Help me understand Mission Planners? (AlexMoon / KER)

[JoeSchmuckatelli]

Returning after a few days off, so please bear with me.

Still trying to wrap my head around my first interplanetary effort.  It's been recommended to me that I look at the KSP Launch Window Planner (AlexMoon) or KER.  I've not yet modded KSP, but I have watched a couple of videos of people using KER, and before I go that route I've some questions.

The basic one is how to use the Launch Window Planner features.  Specifically, what the rainbow graph(s) are telling me.  I've seen them in both the online resource and (briefly) in someone's use of KER.

Here's the online resource: https://alexmoon.github.io/ksp/#/Kerbin/130/Eve/100/false/optimalPlaneChange/false/1/198

If that, in fact, plots the window that I plugged info into, I have questions about the 'rainbow plot'

1.  I'm guessing that the 'cross intersection' is showing me the absolutely lowest delta v it would take to make a transfer (given the date I plugged in), is that right?

2. if that's correct: why isn't that somewhere in the middle of the dark blue?  (b/c if I'm reading this correctly, if I goof up trying to overly precisely hit that window on the cross and leave late, my delta v requirement goes up quite a bit... whereas if I err early, (and stay in the dark blue) I'm only taking a slight delta v hit -- is that correct?  So, shouldn't the optimal point be in the middle of the dark blue area?

3. if I'm reading the info on the right of the graph correctly, my optimal date of 

Departure

Year 2, day 163 at 5:31:12

So, seeing as I'm still in year 1, I need to wait until that timeframe to leave for Eve.  Is there any reason to plot a maneuver node until that time (and can you, without something like KER or Alarm Clock installed?)

4. Finally, can someone explain how / when to use "Ballistic", "Mid-Course Plane Change (I think I get this, but just to be sure), and "Optimal"... i.e knowing the definitions and how/when to use would be extremely beneficial.

 

Thanks in advance 

[Superfluous J]

30 minutes ago, JoeSchmuckatelli said:

I look at the KSP Launch Window Planner (AlexMoon) or KER.

I believe you mean TWP instead of KER

30 minutes ago, JoeSchmuckatelli said:

The basic one is how to use the Launch Window Planner features.  Specifically, what the rainbow graph(s) are telling me.

That's known as a "porkchop plot" because it frequently looks like a pork chop. And they wanted me to get hungry looking at them.

30 minutes ago, JoeSchmuckatelli said:

1.  I'm guessing that the 'cross intersection' is showing me the absolutely lowest delta v it would take to make a transfer (given the date I plugged in), is that right?

To start, yes. You can also click on the plot to get the specifics for that grid point.

30 minutes ago, JoeSchmuckatelli said:

2. if that's correct: why isn't that somewhere in the middle of the dark blue?  (b/c if I'm reading this correctly, if I goof up trying to overly precisely hit that window on the cross and leave late, my delta v requirement goes up quite a bit... whereas if I err early, (and stay in the dark blue) I'm only taking a slight delta v hit -- is that correct?  So, shouldn't the optimal point be in the middle of the dark blue area?

Not necessarily in the MIDDLE, but it should be in there somewhere.

Imagine a mountain that looks like this:

___.......------^\_

----|-------------!-|-

Everything between those lines is the "blue area" of your plot, but the exclamation point is the actual peak.

30 minutes ago, JoeSchmuckatelli said:

3. if I'm reading the info on the right of the graph correctly, my optimal date of 

Departure

Year 2, day 163 at 5:31:12

So, seeing as I'm still in year 1, I need to wait until that timeframe to leave for Eve.  Is there any reason to plot a maneuver node until that time (and can you, without something like KER or Alarm Clock installed?)

Not really, except that you want to be a few days early up in orbit to be ready to go. Note, you will likely not leave at exactly 5:31:12, and may not even leave on day 163. The real world and math don't always match in these cases. But you'll be close, within a day or two probably.

30 minutes ago, JoeSchmuckatelli said:

4. Finally, can someone explain how / when to use "Ballistic", "Mid-Course Plane Change (I think I get this, but just to be sure), and "Optimal"... i.e knowing the definitions and how/when to use would be extremely beneficial.

"Ballistic" means "what do I have to do to just launch from Kerbin Orbit and go to Eve?"

"Mid-course" means "what do I have to do to launch from Kerbin Orbit, make a mid-course correction somewhere in Sun orbit, to go to Eve?"

"Optimal" means "Of those two, which has a lower dV cost?"

30 minutes ago, JoeSchmuckatelli said:

Thanks in advance 

You're welcome

[JoeSchmuckatelli]

14 minutes ago, Superfluous J said:

...

You're welcome

You get a +1 just for this!

 

(The rest is okay, too, I guess.  \

 

 

EDIT:  I thought I saw a porkchop on KER -- is that not an available feature?

Edited June 2, 2020 by JoeSchmuckatelli

[Superfluous J]

1 hour ago, JoeSchmuckatelli said:

EDIT:  I thought I saw a porkchop on KER -- is that not an available feature?

I stopped using KER when Delta V info was added to the stock game. They may have added is since I suppose.

2 hours ago, JoeSchmuckatelli said:

can you, without something like KER or Alarm Clock installed?

I forgot to answer this part.

You can. Place a node anywhere and then use the node editing tool in the lower left (only in map mode), you can put a specific time in there. It's a little dodgy, and I suggest something like KAC or Precise Node. Again, I don't think KER can do that but don't use it anymore.

[JoeSchmuckatelli]

8 hours ago, Superfluous J said:

I stopped using KER when Delta V info was added to the stock game. They may have added is since I suppose.

I forgot to answer this part.

You can. Place a node anywhere and then use the node editing tool in the lower left (only in map mode), you can put a specific time in there. It's a little dodgy, and I suggest something like KAC or Precise Node. Again, I don't think KER can do that but don't use it anymore.

Thanks... what's TWP?

 

(from your first response)

Edited June 2, 2020 by JoeSchmuckatelli

[Curveball Anders]

41 minutes ago, JoeSchmuckatelli said:

Thanks... what's TWP?

Transfer Window Planner

One of several such.

 

[JoeSchmuckatelli]

3 hours ago, Curveball Anders said:

Transfer Window Planner

One of several such.

 

Ah - thanks.  From the documentation, it seems its an ingame version of the alexmoon web based planner.  Can I assume that since it only says 1.7x that it doesn't work for 1.9?

[Superfluous J]

12 minutes ago, JoeSchmuckatelli said:

Ah - thanks.  From the documentation, it seems its an ingame version of the alexmoon web based planner.  Can I assume that since it only says 1.7x that it doesn't work for 1.9?

You can not assume that, but you can try it and see with no risk other than maybe having to restart the game a couple times while installing and uninstalling.

I know for a fact it works in 1.8.1

[Cavscout74]

One thing to be aware of no matter how precisely you try to set up the initial transfer, you almost always have to do a small mid-course correction to actually get where you want.  You aren't producing an instantaneous impulse of the exact dV at the exact maneuver node, you are producing it over seconds or minutes (or possibly hours for ion engines) before and after the node, which causes your actual course to diverge slightly from the ideal from the transfer planner.  This alone is fairly small (usually <100 m/s) and is not the same as the "mid-course plane change" option of the planner.  

[JoeSchmuckatelli]

19 minutes ago, Cavscout74 said:

One thing to be aware of no matter how precisely you try to set up the initial transfer, you almost always have to do a small mid-course correction to actually get where you want.  You aren't producing an instantaneous impulse of the exact dV at the exact maneuver node, you are producing it over seconds or minutes (or possibly hours for ion engines) before and after the node, which causes your actual course to diverge slightly from the ideal from the transfer planner.  This alone is fairly small (usually <100 m/s) and is not the same as the "mid-course plane change" option of the planner.  

Is there a consensus on whether choosing Optimal is any better than picking one of the other two, or are they all generally close?

-- asking b/c it seems to me that with different orbital inclinations, combined with the fact that plane change is less expensive for wider orbits, that trying to just get a ballistic or an optimal without planning a plane change may be less than... optimal

 

[N_Danger]

With KER I just use it for finding a launch window. I then use a Delta V map to plan the mission Delta V budget assuming the most efficient transfer.  I add some extra Delta V to cover contingencies.

The advantage of a transfer window planner is that you can get a rough D/V requirement at any point without waiting for a perfect alignment of the planets.

I use a mid-course correction more for setting my PE than my inclination.

[Rhomphaia]

1 hour ago, JoeSchmuckatelli said:

Is there a consensus on whether choosing Optimal is any better than picking one of the other two, or are they all generally close?

-- asking b/c it seems to me that with different orbital inclinations, combined with the fact that plane change is less expensive for wider orbits, that trying to just get a ballistic or an optimal without planning a plane change may be less than... optimal

 

I would say just go optimal... unless you are going to Moho, where it is best to fully examine all options.