I can't seem to complete To the Mun, Part 2.

[DankMemes]

So when the training first starts, the instructor already has a maneuver node set up for you to land. He tells you to execute the maneuver at low throttle to get closer to the moon. So I turn on SAS, set it to maneuver mode, and burned at low throttle, but it keeps flipping around and around and turning its mode back to stability assist! Someone, please help, I am not sure if I am doing something wrong or if its a glitch.

[monstah]

Moved to Gameplay Questions, where it will better receive the right people's attention  

[Guest]

Pretty sure it's not a glitch. If you're tracking the manoeuvre node, it will flip when you get near the end of the burn: as you get closer to zero, any tiny error you have will get amplified, the manoeuvre node will scoot across the navball, and your autopilot will try to follow it, sending your craft out of control.

Solutions:

(1) Don't use manoeuvre mode. Instead use regular autopilot and track the node manually. When you're close to the end of the burn, cut throttle, and then do a few repeated burns at minimum power to get it as close to target as you need. Note that 0.0 m/s is usually overkill!

(2) Continue to use manoeuvre mode, but cut throttle just before you hit 0 and the node starts jumping around. (Yeah I know, this is like the pizza baking instruction that says to take it out of the oven two minutes before it starts to burn, but it's also equally correct.)

[bewing]

Better to use retrograde, I think.

 

[Zhetaan]

@DankMemes:

It's not a glitch.  You're just reaching the endpoint of the burn.

There are always little sideways errors (sometimes as small as mm/s) involved in any burn.  It's an unavoidable consequence of the fact that no system can ever aim exactly perfectly; this is why correction burns are a thing.

However, when the remaining burn is measured in m/s and the errors are measured in mm/s, the errors don't even register.  When the remaining burn gets below 1 m/s, the errors become more pronounced.  When the remaining burn is zero, the errors are the only thing that register--but the marker on the navball can't tell the difference between the 100 m/s burn you planned and what it thinks is a .001 m/s burn that you can't actually do; it only shows direction.  To keep your rocket from spinning round forever trying to correct what it doesn't need to correct (and usually can't correct anyway), the system automatically switches you to stability assist when your remaining burn gets low enough.  It does the same thing when going retrograde to the surface (if it didn't, then your rocket would try to dive into the ground nose-first on landing) and when moving retrograde relative to target (this is useful when docking).

When you get your remaining burn (that's the gauge to the right of the navball) down to 0.1 m/s, that's usually good enough.  If you can make it 0.0, that's great, but you don't usually need to be so accurate.

[DankMemes]

This is very confusing, I wish KSP's tutorials could be a little easier to understand

[Zhetaan]

11 hours ago, DankMemes said:

This is very confusing, I wish KSP's tutorials could be a little easier to understand

Quite true.  But you came to the right place, so let's take another try.

First, orbital mechanics and manoeuvring is confusing; everything you thought you knew about motion goes right out when you put it in orbit.  When I was learning this, I found it hideously frustrating, but the trick sometimes is to step back and watch someone else do it.

Set some appropriately-themed music....

... And let's see what we can find.

If you want better or different tutorials, then you can look here.  Remember that some of these are old enough that the game mechanics have changed; for orbital operations, however, anything from 2015 and later is okay.  A lot of the stuff from earlier is good, too (they didn't change the Mun's orbit or anything like that) but SAS has changed its behaviour a few times during KSP's development.  If you're committed to learning how to do this using the various hold modes, then stick to the later tutorials.  If you want to learn how to do this stuff by hand as well, then take a look at some of the older stuff.

I found a video series that plays the in-game tutorials (from version 1.1, but nothing has changed in space between 1.1 and today) and it shows the same behaviour that you were complaining of:

I linked it at the end of the burn, but you can clearly see that the node hold switches to stability assist when the remaining burn goes below 1.0 m/s.  The manoeuvre node also flies off the navball to the right; this is both normal and expected.  Even after following the instructions, this video also shows that the burn, as executed, didn't quite lower the periapsis so much as was necessary; to correct this, the player used retrograde hold and that is perfectly acceptable.  Later on, during the actual landing, it shows what happens when using too much retrograde hold; the ship stopped descending and began to climb, and the SAS forced the nose to point down.  This was not a destructive problem because the vessel was high enough off the ground that it did not crash, but it did waste fuel.

And no, I do not know why the navball markers show up in black in this video; it doesn't affect the function.