Delta V Map incorrect? Can someone explain?

[Sirius360]

Hey guys.

I started playing KSP a while ago. Now i want to use a delta v map for more efficiency. I have found this map:

I want to fly to Dres. I have a problem with the delta v calculations. There are two numbers from sunar orbit to intercept. 610 and 1010. I thought the number 610 is to bring the ascending node to 0°. Am I right?
That means if the ascending node is 0° i need 1010m/s to intercept Dres? But there is my problem, I need more than 1010m/s, i need at least 1700m/s.
Here is a screen shot:

 

What am I doing wrong? Do i read the map wrong? Or is the map incorrect?
Why are there exactly two numbers from sunar orbit to intercept with dres? If i add those two numbers i get 1720, that's exactly what i need. But where do I find the delta v needet to bring my ascending node to 0°?

I hope someone can help me.

 

Have a nice day

greetings

[something]

No,  the 610 m/s are to intercept with Dres at 0deg inclination (+950m/s to get there from LKO to Kerbin SOI edge). The 1010m/s are to adjust your inclination to zero deg in a worst case scenario. I can't see the screen shot from my phone so I am guessing:

In order to be efficient you want to do the intercept burn close to Kerbin since doing it from solar orbit requires more delta v due to the Oberth effect. Mech Jeb has a maneuver planner which sets up the nodes for you. It eliminates the fun of finding the correct position yourself but it might help you in order to understand how to get interplanetary. (In fact it did help me a lot to understand why it was so hard to get my very first probe to Duna...)

 

 

 

 

 

 

[Sirius360]

Thank you very much.
You need only 610m/s to get from a sunar orbit to dres!? What am I doing wrong? i need 1700m/s to reack dres. My manuver can't be that wrong..?

[Sirius360]

I have found a tutorial (how to get to dres). He also needs way more delta v to get an intercept with dres. Similar to my manuver node. Here is the Video (Skip to 24:30)

 

[Rhomphaia]

1 hour ago, Sirius360 said:

Thank you very much.
You need only 610m/s to get from a sunar orbit to dres!? What am I doing wrong? i need 1700m/s to reack dres. My manuver can't be that wrong..?

No, you need 950 + 610 = 1560 to go from Kerbin orbit to Dres intercept.  If you are orbiting the sun before you establish the encounter you are using a far less efficient method.

DeltaV maps aren't really good for anthing more than rough estimates.  If you want to plan efficiently use a porkchop plotter such as http://alexmoon.github.io/ksp/

[Plusck]

 

3 hours ago, Sirius360 said:

I want to fly to Dres. I have a problem with the delta v calculations. There are two numbers from sunar orbit to intercept. 610 and 1010. I thought the number 610 is to bring the ascending node to 0°. Am I right?
That means if the ascending node is 0° i need 1010m/s to intercept Dres? But there is my problem, I need more than 1010m/s, i need at least 1700m/s.
Here is a screen shot:

 

 

What am I doing wrong? Do i read the map wrong? Or is the map incorrect?
Why are there exactly two numbers from sunar orbit to intercept with dres? If i add those two numbers i get 1720, that's exactly what i need. But where do I find the delta v needet to bring my ascending node to 0°?

I hope someone can help me.

 

Have a nice day

greetings

Your screenshot doesn't show for me. Did you include it using the "insert other media" button on the bottom right, then using the URL of the image? Beware that you need the "real" URL of the image. Imgur gives several options for pastable URLs which don't all work. The best thing to do is to right-click with "view image" on the pic you want to paste, then copy the URL from the address bar.

 

As for the delta-v maps, those numbers are correct (with very minor improvements possible for some of the numbers, with effort...).

The numbers add up from one node on the map to the next. As @something has pointed out, the numbers inside the thick map "lines" are the minimum dv requirements, while the numbers in the whitespace beside them are max inclination changes.

So from LKO you need 950+610 m/s as an absolute minimum, going up to 950+610+1010 for maximum inclination change if you catch Dres at the wrong bit of its orbit compared to Kerbin.

 

Your screenshot not being visible, it's hard to know where you are. If you are in LKO, then 1700 m/s is a very reasonable escape burn.

Edited March 19, 2016 by Plusck

[Plusck]

4 hours ago, Sirius360 said:

Thank you very much.
You need only 610m/s to get from a sunar orbit to dres!? What am I doing wrong? i need 1700m/s to reack dres. My manuver can't be that wrong..?

Didn't see this before.

What you're missing is the Oberth effect, combined with the fact that you've escaped Kerbin's influence at a crawl and can no longer benefit from the planet's orbital velocity.

The Oberth effect says that the faster you are going in a given orbit (the higher your kinetic energy, and also the higher your kinetic energy compared to your potential energy), the more energy you get out of your propellant. E = mv^2, so as you increase your speed linearly, your energy goes up exponentially.

If you spend 970 m/s or whatever to escape Kerbin's influence, you end up leaving Kerbin's SOI at a crawl. Kerbin's gravity has been pulling on you for a long time, and you have virtually no residual kinetic energy as you leave the system. If you want to raise your orbit to Dres, you have to add the full difference of energy between Kerbin's orbit and Dres's, which could well be equivalent to 1700 m/s (or whatever*).

However, if you add another 700 m/s or so at the start, from low Kerbin orbit (where you are already doing 2300 m/s, don't forget), you will leave Kerbin's influence much faster. Kerbin's gravity will slow you, but much less in the single day you take to reach the SOI edge (as opposed to 15 days or so if you only just crawl out with a 970 m/s burn). You therefore leave Kerbin's SOI with a velocity of about 1700 m/s (or whatever*) in addition to Kerbin's own orbital velocity, which is what it takes to get to Dres.

Which is why any method that tells you to leave a planet's influence before burning to a destination is deeply flawed.

*(I don't know the exact figures, but this sort of number looks reasonable and corresponds to your experience. If you have an added plane change, it gets worse because again, you can use the Oberth effect and your escape angle to do much of the work for you, but not if you are in interplanetary space barely keeping pace with Kerbin)

[KerikBalm]

Notice the icon at the top of the blue 950 m/s bar.... its an ellipse. If you were to go into an eliptical orbit so that you nearly escape kerbin's SOI, then you'd only need a 600-something m/s burn *at periapsis during the right transfer window* to get to dres.

those dV numbers are to be summed up assuming you start from low orbit. You get very little "credit" for m/s expended doing anything else... unless that puts you into an appropriate elliptical orbit, with a low perapsis... ie bascially you already started perapsis kicking for the maneuver.

It is very very very inefficient to go into solar orbit first. I think the 2nd required burn may be even bigger than the burn it would take if you just left direct from LKO... even if its a little smaller... you would have just spent about 1000 m/s to save what... 50 m/s? no, don't do it. Use the Oberth effect, or don't bother using the dV charts...

[DoToH]

On 19/3/2016 at 5:41 PM, Rhomphaia said:

DeltaV maps aren't really good for anthing more than rough estimates.  If you want to plan efficiently use a porkchop plotter such as http://alexmoon.github.io/ksp/

^^ this