when do I execute a maneuver

[Jack5.exe]

Whenever I make a maneuver I always mass it up from missing it and I start exactly on it, what am I suppose to do

[HebaruSan]

7 minutes ago, Jack5.exe said:

Whenever I make a maneuver I always mass it up from missing it and I start exactly on it, what am I suppose to do

Typically half the burn should take place before the maneuver time, and half after.

So if it says it will take 2 minutes, then start burning when you're 1 minute away from the maneuver.

[Urses]

The problem is your plot predicts a situation where you burn full Dv at maneuverpoint in one moment. This is far away from reality. Your way to get right times is plot your maneuver till you have a Dv change. After this you fire your engines at full trust for shortest time and computer calculates a burntime. Here you get this number and as rule of tumb beginn your burn at T - burntime/2 it is not physicaly absolut perfect, but you get as near as possible to your planned trajectory without a call by NASA or Rosskom

Funny Kabooms 

Urses 

[Daniel Prates]

On 11/11/2017 at 12:16 AM, HebaruSan said:

Typically half the burn should take place before the maneuver time, and half after.

So if it says it will take 2 minutes, then start burning when you're 1 minute away from the maneuver.

That's exactly it. The maneuver tool puts the node in the actual middle of the burn, hence firing up engines before the node, 1/2 of the burn time away.

@Jack5.exeThere are many maneuver node mods out there that greatly improve the handling of the node 'gizmo', you should consider checking them.

[Tyko]

Also worth noting that the longer a burn is the less accurate it is. The Manuever node is plotting for an instantaneous burn of the entire DV and the time you spend burning before and after the node can throw your course off. So, if your leaving planetary orbit and your burn is longer than about 4 minutes you might want to think about breaking it up over several burns

there's some good info in this thread:

 

[GoSlash27]

What HebaruSan said.
 I always design my orbital stages to have a minimum acceleration of 0.5G. This allows me to execute interplanetary burns without excessive cosine losses.

Best,
-Slashy

[linuxgurugamer]

1 hour ago, GoSlash27 said:

What HebaruSan said.
 I always design my orbital stages to have a minimum acceleration of 0.5G. This allows me to execute interplanetary burns without excessive cosine losses.

Best,
-Slashy

I remember one mission I had.  I ended up with a 5 hour burn, with an accel of something like 0.05g

[Draalo]

5 hours ago, linuxgurugamer said:

I remember one mission I had.  I ended up with a 5 hour burn, with an accel of something like 0.05g

ever left the SOI of Jool with a MK III cockpit + cabin and ionengins?

 

I had to split one burn into five...

...TWR was so low and batteries doesnt provide longer burns because i burned on the night side...

Ah, memories...

All viewers: you can switch to physical timewarp (x2, x3, x4) while pressing "ALT" and "," or ":" while accelerating with ionengins

Edited November 22, 2017 by Draalo

[linuxgurugamer]

Physical timewarp doesnt help if the system is already overloaded

[FrostedShoe]

It's also worth mentioning the the burn time calculation takes what engines you used last and their thrust, so if you stage to a different engine half way through a burn your burn time will change. I keep making that mistake. If you stage then set up a node, give the engines a quick burst to get the correct burn time.

[Starman4308]

I think technically the best way to minimize finite burn time effects is to split the delta-V down the middle; while splitting burn time is usually a good approximation of that, it becomes more noticeable for very large maneuvers and if you stage to something with a different TWR. Otherwise, short of using a mod or kOS script that handles finite burn times, you'll never be exactly accurate, potentially requiring a correction burn.

[Dunbaratu]

2 hours ago, Starman4308 said:

I think technically the best way to minimize finite burn time effects is to split the delta-V down the middle; while splitting burn time is usually a good approximation of that, it becomes more noticeable for very large maneuvers and if you stage to something with a different TWR. Otherwise, short of using a mod or kOS script that handles finite burn times, you'll never be exactly accurate, potentially requiring a correction burn.

How to do it without any mods:

1 - Note the delta-V magnitude of your manoeuvre node, i.e "1240 m/s" or whatever.

2 - Temporarily place another manoeuvre node on your future path at a point *prior to* the one you want to perform.  Pull one of the knobs until this temp node has a delta-V of exactly half that of the real node.  (i.e. if the real node is 1240 m/s make this one have 620 m/s.)  It does not matter which knob you pull for this.  But it *IS* important that this node must exist at a point on the path *before* the real one, not after it.

3 - That temporary manoeuvre node will tell you how many seconds such a burn would take to achieve the first half of the delta-V of the real node.  Note the seconds.  (of course, here the standard buggy behavior of KSP where it can't figure out the real burn time might rear its ugly head.)

4 - Remove the temp node, but make note of what its burn time was.

5 - Now you know how far to lead the real node by.  Lead it by the amount of time the temporary node showed.

Edited December 9, 2017 by Steven Mading