Measurement of middle atmospheric ozone density profile by rocket-borne radiometer onboard KSR-II

KSR-II, a two-stage sounding rocket of KARI was launched successfully at the Korean Peninsula on June 11, 1998. The apogee of the rocket was 137 km. For the ozone measurement, 8-channel UV and visible radiometers were onboard the rocket. The rocket measured an in situ stratospheric and mesospheric ozone density profile over Korea during its ascending phase using the radiometer and transmitted the data to ground station in real time. The maximum ozone density occurs near 25 km. Retrieved profile has a random error (1σ) of approximately 15% for altitude below 20km, 7% between 20-50 km and 10% greater than 50 km. The retrieved data were compared with Dobson spectrophotometer, ozonesonde, and HALOE onboard the UARS. Our results are in reasonable agreements with others.     

Cascade-type guidance law design for multiple-UAV formation keeping

A procedure to compute guidance commands for controlling the relative geometry of multiple unmanned aerial vehicles (UAVs) in formation flight is proposed. The concepts of branch, global leader, and local leader/follower are used to represent the whole formation geometry. A positive-definite function defined in terms of the formation error is then introduced and the Lyapunov stability theorem is used to obtain the cascade type guidance law. This scheme leads to the synchronized flight of all UAVs while maintaining formation geometry. The results of a high fidelity nonlinear simulation of a reconnaissance and surveillance mission example are presented to show the effectiveness of the proposed guidance law.     

Lunar cosmic ray radiation environments during Luna and Lunar Reconnaissance Orbiter missions

The RV-2N-series instruments onboard Luna missions and the Cosmic Ray Telescope for the Effects of Radiation (CRaTER) instrument onboard Lunar Reconnaissance Orbiter (LRO) were designed to characterize the global lunar radiation environment and its biological impacts by measuring cosmic ray (CR) intensity. In this study, we have shown that the RV-2N-series instruments onboard of Russian Luna missions and the CRaTER reliably detect both background CRs and solar proton events (SPEs) in the lunar radiation environment using the proton intensity measured by the RV-2N-series onboard Luna missions out of the Russian Luna program for the exploration of the Moon (November 1970–August 1975) and the CR intensity on the Moon observed by the CRaTER (June 2009–March 2011). Those were compared with the CR intensities observed by neutron monitors (McMurdo, Thule, Oulu) on the Earth. The sunspot number is used as the index of solar activity (NOAA National Geophysical Data Center). As a result, the background CR intensities on the Moon turned out to have a good anti-correlation with the solar activity. We have also identified the proton intensity increasing events on the Moon which have the similar profiles to those observed by neutron monitors on the Earth. Most of these events show the significant increase of proton intensities in the lunar radiation environment when the SPEs associated with solar eruptions are verified. Therefore, most of the proton intensity increasing events are associated with the energetic solar particles in the lunar environment.     

Biased PNG law for impact with angular constraint

A new homing guidance law is proposed to impact a target with a desired attitude angle. It is a variation of the conventional proportional navigation guidance (PNG) law which includes a supplementary time-varying bias. The proposed guidance law does not require a time-to-go estimation and has a simpler form. Analytic conditions for fulfilling the guidance goal are also provided. Simulation results demonstrate that the proposed guidance law has wider launch envelopes than the previous one and shows a good performance even against a maneuvering target     

VLSI architecture for SAR data compression

As a step towards a real-time signal aperture radar (SAR) correlator, custom very large scale integration (VLSI) architectures are developed. Considering the extremely short word length of the data, we derive three architectures with massive parallelism in bit space. Unlike frequency methods, no. degradation is introduced during convolution. Optimized for time and space, they are highly suited to VLSI implementation, and a small architecture with 80 taps operating at 10 MHz has been built using an FPGA     

Prescreening during image formation for ultrawideband radar

Standard radar image formation techniques waste computational resources by full resolving all areas of the scene, even regions of benign clutter. We introduce a multiscale prescreener algorithm that runs as part of the image formation processing step for ultrawideband (UWB) synthetic aperture radar (SAR) systems. The prescreener processes intermediate radar data generated by a quadtree backprojection image former. As the quadtree algorithm iterates, it is resolving increasingly finer subpatches of the scene. After each quadtree stage, the prescreener makes an estimate of the signal-to-background ratio of each subpatch and applies a constant false alarm rate (CFAR) detector to decide which ones might contain a target of interest. Whenever the prescreener determines that a subpatch is not near a detection, it cues the image former to terminate further processing of that subpatch. Using a small database of UWB radar field data, we demonstrate that the prescreener is able to decrease the overall computational load of the image formation process. We also show that the new multiscale prescreener method produces fewer false alarms than the conventional two-parameter CFAR prescreener applied to the completely formed image     

Deployable space structure control using adaptive predictive controller with notch filter

The present study addresses the adaptive predictive controller with adaptive notch filter for the tip position control of a deployable space structure model. An adaptive notch filter is designed to estimate multiple bending mode frequencies of the deployable manipulator and to minimize the effect of bending vibration. The results show that the adaptive predictive controller with adaptive notch filter is quite effective controlling the tip position of a deployable space structure under poor modeling information.     

Capturability of the 3-dimensional pure PNG law

Although a lot of effort has been recently devoted to the capturability analysis of the pure proportional navigation guidance (PPNG) law, there are still significant discrepancies between the analysis results and the actual capturability of the PPNG law. In this paper, a Lyapunov-like approach along with a vector analysis method based on the so-called LOS (line of sight) plane is introduced to analyze the capturability of the 3-dimensional PPNG law against a target maneuvering arbitrarily with time-varying normal acceleration. Thereby, our analysis result can explain the high capturability of the PPNG law theoretically much better than those presented in the prior literature. In our capturability analysis, the nonlinear dynamics of 3-dimensional pursuit situations have been taken into full account. Our approach is also expected to be useful for the design and analysis of other PPNG-like missile guidance laws     

Missile autopilot design via functional inversion and time-scaled transformation

This paper presents a new approach to acceleration control of STT (Skid-To-Turn) missiles. In the design and stability analysis of our autopilot, we assume perfect roll-stabilization but consider fully all other nonlinearities of the missile dynamics including the coupling effect due to bank angle. Our autopilot controller consists of a partial-linearizing controller and a dynamic compensator. The partial-linearizing controller along with a time scaled transformation can convert the nonlinear missile dynamics to the so-called normalized system which is completely independent of Mach number and almost independent of air density. The dynamic compensator is designed based on this normalized system. This normalized system greatly simplifies the design process of an autopilot controller regardless of flight conditions. Our autopilot controller can provide fast and exact set-point tracking performance but without the slow-varying conditions on angle of attack and side-slip angle required often in the prior works.     

Solar polar magnetic field dependency of geomagnetic activity semiannual variation indicated in the Aa index

Three major hypotheses have been proposed to explain the well-known semiannual variation of geomagnetic activity, maxima at equinoxes and minima at solstices. This study examined whether the seasonal variation of equinoctial geomagnetic activity is different in periods of opposite solar magnetic polarity in order to understand the contribution of the interplanetary magnetic field (IMF) in the Sun-Earth connection. Solar magnetic polarity is parallel to the Earth’s polarity in solar minimum years of odd/even cycles but antiparallel in solar minimum years of even/odd cycles. The daily mean of the aa, Aa indices during each solar minimum was compared for periods when the solar magnetic polarity remained in opposite dipole conditions. The Aa index values were used for each of the three years surrounding the solar minimum years of the 14 solar cycles recorded since 1856. The Aa index reflects seasonal variation in geomagnetic activity, which is greater at the equinoxes than at the solstices. The Aa index reveals solar magnetic polarity dependency in which the geomagnetic activity is stronger in the antiparallel solar magnetic polarity condition than in the parallel one. The periodicity in semiannual variation of the Aa index is stronger in the antiparallel solar polar magnetic field period than in the parallel period. Additionally, we suggest the favorable IMF condition of the semiannual variation in geomagnetic activity. The orientation of IMF toward the Sun in spring and away from the Sun in fall mainly contributes to the semiannual variation of geomagnetic activity in both antiparallel and parallel solar minimum years.