1,720,987 research outputs found
A Search Algorithm for Stochastic Optimization in Initial Orbit Determination
Full text linkOptical observations constitute a source of angular measurements of a
satellite pass. Commonly, these observations have short durations with respect
to the satellite orbit period. As a consequence, the use of classical orbit
determination algorithms, as Laplace, Gauss or Escobal methods, give very
poor results. This thesis faces with the problem of estimating the orbital
parameters of an orbiting object using its optical streak acquired by a telescope
or a high accuracy camera. In this thesis a new technique is developed for
the Initial Orbit Determination from optical data by exploiting the genetic
algorithms. The algorithm works without restrictions on the observer location.
A recent challenging problem is the Initial Orbit Determination with space-
based observations. This thesis focuses on the problem of determinating the
orbital parameters of a satellite from an orbiting observer in LEO, using
short time observations. We present the results based on a simulation with
the observer on a sun-synchronous orbit with a single observation of just
60 s. Monte Carlo simulations are presented with di erent levels of sensor
accuracy to show the reliability of the algorithm. The algorithm is able to yield
a candidate solution for each observation. The coplanar case is analyzed and
discussed as well. Several test show the reliability of the algorithm varying the
number of the observations, the initialization method, the observation period
and the noise seed
A genetic algorithm for Initial Orbit Determination from a too short arc optical observation
No full textOptical observations constitute a source of angular measurements of a satellite pass. Commonly, these observations have short durations
with respect to the satellite orbit period. As a consequence, the use of classical orbit determination algorithms, as Laplace, Gauss or Escobal methods, give very poor results. The present work faces with the problem of estimating the orbital parameters of an orbiting object using its optical streak acquired by a telescope or a high accuracy camera. In the paper a new technique is developed for the Initial
Orbit Determination from optical data by exploiting the genetic algorithms. The algorithm works without restrictions on the observer
location. A recent challenging problem is the Initial Orbit Determination with space-based observations. This work focuses on the problem of determinating the orbital parameters of a satellite from an orbiting observer in LEO, using short time observations. We present the results based on a simulation with the observer on a sun-synchronous orbit with a single observation of just 60 s. Monte Carlo simulations are presented with different levels of sensor accuracy to show the reliability of the algorithm. The algorithm is able to yield a
candidate solution for each observation. The coplanar case is analyzed and discussed as well
Space debris orbit determination from an ISS onboard camera
No full textAn autonomous system for the orbit determination of space debris has been studied for a new payload on the ISS. Space based observations could be a very important source for optical observations. An ISS onboard camera could provide measurements for a large class of satellites on different orbits. The high chances of observations and the possibility of scanning large regions of the sky suggest that the camera should be in continuous activity with different modes. This article will present a possible site for the installation of the camera, the treatment of the images to obtain the angular measurements and a genetic algorithm to estimate the orbital parameters of the observed object. The genetic algorithm will use the time-tagged orbital angular observations and a very accurate estimation of the camera site in order to evaluate the target orbit. The algorithm will use only two variables to determine the output: the initial and the final relative distance between observer and target, these two values will identify uniquely the orbit of the observed object. The camera will be mounted on a pan-tilt system to obtain longer observations by tracking the object. The possible high angular velocities, the conditions of illumination and the relative positions force the orbit determination algorithm to be efficient and reliable also on very short arc passes. The camera system will be characterized by a very compact design, low power consumption and low mass. The electric system will be capable to operate continuously in the space environment. The system will downlink data from the angular observations, the on-board estimated orbital parameters and some images to allow the testing of the performances and the off-line processing to obtain a better estimation
Inverse dynamics particle swarm optimization for spacecraft minimum-time maneuvers with constraints
Full text linkThe problem of spacecraft time-optimal reorientation maneuvers under boundaries and path constraints is solved using the Particle Swarm Optimization technique. Keep-out constraints for an optical sensor are taken into account. A novel method based on the evolution of the kinematics and the successive obtainment of the control law is presented and named as Inverse Dynamics Particle Swarm Optimization. It is established that the computation of the minimum time maneuver with the proposed technique leads to near optimal solutions, which fully satisfy all the boundaries and path constraints
Experimental results of a terrain relative navigation algorithm using a simulated lunar scenario
Full text linkThis paper deals with the problem of the navigation of a lunar lander based on the Terrain Relative Navigation approach. An algorithm is developed and tested on a scaled simulated lunar scenario, over which a tri-axial moving frame has been built to reproduce the landing trajectories. At the tip of the tri-axial moving frame, a long-range and a short-range infrared distance sensor are mounted to measure the altitude. The calibration of the distance sensors is of crucial importance to obtain good measurements. For this purpose, the sensors are calibrated by optimizing a nonlinear transfer function and a bias function using a least squares method. As a consequence, the covariance of the sensors is approximated with a second order function of the distance. The two sensors have two different operation ranges that overlap in a small region. A switch strategy is developed in order to obtain the best performances in the overlapping range. As a result, a single error model function of the distance is found after the evaluation of the switch strategy. Because of different environmental factors, such as temperature, a bias drift is evaluated for both the sensors and properly taken into account in the algorithm. In order to reflect information of the surface in the navigation algorithm, a Digital Elevation Model of the simulated lunar surface has been considered. The navigation algorithm is designed as an Extended Kalman Filter which uses the altitude measurements, the Digital Elevation Model and the accelerations measurements coming from the moving frame. The objective of the navigation algorithm is to estimate the position of the simulated space vehicle during the landing from an altitude of 3 km to a landing site in the proximity of a crater rim. Because the algorithm needs to be updated during the landing, a crater peak detector is conceived in order to reset the navigation filter with a new state vector and new state covariance. Experimental results of the navigation algorithm are presented in the paper
UNISAT-5: A MICROSATELLITE FOR SPACE DEBRIS MONITORING
No full textSpace missions must take into account a relatively new threat, which is represented by space debris. This problem
has arisen in the last 25 years and requires specific strategies for mitigation, with the main intent of avoiding
collisions between orbital debris and spacecraft. Space debris monitoring and orbit determination is an essential
premise to this task. In the last decade GAUSS has been involved in optical space debris surveillance, participating
to the IADC joint observation campaign and manufacturing the first Italian observatory completely dedicated to
space debris monitoring. GAUSS has been also a pioneer in educational microsatellites, namely with UNISAT,
EDUSAT and UniCubeSat-GG missions. Combining these two experiences GAUSS students and researchers are
designing a microsatellite with a compact digital imaging system on board. The UniSat-5 mission purpose will be
space debris monitoring, taking advantage of an in situ observation above Earth’s atmosphere. One of the key
elements of observing on orbit is that many atmospheric phenomena would be avoided, such as diffraction and EM
absorption. Hence images would gain more contrast and solar spectral irradiance would be higher for the whole
visible spectrum. The system is composed of a Schmidt-Cassegrain reflector, a camera, C band and S band
transceivers and two antennas. The system is independent from the rest of the spacecraft. The camera is equipped
with a panchromatic 5Mpix sensor. The transceivers and their custom-designed antennas operate on ISM 2.4GHz
and 5GHz Wi-Fi bands, and Unisat-5 OBDH can switch between the two. The ground segment is composed of a
high gain antenna dish, which will be used to establish a TCP/IP wireless link. Every component of this system is an
off-the-shelf product. The space debris observation will work in pair with the attitude determination system, as well
as the orbit determination system. A dedicated software will provide information on the amount of possible
observable targets. The high relative angular velocities and the consequent arc will provide data for a rough initial
orbit determination. Further observations with the correlation of the targets are required to better estimate the orbit.
UniSat-5 micro-satellite will be launched during Q4 2012 by a Kosmotras DNEPR LV; it will be injected in a Sun
Synchronous Orbit. UniSat-5 will be the first university satellite for space debris monitoring, and it will test the
technology for the future design of a formation flight for on orbit optical debris detection
Autonomous guidance and control with hazard avoidance for a Lunar lander
No full textThis work deals with an algorithm based on a linear programming approach to establish the guidance and the control of a Lunar Lander in its final descent phase. The linear programming problem is described and set; in our method the soft-landing manoeuvre depends on the initial state of the lander, the desired landing site and the time of flight needed to complete the manoeuvre. Then, the Pulse Width Modulation is used to make the control sequence obtained exertable by a non-throttleable engine and a strategy is proposed to modify the results of the Pulse Width Modulation in order to achieve a safe landing. A method is shown to take into account the variation of mass of the lander during the descent and a proposal for an algorithm for the estimation of the time of flight is presented. The proposed guidance and control algorithm is tested to evaluate its performances, including cases when a retargeting is needed
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