Low Earth Orbit targeting

Anyone interested in spaceflight quickly realizes that the way spacecraft are steered is fundamentally very different from how airplanes operate. Orbital maneuvering by and large is a waiting game in which thrusters are ignited at just the right time for maneuvering burns, followed by a coasting period before another burn starts.

It is comparatively easy to understand the essential ideas of things like insertion burns, Hohmann transfers or de-orbit burns in analytical 2-body gravity models. However, when one has to deal with a more realistic situation, this is simply not good enough.

In reality Earth's gravity field is not spherical - due to its rotation, Earth bulges at the equator, hence gravity is stronger there than over the poles because there's more mass. At higher latitudes, the gravity field always pulls towards the equator - this is the so-called J2 perturbation of the field. The effects are not small - if you use analytical expressions to try to plot a rendezvous with another orbiting object, you might be off by 10 km and more. Due to the J2 (and the smaller J3) perturbation, orbits are not even constant like in the ideal situation - they drift over time. Understanding this needs a fast numerical tool capable of computing and visualizing orbits in J3 gravity, and understanding and planning maneuvers under such conditions requires a tool able to fit burn parameters such that the resulting trajectory fulfills certain constraints. The LEO targeting software is intended to provide these capabilities.

Download

The source code of the simulation is available under the GNU General Public License 2.0+ - in short, you may use, re-distribute and modify the software freely, but you are required to provide the source code and license any additions/changes also GPL if you re-distribute.

The tarball extracts into its own subfolder, the code is inside the src/ folder, the doc/ folder contains a manual, the config/ folder a few sample configuration files. A few tutorials on how to use the software are found below. There is no Linux executable provided.

Download LEO targeting v0.2
Windows executable v0.2

Tutorials

Setting up orbits
The Molniya orbit
Properties of J2 and J3 gravity
Hohmann transfer
PEG-4 targeting
Shuttle insertion
Shuttle deorbit burn
Geosynchronous insertion
Ion thruster insertion

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Created by Thorsten Renk 2017 - see the disclaimer and contact information.