Transfer Window Planner + Dres

[strider3]

A question for you all regarding getting to Dres, from Kerbin, using the Transfer Window Planner mod. When TWP creates a maneuver node to Dres, with its inclined orbit in relation to Kerbin's, does it expect me to be at a 0* inclination orbit around Kerbin...or does it want me to try and match the inclination of Dres, while I am in Kerbin orbit, before hitting the maneuver node?

Either way, what would be an "acceptable" variance to the required inclination?

I ask because using the node created by TWP for Kerbin to Dres rarely get's me an actual Dres encounter...it usually requires lots of "fiddling" with the node to get an encounter...LOTS of fiddling.

Thanks, as always, for any insight, gang.

Edited March 10, 2019 by strider3

[Tyko]

TWP will give you the departure angle. The DV budget calculation assumes you're starting from an equatorial / 0 degree orbit.

Dres has a really small SOI, so getting an encounter is tough.  Here are a couple of suggestions

• Use one of the maneuver node mods - Precise Maneuver or Precise Node let you type in the values TWP provides allowing you to be accurate to at least one decimal place. Once you have the values typed in you can tweak you maneuver by very small increments to get as close as possible
• You'll likely still have to account for slight errors in the burn because the SOI is so small. Just get it really really close then plan a mid-course correction change. After you complete your initial maneuver drop another maneuver node about halfway to Dres and fine tune it there. Typically these mid-course changes use very little DV and doing it halfway will give you the optimal place to adjust inclination. 

[strider3]

Thanks Tyko. I do use Precise Maneuver which allows me to copy and paste the maneuver from TWP...very helpful. I just wanted to make sure I was doing everything possible and, after reading your reply, it seems I am.

Thank you!

Edited March 11, 2019 by strider3

[Tyko]

sure thing...I find that some trial and error with Precise Maneuver helps...i'll use the key pad to quickly make small changes to the Prograde, Normal and Radial settings and see which directions bring me closer then just patiently tap away at the keys and watch the numbers drop until I get as close as I can. It can take some tapping, but by adjusting your increment value for each tap you can get very precise maneuvers.

The only challenge then is actually doing the burn accurately. One additional note - depending on your TWR your burns can get pretty long. If you're burning from LKO and your burn is over 4-5 minutes you're moving around the planet so fast that you'll lose accuracy and efficiency at the beginning and end of the burns. To correct for that you can:

• Increase your TWR so you have shorter burns - the easist, but you have to plan for the greater mass
• Raise your orbit so the orbital path is straighter - the lower the orbit the tighter the circle you're flying in.
• Do the transfer over multiple orbits - it's called a periapsis kick - you do the first burn to raise your AP higher, but not all the way out of Kerbin's SOI. then ride around your orbit til you're back at PE for another burn. Depending on how low your TWR is you may have to do several kicks. on the final pass you push your AP out of Kerbin SOI and complete your transfer burn. This is fun when it's done right, but it's easier to do one of the first two methods above   

Edited March 11, 2019 by Tyko

[strider3]

Tyko, do any of your suggestions above increase the DV required as opposed to just leaving Kerbin from 350k? The periapsis kick sounds like it may make TWP info "obsolete", as it asks for your Kerbin orbit and I assume it's wanting a "round" orbit for it's calculations? Although I would enter my final Kerbin departure orbit as my Kerbin periapsis in TWP ( I assume), my Kerbin apoapsis would be much higher. How would I do a periapsis kick with TWP...is it possible?

Thanks buddy!

Edited March 15, 2019 by strider3

[DStaal]

The only one of Tyko's suggestions that would increase the total DV required is to raise the orbit - which will be partially offset by lowering the DV required for the transfer burn, but only partially.  As for the periapsis kick - the ideal way to do it is to calculate the burn from TWP first, and then break that burn down into several pieces so that your final burn puts you on the same departure 'orbit' as the TWP burn would.  There is a mod for that, though it hasn't been updated in a while and I haven't tried it recently.  (It was also took a bit of experience to use, and know that your errors in your burns are going to mulitiply.)

 

[Tyko]

2 hours ago, Victor3 said:

Tyko, do any of your suggestions above increase the DV required as opposed to just leaving Kerbin from 350k? The periapsis kick sounds like it may make TWP info "obsolete", as it asks for your Kerbin orbit and I assume it's wanting a "round" orbit for it's calculations? Although I would enter my final Kerbin departure orbit as my Kerbin periapsis in TWP ( I assume), my Kerbin apoapsis would be much higher. How would I do a periapsis kick with TWP...is it possible?

Thanks buddy!

Two nice things about doing the "raise your orbit" method 1) the extra DV for higher orbit is small and handled by the launch vehicle, so you don't have to change your payload and 2) you can use TWP numbers directly because you just tell TWP you're starting from a higher orbit

[strider3]

Thanks gang!!