• 0

# Maneuver nodes are crazy. I want to know WHEN to start my burn because i start it 40 secs before. It does not matter on planets but it matters when docking. My version is 1.12 if that helps.

## Question

Maneuver nodes are crazy. I want to know WHEN to start my burn because i start it 40 secs before. It does not matter on planets but it matters when docking. My version is 1.12 if that helps. My maneuver node says ill be near it 0.2KM seperated, but for some reason when i execute the burn, its either a huge number like 3 KM or it does not even show the intersects. I dont really care about this while going on interplanetary missions, but it would be helpful to know.

## Recommended Posts

• 0

you have to realize that in space, 3 km is not a huge number. In space, 3 km is a very close approach, and it requires a lot of precision to achieve even that. the difference between 0.2 km and 3 km is a tiny, insignificant fraction of a second in shutting down the engine sooner or later.

So, what you should do to get rendez-vous is

- make those manuevers very carefully, because the slightest imprecision on when you stop the engine will chance the encounter by kilometers.

- after you get a 3 km approach, make a second manuever to refine that. wait until you are closer to the approach, and it will be less sensitive to tiny variations.

##### Share on other sites

• 0

I wholeheartedly agree with @king of nowhere, especially on that last point about multiple burns.  I have found that I will end up doing one burn to "get close", and then another one to "get close".  And then sometimes, just for fun, I'll end up having to do a third burn to get close enough where I can start docking procedures.

Keep in mind that you are talking about an infinitesimally small section of space where you are trying to get 2 objects moving at different speeds and in different directions to try to come really close to each other without crashing into one another.  And this isn't like driving a car, where you are bound by a linear circle for directions.  You are IN SPACE, meaning you have the full cube of directions to travel.  With both objects.

Patience, young grasshopper.  Time and practice will make this all seem relatively insignificant.

Edited by Scarecrow71
##### Share on other sites

• 0
3 hours ago, Lashlbhat said:

My maneuver node says ill be near it 0.2KM seperated, but for some reason when i execute the burn, its either a huge number like 3 KM or it does not even show the intersects.

Some more suggestions:

• Watch the map view during the burn to get a sense of how it's changing and how fast
• Right click the close approach marker to keep it visible during the burn, then cut the engines the instant it starts to tick upwards
• If you need more precision, use lower thrust
• RCS can be helpful for fine tuning a rendezvous, both due to the low thrust and the fact that well-placed RCS thrusters are omnidirectional. If you press R and then tap H, N, I, J, K, and L, you can get a sense of which directions get you a closer approach and which push you farther away. Usually it's not too hard to get your actual close approach down to 0.0 km this way.
##### Share on other sites

• 0

This question about playing the game has been moved here from KSP Discussion.

KSP Moderation Team

##### Share on other sites

• 0
7 hours ago, HebaruSan said:

If you need more precision, use lower thrust

I generally alter thrust percent on my engines to get finer control over burn times and how powerful the actual burn is.

##### Share on other sites

• 0
13 hours ago, king of nowhere said:

you have to realize that in space, 3 km is not a huge number. In space, 3 km is a very close approach, and it requires a lot of precision to achieve even that. the difference between 0.2 km and 3 km is a tiny, insignificant fraction of a second in shutting down the engine sooner or later.

So, what you should do to get rendez-vous is

- make those manuevers very carefully, because the slightest imprecision on when you stop the engine will chance the encounter by kilometers.

- after you get a 3 km approach, make a second manuever to refine that. wait until you are closer to the approach, and it will be less sensitive to tiny variations.

I know, but when do i decide to execute my burn? is there a fixed time like 40 seconds or it depends on the time you need to burn? (Example: Burn time: 1 minute 40 seconds. So i start my burn at 1 minute 40 seconds. Does that ensure my maneuver node is ALMOST perfect?)

##### Share on other sites

• 0
23 minutes ago, Lashlbhat said:

I know, but when do i decide to execute my burn? is there a fixed time like 40 seconds or it depends on the time you need to burn? (Example: Burn time: 1 minute 40 seconds. So i start my burn at 1 minute 40 seconds. Does that ensure my maneuver node is ALMOST perfect?)

It depends on the maneuver and situation, but in general (almost always) having half your burn before and half after the node is best/good enough. There's a setting in the game that will show you when to start your burn and that's all it does, half the time your burn would take before you reach the node.

##### Share on other sites

• 0
12 minutes ago, Lashlbhat said:

I know, but when do i decide to execute my burn? is there a fixed time like 40 seconds or it depends on the time you need to burn? (Example: Burn time: 1 minute 40 seconds. So i start my burn at 1 minute 40 seconds. Does that ensure my maneuver node is ALMOST perfect?)

It depends on the burn.

Reason being: the maneuver node is a single point in space-time. You reach and pass it in a single instant. But, running your engine to affect the change of velocity you want takes some time. The more dV you wish to spend, and the heavier your spacecraft, the longer it takes; the more thrust you have, the shorter.

If you think about that, it makes logical sense to center your burn on the maneuver node in almost all cases. You'll have half your burn before the node, and half your burn after it. Both introduces a small error because you are not perfectly on the node, but because you have an even split before and after, these errors actually cancel each other out near-perfectly.

In the settings menu, under "general", you can toggle "show extended burn indicator". I honestly forget what the exact difference is between leaving it off and turning it on, because I simply always turn it on by default and never play without it. But when I make a maneuver node, I have little buttons next to the burn time that let me set a split. It defaults to 50%, which means an even split before and after the node, and that's perfect for 99% of all cases. And there are three bits of timing information: "Node in T - xx:xx", which means how far away the actual node is; "Burn Time", which is how long the actual burn takes; and "Start Burn in", which gives you a countdown for when you need to ignite your engine. This last field will change depending on how you set your split. But as mentioned, 50% is perfect for almost any case.

##### Share on other sites

• 0
3 hours ago, Streetwind said:

It depends on the burn.

Reason being: the maneuver node is a single point in space-time. You reach and pass it in a single instant. But, running your engine to affect the change of velocity you want takes some time. The more dV you wish to spend, and the heavier your spacecraft, the longer it takes; the more thrust you have, the shorter.

If you think about that, it makes logical sense to center your burn on the maneuver node in almost all cases. You'll have half your burn before the node, and half your burn after it. Both introduces a small error because you are not perfectly on the node, but because you have an even split before and after, these errors actually cancel each other out near-perfectly.

In the settings menu, under "general", you can toggle "show extended burn indicator". I honestly forget what the exact difference is between leaving it off and turning it on, because I simply always turn it on by default and never play without it. But when I make a maneuver node, I have little buttons next to the burn time that let me set a split. It defaults to 50%, which means an even split before and after the node, and that's perfect for 99% of all cases. And there are three bits of timing information: "Node in T - xx:xx", which means how far away the actual node is; "Burn Time", which is how long the actual burn takes; and "Start Burn in", which gives you a countdown for when you need to ignite your engine. This last field will change depending on how you set your split. But as mentioned, 50% is perfect for almost any case.

So,  if i want to have an almost perfect maneuver node burn, I have to start half my burn before the maneuver node, and half of it AFTER? like for example: 1 minute 40 secs burn means i have to slice that in half (50 seconds) and then start my burn at T - 50 seconds and end my burn at T- 50 seconds. I dont know if it works, since im posting it at the end of my play-time, so i'll try it tommarow. But if it works, Thanks!

##### Share on other sites

• 0
2 hours ago, Lashlbhat said:

So,  if i want to have an almost perfect maneuver node burn, I have to start half my burn before the maneuver node, and half of it AFTER? like for example: 1 minute 40 secs burn means i have to slice that in half (50 seconds) and then start my burn at T - 50 seconds and end my burn at T- 50 seconds. I dont know if it works, since im posting it at the end of my play-time, so i'll try it tommarow. But if it works, Thanks!

yes, this is the best way.

but do keep in mind, your burn still will never be 100% accurate, and you will need to make little correction manuevers later.

real space missions use correction manuevers too.

##### Share on other sites

• 0
21 hours ago, Lashlbhat said:

Maneuver nodes are crazy. I want to know WHEN to start my burn because i start it 40 secs before. It does not matter on planets but it matters when docking. My version is 1.12 if that helps. My maneuver node says ill be near it 0.2KM seperated, but for some reason when i execute the burn, its either a huge number like 3 KM or it does not even show the intersects. I dont really care about this while going on interplanetary missions, but it would be helpful to know.

If docking is your issue, you might find this to be helpful:

##### Share on other sites

• 0
2 hours ago, king of nowhere said:

yes, this is the best way.

but do keep in mind, your burn still will never be 100% accurate, and you will need to make little correction manuevers later.

real space missions use correction manuevers too.

It worked! i got an almost perfect docking window!

##### Share on other sites

• 0

I docked! Thanks to everyone's advice!

## Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

×   Pasted as rich text.   Paste as plain text instead

Only 75 emoji are allowed.