Ways of reaching Duna

[Arkonor]

Firstly, yes, I have read the tutorials, but the problems I am encountering are not mentioned (unless they are somewhere in the dozens of pages of each thread) To avoid the need of long explanations I'm going to the point

- The two biggest problems until now are:

1) Using the in-game maneuver planner you can only see the delta V of the first maneuver. So I'm going blind until I pass that node and erase it. I would want something better to plan how much delta V I'm going to spend in each node.

2) In the cases when the planner shows that I'm going to do a fly-by near Duna, the closest approach is around 40 million kilometers. Changing any parameter in the maneuver node loses my target and I have to start over again. Therefore, I can't correct it using aerobraking (too far from the atmosphere) nor using the gravity to brake (I barely manage to pass close to the planet) To get the most window to do the trip I'm using this calculator http://ksp.olex.biz/ . At least the planet phase is correct, the ejection angle is more difficult to adjust but I try to approach the best I can do it.

- Also, I've tried other forms to save delta V, like planning a gravity boost on Mün by passing twice (first time to get a wide orbit around Kerbin, and the second to leave the Kerbin system, and eyeballing the ejection angle) However, it's not possible to know if I am saving fuel or not because I can't see the delta V in each node. This maneuver is very restrictive because it gives you a fixed apoapsis, so you can't place the next node anywhere you want to do a prograde burn to raise it. It must be near the point you are leaving the Kerbin system, so if if the planet is not in the intersection of its orbit and your apoapsis, everything is futile.

* Sometimes I have to change these maneuvers because they modify greatly my orbital plane

PS I'm always starting from a 600km circular orbit around Kerbin, so I can use the maximum speed in the time warp to wait until the planets are in the right position. That leaves me a delta V of 1550 m/s aprox for my probe.

PS2 Next time I'll try to plan an insertion orbit against the direction of Duna to see if that helps to brake.

Edited August 29, 2013 by Arkonor

[wilt57]

First off, warp on the pad instead of at 600 km. This will allow you to warp at full speed, spend less fuel reaching orbit, and make a more efficient ejection burn due to Oberth effect.

Second, interplanetary burns are like golfing, if you've ever golfed. Sure, we want a hole-in-one, but the chances of that happening are low. Instead, we settle for a drive that covers most of the distance and is straight enough towards the cup. Then we make an approach shot that will hopefully get us onto the green as close to the cup as possible. Lastly, we try to one-put our way to the cup. Like golf, try for a hole-in-one, but realize that you will have to make multiple burns (strokes) to achieve your goal. After the big ejection burn, set up a second maneuver node right after you've left Kerbin's SoI. Either here or at the approaching AN or DN. Here you will try to lower your PE as much as possible while also aligning your inclinations. After you have entered your target's SoI, make a third burn to put your PE at the desired altitude for either an aerobrake maneuver or direct curcularization burn.

Also, when making your ejection burn from Kerbin orbit, remember to start your burn roughly half before the node. Any large, long burn should be split up this way.

If I've missed your problem, my apologies.

[capi3101]

Wilt57's got it. Only thing I'll add is that to get into position for aerobraking, you might need to consider radial burns once you hit Duna's SOI. The earlier you do them, the less delta-V you'll have to expend. Yes, I know radial burns are inherently inefficient, but if the choice is between achieving orbit and getting flung back out into interplanetary space...

[Knas]

I don't know what you are talking about, I don't know math But I way I use to do it is: First I slingshot of the Mun to get me into a sun orbit. Then I just get an encounter with Duna, an other way is that you place a manuver node in a orbit of Kerbin, and try to get an encounter, if you don't get an encounter, but is very close to do it. Just do the manuver, once out of Kerbins SOI, you try to get an encounter using the yellow markers on the manuever node or/and the blue circles. You can place it anywhere on you want on your sun orbit to duna, but I usually set it in the middle. Hopefully you understand me, my english is not that good, but I hope you understand and that this helps. And other way is, if you actually get an encounter with duna in orbit of Kerbin, and do the manuever, and still have an encounter, time warp untill you are out of kerbins SOI then change the manuver. Because it would have changed. And if you want to change periapis/apoapis of the encounter, I dont know how they are spelled, you change the manuver just a bit before you are about to get into duna SOI.

[Johnno]

1) Using the in-game maneuver planner you can only see the delta V of the first maneuver. So I'm going blind until I pass that node and erase it. I would want something better to plan how much delta V I'm going to spend in each node.

This is only partially true. Only the initial (next upcoming) burn's delta-v requirement is shown next to your navball, however you can place further nodes onto your planned trajectory, adjust them accordingly, then when you click the map to close the manouver node 'editor' you can mouse over those nodes to see their required delta-v. Like so:

Clickie for hires

To help you further I'd advice trying this calculator instead of the one you're using, it'll give you orbit insertion delta-v among other things plus the ability for picking your departure date rather than relying on a single window: http://alexmoon.github.io/ksp/

Also here's a good tool for aerobraking: http://alterbaron.github.io/ksp_aerocalc/

And parachute calculator: http://ksp.freeiz.com/

[Arkonor]

Thank you for all of your responses. They have been helpful in several ways.

Tonight was the first time I have ever delivered something into a stable dunar orbit. Most of the time I was tweaking the orbit so it encountered the planet WITHOUT passing the Duna orbit. It was impossible and it consumed a lot of time. So, in the end I chose to escape from Kerbin SoI with a single push (the double münar boost consumed more delta V, and a single münar boost didn't give me a decent trajectory because it intersected Kerbin's orbit) In interplanetary space, the only maneuver I could do to lower my periapsis at Duna was to burn retrograde shortly before entering Duna's SoI, it went from 22m KM to 8 more or less (and 22 was my best attempt maneuvering over Kerbin, the worse, 40m or so) Meanwhile, I learned how to use the alarm clock to pause the game and kill the warp, it was a very productive time to test things, think, and pray for a non-destructive nor very far encounter with Duna. Once inside the planet's SoI, and seeing the weird polar fly-by over Duna, my kerbals in the control room calculated several ways to reduce more over the periapsis and to attempt a succesful aerocapture. After several minutes testing things in the simulator and moving the hands a lot in front of their faces to rehearse the complex maneuver, they came up with a solution. Instead of the classic "pedal-to-the-metal" retrograde burning they love so much, the radial burning proved to be a much more resourceful idea. Since Duna's air is so thin and low, as much as the remaining fuel in my probe's tanks, the maneuver took place at 10km over the north pole surface. Fortunately, physics are not so reallistic to make my ship burn like a match, though the visual effects were impressive. Those were my truly 7 minutes of terror (in fact it was much less, but high speed and terror are capable of bending the fabric of space-time), the ship started to brake a lot, the apoapsis was in free fall and also the periapsis, just a tad slower. Later I would recall that my probe was fitted with a parachute (for unknown reasons, the safety department usually attach these things whenever they had the chance to sneak into the hangar) The thin vapors of fuel, less than a liter, were incredibly efficent because they allowed me to raise my periapsis from 8000m up to 52km, and lowering the apoapsis up to 450km when the engine died.

Tomorrow I'll post pictures if you want.