www.spacealliane.roA RSS feed containing the latest Space Alliance science and news articles.Copyright 2026 Space Alliance The light measurement technology has evolved during the years from the old traditional film based photography to one where electronic images are the choice. The imaging recording device is one of the most critical components so understanding the process of how the light images are recorded can increase the quality of the light measurement data.© Copyright 2010 www.spacealliance.ro The light measurement technology has evolved during the years from the old traditional film based photography to one where electronic images are the choice. The imaging recording device is one of the most critical components so understanding the process ...enhttp://www.spacealliance.ro/articles/view.aspx?id=201003230327http://www.spacealliance.ro/articles/view.aspx?id=201003230327Tue, 23 Mar 2010, 03:29:59 GMT  Based on the operating principle, the CCDs are categorized in four major classes: -linear CCDs -interline CCDs -full frame CCDs -frame transfer CCDs © Copyright 2010 www.spacealliance.ro Based on the operating principle, the CCDs are categorized in four major classes: 1. linear A linear CCD is actually consisting in a single row of pixels which needs to be repositioned by a special mechanism in order to construct the image. By that is a complex system which means is slower and leaves the possibility of potential failures Bellow is an example of this architecture-Atmel...enhttp://www.spacealliance.ro/articles/view.aspx?id=201003190321http://www.spacealliance.ro/articles/view.aspx?id=201003190321Fri, 19 Mar 2010, 03:28:12 GMT   A very important device on any spacecraft is the one which determines the spacecraft’s attitude. There are many different methods by which the attitude of a satellite can be determined, but one of the mostly widely used is the star tracker. © Copyright 2010 www.spacealliance.ro Star tracker specifications A very important device on any spacecraft is the one which determines the spacecraft’s attitude. There are many different methods by which the attitude of a satellite can be determined, but one of the mostly widely used is the star tracker. Other methods for determining attitude exist, but none c...enhttp://www.spacealliance.ro/articles/view.aspx?id=201002260821http://www.spacealliance.ro/articles/view.aspx?id=201002260821Fri, 26 Feb 2010, 08:28:43 GMT   Star sensors measure star coordinates in the spacecraft frame and provide attitude information when these observed coordinates are compared with known star directions obtained from a star catalog. In general, star sensors are the most accurate of attitude sensors, achieving accuracies to the arc-second range.© Copyright 2010 www.spacealliance.ro Introduction Researchers in the field of spacecraft dynamics and control are concerned with creating accurate and understandable physical models of satellites. These simulations help to verify principles of motion and to test control designs for both attitude and orbit...enhttp://www.spacealliance.ro/articles/view.aspx?id=201002250904http://www.spacealliance.ro/articles/view.aspx?id=201002250904Thu, 25 Feb 2010, 09:16:25 GMT In the ancient times, it was noticed that some lights moved on the sky while the others remained in the same position in relation to each other. Stars which appeared to be closed together were grouped into constellations. Stars which changed their position were called planets and the seven ones observable directly by eye were considered in order of speed of apparent movement Moon, Mercury, Venus, Sun, Mars, Jupiter and Saturn. Today a lot of ancient mysteries have been solved, but much more are still to be investigated. This article is an introduction to some of the astronomy issues like absolute and apparent magnitude, relation between magnitude and distance, luminosity of a star, star's flux, spectral classes, colour index and temperature of a star, star distance, pa...enhttp://www.spacealliance.ro/articles/view.aspx?id=200903060702http://www.spacealliance.ro/articles/view.aspx?id=200903060702Fri, 06 Mar 2009, 07:15:55 GMT Operating a voice system depends largely on the skills of the involved persons. Proper voice procedure training should provide the operators with the basic knowledge of how to improve their skills in the use of radio communication. Even the best systems can suffer from interference and because of this is possible than the other part cannot hear (understand) the information passed. Therefore it is extremely important that proper voice procedure is used to save time. Briefly, a voice procedure is a set of rules designed to provide security, accuracy and discipline when speaking on the voice loop. Phonetic alphabet Letters, numbers and symbols It is most important to use the accepted phonetic alphabet for letters and digits for al...enhttp://www.spacealliance.ro/articles/view.aspx?id=200903060647http://www.spacealliance.ro/articles/view.aspx?id=200903060647Fri, 06 Mar 2009, 06:52:11 GMT The concept of proper motion in astronomy is defined as the apparent movement of a star on the celestial sphere, usually measured as seconds of arc per year. It is due both to the actual relative motions of the sun and the star through space. The proper motion reflects only transverse motion (the component of motion across the line of sight to the star); it does not include the component of motion toward or away from the sun. The most distant stars show the least proper motion. The average proper motion of the stars that can be seen with the naked eye is 0.1'' per year. The proper motion of a star is its apparent angular movement per year on the celestial sphere. It is a combination of its actual motion through space and its motion relati...enhttp://www.spacealliance.ro/articles/view.aspx?id=200903060636http://www.spacealliance.ro/articles/view.aspx?id=200903060636Fri, 06 Mar 2009, 06:40:07 GMT The Hipparcos and Tycho Catalogues are the primary products of the European Space Agency's astrometric mission, Hipparcos. The satellite, which operated for four years, returned high quality scientific data from November 1989 to March 1993. Each of the catalogues contains a large quantity of very high quality astrometric and photometric data. In addition there are associated annexes featuring variability and double/multiple star data, and solar system astrometric and photometric measurements. Although in general only the final reduced and calibrated astrometric and photometric data are provided, some auxiliary files containing results from intermediate stages of the data processing, of relevance for the more-specialized user, have also been retained for publication. The global data...enhttp://www.spacealliance.ro/articles/view.aspx?id=200903060623http://www.spacealliance.ro/articles/view.aspx?id=200903060623Fri, 06 Mar 2009, 06:30:16 GMT Spacecraft attitude is briefly the angular orientation of a spacecraft body vector with respect to an external reference frame. A spacecraft attitude determination and control system typically uses several sensors and actuators and because attitude is described by three or more variables (apart from the angles, one can add the rotational speed etc), the difference between the desired and the measured state is complicated to be evaluated, most of the time being either undetermined or over-determined. The attitude of a spacecraft is its orientation in space. The motion of a rigid spacecraft is specified by its position, velocity, attitude and attitude motion. The first two quantities describe the translation motion of the center of mass of the spacecraft and are the subject of wh...enhttp://www.spacealliance.ro/articles/view.aspx?id=200903060613http://www.spacealliance.ro/articles/view.aspx?id=200903060613Fri, 06 Mar 2009, 06:16:28 GMT The Lagrangian points are locations in space in the vicinity of two orbiting masses where the gravitational forces and the orbital motion balance each other to form a point at which a third body of negligible mass would be stationary relative to the two bodies. There are a number of web resources describing the Lagrangian points, some of them offering a very good introduction and description of the 5 Lagrangian points, while others insist on the techical aspects of the problem. Nonetheless, in the following article we'll try to add to the non-mathematical and intuitive descriptions available on the web (like, for instance, the ESA page related to the 5 lagrangian points or the Wikipedia article ) a detailed-mathematical view of the problem, starting from the technical defintion wh...enhttp://www.spacealliance.ro/articles/view.aspx?id=200903060441http://www.spacealliance.ro/articles/view.aspx?id=200903060441Fri, 06 Mar 2009, 05:00:38 GMT This article intends to give to the reader an overview of the state of the art attitude sensors used for the modern missions. Attitude determination uses a combination of sensors and mathematical models to collect vector components in the body and inertial reference frames, typically in the form of a quaternion, Euler angles or rotation matrix. The main sensors available on satellite area are: Earth sensors There are different earth sensors available on the market like horizon crossing indicators and horizon scanners. The sensors use the difference of the infrared light emitted by Earth and the one emitted by the deep space in order to detect the horizon, and then they return the vector to the approximate center of the Earth.   Sun sensor ...enhttp://www.spacealliance.ro/articles/view.aspx?id=200903060439http://www.spacealliance.ro/articles/view.aspx?id=200903060439Fri, 06 Mar 2009, 04:40:02 GMT This article intends to be a summary of the attitude actuators for spacecrafts either active or passive. It will introduce the reader to the basic attitude control hardware in use for the modern platforms. The attitude control of a spacecraft can be considered being either actively controlled (meaning that a controller calculates necessary control torques and acting on the satellite to adjust its attitude to a desired position) or passively controlled (meaning that the satellite uses external torques that occurs due to its interaction with the environment and thus they cannot be avoided, in this case the disturbances being used for forcing the attitude of the satellite). In general, the active control assures 3 axes stabilization, while the passive control gives the opportunity...enhttp://www.spacealliance.ro/articles/view.aspx?id=200903060429http://www.spacealliance.ro/articles/view.aspx?id=200903060429Fri, 06 Mar 2009, 04:31:24 GMT This article makes reference to the satellite state representations which include: 1. The keplerian elements Seven (or eight) numbers are required to define a satellite orbit. This set of seven numbers is called the satellite orbital elements, or sometimes "Keplerian" elements. These numbers define an ellipse, orient it about the Earth, and place the satellite on the ellipse at a particular time. In the Keplerian model, satellites orbit is an ellipse of constant shape and orientation. The Earth is at one focus of the ellipse, not the center (unless the orbit ellipse is actually a perfect circle). 2. NASA TLE format This is the format used by NASA to distribute satellite elements in their NASA Prediction Bulletin.NORAD, or North American Aerospace Defense Command, ...enhttp://www.spacealliance.ro/articles/view.aspx?id=200903060426http://www.spacealliance.ro/articles/view.aspx?id=200903060426Fri, 06 Mar 2009, 04:27:33 GMT Propagation means evaluation of the orbital position of the spacecraft through a series of timestamps using a specified orbital model and perturbations. Mainly methods for propagating a spacecraft in its orbit are divided as analytically and respective numerically. While numerical propagation evaluates the motion of the satellite over many small timestamps, integrating the solution, to find the final spacecraft’s position after a given time span, the analytical method uses a set of equations to evaluate the discrete solution of a satellite’s position at a given time. The numerical solution reaches the best accuracy, however due to the intensive computations requested (it has to integrate the entire period from the initial time to the current time) it has been successfully ...enhttp://www.spacealliance.ro/articles/view.aspx?id=200903060423http://www.spacealliance.ro/articles/view.aspx?id=200903060423Fri, 06 Mar 2009, 04:24:10 GMTenhttp://www.spacealliance.ro/articles/view.aspx?id=200903060421http://www.spacealliance.ro/articles/view.aspx?id=200903060421Fri, 06 Mar 2009, 04:22:05 GMTenhttp://www.spacealliance.ro/articles/view.aspx?id=200903060418http://www.spacealliance.ro/articles/view.aspx?id=200903060418Fri, 06 Mar 2009, 04:19:52 GMT This article intends to bring into attention some of the classical topics like: 1. The rigid body model 2. Angular momentum and inertia matrix 3. Rotational kinetic energy of a rigid body 4. Moment of inertia about a selected axis in the body frame 5. Principal axes of inertia 6. Ellipsoid of inertia and the rotational state of a rotating body 7. Kinematic equations of motion 8. Euler’s moment dynamic equations of motion A special chapter is related to the attitude prediction which requires a model of the environmental disturbances torques acting on the spacecraft: 9. Perturbations-influence of the external torques on the spacecraft attitude        9.1 Gravity gradient torque        9.2 Radiation tor...enhttp://www.spacealliance.ro/articles/view.aspx?id=200903060415http://www.spacealliance.ro/articles/view.aspx?id=200903060415Fri, 06 Mar 2009, 04:16:38 GMTenhttp://www.spacealliance.ro/articles/view.aspx?id=200903060411http://www.spacealliance.ro/articles/view.aspx?id=200903060411Fri, 06 Mar 2009, 04:13:26 GMTenhttp://www.spacealliance.ro/articles/view.aspx?id=200903060407http://www.spacealliance.ro/articles/view.aspx?id=200903060407Fri, 06 Mar 2009, 04:10:25 GMT