What should I do to my orbit?

[FinnBot5000]

I am making a space station and have been adjusting its orbit before I decouple the fuel and engine. It is kind of a stupid question but is there anything else I should do to my orbit before I decouple my engines? It is already at 0 inclination and 0 eccentricity.

[maddog59]

That's a pretty clean orbit ... far nicer than anything I've ever put up. But as to your question ... I suppose it depends on what you plan on using the station for. I often leave my tanks and engines available in case I want to move my stations for some reason. Only done it once, actually. I actually started launching vehicles with docking ports at both ends, so I could add the tanks to a station as a fueling depot, and dropping off the engines when I was ready to add on to that end. 

[Vanamonde]

Before you get too fixated on precision, remember that due to tiny round off errors in the game's internal math, orbits will not stay perfect. You could leave the engines on for further adjustments, or do what most of us do and just live with a little imprecision.  

[OhioBob]

The only thing I can suggest is to make sure your station is in a high enough orbit that there is room below it for smaller and faster orbits.  You don't want to make the mistake of having your station in such a low orbit that it becomes difficult for shuttle flights to the station to catch up with it and rendezvous.

Edited October 2, 2021 by OhioBob

[FinnBot5000]

1 hour ago, maddog59 said:

I often leave my tanks and engines available in case I want to move my stations for some reason.

Hmm, seems smart. Too bad I build it so that even if I opened the payload fairing that is covering the station, I built it so that the docking port is covered by the fuel tanks.

1 hour ago, Vanamonde said:

Before you get too fixated on precision, remember that due to tiny round off errors in the game's internal math, orbits will not stay perfect. You could leave the engines on for further adjustments, or do what most of us do and just live with a little imprecision.  

I think I will just have to live with it, I just wanted a nice-ish orbit (and then got a little carried away making it as perfect as I could get it).

43 minutes ago, OhioBob said:

The only thing I can suggest is to make sure your station is in a high enough orbit is high that there is room below it for smaller and faster orbits.  You don't want to make the mistake of having your station in such a low orbit that it becomes difficult for shuttle flights to the station to catch up with it and rendezvous.

It is about 230,000 m? Do you think that will be good enought?

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Thank you everyone for the advice btw!

Edited October 2, 2021 by FinnBot5000

[Vanamonde]

Yes, 230kms should be fine. 

[AHHans]

12 hours ago, FinnBot5000 said:

It is about 230,000 m? Do you think that will be good enought?

I put my Kerbin refueling station into a 500 km orbit. So 230 km is totally wrong! And you immediately need to change it to the only acceptable value!!111!

_{P.S. In case you didn't notice: If you did some irony here, feel free to keep it.}

[maddog59]

On 10/2/2021 at 8:49 AM, AHHans said:

I put my Kerbin refueling station into a 500 km orbit. So 230 km is totally wrong! And you immediately need to change it to the only acceptable value!!

"And so began the great Orbit Wars of the Kerbin Empire." 

[maddog59]

On 10/1/2021 at 7:51 PM, FinnBot5000 said:

It is about 230,000 m? Do you think that will be good enought?

It kind of depends on where your typical insertion orbit is. For instance, I typically shoot for getting my ships into an orbit of ~90km. My stations are anywhere between 250 and 300km, so I can usually get to a transfer node within a few (2 - 4) orbits. When my stations are lower than that, I find I have to wait longer, or, if I'm impatient, boost to a much higher orbit to reduce the number of orbits before hitting the transfer node.

Since the MJ2 maneuver node utility figures it out and will raise your altitude if your current relationship means more than a certain number of orbits before the transfer burn, there must be a formula out there that can give you a rough idea of, if your station is at X km, your ship should be at Y km to get a transfer node within Z orbits. But that formula is going to be way too much for my pretty little head.  

[Zhetaan]

On 10/4/2021 at 5:20 PM, maddog59 said:

Since the MJ2 maneuver node utility figures it out and will raise your altitude if your current relationship means more than a certain number of orbits before the transfer burn, there must be a formula out there that can give you a rough idea of, if your station is at X km, your ship should be at Y km to get a transfer node within Z orbits. But that formula is going to be way too much for my pretty little head.  

MechJeb just compares your orbital period to the time needed to reach the next transfer node.  If it equals more than five orbits (though that is user-editable), then it adjusts the semimajor axis of your orbit by the ratio of (1 + (1.25 / PhasingOrbits))^(2/3).  If you go with the default number of five orbits, then it's just 1.25^(2/3) or approximately 1.16--but the important part is that it adjusts the orbit by enough to guarantee that a transfer window will appear within the acceptable number of orbits in the new orbit, but does not adjust by so much as to be prohibitively expensive in propellant costs.  It's not really trying for milligram efficiency or millimetre precision:  it's like someone who is travelling through the woods and doesn't know exactly where the next town is, but knows that there's a long river leading to it, and so knows that finding the river--which is a lot easier to do, even though it will add time to the journey--will be good enough as a first step.

It's done in terms of ratios, not kilometres, because distance in kilometres has varying importance relative to your altitude.  If you're at Minmus's altitude, then orbiting 100 kilometres closer to Kerbin will make a negligible change to your orbital period.  If you're orbiting at 75 km altitude, then going 100 km closer will be quite a dramatic change, indeed.