# NASA GMAT: Any good tutorials or methods to learn how to use patch points and control points to come up with viable and optimal trajectories?

I'm a beginner to trajectory design, and have to use NASA's GMAT software. It's been a few weeks now, and I have done the first four tutorials and managed to create a (very unrealistic and sub-optimal) trajectory taking a spacecraft from the Earth to a Sun-Earth L2 halo orbit and then Mars with B-Plane targeting. Very crude and using too many burns, but at least I consider it a step forward.

However, in order to properly solve complex trajectory problems one has to use patch points and control points, involving multiple spacecraft representing the different desired positions of the spacecraft, backpropagation, various commands to impose velocity and position continuity between them, etc.

I did the first 4 tutorials with ease and successfully learned from them, but then the fifth tutorial ("Optimal Lunar Flyby using Multiple Shooting"), which is supposed to be an introduction to using control points and patch points, is a massive leap from the previous one, and doesn't really explain the logic behind the method or steps in detail. I am still trying to do it, but in the meanwhile, are there any resources online for a beginner which I can use to better understand this method of trajectory optimizaton? Can't find much online other than mentions of the terms in academic papers.

For that matter, what is the most active online community for GMAT discussions? The link on GMAT's startup screen is dead, and its online presence in general is kind of weird. What I assume is the official website is a bit of a mess, having a lot of dead links. Surprising considering it's software made by NASA and used in various real-life missions.

• This answer might help Commented Jan 26, 2022 at 12:46