What did I do wrong in my Duna mission?

[Invader Jim]

I have a satellite and launched it within one day of my window according to http://alexmoon.github.io/ksp/. I arrived in Duna SOI but it says it will take me 3,000 DV to get into a high Duna orbit. I have ~4700 DV but I expected this to cost a lot less. What did I do wrong?

Edited May 19, 2015 by Invader Jim

[Solarapple]

I dunno. Just aerobrake it, or do you not have a heatshield?

[Eric S]

Screenshots would help. What's your velocity within Duna's SoI?

[icedown]

Did you make any course corrections enroute?

[cybersol]

Sounds like you are coming in hot! This happened to me too on all my early transfers, and I bet its fairly common. What you probably did was setup the encounter with a flatter, more direct profile. In contrast, an optimal Hohmann transfer to Duna is a rounder half-ellipse where you Kerbol apoapsis just barely intercepts the planet at the precise moment it is there to greet you with open arms. The planner you linked includes an ejection angle, and that angle, in addition to the window timing, is the key to getting this optimal rounder transfer.

[Invader Jim]

Screenshots would help. What's your velocity within Duna's SoI?

I think is was ~10,000 m/s

[Invader Jim]

Now I am experimenting with a satellite in LKO. If I put my node at 150 Kerbin prograde and then keep pulling the prograde symbol I get an intersect on the opposite side (roughly 180 degrees) of the solar system. It says it will take me 295 days to get there and ~1,000 DV. I thought I read it was a 70 day journey. This is day 230 in year 1. I think I am catching on but I am not sure how to make it in shorter time.

[cybersol]

Yeah that sounds pretty close to what the transfer planner predicts, which is 1030 m/s and 270 days travel time for a 100 km Kerbin orbit to 100 km Duna orbit leaving about a day later. If you perform those maneuvers, you should end up with an insertion dV much closer to what it predicts, which is 641 m/s. Also, as someone else pointed out, since Duna has an atmosphere, you could try to use it to aerobrake into your Duna orbit. That would save you a lot or even almost all of the insertion costs, but it can be a little more tricky. Definitely save/load before the first few times you try it.

[Superfluous J]

Hohmann transfers meet the target 180 degrees away from where you start. It's how they work.

Burning to slow down in a high orbit is inefficient, though. You want to come in low and burn at your very low periapsis. Or better yet, aerobrake. To hit a high orbit I bet you want to aerobrake somewhere in 22-23km range. Put your periapais about 22.5km and let air resistance do the rest.

[MarvinKitFox]

It says it will take me 295 days to get there and ~1,000 DV. I thought I read it was a 70 day journey.

Kerbal days, or earth days?(for each of your two figures above)

[Invader Jim]

Kerbal days, or earth days?(for each of your two figures above)

I use Kerbal days.

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Hohmann transfers meet the target 180 degrees away from where you start. It's how they work.

Burning to slow down in a high orbit is inefficient, though. You want to come in low and burn at your very low periapsis. Or better yet, aerobrake. To hit a high orbit I bet you want to aerobrake somewhere in 22-23km range. Put your periapais about 22.5km and let air resistance do the rest.

What is the best way to come in low? Should I try a maneuver just before I enter the SOI or just after I enter the SOI?

[xtoro]

I use Kerbal days.

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What is the best way to come in low? Should I try a maneuver just before I enter the SOI or just after I enter the SOI?

Doing your correction burn half way between kerbin and duna soi will use the least amount of delta v.

[Invader Jim]

Doing your correction burn half way between kerbin and duna soi will use the least amount of delta v.

Dumb question - how do I see how I am going to approach? Some of the time I can tell from the little encounter icon that I will enter in front of or behind the planet but I have no idea to know how close my periapsis will be to the planet until I actuall arrive at the encounter.

[UmbralRaptor]

Dumb question - how do I see how I am going to approach? Some of the time I can tell from the little encounter icon that I will enter in front of or behind the planet but I have no idea to know how close my periapsis will be to the planet until I actuall arrive at the encounter.

Hit tab in map view to cycle through bodies until you're focused on Duna.

[Starhawk]

Create the maneuver node. If you click on Duna when in map view, there is an option to 'Focus View'. If you focus on Duna and zoom in you will have a good view of the encounter, including the periapsis. You can turn the camera around so that your maneuver node is behind Duna. After that, it's a 'simple' matter of adjusting the maneuver node until you have the encounter where you want it.

Hope that makes sense.

Happy landings!

[Cardano]

It wont be too much worse to burn at Duna SOI, but the mid point burn is optimal.

And if seeing the normal maneuver node while focus viewed on Duna is challenging ( or if you mix up normal and prograde when you grab them because they are basically on top of each other from that far away ) you can use 'precise node' to give you a simple window where you can make progressively smaller adjustments to the burn in the three cardinal directions separately.

Took me a while to get used to focus viewing the target while manually grabbing the maneuver node markers on the screen so eventually I went looking for something better.

and Aerobraking is the 'free' dV option when possible but it takes lots of practice figuring out how much dV you want to drop = how low in the atmo to target your PE. now that Aero has gotten a workover, it's even more complex because your angle of attack through the aerobrake matters quite a bit - so you have to keep tabs on your drag profile as you are performing the aero maneuver. Fun though, and very exciting.

Cheers!

Cardano.