Earth-centered Orbit Research Articles

Flexible heliogyro solar sail under solar radiation pressure and gravitational force

This study proposes a formulation for the dynamics of a flexible multibody heliogyro solar sail undergoing rigid body motion and multi-blade vibration. The heliogyro solar sail consists of a rigid central hub and flexible solar multi-blades. The floating frame approach is applied to describe large translational and rotational motions, as well as blade deformations, including the flap, lag, and twist modes. First, the solarelastic instability induced by Solar radiation pressure (SRP) is revisited in the linear stability and nonlinear transient analysis. Then, the gravity-induced instability on the heliogyro solar sail is proposed, and the 1st flap mode is shown to become divergent under gravitational force. Strain energy variation is applied to determine the contribution of the divergent behavior after the onset of the instability. Finally, suitable operational spin speed and altitude in the Sun-synchronized Earth-centered orbit are proposed for the stabilized flexible heliogyro solar sail mission.

A Comprehensive Study on Space Debris, Threats Posed by Space Debris, and Removal Techniques

After exploring space for more than 50 years for research, study and defense purposes, the region above the atmosphere of earth is highly polluted by orbital debris. Figure 1 shows the total number of rocket launches in period of nine years. This has become a concern for placing satellites in their respective orbits and their safe functioning during their mission. Space debris or orbital debris colloquially known as space junk are parts of the non-functional satellites, thermal blankets, booster stages of the rockets. Those satellites are placed in the several orbits according to their missions. Mainly, they are placed in LEO (Low Earth Orbit), an earth centered orbit ranging from 200 to 2000 kilometers. Some are also placed in GEO (Geostationary Earth Orbit), at an altitude of 36000 kilometers and some are placed in the Higher Earth Orbit. Since the dawn of space age, approximately 7000 rockets have been launched, placing their payloads in several orbits of the Earth, revolving at several kilometers per second. And more than half of these objects are present in LEO. It is estimated that their sizes vary from a few millimeters to few meters, the largest being the European Envisat. Because of their high speeds, pieces of debris not more than a millimeter apart also poses a huge risk to current and upcoming space missions. Since the risk is increasing exponentially and is of great concern for all the space-faring nations, there is a need for the active removal of space debris. Hence, in this paper, the authors have analyzed the threat that space debris poses, and some of its removal techniques that have been proposed by scientists and space organizations. The authors have also suggested a few more of these Active Debris Removal techniques.

Wavelike Patterns in Precessing Elliptical Rings for Swarming Systems

A continuum model for a swarm of devices is investigated with the devices moving along precessing elliptical Earth-centered orbits. Wavelike patterns in these precessing elliptical rings with peaks in swarm density are found that can be used to provide enhanced coverage for Earth observation and space science. Two orbital models are considered for the purpose of comparison: perturbed by and solar radiation pressure, and perturbed by and , respectively, each with a different frozen eccentricity. By removing osculating orbital elements, only the long-period orbit eccentricity and argument of perigee are chosen to derive closed-form solutions to the continuum model for the swarm density. Zero-density lines in the swarm density are found, as well as infinite density at certain boundaries. Comparison between the analytic and numerical number density evolutions is made to yield the range of applicable eccentricity based on the maximum error tolerance, as well as the minimum number of swarm members required to approximate continuous evolution. Closed-form solutions are then derived to predict the number density of swarm devices for magnetic-tail measurement and Earth-observation applications.

태양돛 우주선의 궤도천이 기법 연구

태양돛은 태양복사압을 이용하여 연료소모 없이 우주선에 지속적인 추력을 제공하는 방식으로, 심우주 임무나 지속적인 궤도기동이 필요한 임무에 적합하다. 본 논문에서는 태양돛의 기본 원리를 소개하고 태양중심, 행성중심 궤도에서의 국소최적제어 기법을 연구하였다. 각각의 최적제어 기법에 대한 시뮬레이션을 수행하였다. 핼리혜성 랑데부 궤적을 생성하였으며, 여러 가지 행성탈출 기법을 비교하였다. Solar sail propulsion uses solar radiation pressure to propel spacecraft without propellant, and it is useful for deep-space missions and continuos orbit maneuver missions. After a brief introduction of solar sail dynamics, locally optimal trajectories in Sun-centered and Earth-centered orbits are analyzed. Numerical simulations for the optimal trajectories are performed. Trajectory for the rendezvous with Halley comet is generated, and different planet escape methods are compared.

Free return orbit design and characteristics analysis for manned lunar mission

Point return orbit (PRO) of manned lunar mission is constrained by both lunar parking orbit and reentry corridor associated with reentry position. Besides, the fuel consumption and flight time should be economy. The patched conic equations which are adaptive to PRO are derived first, the PRO is modeled with fuel and time constraints based on the design variables of orbit parameters with clear physical meaning. After that, by combining analytical method with numerical method, a serial orbit design strategy from initial value design to precision solution is proposed. Simulation example indicates that the method has excellent convergence performance and precision. According to a great deal of simulation results by the method, the PRO characteristics such as Moon centered orbit parameters, Earth centered orbit parameters, transfer velocity change, etc. are analyzed, which can supply references to the manned lunar mission orbit scheme.

Manmade Objects–A Source of Confusion to Asteroid Hunters?

On October 7, 8, and 9, 1970, Charles Kowal, in search of fast-moving asteroids, exposed three photographic plates of an area of the sky near the ecliptic with the 122 cm Schmidt reflector of the Hale Observatories. Several weeks later Eleanor Helin of the California Institute of Technology examined the plates under a blink microscope and discovered a fast-moving object of about 15 mag. During the 15 min exposures the object had left a slightly bumpy trail indicating light variations with a period of a few minutes.Four positions of the object were reported to the author, who derived the heliocentric orbit defined in table I. From table II it is seen that the residuals of that orbit are not very satisfactory. Note that the third and the fourth position represent the end points of the same trail. There is a clear indication that after October 9, the predicted heliocentric positions would soon diverge from the actual positions. This circumstance, and the fact that the orbit is so similar to that of Earth, suggested that the object could actually be moving in an Earth-centered orbit.