Spacecraft dynamics is the subfield of celestial mechanics which studies human-created objects’ movements through space. It encompasses calculations, refinement and planning for such bodies such as spacecraft or satellites.
Spacecraft Dynamics block computes position, velocity and attitude over time of six degree-of-freedom rigid-body systems with six degrees-of-freedom rigid bodies. Mass tab allows specifying an initial mass value m, mass flow rate dm/dt and inertia tensor imom.
Attitude refers to a spacecraft’s orientation, making its precise measurement critical in ensuring it does not end up millions of miles off course. Tiny thrusters used for controlling this aspect of space travel make small adjustments that keep its course on target.
As spacecraft attitude cannot be determined with one measurement alone, its estimates must be estimated from various sensors (often using a Kalman filter). Gyroscopes are most frequently used for attitude estimation while sun and moon position and horizon detectors and magnetometers may also provide valuable data for attitude estimation.
GMAT attitudes are typically represented using the Attitude Ephemeris Message (AEM) format outlined by CCSDS 504.0-B-1. An AEM file comprises of a header section containing high level information about its format as well as two blocks: Metadata and Data; in particular, Data contains initial attitude information in either quaternions, direction cosine matrices or Euler angles sequences depending on which representation method has been selected by GMAT.
An orbit of a spacecraft depends on two factors: velocity — which measures how fast the craft travels straight-line — and Earth’s gravity force. As satellites get closer, their velocity must increase in order to counter the intensified gravitational pull.
At lower altitudes, spacecraft may encounter trace amounts of Earth’s atmosphere which create drag that gradually decays their orbit until they return home. At higher altitudes this effect is greatly diminished.
Spacecraft designed to reach planets must enter an interplanetary trajectory at precisely the right moment; this can be accomplished using its engine to decelerate and achieve orbit insertion.
Spacecraft thrust is determined by two forces – gravity pulling it toward Earth and centripetal forces due to circular movement – balancing against propulsion forces provided by their engines.
This block can be configured to simulate a spacecraft constellation by providing multiple values in Mass, Orbit and Attitude tabs. As a result, each satellite will be represented as a constellation by row outputs corresponding to individual satellites while state outputs include current time tutc and transformations from inertial frame to fixed frame qicrf2ff outputs.
This capstone course builds upon the skills acquired in rigid body Kinematics, Kinetics and Control courses to explore vehicle dynamics of spacecraft in orbit – particularly its attitude. Students gain skills necessary for analyzing natural spacecraft orientation motion as well as stabilizing stability using feedback control.
As part of its powered flight mission, spacecraft must enter and land on planets or small bodies to complete its mission. To achieve success during this entry-to-landing (EDL) phase requires high degrees of accuracy and fidelity for testing system performance in environments which are impossible to replicate before launch.
The Spacecraft Dynamics block can be configured to model either a single spacecraft or constellation of spacecrafts, with model parameters being defined on the Mass, Orbit, and Attitude tabs. Mass m, mass flow rate m/dt, and inertia tensor Imom serve as inputs into this block and integrated to form its dynamics system equations.
The system equations control a spacecraft’s velocity and acceleration, producing a trajectory which could take many forms depending on its starting point, gravitational forces acting on it and trajectory options available to it. These could include circles, ellipses, parabolic paths or hyperbolas depending on which may prevail at any one time.