New Examples

Earth orbit optical navigation

The new EarthOrbitOpticalNav demo script shows you how to implement optical navigation in Earth orbit. The system would use a star camera pointed north towards the pole stars and an earth sensor that would measure the earth chord. The measurements would be processed by an Unscented Kalman Filter. The orbit dynamical model would be selected to provide the fidelity needed for the required orbit accuracy.

The views below show the results in geosynchronous transfer orbit. The errors are worst at perigee as the spacecraft is moving very quickly. Propers setting of the UKF constants is needed to prevent the filter from "thinking" that a hyperbolic orbit is a possibility.

Asteroid proximity operations

Several new functions have been added that support operations around asteroids. Asteroid operations are more like formation flying than orbiting around planets and moons.

The views below show the "orbit" around the asteroid which is achieved by radial thruster firing. The second plot shows acquisition of the circular orbital rate about the asteroid.

Europa environment

When designing spacecraft to operate near Europa you need to be mindful of the environment which includes the Jovian magnetic field Europa's atmosphere. The first figure shows the atmosphere of Europa. The second figure shows the Jovian magnetic field at the center of Europa.

Planetary landers

Landers will be used to deliver payloads to the moons of Saturn and Jupiter. Eventually soft landers will be needed to land on Mars for human missions. This demo shows a landing algorithm that starts with a bilinear tangent guidance algorithm. This is an analytical solution based on constant gravitation acceleration and a flat surface. When the spacecraft nears the surface, we first null vertical velocity and then both horizontal and vertical velocity before switching to a bang-bang terminal controller. The following plots show the velocity during landing and the terminal descent.

Star Camera Centroiding

The toolbox provides a two step method to achieve very accurate centroid locations in the camera focal plane. The first step uses a center-of-mass calculation to get an approximate location. The next step fits a model of the star point spread function to the measured pixels to get a finer measurement. The ultimate accuracy will depend on the nature of your imager, the quality of your camera lenses and the accuracy of the camera calibration.

The first figure shows the imager output without noise. The second shows the various models for point spread functions used for fitting the measurements.

Magnetic Hysteresis

Nanosatellites have caused a renewed interested in magnetic control of satellites, and passive hysteresis damping in particular. Modeling actual hysteresis rods on a satellite is not trivial, and generally requires empirical data on the properties of the rods selected. Our newest CubeSat simulation demonstrates damping using rods in LEO. A permanent magnet is modeled using a constant dipole moment, and we expect the satellite to align with the magnetic field and damp. We evaluate the results by plotting the angle between the dipole and the Earth’s magnetic field and the body rates.