Harry Seldon's blog

Fractals, Chaos, and Control Systems on Rails


Control Systems 102: GNC, Guidance

Posted by Harry Seldon on May 12, 2009

This post is part of a series about Guidance, Navigation and Control. See the table of contents here.


Guidance refers to the questions ”where am I going to?”, ”How can the vehicle follow a trajectory?”. The trajectory itself is prepared by the Flight Planning System (FPS) (or Mission Planning System, MPS). During the flight, the Flight Management System (FMS) knows the trajectory and gives the current portion to the Guidance System (GS) . The Guidance System is in charge of converting the high level parameters (trajectory, waypoint positions) into a set of lower level orders that can be understood by the control, typically altitude, heading or directly a load factor, that is an acceleration. In some cases the guidance can have the role to compute a trajectory between 2 points.
It is also in charge of maintaining the trajectory and the other high level parameters. That means the guidance is itself a control loop. Typically the guidance is the Position Control System (PCS).
This is where things become tricky. Piloting and Guidance are essentially similar. The difference to keep in mind is that the pilot is a low level control loop whereas the guidance is a high level control loop. A nice world would be a world where guidance and pilot loops are two independent loops. Unfortunately both are coupled, and designing one, you need to keep the other one in mind.


Next chapter will be about GNC and human pilot.

Stability and Control
About GNC written GN&C or GCN written GC&N
About the human pilot
About control loops

Posted in | no comments | Tags , , , , , , , , , , , , | atom



Use the following link to trackback from your own site:

  1. If economy was an airplane, that airplane would go across a severe zone of turbulences. Then, a passenger would ask the air hostess “can I talk to the pilot, please? Because this pilot does not seem very good”. The hostess would answer...


Leave a response

Leave a comment

Markdown enabled



Recent Comments

Recent Posts


actuators aircraft atc blog chaos chaos_theory charts control controllers controls crisis economy finance flight fractals git gnc gs guidance linux mandelbrot marketing navigation ns ofc on pilot rails ruby sas scs sensors statistics systems techcrunch thinkosphere tutorial typo ubuntu wifi