• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.42 no.7
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• pp.544-551
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• 2014

A program of launch vehicle performance analysis is composed for the education of the conceptual design of launch vehicles and the requirement analysis for the propulsion system design. The program is applied for the mission analysis of space launch vehicles based on KSLV-II with liquid rocket boosters. The 75-ton class liquid rocket engine is assumed for the boosters by referring the mass ratio of KSLV-II second stage. The launch performance analysis is carried out for KSLV-II with 2, 3 and 4 boosters by targeting the circular orbit of 700 km altitude. The trajectory is assumed as two-dimension considering the variation of the flight environment. Payload of advanced KSLV-II could be increased to maximum 3 tons, though it is limited by the thrust performance of the upper stage.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.22 no.1
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• pp.16-23
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• 2011

This paper suggests a motion compensation technique using GPS/IMU data in order to compensate for phase error caused by undesired motion of radar platform. An actual flight trajectory would be deviate from an ideal straight-constant trajectory with a constant velocity for SAR imaging, due to pitch, roll and yaw motion of aircraft caused by turbulence. This leads to blurred SAR images due to inter-pulse phase errors as well as along-track velocity errors. If the motion compensation is carried out to reduce those errors, SAR image quality can be significantly improved. Simulation results show that the motion compensation technique introduced in this paper is an effective tool to improve SAR image quality against severe motion of radar platform.

• Journal of the Korean Society of Propulsion Engineers
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• v.24 no.1
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• pp.17-23
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• 2020

Upper stage of launch vehicle mainly injects a lunar explorer from low earth orbit to the moon at a distance of 380,000 km. In foreign lunar explorer, the upper stage is separated from the explorer after the explorer is injected into the earth-moon transfer trajectory, and the lunar explorer then uses on-board propellant to carry out mid-course correction maneuvers and lunar orbit insertion maneuvers. This study describes a newly presented small liquid upper stage. Using a small liquid upper stage with a wet mass of 2.9 tonnes, the lunar explorer not only can be injected earth-moon transfer trajectory but also can be performed lunar orbit insertion. This study provides acceptable mass range of the lunar explorer and the scope of acceptable mission range also describes based on the launch from Naro Space Center.

• International Journal of Aeronautical and Space Sciences
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• v.18 no.3
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• pp.545-554
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• 2017

Among various applications of the High Altitude Long Endurance (HALE) Unmanned Aerial Vehicle (UAV), this paper has a focus on the Global Positioning System (GPS) utilizing pseudolite and its improved performance, particularly during the multi-purpose missions. In a multi-purpose mission, the HALE UAV follows a specified flight trajectory for both navigation applications and missions. Some of the representative HALE missions are remote exploration, surveillance, reconnaissance, and communication relay. During these operations, the HALE UAV can also be an additional positioning signal source as it broadcast signals using pseudolite. The pseudolite signal can improve the availability, accuracy, and reliability of the GPS particularly in areas with poor signal reception, such as shadowed regions between tall buildings. The improvement in performance of navigation is validated through simulations of multi-purpose missions of the solar-powered HALE UAV in an urban canyon. The simulation includes UAV trajectory generation at stratosphere and uses actual geographical building data. The results indicate that the pseudolite-equipped HALE UAV has the potential to enhance the performance of the satellite navigation system in navigationally degraded regions even during multi-purpose operations.

• Journal of Astronomy and Space Sciences
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• v.33 no.4
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• pp.323-333
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• 2016

In this study, the uncertainty requirements for orbit, attitude, and burn performance were estimated and analyzed for the execution of the $1^{st}$ lunar orbit insertion (LOI) maneuver of the Korea Pathfinder Lunar Orbiter (KPLO) mission. During the early design phase of the system, associate analysis is an essential design factor as the $1^{st}$ LOI maneuver is the largest burn that utilizes the onboard propulsion system; the success of the lunar capture is directly affected by the performance achieved. For the analysis, the spacecraft is assumed to have already approached the periselene with a hyperbolic arrival trajectory around the moon. In addition, diverse arrival conditions and mission constraints were considered, such as varying periselene approach velocity, altitude, and orbital period of the capture orbit after execution of the $1^{st}$ LOI maneuver. The current analysis assumed an impulsive LOI maneuver, and two-body equations of motion were adapted to simplify the problem for a preliminary analysis. Monte Carlo simulations were performed for the statistical analysis to analyze diverse uncertainties that might arise at the moment when the maneuver is executed. As a result, three major requirements were analyzed and estimated for the early design phase. First, the minimum requirements were estimated for the burn performance to be captured around the moon. Second, the requirements for orbit, attitude, and maneuver burn performances were simultaneously estimated and analyzed to maintain the $1^{st}$ elliptical orbit achieved around the moon within the specified orbital period. Finally, the dispersion requirements on the B-plane aiming at target points to meet the target insertion goal were analyzed and can be utilized as reference target guidelines for a mid-course correction (MCC) maneuver during the transfer. More detailed system requirements for the KPLO mission, particularly for the spacecraft bus itself and for the flight dynamics subsystem at the ground control center, are expected to be prepared and established based on the current results, including a contingency trajectory design plan.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.10
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• pp.918-926
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• 2007

Military aircrafts usually operate at the area with lots of threats such as radars and surface-to-air missiles. Aircraft also faces with the unexpected or pop-up threats. Under this environment, a safe flight path should be generated to lead a mission successful. In this paper, a new path planning algorithm is proposed to provide less dangerous flight path efficiently. Of many path planning algorithms, a potential method is considered, because it has advantages of computation efficiency and smooth path generation. Trajectory generation under the condition of maximum range is studied so that the aircraft may reach the target area without refueling. The algorithm to cope with an unexpected situation is also proposed by adopting the concept of initial direction vector, additional force, and a new mapping function. The performance of the proposed algorithms is demonstrated for SEAD (Suppression of Enemy Air Defences) mission by numerical simulation.

• The Bulletin of The Korean Astronomical Society
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• v.43 no.1
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• pp.51.3-52
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• 2018

Since Voyager 1 passed the Heliopause in 2012, it has provided the observations of the charged particles in the local interstellar medium. However, Voyager 1 only provides the information along with its trajectory. In order to understand the global view of the interstellar plasma flow surrounding the Heliopause, we need another tool. When the interstellar plasmas approach the Heliopause, the ions are deflected around the Heliopause due to the draping of the interstellar magnetic field. The draping of the interstellar magnetic field is strongly connected with the shape of the Heliopause. A fraction of the diverted ions exchanges their charges with the undisturbed primary interstellar neutral atoms, and then the ions become neutral atoms called the secondary interstellar neutral atoms. The newly created neutral atoms carry information on the diverted flow of the interstellar ions, and a fraction of them can travel to the Sun. Therefore, the secondary component of the interstellar neutrals is an excellent diagnostic tool to provide important information to constrain the shape of the Heliopause. The secondary interstellar neutrals are observed by Interstellar Boundary Explorer (IBEX) at Earth's orbit. Since 2009, two energetic neutral atom cameras on IBEX have measured neutral atoms and it has provided sky maps of neutral atoms. In this presentation, we will discuss the directional distribution of the secondary interstellar neutrals at Earth's orbit. In the sky maps, the primary interstellar neutral gas is seen between $200^{\circ}$ and $260^{\circ}$ in ecliptic longitude and the secondary components are seen in the longitude range of $160^{\circ}-200^{\circ}$. We also present a simplified model of the outer heliosheath to help interpret the observations of interstellar neutrals by the IBEX-Lo instruments. We extract information on the large-scale shape of the Heliopause by comparing the neutral flux measured at IBEX along four different look directions with simple models of deflected plasma flow around hypothetical obstacles of different aspect ratios to the flow. Our comparisons between the model results and the observations indicate that the Heliopause is very blunt in the vicinity of the Heliospheric nose, especially compared to a Rankine half-body or cometary shape.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.15 no.3
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• pp.311-318
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• 2004

It is required to design the RF link with sufficiently stable signal margin to minimize bit errors and improve the quality of received data in the telemetry system modulated digitally like PCM/FM. In case of the vehicle flying at a high speed, the variation of the gain pattern between transmitting and receiving antenna and the fee space loss due to flight distance cause the fluctuation of link. In this paper, KSR(Korea Sounding Rocket)- III, the first domestic liquid rocket which was successfully launched in Nov. 2002 is introduced. The SNR(signal-to-noise ratio) variation of the telemetry signal which was measured at S-band ground station, the one which was simulated considering the flight trajectory, and the attitude variation such as roll, pitch and yaw are compared, analyzed, and agree very well. In addition, two virtual flying situations are simulated and evaluated-only one antenna is equipped in one case, and rocket is roll-free in the other.

• Aerospace Engineering and Technology
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• v.8 no.2
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• pp.105-112
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• 2009

Telemetry data is very important for the Launch Mission and Flight Safety Control during the Space Launch. In Naro Space Center, several telemetry stations such as a small station in the NARO space center, two stations in Jeju and a downrange station on a ship are deployed for the stable acquisition/receiving of the telemetry signals. In this paper, the Link Margin and Reliability for the telemetry are analyzed to evaluate the probability of the signal receiving of each station. Even though the proper analysis is to using the on-board EIRP(Effective Isotropic Radiation Power) values in the direction of the ground station considering the predicted flight trajectory and the locations of the stations, the global EIRP of 95% spatial coverage has been used for the analysis, due to the limitation of the available data.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.9
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• pp.752-759
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• 2018

This paper presents methods and results of nonlinear simulations for a guided munition for verifying stability at slow spin. The munition is launched by an artillery and it deploys the rear fins to reduce its spin. While the spin speed command is set to 1 rps and 3 rps, wind gusts of 3m/s, 7m/s, 10m/s, and 15m/s in amplitude, and 26 different directions were generated as disturbance for each simulation run. Whereas the munition with the spin speed of 3 rps didn't flip, that with 1-rps spin flipped under some gusts. However, the gusts which increase airspeed in the flight direction didn't introduce harmful effect. Most importantly, all the flips of the munition was observed near the end of the simulation where the munition is going down. No problem was observed near the summit of trajectory.