observation - Mobile) which is a mobile satellite laser ranging (SLR) system developed by the Korea Astronomy and Space Science Institute (KASI) and Korea Institute of Machinery and Materials (KIMM). The tracking mount comprises a few core components such as bearings, driving motors and encoders. These components were selected as per the technical specifications for the tracking mount of the ARGO-M. A three-dimensional model of the tracking mount was designed. The frequency analysis of the model predicted that the first natural frequency of the designed tracking mount was high enough. The tracking controller is simulated using MATLAB/xPC Target to achieve the required pointing and tracking accuracy. In order to evaluate the system repeatability and tracking accuracy of the tracking mount, a prototype of the ARGO-M was fabricated, and repeatability tests were carried out using a laser interferometer. Tracking tests were conducted using the trajectories of low earth orbit (LEO) and high earth orbit (HEO) satellites. Based on the test results, it was confirmed that the prototype of the tracking mount and controller of the ARGO-M could achieve the required repeatability along with a tracking accuracy of less than 1 arcsec.     

Procedure and methodologies for managing the risk of space object reentry

This paper proposes a procedure for managing the risk of reentering space objects and risk assessment methodologies used for the process. The proposed procedure comprises three phases encompassing the whole reentry stages of space objects. Mathematical models for assessing the impact risk of the reentering space objects by utilizing the information available during different risk management phases and the recommended risk analysis results for public communication are presented. The concept of the conditional casualty expectation is proposed as the metric representing the reentry risk and the method to compute its profile is introduced. A case study on the risk management procedure with the dataset on an actual reentry event is conducted to demonstrate the efficacy of the proposed procedure.     

Towards accurate atmospheric mass density determination Using precise positional information of space objects

This paper presents a new method of deriving atmospheric mass densities with a high temporal resolution from precise orbit data of low earth orbiting (LEO) space objects. This method is based on the drag perturbation equation of the semi-major axis of the orbit of LEO space objects which relates the change rate of the semi-major axis to the atmospheric mass density. The effectiveness of the new method is evaluated using the GFZ-ISDC GPS rapid science orbit (RSO) products of the CHAMP satellite over a time period of 3 months. The densities derived using this new method and obtained from accelerometer data are compared and good agreements are achieved. An example of using the derived density to generate good orbit prediction for CHAMP is presented.     

Changes in sea-level pressure over South Korea associated with high-speed solar wind events

We explore a possibility that the daily sea-level pressure (SLP) over South Korea responds to the high-speed solar wind event. This is of interest in two aspects: first, if there is a statistical association this can be another piece of evidence showing that various meteorological observables indeed respond to variations in the interplanetary environment. Second, this can be a very crucial observational constraint since most models proposed so far are expected to preferentially work in higher latitude regions than the low latitude region studied here. We have examined daily solar wind speed V, daily SLP difference ΔSLP, and daily log(BV²) using the superposed epoch analysis in which the key date is set such that the daily solar wind speed exceeds 800 km s⁻¹. We find that the daily ΔSLP averaged out of 12 events reaches its peak at day +1 and gradually decreases back to its normal level. The amount of positive deviation of ΔSLP is +2.5 hPa. The duration of deviation is a few days. We also find that ΔSLP is well correlated with both the speed of solar wind and log(BV²). The obtained linear correlation coefficients and chance probabilities with one-day lag for two cases are r ? 0.81 with P > 99.9%, and r ? 0.84 with P > 99.9%, respectively. We conclude by briefly discussing future direction to pursue.     

The Jupiter Energetic Particle Detector Instrument (JEDI) Investigation for the Juno Mission

The Jupiter Energetic Particle Detector Instruments (JEDI) on the Juno Jupiter polar-orbiting, atmosphere-skimming, mission to Jupiter will coordinate with the several other space physics instruments on the Juno spacecraft to characterize and understand the space environment of Jupiter’s polar regions, and specifically to understand the generation of Jupiter’s powerful aurora. JEDI comprises 3 nearly-identical instruments and measures at minimum the energy, angle, and ion composition distributions of ions with energies from H:20 keV and O: 50 keV to >1 MeV, and the energy and angle distribution of electrons from <40 to >500 keV. Each JEDI instrument uses microchannel plates (MCP) and thin foils to measure the times of flight (TOF) of incoming ions and the pulse height associated with the interaction of ions with the foils, and it uses solid state detectors (SSD’s) to measure the total energy (E) of both the ions and the electrons. The MCP anodes and the SSD arrays are configured to determine the directions of arrivals of the incoming charged particles. The instruments also use fast triple coincidence and optimum shielding to suppress penetrating background radiation and incoming UV foreground. Here we describe the science objectives of JEDI, the science and measurement requirements, the challenges that the JEDI team had in meeting these requirements, the design and operation of the JEDI instruments, their calibrated performances, the JEDI inflight and ground operations, and the initial measurements of the JEDI instruments in interplanetary space following the Juno launch on 5 August 2011. Juno will begin its prime science operations, comprising 32 orbits with dimensions 1.1×40 RJ, in mid-2016.