Maneuver nodes and burn. help!

[AmIEgged(]

I have tried the tutorial part 1 of going to the mun countless times but i just keep messing up. To go to the mun in the tutorial they tell me that for best results, the burn should be initiated roughly half of the duration of the burn before the indicated burn time. So my burn time is 7 minutes. This is where I am confused. I'm not sure if the burn time is supposed to be that long just to get to the mun. Ok, so I start burning fuel at around t-3,1/2 minutes to my maneuver. But of course i run out of fuel when i still have about 3 minutes of burning left. Help very appreciated!!

[Shukinen]

look into scott manley's tutorial on youtube, you will learn a lot out of these vids

[Woody]

The estimated burn time can be off initially before you start the burn. One way to check is make the node, aim at the marker, and burn for a second, it should adjust to being closer to the actual burn time. This will not effect the predicted course that much.

A 7 minute burn to get an encounter with the Mun means you are using a very low thrust motor, have a vehicle with a lot of mass, or a combination of both. Basically a low thrust to weight ratio. 7 minutes is an excessive burn time for a Mun encounter.

A low TWR does not mean you can not make the encounter happen, but not enough Delta-V means it will not happen. Delta-V is the amount of velocity change your vehicle can accomplish, either increasing or decreasing it.

When burning for an encounter do it in the map view so you can see the course change.

In your situation my guess is a low TWR and not enoough Delta-V. Try changing the engine you are using to something with a little more thrust. If that does not work add more fuel, if that fails download MechJeb or Engineer. Use one of these mods in the VAB to see the TWR and Delta-V and google KSP Delta-V map. Doing this will give you a good idea of where you are failing in your design.

[The_Mell]

I just checked the tutorial and it should be a necessary speed of 750m/s and a burn of about 2min30sec leaving you with the bigger tank half full, i.e. 2/3 of fuel was used.

Did you move the maneuver node to periapsis?

[Aethon]

I havent done the tutorial since the new versions came out but IIRC, you need to transfer fuel around the supplied ship because it's not designed very well.

Hope this helps.

[AmIEgged(]

Originally posted by The_Mell:

I just checked the tutorial and it should be a necessary speed of 750m/s and a burn of about 2min30sec leaving you with the bigger tank half full, i.e. 2/3 of fuel was used.

Did you move the maneuver node to periapsis?

I looked at all the tutorials but what bothers me is that i copy the exact same ship as tutorials online, same fuel, engine etc, but i see their burn time is like 13 seconds and i get 4 minutes. Also i try to watch tutorials on maneuver nodes but theyre just so confusing. When you said is my maneuver node on the mun periapsis or kerbin periapsis? Whenever i try to put a maneuver node for the mun, I always miss the moon because my burn time changes, even though im using the same engine. It says 20 second burn. At t-10 seconds of maneuver node I start burning the same engine but now i have a 4 minute burn which tottaly ruins everything!

[The_Mell]

The tutorial of KSPs to the Mun part1 tells you to place your node on periapsis (around Kerbin).
Then all you need to do is to pull the prograde marker, green circle. Have your navball open while doing so (not sure if this is standard or you must click on it) and check needed speed, scale at right side - should be around those mentioned 750m/s.

Burn time can be a bit tricky because it is usually only calculated after you throttled an engine up. So after staging or at beginning of tutorial it doesn't show a time properly.
After firing up the engine to full throttle by either holding shift until left bar is at top or pressing 'z', burn time on right side should read those mentioned two&half minutes.

Mh, i must admit for a KSP veteran like me your problem sounds weird because the tutorial mission to the Mun part1 should be easy.
At the moment i can only think about 2 more pontenial origins for your problem:
You don't point the vessel towards the blue marker which shows you the direction of planned maneuver node.
Or there is a bug.

Make a screenshot next time and post it here - maybe that would help us to help you.

[AmIEgged(]

I got my burn time down to 2 minutes, I'm not sure if that's right but if it is, maybe because when was making my maneuver node i pulled on the radial out marker, instead of the prograde marker which I guess was making the burn time unnecessarily long

[Magoobleheimer]

Originally posted by Benjiforest5:

I got my burn time down to 2 minutes, I'm not sure if that's right but if it is, maybe because when was making my maneuver node i pulled on the radial out marker, instead of the prograde marker which I guess was making the burn time unnecessarily long

It's that 'aahhh' moment. Yes, you want to speed up to go to the Mun. Not turn right.
Now your in for some real fun!

[The_Mell]

[Empiro]

It sounds like you're learning and gaining experience which is good.

In general, most of your burn time should be on (or close to) the green prograde or retrograde directions. You should only be burning radially and normally to make small adjustments. If you're spending lots of fuel doing those kinds of burns, then often times, you could have avoided that by doing things different earlier on.