Fun with Longitudes ( & their Ascending nodes)

[Bathalas]

Every few months I'll come back to KSP and start a career, and I'll have to re-figure out things. One of those things is always how to satisfy the LAN requirements of satellite contracts. A google search will pull up forum results that basically boil down to "it doesn't matter" or "eye ball it," which are answers I find rather lacking for my play style, though if you're running a pure stock game, those are probably the only real answers. But I run a lot of mods, and enjoy the building and planning of an efficient rocket. So here is what I have come up to help those like me (apologies if this is somewhere else on the forums. Just haven't found it).

 

1) LAN matters! - Crunching the numbers for orbital parameters can get messy, fast, especially for amateurs (like me!). But LAN isn't just a throw away line meant to add flavor. For non-equatorial orbits, LAN will determine the angle the major axis runs through the body  being orbited. Being off by more than a few degrees (+/- 3ish) will keep you from completing the contract, even if your AP, PE, and inclination are all otherwise spot on.

2) Change is expensive - You can fix your LAN in orbit, but it will cost a ton of delta-v. More than just an inclination change. A lot more, in fact. If you are significant;y off from the target LAN, you'll be having to make plane changes on all three axes. That's terribly inefficient! 

3) Add-ons can help...and confuse - I like MechJeb. I'm a terrible pilot, and it makes a lot of the mundane things easier. But it has a LAN problem. I don't know the nuts and bolts of it, but at KSC, it will not give you the right readout for LAN. Once you get into orbit, it's fine. Luckily, Kerbal Engineer Redux does give the right value

 

Given all that, what I have done is add KER's LAN readout to it's HUD (it's actually the only thing I use KER for in-flight), and use that and the warp to launch into the correct LAN for peak efficiency.. Assuming a relatively efficient ascent profile, you'll use L=T+87, where L is the LAN at KSC and T is the LAN you want for your orbit. Just warp until about 90 minutes before the Target LAN comes up, the fire away.

It's deceptively simple, so I'm sure many have already figured it out, but I thought I'd share my findings. 

 

TO THE MUN!

[Ten Key]

The seems like a useful observation. . .I know I'm usually stuck "eye balling" it, with somewhat mixed results. 

I'm going to move this over to the Tutorials section, where it should be easier to find long term.

Welcome to the forums Bathalas, and thanks for the heads up.

[Spricigo]

46 minutes ago, Bathalas said:

2) Change is expensive -  You can fix your LAN in orbit, but it will cost a ton of delta-V

WRONG! DeltaV is measured in km/s, not tons!

Seriously, maybe, at least in part, a side effect of not using a good method for that adjustment . Since the usual answer is 'it don't matter'/ 'eye ball it'  seems people usually don't put much effort in doing it efficiently.

[Bathalas]

14 minutes ago, Ten Key said:

The seems like a useful observation. . .I know I'm usually stuck "eye balling" it, with somewhat mixed results. 

I'm going to move this over to the Tutorials section, where it should be easier to find long term.

Welcome to the forums Bathalas, and thanks for the heads up.

Thanks! I wasn't sure where to start it myself.

[Geschosskopf]

9 hours ago, Bathalas said:

Given all that, what I have done is add KER's LAN readout to it's HUD (it's actually the only thing I use KER for in-flight), and use that and the warp to launch into the correct LAN for peak efficiency.. Assuming a relatively efficient ascent profile, you'll use L=T+87, where L is the LAN at KSC and T is the LAN you want for your orbit. Just warp until about 90 minutes before the Target LAN comes up, the fire away.

Waiting to launch until the AN (or DN, it really doesn't matter which) is directly over KSC is fine for orbits of Kerbin, but it doesn't help at other planets, where you will almost always arrive at a rather different inclination (or at least will have a rather different LAN) from the target orbit.  In this case, you first have to match planes with the target orbit.  Because there's no ship in the target orbit, you can't set it as a target, so you have to eyeball the location of your AN/DN relative to the target orbit by careful manipulation of the camera in the map view.  But once you match planes with the target orbit, you will have given yourself the contract LAN.  Then it's just a matter of adjusting your Pe and Ap to meet the contract parameters.