what is the most efficient method to intercept a planet?

[jaunco325]

Some time ago they gave me a table with the indicators of "fuel" necessary to reach each planet. and when I look at the amount needed to intercept "eve" or "dune" and it's much less than what I actually spend to get there. I do not know what I'm doing wrong

[Superfluous J]

15 minutes ago, jaunco325 said:

. I do not know what I'm doing wrong

Describe what you do, and then we can give pointers.

[jaunco325]

after exiting kerbin's orbit. The first thing I do is accommodate the orbit of the ship, so that it is parallel to that of that planet. and then slow down / accelerate the ship, in order to reduce / widen the opposite side of the orbit, and thus intercept it. finally, once the overflight of a planet is reached, slow down the ship to stay in orbit.

[antipro]

31 minutes ago, jaunco325 said:

after exiting kerbin's orbit. The first thing I do is accommodate the orbit of the ship, so that it is parallel to that of that planet. and then slow down / accelerate the ship, in order to reduce / widen the opposite side of the orbit, and thus intercept it. finally, once the overflight of a planet is reached, slow down the ship to stay in orbit.

you leave Kerbin SoI, you match the target orbit plane then you do an Hohmann transfer. perfect.
I think this is not the most efficient way cause you can intercept a planet with 1 burn only by taking advantage, in terms of savings DeltaV, from the
https://en.wikipedia.org/wiki/Oberth_effect

I suggest to install Mechjeb mod , so you can use the "Advanced Transfer to another Planet" feature
and Astrogator mod that instead uses a 2-nodes maneuver, it's less efficient but put you into an equatorial orbit pretty easily.

Edited December 2, 2020 by antipro

[jaunco325]

I don't understand what I have to do. speed up the ship during the escape from kerbin, so that it has a slower solar orbit? although this already makes the table, mentioned above, meaningless

[antipro]

1 hour ago, jaunco325 said:

I don't understand what I have to do.

I don't know as you do not provide any other information about the situation you're experiencing.
I was only suggest ya to install a couple of autopilots that let you save some dV.

Edited December 3, 2020 by antipro

[Superfluous J]

@jaunco325 You don't do each burn on the table one by one. you add up the necessary numbers and then do ONE burn with the sum of the numbers.

...sometimes...

Yeah the table can be confusing at first. But keep at it and it'll become a handy reference. It's just not so good a teacher.

To go to - say - Duna, you do ONE burn from Low Kerbin Orbit. That burn will be (roughly) 950m/s to get out of Kerbin's sphere of influence plus 130 m/s to keep extending your Sun orbit to Duna. But you don't burn 950, coast, then burn 130. You actually burn 950+130 = 1180m/s.

But you can't "just" do that. you have to burn at the right time, and in the right direction.

The right time is found pretty easily for Duna by eye. In the Tracking station, zoom way out so you can see the Sun, Kerbin, and Duna. If you rotate the view so Sun is on the Left and Kerbin is on the right (3:00 on an analog clock), the correct time to leave is when Duna is directly above Kerbin (at about 1:30-2:00 on the analog clock, give or take). This is when looking DOWN on the system from above the North Pole of each world. In this diagram I've described, Kerbin should be moving upward in its orbit and Duna moving up and left. They're orbiting counter-clockwise.

The right Direction is "forward" in relation to Kerbin. You want to create a maneuver node on your ship's Low Kerbin Orbit with 1180m/s prograde, and then drag that maneuver node around until it makes your ship leave Kerbin FORWARD in Kerbin's orbit around the Sun. This means that you'll be burning on the night side of Kerbin, a bit past sunset from your ship's perspective. Make that maneuver, then zoom out and hopefully you'll see that your resultant Sun orbit gets close to Duna. With a little tweaking, you may even get an encounter. Target Duna, and you'll hopefully at least get some close approaches.

Just remember, this is not just about getting to Duna. You're learning a SKILL here and it's going to take some time. But once you get all the little parts of it, you can apply them EVERYWHERE.

Edited December 3, 2020 by Superfluous J

[jaunco325]

1 hour ago, antipro said:

I don't know as you do not provide any other information about the situation you're experiencing.
I was only suggest ya to install a couple of autopilots that let you save some dV.

my problem is that the table tells me that to get to eve (for example), 430dV is needed. but I consume more than 300 to align the orbit and approximately 600 for the interception, 900 in total approximately.

1 hour ago, Superfluous J said:

@jaunco325 You don't do each burn on the table one by one. you add up the necessary numbers and then do ONE burn with the sum of the numbers.

...sometimes...

Yeah the table can be confusing at first. But keep at it and it'll become a handy reference. It's just not so good a teacher.

To go to - say - Duna, you do ONE burn from Low Kerbin Orbit. That burn will be (roughly) 950m/s to get out of Kerbin's sphere of influence plus 130 m/s to keep extending your Sun orbit to Duna. But you don't burn 950, coast, then burn 130. You actually burn 950+130 = 1180m/s.

But you can't "just" do that. you have to burn at the right time, and in the right direction.

The right time is found pretty easily for Duna by eye. In the Tracking station, zoom way out so you can see the Sun, Kerbin, and Duna. If you rotate the view so Sun is on the Left and Kerbin is on the right (3:00 on an analog clock), the correct time to leave is when Duna is directly above Kerbin (at about 1:30-2:00 on the analog clock, give or take). This is when looking DOWN on the system from above the North Pole of each world. In this diagram I've described, Kerbin should be moving upward in its orbit and Duna moving up and left. They're orbiting counter-clockwise.

The right Direction is "forward" in relation to Kerbin. You want to create a maneuver node on Kerbin's orbit with 1180m/s prograde, and then drag that maneuver node around until it makes your ship leave Kerbin FORWARD in it's orbit. This means that you'll be burning on the night side of Kerbin, a bit past sunset from your ship's perspective. Make that maneuver, then zoom out and hopefully you'll see that your resultant Sun orbit gets close to Duna. With a little tweaking, you may even get an encounter. Target Duna, and you'll hopefully at least get some close approaches.

Just remember, this is not just about getting to Duna. You're learning a SKILL here and it's going to take some time. But once you get all the little parts of it, you can apply them EVERYWHERE.

So, the consumption of 950 to escape kerbin and 130 to reach dune do I have to do them at the same time?

[antipro]

2 hours ago, jaunco325 said:

my problem is that the table tells me that to get to eve (for example), 430dV is needed. but I consume more than 300 to align the orbit and approximately 600 for the interception, 900 in total approximately.

I presume you're referring at this map:


I don't know much about it, I don't use it, sorry but for what I understand it says:
from "Elliptical Orbit to SoI Edge" to an Eve "Intercept", it is needed 430ms.
I just tried from that position and I need 480ms to "Intercept" Eve too, with one burn only.



But from a Kerbin 120Km equatorial orbit I only need 1045ms to flyby Eve, which is a bit better than what the map says: 950+430=1380.
I can't try automatically at 80km kerbin orbit, like the the map says, cause MJ doesn't work well at that low altitude.
So I don't understand the map me too. I'm sorry I can't help you much than this.
I'm sure an user with more knowledge will come soon.

Edited December 3, 2020 by antipro

[Superfluous J]

1 hour ago, jaunco325 said:

So, the consumption of 950 to escape kerbin and 130 to reach dune do I have to do them at the same time?

Exactly. Also, at the right time and in the right place.

[jaunco325]

if that table i mean.
now I understand, thank you both for the help.
I imagine how difficult it must be to hit him at the right time.