Using a maneuver node to plan a suicide burn

[JebNeedsHelp]

I know I've seen this mentioned twice in other threads, but even though I've used maneuver nodes to plan encounters for a while now, I still can't figure out how to make this work regarding a suicide burn. The wording of the other posts just didn't quite make it clear, to me, anyway, just what I'm supposed to do (I guess I'm part Kerbal that way ). Could somebody give me a step-by-step? I'd greatly appreciate it.

Thanks in advance!

JNH

Edited August 29, 2014 by JebNeedsHelp

[GreeningGalaxy]

Can someone fill me in on what the exact working definition of 'suicide burn' is?

Is that where you just point at the thing you want to go to and burn until you get an encounter, or is that something else?

[DeMatt]

Can someone fill me in on what the exact working definition of 'suicide burn' is?

Is that where you just point at the thing you want to go to and burn until you get an encounter, or is that something else?

The basic takeoff sequence consists of two maneuvers: a "takeoff" burn to give your rocket an apoapsis at your desired orbital altitude, and a "circularization" burn (at said apoapsis) to convert your suborbital flight into a circular orbit. The basic landing sequence consists of the opposite maneuvers in reverse sequence: a "deorbit" burn to convert your circular orbit into a suborbital trajectory, and a "landing" burn to set your rocket gently down on the surface.

"Landing" burns, if they are performed as the EXACT opposite of the "takeoff" burn, are known as "suicide" burns. Why? Because the ideal "suicide" burn involves your rocket firing its engines in one full-power blast that starts just early enough to bring the rocket to a halt just as its landing gear touches the ground. Firing just a hair too little, or too late, results in a crash.

I know I've seen this mentioned twice in other threads, but even though I've used maneuver nodes to plan encounters for a while now, I still can't figure out how to make this work regarding a suicide burn. The wording of the other posts just didn't quite make it clear, to me, anyway, just what I'm supposed to do (I guess I'm part Kerbal that way ). Could somebody give me a step-by-step? I'd greatly appreciate it.

The basic idea is:

1. Add a maneuver node to your suborbital trajectory where it touches the ground.
   
2. Adjust the node to zero out your trajectory.
   
3. Note the burn time.
   
4. Start the burn early, so that it completes as you (theoretically) reach the node.
   

[Taki117]

Can someone fill me in on what the exact working definition of 'suicide burn' is?

Is that where you just point at the thing you want to go to and burn until you get an encounter, or is that something else?

A "Suicide Burn" is basically where you fire your engine at full throttle at the last possible moment to land. If you mistime it at best you will break your landing legs. At worst rapid unplanned dis-assembly as a direct result of excessive speed upon impact with the surface.

[Sirine]

I've seen a mod that does that. But I can't recall the name.

[The Yellow Dart]

Suicide burns are easier to do with maneuver nodes but are still quite difficult to get perfect. Ultimately you will need a combination knowledge and experience to get them just right with maximum efficiency and accuracy every time. In my experience, as stated above, line up and lower your orbit through your desired landing site, then set up a node right at the point where the orbit line intersects the surface. This is the first point where you need experience over knowledge because the map screen planet models don't match perfectly with the actual terrain so you must make an educated guess based on past experiences. Then, as Dematt said, pull retrograde until the node flicks back & forth to null your velocity. Now if you want a suicide burn that is safe and fairly accurate, start your burn when burn length and time to node are equal. This will give you plenty of leeway but also bring you to a halt before you reach the landing site, and still a little ways up above the surface. To get as close as you can you have to wait a length of time after your burn time and time to node match. Exactly how long depends on your thrust to weight and the difference between the map terrain and the real terrain and only experience can tell you(and it can often be wrong as well). It is a nerve wracking couple of seconds I can tell you. Good luck & Happy landings!

[JebNeedsHelp]

DeMatt, I just tried what you said for a Mun landing, and still chickened out a bit, starting the burn early just because it looked like I was picking up a lot of speed falling. I wound up erring way on the side of caution, like The Yellow Dart mentioned, but on the plus side, I did uses a lot less fuel than I would have without using the node. I'm sure I'll get better with practice. Thanks, guys!

[Callmedave]

This explains it for me too. I have a science lander orbiting the mun that visits each biome then docks to an orbiting lab for a clean. Il try the suicide burn on my next landing. Iv been guessing it out and wasting a lot of fuel.

[SRV Ron]

Once you get the orbital speed down to zero, tilt your ship to be vertical to the retrograde marker and 90* on the nav ball. You should have aimed to get vertical around 5000 meters on Mun or 2000 meters on Minmus. Get a feel for controlling vertical speed while keeping the retrograde marker on the vertical marker to control drift. Let the ship come down fairly fast slowing down as you near the surface. Touchdown around 5m/sec or less. Have drift near zero to avoid tipping over.

Why be vertical at 5000 meters on Mun? Check the altitude as this lander approaches the surface.

Edited August 29, 2014 by SRV Ron