China
Africa
Explore chapters and articles related to this topic
Low-Gravity Environment
Published in Basil N. Antar, Vappu S. Nuotio-Antar, Fundamentals of Low Gravity Fluid Dynamics and Heat Transfer, 2019
Basil N. Antar, Vappu S. Nuotio-Antar
An object released motionless relative to the spacecraft at some distance from the center of mass along the radial vector from the center of the Earth will have an orbit slightly different from that of the spacecraft. Since the velocity required to maintain a circular orbit varies inversely with the square root of the distance from the center of the Earth, this object will have a slightly different velocity which will put it into an elliptical orbit with a different period. This trajectory will cause the object to slowly drift away from its initial position as the spacecraft describes its orbit around the Earth. The accelerations required to continuously alter the trajectories of such interior objects to keep them in the same relative configuration are of the order 10–7g0 for each meter of radial displacement from the spacecraft’s center of mass.
Aerospace Controls
Published in William S. Levine, Control System Applications, 2018
M. Pachter, C. H. Houpis, Vincent T. Coppola, N. Harris McClamroch, S. M. Joshi, A. G. Kelkar, David Haessig
An important case of interest is that of a spacecraft in a circular orbit. In such a case, it is natural to describe the orientation of the spacecraft not with respect to an inertially fixed coordinate frame, but rather with respect to a locally horizontal-vertical coordinate frame as reference, defined so that the X axis of this frame is tangent to the circular orbit in the direction of the orbital motion, the Z axis of this frame is directed radially at the center of attraction, and the Y axis completes a right-hand orthogonal frame. Let the constant orbital angular velocity of the locally horizontal coordinate frame be (
Using visualisations to develop skills in astrodynamics
Published in European Journal of Engineering Education, 2020
Lucinda Berthoud, Jonathan Walsh
This exercise addressed the skill ‘Interpreting ground tracks’ and the misconception ‘Forgetting that Earth rotates when considering ground tracks’. Ground tracks are presented as 2D plots on a map of the planet concerned. A simple inclined circular orbit gives a sinusoidal ground track. Ground tracks can take on unexpected forms, such as loops, but the cause of these forms becomes clearer when they can be matched with the 3D view of the spacecraft orbiting above the rotating body. At the beginning of the laboratory, a demonstration script showed three types of orbits with their matching ground tracks for the students to explore. The students were asked to compare the ground track with the orbit, to see how they link. They were then asked to work out the inclination of an orbit from the ground track plot only and then to compare it with the 3D orbit. Figure 4 shows the ground tracks for three different types of orbits using GMAT.
Immersion and invariance-based integrated guidance and control for unmanned aerial vehicle path following
Published in International Journal of Systems Science, 2019
Kenan Yong, Mou Chen, Qingxian Wu
The objective pursued in this paper is to develop the IGC scheme for the path-following UAV to guarantee that all the signals of the closed-loop system are bounded. Meanwhile, the UAV trajectory can asymptotically track a circular orbit as where is the reference centre, is the path length, and is the radius with the minimum turn radius . To further define the asymptotic stability of path following, let be the UAV trajectory and parameterised by its local position vector . As stated by Gates (2010), the UAV trajectory can be said to be asymptotically track the desired path if where is a correctional constant angle. In Figure 1, the symbols of variables in the desired path (1) and condition (2) are given.
Analysis of in-site grinding process using new equipment for calendar roll machines
Published in Materials and Manufacturing Processes, 2019
Senthil Kumar Ayyappan, Ramesh Babu Subramaniam
Roll balancing is the manipulation of the center of gravity so that it falls along the axis, around which it must revolve. An unbalance will tend to rotate the roller about the center of gravity, with the journals tracing some circular orbit. To overcome all the above problems in-site, grinding methodology can be considered to meet the needed tolerance and finish requirements.[14,15] In this work grinding of rollers in-site is introduced. The main objective of the work is to analyze the performance of the newly fabricated equipment for cambering the rolls in-site and to reduce the nonproductive time and the cost of cambering the rolls.