Transfer Window Planner is...way off?

[strider3]

I've entered my Kerbin orbit, my desired Dres orbit and my date window...and here's the rather useless maneuver I get:

As you can see my apoapsis is nowhere near a Dress encounter, let alone near Dres...it's just past a Duna orbit. I'm having a hard time understanding why this tool is useful? It almost never gets me where I need to go. The one consideration I wonder about...I've got almost a year until the node and launch window...do TWP calculations only work when very close to the launch window? If so...it's not a very useful tool for long range mission planning, is it? Does TWP not consider the position of Kerbin, in relation to Dres, at the time of the maneuver node it gave me? If it doesn't, then what is the point of this mod? It seems to me that TWP would take all these considerations into account and give me an encounter...no matter what. If it takes a bazillion DV, so be it...I will spread the window dates to get me a usable DV...give me an encounter, every time, no matter what date window I choose. The map above is for the lowest DV within a 3 year launch window possibility...is TWP just looking at lowest DV, instead of actual target encounter? That does me little good...I need a maneuver node that gets me an encounter with the target body...every time...nothing else really matters to me. Yes, I know..."You might have to tweak the node to get an encounter"...SIGH! Try "tweaking" the above node...good luck.

Am I not using this mod correctly?

Edited July 18, 2020 by strider3

[HebaruSan]

What TWP doesn't consider is your craft's position in its starting orbit at the time of the burn. Notice how your initial orbit goes inwards towards the sun? That's because you're facing some weird random direction instead of solar-prograde when the burn occurs. You need to zoom in on Kerbin's SOI and drag the maneuver around to what will be the right spot when the time comes.

If you want a mod that does take into account the craft's position, try the leftmost link in my forum signature.

[strider3]

6 minutes ago, HebaruSan said:

What TWP doesn't consider is your craft's position in its starting orbit at the time of the burn. Notice how your initial orbit goes inwards towards the sun? That's because you're facing some weird random direction instead of solar-prograde when the burn occurs. You need to zoom in on Kerbin's SOI and drag the maneuver around to what will be the right spot when the time comes.

If you want a mod that does take into account the craft's position, try the leftmost link in my forum signature.

Thank you, sir. I will give Astrogator a try. At this point I will try anything that makes actual working transfers. Can you tell me...does it allow copying and pasting of the transfer node requirements to "Precise Maneuver" mod or any other maneuver node mods?

[HebaruSan]

Just now, strider3 said:

Thank you, sir. I will give Astrogator a try. At this point I will try anything that makes actual working transfers. Can you tell me...does it allow copying and pasting of the transfer node requirements to "Precise Maneuver" mod or any other maneuver node mods?

There's a button to generate a stock maneuver, which you can then manipulate with whatever mods you want.

[strider3]

9 minutes ago, HebaruSan said:

There's a button to generate a stock maneuver, which you can then manipulate with whatever mods you want.

Sweet! I'm off to give it a try. Thanks!

Which version will I need for KSP 1.7.3? I see only the "latest" version,  I will assume it works with 1.7.3.

Edited July 18, 2020 by strider3

[strider3]

I have Astrogator in my GameData folder...how do I bring it up to use it?

[Streetwind]

For what it's worth: Transfer Window Planner includes built-in functionality to address this problem, by showing you exactly where you must put the maneuver node.

...Well, technically the information has always been provided, even by Alexmoon's website-based calculator on which TWP is based. Somewhere, it'll say something like "Ejection angle: 162° to prograde". That is the information you need. And because you did not use that information, your resulting orbit is completely off. If you had properly positioned your node based on this number, it would have given you the correct transfer orbit 100% of the time (as long as your dV inputs were also correct - see below).

Now, it's perfectly fair to say "what does that even mean". It's just a number you get along with a bunch of other numbers, and it isn't explained why it's there. How could you have known? And even if you knew - how do you even use it?

For this reason, you can tell the ingame mod to actually draw this angle onto the screen for you, and show you precisely where your node must sit. Here is a screenshot (from a slightly older version) of how it works.

Additionally, something that trips people up sometimes is the Ejection dV figure. That's the amount of dV you must add to the maneuver node. However, this is not just prograde dV - it's the composite of prograde dV and normal dV. And you need the individual numbers in order to set up the node. Bit of an unfortunate design choice to hide them, no question there, but it's a direct port of the webapp that did the same... anyways. You can find the individual numbers by either clicking on "copy transfer details", or via the little (i) icon on the right side.

[strider3]

14 hours ago, Streetwind said:

For what it's worth: Transfer Window Planner includes built-in functionality to address this problem, by showing you exactly where you must put the maneuver node.

...Well, technically the information has always been provided, even by Alexmoon's website-based calculator on which TWP is based. Somewhere, it'll say something like "Ejection angle: 162° to prograde". That is the information you need. And because you did not use that information, your resulting orbit is completely off. If you had properly positioned your node based on this number, it would have given you the correct transfer orbit 100% of the time (as long as your dV inputs were also correct - see below).

Now, it's perfectly fair to say "what does that even mean". It's just a number you get along with a bunch of other numbers, and it isn't explained why it's there. How could you have known? And even if you knew - how do you even use it?

For this reason, you can tell the ingame mod to actually draw this angle onto the screen for you, and show you precisely where your node must sit. Here is a screenshot (from a slightly older version) of how it works.

Additionally, something that trips people up sometimes is the Ejection dV figure. That's the amount of dV you must add to the maneuver node. However, this is not just prograde dV - it's the composite of prograde dV and normal dV. And you need the individual numbers in order to set up the node. Bit of an unfortunate design choice to hide them, no question there, but it's a direct port of the webapp that did the same... anyways. You can find the individual numbers by either clicking on "copy transfer details", or via the little (i) icon on the right side.

I was under the impression (mistakenly??) that using the "copy transfer details" feature in TWP and pasting this into a Precise Maneuver node would enter all the information to that node, including Ejection Angle?

Here's the latest attempt with TWP info pasted into PM. Much closer this time and the TWP info seems to copy over just fine into the node. Still not an encounter but hopefully some tweaking will get it done...that's the annoying part...the lengthy tweaking to make an encounter.

Edited July 18, 2020 by strider3

[HebaruSan]

16 hours ago, strider3 said:

Sweet! I'm off to give it a try. Thanks!

Which version will I need for KSP 1.7.3? I see only the "latest" version,  I will assume it works with 1.7.3.

Going by the CKAN metadata, the last version for KSP 1.7 was v0.9.2. The latest version is for KSP 1.8–1.10.

https://github.com/HebaruSan/Astrogator/releases/tag/v0.9.2

16 hours ago, strider3 said:

I have Astrogator in my GameData folder...how do I bring it up to use it?

It adds an icon to the toolbar, like TWP does. It's a folded map made up of a black sky with stars.

[strider3]

5 minutes ago, HebaruSan said:

Going by the CKAN metadata, the last version for KSP 1.7 was v0.9.2. The latest version is for KSP 1.8–1.10.

https://github.com/HebaruSan/Astrogator/releases/tag/v0.9.2

It adds an icon to the toolbar, like TWP does. It's a folded map made up of a black sky with stars.

OK, that may explain why I didn't see any icon after installing. I'll try the correct version.

[strider3]

Here's the result with Astrogator. What I like is that it automatically created a 2nd, mid-course correction and gets an encounter with no tweaking required . What it does not allow (as far as I can tell) is a change to the window "opening"...for example I can't reduce the time window to a year earlier like I can in TWP. Yes that results in a less efficient, higher DV transfer but sometimes an earlier launch window has its uses.

Edited July 18, 2020 by strider3