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[1.1.3] MechVal - new HowTo: Departure Burn (v0.03 2016/09/30)

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MechVal - Your Low T Auto-Co-Pilot

makes the impractical possible 


[ Ignore the MechJeb windows, except the 0.3 m/s2 max acceleration. The important thing to ask is How would I build those nodes? How can I tell where my low TWR vessel is going to go?]

Take the guess work out of very low TRW interplanetary transfers ...

  • How long will it take to Pe Kick ready for a departure burn?
  • How much will Kerbin radial my orbit as I crawl out of the gravity well?
  • Where & when should I put my Pe to kick it all off?
  • Where will my trajectory go anyway? 

Got 'no time' for low thrust? Less IS Moar - just doing the vanilla Pe kicks could let you slash your propellant mass = moar thrust!

MechVal will hold your hand and do all the tedious node management:

  • Set your desired maneuver node
  • MechVal will split off a Pe kick sequence. 20 nodes? let MechVal manage that mess!
  • If you have the thrust use it on the residual departure node, or...
  • MechVal can split that into little chunks that let you see how the planet will mess with you
  • Tell MechVal to 'Pull all of those 40 nodes back 180 seconds' and she'll painstakingly adjust each node individually - even the 20 kick nodes that are all on top of each other - try and do that by hand.


I've tidied and packaged some kOS scripts that I've used to setup very low thrust & high isp maneuver sequences. So far mainly support for doing the initial interplanetary transfer. I am cleaning up capture sequences. I want to add physics warped execution, PeBraking, AeroBraking, and support for lower isp craft.

on spacedock.info

Install: instructions are in MechVal.txt - basically unzip to Ships/Script NOT GameData

Prerequisites: kOS Scriptable Autopilot System I'd always thought kOS looked neat, but a bit imposing to get a grip on - install is simple, then add a part your your craft - that's all you need to use MechVal.


Is MechVal an Auto Pilot? Right now I have to say she's an auto-astrogator, a specialized maneuver planner - but I think when I add node execution and auto-aerobraking it will be fair to say she's an auto-co-pilot.

Does MechVal share nodes with MechJeb, Precise Node, etc? Yes. KSP provides a maneuver node system any mod that wants KSP to display it's maneuvers in the map view has to use KSPs node system - so they will all inter-operate. One caveat is that they don't necessarily update their GUI when the underlying node is changed. MJ will 'notice' being deleted and shift to display another, but he won't notice changes numbers - just use the little arrows to move the the next/previous node and back to see any update.


How To MechVal

Pe Kicking A Transfer Burn with a head start

Departure Burn Crawling out of the gravity well


Change log:

v 0.02 - fix to mvPeKickNode - final departure node adjustment was messing normal / radial

v 0.03 - add:
        mvDeltaMagNodeFrom - move deltaV from one node to another
        mvDeltaSplitsedNodeMagSeconds - add delta to the end of a chain of nodes preserving their size and spacing
        mvDeltaSplitsedNodeMag - as above but uses ship max acceleration
        mvDeltaSplitsedNodeMagThrottle - as above but uses throttled ship max acceleration

Edited by DBowman
new How To and version
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31 minutes ago, DerekL1963 said:

Will MechVal work with MechJeb created nodes?

Sure any node KSP knows about is 'fair game'. Where you need to tell MechVal which node you are tweaking use the number MJ uses. You can use MV for changing the magnitude (while respecting all the normal, radial, prograde components), splitting a node in 2, splitting into Pe Kicks, or splitting a burn into many chunks (in a couple of ways like time&deltaV, or time&throttleLimit)

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2 hours ago, GSUI5051 said:

Can you make a brief introduction video to explain how it works and difference between MJ & MW?

He pretty much covered it the desc, MechVal just handles those long interplanetary burns where you have to split it around different orbits.

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2 hours ago, GSUI5051 said:

Can you make a brief introduction video to explain how it works and difference between MJ & MW?

I'd been thinking to make some 'how to' posts with screen shots and script fragments. I'll reference them from the OP as I do.

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This looks pretty useful.

But I think the fact that it needs kOS, and that it's *not* to be installed in the normal "extract the ZIP to your game folder and it ends up in GameData/" sort of way should probably get a bit more "top billing" in the description and not be buried so deep in the description.  I'm not sure if it would violate the rules for hosted mods to do the following, but maybe it could also be packaged in such a way that if you did do so, it would still be in the "right place" (i.e. have it extract the files to Ships/Scripts/mechval/*.ks files, or something like that.  (Definitely add that extra "mechval/" folder in the path if you do, just so you don't clobber over any scripts the user may have already written).)


Edited by Steven Mading
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5 minutes ago, Tex_NL said:

How is this different from MechJeb? Does it contain original code or is it just a blatant rip-off? It looks identical. Even the icons and side menu are 1 on 1 copies.

I think it's made for calculate maneuver of ion probes or other low TWR ships.

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2 hours ago, Tex_NL said:

How is this different from MechJeb? Does it contain original code or is it just a blatant rip-off? It looks identical. Even the icons and side menu are 1 on 1 copies.

The original post is quite clear - it splits long nodes into short ones.  MechJeb doesn't do that.

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4 hours ago, Tex_NL said:

How is this different from MechJeb? Does it contain original code or is it just a blatant rip-off? It looks identical. Even the icons and side menu are 1 on 1 copies.

The mechjeb windows showing in the screenshot aren't part of this mod at all.  They're just coincidentally in view when the screenshot was taken.  The actual user interface, which is the kOS terminal, isn't in the screenshot, probably because there's not really much to show there.  All the interesting stuff to look at is on the map screen - with the split apart nodes.

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Yeah, the fact that these are kOS scripts and not a normal addon should be more prominent.  This does seems like a cool option if you have kOS installed.  For everyone else there's Maneuver Node Splitter:


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Wait... this is a bunch of kOS scripts, and NOT a plugin itself?... If thats the case, then yes, PLEEZE make it more clear that kOS IS A REQUIRED DEPENDENCY!...

If that is NOT the case, then please ignore my comment... :)

Either way, THANK YOU for the work putting this together... :)

Really??... The only thing that could possibly make anyone think this is MJ related, is the name, and the (possibly unfortunate) screenshot in the OP, where MJ windows are open... The full functionality of this is something that MJ does NOT do AT ALL... Also, even tho "auto-pilot" is mentioned, all I read are references to handling complicated node maneuvers... Even if this mod executes the burns automatically, I would NOT consider this even close to an auto-pilot...

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8 minutes ago, ZooNamedGames said:

Still lost on how this isn't a discount MJ.

Because MechVal doesn't do what MJ does, and MJ doesn't do what MV does.

Most of what's shown on the screenshot is MechJeb, and the author makes no claim that it is part of MechVal; MechVal is a set of kOS scripts used to split up the MJ maneuver node into a bunch of periapsis kicks.

To the OP: It would probably be less confusing if the MechJeb windows were removed from the screenshot, so it's showing primarily just the resultant maneuver nodes.

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MechVal How To: Pe Kicking
A Transfer Burn with a head start

An easy introduction to kOS, MechVal, and the mysteries of Pe Kicking.

This tutorial covers the simplest, and most generally useful thing that MechVal makes easy - the Pe Kicked interplanetary transfer.

For those who are not familiar:

You do a series of burns at Pe, each burn raises your vessels orbital energy and corespondingly reduces your final transfer burn. So rather than burn 1040 m/s in one go you can do four burns of 260 m/s, three Pe Kicks and a transfer burn.

Why is this a good thing even for not so low thrust vehicles:

  • KSP models nodes as impulsive / instantaneous burns, the further you are from that ideal the further your trajectory will be from what KSP shows you.
  • If your burns are shorter and you are using nukes you'll need less radiator mass = higher payload.
  • You won't lower your Pe so much in the first half of the burn so you can be in a lower departure orbit = more Oberth.
  • Since you burn closer to prograde the burns should be more efficient.
  • You will get a couple of chances to re-tune your burn for the last few hundred m/s.

 nxJFRFLl.png http://imgur.com/nxJFRFLl.png here is a Duna Colonial Transporter I'd been messing about with; crew capacity 23, 10 ton cargo to Duna and return. TWR 1/3, 3 m/s^2 - so not really low thrust, a six minute burn to do a nominal 1040 m/s Duna transfer. I'll use this to illustrate how to MechVal Pe Kick.

  • make sure kOS is installed and a computer is added to your vessel.
  • make sure MechVal is installed - just unzip the files into Ships/Script. You can copy MechValCmds.ks and use it as your 'terminal' script.

The steps we follow are:

  • Setup a trajectory on a guide probe to use as a reference. I have a probe in common departure orbits for this kind of thing.
  • Setup the same trajectory from your craft - target the guide probe and you can see both. At any time you can make sure you have not messed up your transfer trajectory.
  • Use MechVal's mvPeKickNode() function to split out three Pe Kick nodes from the transfer node.
  • This will leave the departure node in some random place on the last/highest Pe Kicked orbit.
  • Use MechVal mvDeltaMagNode() to increase / decrease the period of the highest Pe Kick orbit until you bring the departure node over the top of all the others.
  • Use mvDeltaMagNode() to make the opposite changes to the final node ( I'll make a function to do these together)
  • Now you will have a trajectory the loops around Kerbin at least three times and then does a departure burn.

I have full details in this album and call out highlights below:

From your vessel click kOS icon and then the picture of a terminal to open ... a terminal. Type:

switch to 0. <enter>

this just tell kOS to run scripts that are at KSC, if you are playing career you might have to move the MechVal scripts 'to your ship'.


ZOxddACl.pnghttp://imgur.com/ZOxddACl.png I've just run mvPeKickNode( 1, 260, 800, 3 ) - split the first node, into chunks of 260 m/s, no more than 800 m/s, start as late as possible within 3 orbits from now. Note: 

  • kOS does not let you call functions with arguments from the terminal, so you have to edit a file (  yourFile.ks ) containing the script and then type: run yourFile. As it turns out this is what you want anyway since you build up a record of what you did.
  • KSP has a bug so it sometimes does not show your trajectory if nodes overlap in the right way - but you can see the string of Aps.
  • The highest Ap is 1 day away, and the departure burn is 3 days away so we will have a couple of highest orbits to tune if we want.


5ALvnRNl.pnghttp://imgur.com/5ALvnRNl.png Increasing the Ap brings the departure node back toward all the others - using mvDeltaMagNode( 3, 5 ) - change node 3's magnitude by +5 (respecting the direction implied by prograde, normal, radial).


sdGrAAol.pnghttp://imgur.com/sdGrAAol.png too far, start using mvDeltaMagNode( 3, -1 ) - it's like using MJ's +/- buttons - but without worrying about the components.


K5Y9jkil.pnghttp://imgur.com/K5Y9jkil.png ok all the nodes are now over the guide node, so the transfer will happen at the right time at the right place at Pe


fppub8Fl.pnghttp://imgur.com/fppub8Fl.png Adjusting the last kick magnitude means our total burn is a little off now, fix the departure burn using mvDeltaMagNode( 4, ? ). I'll make a mvDeltaMagNodeFrom( nodeToChange, nodeToAntiChange, delta )  so this step will disappear.


eyy4wxhl.pnghttp://imgur.com/eyy4wxhl.png Let MJ execute the nodes. MJ focuses on deltaV we'd rather he focus on Ap, I'll make an mvExecuteToAp( nodeNumber ) to do that.


cGyMN1Xl.pnghttp://imgur.com/cGyMN1Xl.png all the kicks are done. We have one Pe where we could tune if we wanted, or crew could rendezvous if we had done 40 kicks to get Ap out way past the Mun.


uyRqSuil.pnghttp://imgur.com/uyRqSuil.png Use MJ to tweak our closest approach.

Edited by DBowman
add the pics
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