vector000/pegas

Powered Explicit Guidance Ascent System - a KSP & RO autopilot using the Space Shuttle guidance algorithm, UPFG

PEGAS

Powered Explicit Guidance Ascent System, from here referred to as PEGAS, is an ascent autopilot for Kerbal Space Program made and ran in kOS, designed to control launch vehicles under a modified version of the game running Realism Overhaul. Its unique feature is an implementation of a real-word rocket guidance algorithm: Unified Powered Flight Guidance, as used in the Space Shuttle GN&C computer for the standard ascent flight mode. Short list of what PEGAS is capable of:

• estimation of a launch window,
• calculation of a launch azimuth,
• simple atmospheric ascent by pitching over and holding prograde with zero angle of attack,
• automatic guidance to orbits defined by:
  • apoapse
  • periapse
  • inclination
  • longitude of ascending node
  • or, alternatively, selecting an existing target,
• executing of timed events (engine ignition, payload fairing jettison etc.),
• automatic staging with ullage handling.

More info on my KSP forum thread, also see my prototype repository.

Version 1.1 is here!

How to use

1. Make sure you have kOS installed. Note: basic knowledge of kOS will be very handy.
2. Dowload files from this repository's kOS folder and place them in your Script folder.
3. Define your vehicle and mission - see tutorial and reference.
4. Once on the launch pad, load the definitions from pt. 2. and type run pegas. in kOS terminal.

How to get help

PEGAS is not a magical do-it-all, it needs some effort set up and get running. It has been tested with several launch vehicles, from real-world launchers like Atlas V or Saturn V, through user-made vehicles, both in RO and vanilla settings. However, I cannot guarantee that it will handle any vehicle or that it is entirely bug-free. Likely, it will take you several tries before you get your rocket flying - and maybe you will find yourself unable to do that at all. I am willing to provide support, correct bugs and (to some extent) introduce new functionalities to PEGAS. In case of problems: read the how to submit issues page and then visit the issue tracker.

Demo

Here is a video demonstration of the initial release of PEGAS in action, flying an Atlas V to parking orbit aligned with the International Space Station. It mostly focuses on explanation of the underlying guidance algorithm, only showcasing what functions PEGAS has instead of explaining how to use them. For that I strongly recommend reading the tutorial.

Note about this repository

I have been using tabs throughout the whole code, having its length set to 4 spaces in all my editors. I was unaware that github uses length of 8 - as a result, some of the .ks files look really bad. If your eyes hurt, you can force github to display them with tab size of 4 spaces by adding ?ts=4 to the URL of the file you're viewing. Unfortunately there is no way to make it a global setting (or even configure it for the repository).