flyby ike at 0° inclination

[antipro]

hi, my objective is to flyby Ike with an inclination of 0°.
the problem is that Ike has a relative inclination of:
0,2 according to the wiki and 0,06 according to KER.

I bet on KER but what is the correct one?



Anyway small or smaller, Ike has a relative inclination, so I can't use Duna to change inc,
Consequently I can't change the Ike inc until I am in the Ike SoI, but in the flyby orbit there's only an AN and is located after the Pe.

At this point I did this, as shown in the video below.
https://www.dropbox.com/s/s4y0w50jdy4o8s6/ike inc 0.mkv?dl=0

I first did the smallest possible executable (0.14°) MJ change inc maneuver when still in duna SoI, in order to move the AN before the Ike Pe.
Secondly I corrected the inc to 0° once I was in Ike SoI at the AN.

Is there a more elegant way to flyby Ike with an inclination of 0°?

Edited December 15, 2020 by antipro

[bewing]

There is an ascending or descending node outside Duna's SOI. That is the only place you can burn to achieve a zero inclination. Can the game show you where that is? No. Sometimes, you can figure out approximately where it is with your eyeballs. But for an inclination of less than a degree, you're out of luck. The only remaining thing you can do is adjust your inclination the normal way, after you've entered the SOI.

 

Edited December 15, 2020 by bewing

[Spricigo]

 

2 hours ago, antipro said:

hi, my objective is to flyby Ike with an inclination of 0°.

Any reason in particular?

I'm asking because not that many of  us would care for more than a couple of degrees of precision just for the sake of being precise. If that is required for something else  maybe there is a better way to meet your goal.

 

2 hours ago, antipro said:

0,2 according to the wiki and 0,06 according to KER.

I bet on KER but what is the correct one?

Both are correct. Just happens they aren't the same thing.

0.2º ref Duna

0.06º ref Kerbin

3 hours ago, antipro said:

Consequently I can't change the Ike inc until I am in the Ike SoI

That is not correct at all. You can change inclination anywhere, any normal/anti-normal burn will change your inclination.  What is generally correct is that is hard to predict how your inclination in Duna SoI will relate to your inclination in Ike SoI(same situation for the Sun-Duna SoI transition, for that matter). However, it just happens that in this particular case we know we 0 relative inclination to Ike in Duna SoI will result in 0 inclination in Ike SoI; IOW Ike's orbital plane matches Ike's equatorial plane.

In any case, I'd say It get more are more elegant farther away Ike's SoI the inclination is matched. If nothing else because it become harder and harder. Nonetheless, zero inclination can only be achieved at AN/DN, as Bewing pointed.

[Superfluous J]

4 hours ago, antipro said:

hi, my objective is to flyby Ike with an inclination of 0°.

23 minutes ago, Spricigo said:

Any reason in particular?

I came to ask this too.

If you want it because you want to figure out the math, stop now. What I'm going to give you is my "it works" approach.

First, you need an in-game indicator of what "equatorial" is. There are 3 ways that I know of to do this:

1. Take a satellite or other contract that says it's an equatorial orbit. "Stationary" orbits are always equatorial, but "synchronous" orbits don't need to be.
2. Take a rescue or salvage contract that's 1 star, and hope it's equatorial.
3. Cheat a vessel into orbit around Ike. That vessel will be equatorial by default.

Now that you have a reference, just keep playing with maneuver nodes until you get the flyby you want. Once you can't tell if it's equatorial or not, that's close enough and you can stop. Errors in your burns will make any more precision in your maneuver node useless anyway.

Edited December 15, 2020 by Superfluous J

[antipro]

2 hours ago, Spricigo said:

Any reason in particular?

I was sure you would ask me. eheh..
I have an obsession with equatorial orbits.
Jokes apart.. to make it cooler, to make it harder, to complicate a simple mission, to fly over ike equator, in case of landing to save dV needed to return in orbit,
I don't know, maybe I'm just mad.

 

2 hours ago, Spricigo said:

Both are correct. Just happens they aren't the same thing.

0.2º ref Duna

0.06º ref Kerbin

you're right, I didn't see the reference planet was kerbin, thanks.
indeed ike inclination is 0.2°.

 

 

2 hours ago, Spricigo said:

That is not correct at all. You can change inclination anywhere, any normal/anti-normal burn will change your inclination.

well, of course I know it, but I was talking about that since ike isn't in a duna eq orbit, I cannot use duna as reference to change inclination in duna soi at its AN/DN.

 

2 hours ago, Spricigo said:

is hard to predict how your inclination in Duna SoI will relate to your inclination in Ike SoI

this is what I'm talking about, isn't hard, it's impossible.

 

2 hours ago, Spricigo said:

However, it just happens that in this particular case we know we 0 relative inclination to Ike in Duna SoI will result in 0 inclination in Ike SoI; IOW Ike's orbital plane matches Ike's equatorial plane.

Excuse me, I can't get this point. isn't it obvious? ok.. so in other words ike has not axial tilt, then?

 

2 hours ago, Spricigo said:

In any case, I'd say It get more are more elegant farther away Ike's SoI the inclination is matched. If nothing else because it become harder and harder.

Can't understand this, can't translate, sry.

  

2 hours ago, Spricigo said:

Nonetheless, zero inclination can only be achieved at AN/DN, as Bewing pointed.

this is obvious, isnt'it?

 

2 hours ago, Superfluous J said:

If you want it because you want to figure out the math, stop now

I don't wanna figure out math, or anything else apart how to achieve what I wanna do: flyby ike at 0° with as few maneuvers as possible, in an efficient and elegant way.
 

Edited December 15, 2020 by antipro

[antipro]

6 hours ago, bewing said:

There is an ascending or descending node outside Duna's SOI. That is the only place you can burn to achieve a zero inclination. Can the game show you where that is? No.

it is outside duna's soi in that situation cause AN is close to ike, but it could be even in duna's soi and be equally not visible.
is what I've done, I've inclined the orbit to move the node into ike soi near the edge.



 

Edited December 15, 2020 by antipro

[Spricigo]

1 hour ago, antipro said:

I don't know, maybe I'm just mad.

As good a reason as any.  

People asking for help in this forum usually just want some solution for their issue. From previous post/threads I was under the impression  you would be more interest in a cool solution. just asking to be sure.

1 hour ago, antipro said:

I cannot use duna as reference to change inclination in duna soi at its AN/DN.

Good thing that is not what I proposed. The idea was to rather use Ike as a reference.  Bad thing that what I proposed didn't work either, see bellow about axial tilt.

1 hour ago, antipro said:

 it's impossible.

nah! It can be done with some scary math...theoretically... Granted that I lack the will to do it myself.

1 hour ago, antipro said:

so in other words ike has not axial tilt, then?

That was what I assumed at the time of my previous post. Sadly  it happens that is no tilt relative to Kerbin's axis and I was just remembering it wrong. 

 

At this point it seems the alternatives are: 1.zero out inclination once in Ike's SoI 2. having something in Ike's orbit to use as target/reference. 3. A krakenload of trial and error and ridiculous amounts of luck. Neither strike me as efficient or elegant, at least not as much as yo requires.

[paul_c]

I am fairly new to this so don't fully understand advanced orbital mechanic stuff, but I know the basics. I think its fair to say:

* With the limited tools in stock KSP, its difficult to do a precision orbital insertion except for the case (where the minor body is on a 0deg inclination) of 0deg or 180deg, by 'aiming for its equator' by minimising Pe by burning normal/antinormal
* If the sub-body is on an inclined orbit, then the above would insert you into a matching inclined orbit
* There is a trade-off between efficiency of doing a future inclination setting far away (ie in the major body's SOI, before the orbital insertion) and the (by definition, because its a minor body to the other) lesser dV needed in a sub-body's SOI

Personally I like these kinds of challenges and would love to do a scenario where you MUST absolutely minimise dV and rocket cost, and squeak into a planned/contracted orbit with the minimal fuel etc. However KSP's career thing doesn't really work like that or encourage it, because 1) just adding say another 100dV is cheap; 2) future contracts of "move the satellite...." mean it makes sense to have spare fuel. In the real world, I guess you'd have spare fuel for a lifetime of stationkeeping from perturbences (which don't occur in KSP) and an end-of-life de-orbit or raise to graveyard orbit (which I've not been asked for in KSP's career...) 

[antipro]

I don't want to drag over this thread, which is already drifting off-topic, but concluding
The 1st maneuver, the one far away in Duna SOI, can be achieved by using MJ "Change Inc." which I used or MJ "Change Longitude of AN".
I display the 2nd maneuver, the one in Ike SOI, in order to show how I've reached a precision of 0.00000° manually but with MJ help.
shortly:
1 - Reduced engine thrust to 0.5, cause longer burn time = MJ increases precision.
2 - Enable The Softer
3 - MJ Execute
4 - Manual RCS adjustment.

Video(1m29s): https://www.dropbox.com/s/1ltn8tjq4lyuvek/ike inc zero.mkv?dl=0

Edited December 16, 2020 by antipro