Contracts: How to (efficiently) adjust your LAN/Arg of Pe?

[Mad Vlad]

Hi all,

Something that's been making me avoid the relatively moneyspinning contracts for putting satellites into very specific orbits is that I don't really know how to adjust my Longitude of Ascending Node and Argument of Periapsis with any certainty. I use MechJeb for telemetry readout only and would like to know what is the most efficient way of adjusting these two parameters. I've tried having a play about with this, but in all honesty, I've just turned decent orbits into highly eccentric sub-orbital abortions and ran out of delta V.

My thoughts have been that I need to burn Nml+ to fix the LAN (but how can I tell when this point should be? ) Then once I fix the LAN, I then need to do something to change the Arg Pe, but I have no idea how to do that. After those have been fixed, I then adjust my Ap/Pe as normal burning Pro/Ret as necessary. It's those two sticking points that I'm struggling with (and of course, how to elegantly do this without having to burn thousands of m/s of dV would be awesome).

Help please? Thanks in advance!

[MarvinKitFox]

Moving from one orbit to another:

If the orbital planes are within about 30 degrees of each other, adjust directly from one to the other, as you describe.

rough guide to technique:

* Look at where the two orbits cross, when facing directly at the planet. There will be two such crossings. Pick the one where you are furthest from the planet. Here, and only here, is where you want to change your plane.

* Now change your perigee to exactly match the new orbit. Using fancy footwork you can do this combined with the step above, but it gets non-obvious very quickly.

* Now change your apogee to match.

If the two orbit differ by more than 30 degrees (in *any* direction), you would be better off by extending your current orbit out to almost infinity, doing a nearly cost-free plane change there, and joining the second orbit.

*Same as the above case, but first pick the crossing where you are *closest* to the planet, and burn prograde to extent your apogee waaaaaaay out.

*now, treat it as a normal plane->Apogee->perigee matching set of maneuvers

By first heading far out, you actually reduce the total delta-v needed.

[Superfluous J]

I literally ignore those numbers. I do everything by eye in map mode. I also don't bother aligning the orbits first, though it's a valid approach if it works for you.

1. Get your trajectory touching the target orbit trajectory. MAKE SURE YOU'RE GOING THE RIGHT WAY. Also, the closer you can get to "kissing" the oribit the better. What I mean, is, touching it without crossing it inward to outward, or at a crazy angle. Just come in, touch, and back off.
   
2. Create a maneuver node at that point and fiddle with it until your resultant orbit matches that orbit.
   
3. Do that burn.
   
4. Profit! Literally. You will generate profit from this.
   

[WuphonsReach]

Install Precise Node mod - adjust orbit with number pad.

My usual tactic is:

- Use 5/8 and 7/9 to adjust inclination while keeping the dotted line inside the colored line boundary, without putting the Pe inside the orbital body. Do the inclination burn.

- Switch to a top-down view, use 5/8 and 4/6 and 1/3 to move the hula hoop around into the proper position.

If you have DV to spare, you can match up most orbits within 2-3 burns.

[Laie]

What 5thHorseman said. It is really that simple. It is very much like a rendezvous: you have to come across the target trajectory, and at the moment you cross it, you "match velocities" so that you stay on that trajectory. The only difference is that there's no other ship to meet, so you are at liberty to touch and match whenever you like.

As you're using Mechjeb, I suggest you try the Node Editor. Even if only to display the numbers. I like to start with normal until the plane sits, then prograde until the size is about right, then radial to shift Apo/Peri around.

[GoSlash27]

MarvinKitFox and 5thHorseman have covered all the basics here.

I recommend completing satellite contracts whenever possible. I've built pretty much my entire career executing these. Orbits around Kerbin, Mun and Minmus are cheap, quick, easy, and net you lots of cash and science.

Maybe we should put up a tutorial on this?

Best,

-Slashy

[Jimbimbibble]

You can also launch almost into the target orbit. Wait until the space center is directly below the target orbit, then launch and turn the rocket to the desired inclination. Remember that a heading of 90 degrees is 0 inclination and you may have to turn north or south depending on whether you're launching at an ascending or descending node. If you do this right you can get within 1-2 degrees of the target.

[Superfluous J]

Maybe we should put up a tutorial on this?

I'm hoping to have a video up before Monday dawns

[Superfluous J]

I'm hoping to have a video up before Monday dawns

I've just posted the first of what will be at least a 4-video series. In the first video I show you a $6,800 satellite that can complete any Kerbin, Mun, or Minmus satellite contract. I then show you how to use that rocket to complete a simple equatorial orbit without paying attention to any of the numbers on the screen.

In video 2 I'll be doing a tougher Kerbin orbit (Either a Kolniya orbit or one that goes mostly backwards, or at least one that's crazy tilted), and videos 3 and 4 will detail Mun and Minmus encounters even though they're very similar.

[Spheniscine]

I also have written a tutorial for satellites here: http://www.lets-play-sphen.com/?p=509

[eddiew]

I've just posted the first of what will be at least a 4-video series. In the first video I show you a $6,800 satellite that can complete any Kerbin, Mun, or Minmus satellite contract. I then show you how to use that rocket to complete a simple equatorial orbit without paying attention to any of the numbers on the screen.

Nice guide, should help out a lot of folks Have you ever considered using FAR and getting into spaceplanes? Can't recall seeing you fly any, but you might enjoy the cost efficiency of getting satellites to LKO with a plane that'll come back for 100% refund. Couple of nodes down the tree, a little Rockomax engine can give you a tiny probe with 3300 delta-v; probably get out to Duna or Eve if you're adventurous with aerobraking! That and you can fit 2-3 satellites of this size into one cargo bay

Admittedly solid boosters and 909s are pretty durn cheap, but you know, principles!

[MoridinUK]

Nice advice, but I need some delt-v advice. The orbit I need for my equatorial sat is an Ap of 30,792,903 m and a Pe of 25,581,614. I'm thikning I'm gonna need a couple of 2k delta v for this one? The other sat contract is for mun, but with an incline orbit of some 141 degrees... I've not explored Mun yet, in fact I got a little upset I couldn't do an eva for each biomove in high orbit over kerbin!

[WuphonsReach]

Minimus/Mun contracts can be handled by pretty much anything that makes it to LKO with 1500+ DV left in the tank. LV-909 + a T400 fuel tank payload fits that bill. If you have 2500+ DV in the tank, you can handle multiple contracts, even multiple severe inclination changes around Mun/Minimus.

25Mm-31Mm is about the distance to Minimus, so you'll need about 1000-1200 DV. But I'd pack 2000 DV just to make sure you have enough to play with.

[Superfluous J]

Nice advice, but I need some delt-v advice. The orbit I need for my equatorial sat is an Ap of 30,792,903 m and a Pe of 25,581,614. I'm thikning I'm gonna need a couple of 2k delta v for this one? The other sat contract is for mun, but with an incline orbit of some 141 degrees... I've not explored Mun yet, in fact I got a little upset I couldn't do an eva for each biomove in high orbit over kerbin!

As I say in my video, the ship I make (and the much smaller ship that Spheniscine made that requires you having unlocked the 48-7S) can complete ANY contract in Kerbin's SOI, Mun's SOI, or Minmus' SOI. The small difference in dV required, coupled with the graininess of the parts available, means you'll usually either have too much or too little fuel for your task assuming you fill your tanks full before launch. So, I built my ship with enough dV to do the most dV-intensive contracts and found that you don't really waste that much just using the same one for the low-dV contracts.

[MoridinUK]

Well I messed it all up, I took a contract to test the LV-1 engine, so I strapped one to a sat (stayputnik, baterries, raction wheel, panels and antenna) fired it into space to discover I had like 4500 delta V to play with. So I played with putting it in the right orbits for the currently available contracts to get a more perfect idea of the delta V I'd need. But the contracts had vanished! This wasn't really fair, I understand them going if I've achieved them already, but I did so only with an experimental part I certainly can't lock! I just lost 700k worth of contracts.. (I'm a wimp playing in normal)

[MacroNova]

For a while I was really frustrated by the Kerbin Tundra orbit contracts. Waiting for the planet to rotate so the KSC was underneath the orbital path, and launching at an inclination made a huge difference.

[Janos1986]

I don't get it. Seriously, I don't.

I'm seeing tons of threads of people having trouble with fine tuning of orbits while I complete satellite contracts by the dozen by simply eyeballing orbits (or using KER data for Mission Controller contracts) without even being so precise about it.

Is there a rising degree of precision I'm not aware of?

I miss the tricky part of contract orbits,really.

[Superfluous J]

I don't get it. Seriously, I don't.

I'm seeing tons of threads of people having trouble with fine tuning of orbits while I complete satellite contracts by the dozen by simply eyeballing orbits (or using KER data for Mission Controller contracts) without even being so precise about it.

Is there a rising degree of precision I'm not aware of?

I miss the tricky part of contract orbits,really.

You're not missing anything. The descriptions of the contracts imply you need to place your periapsis at a certain place, and your apoapsis at a certain place, and have them be all exact. The player gets out into space and trying to tweak all these things together is like a Rubik's Hypercube. You can't even figure out how to change one thing and by trying to do it, end up messing up all the other things.

Eyeballing the orbits and just making a maneuver node to get close is 100% assured to work and 1000% easier than even GLANCING at the particulars in the contracts window.

[MoridinUK]

As I say in my video, the ship I make (and the much smaller ship that Spheniscine made that requires you having unlocked the 48-7S) can complete ANY contract in Kerbin's SOI, Mun's SOI, or Minmus' SOI. The small difference in dV required, coupled with the graininess of the parts available, means you'll usually either have too much or too little fuel for your task assuming you fill your tanks full before launch. So, I built my ship with enough dV to do the most dV-intensive contracts and found that you don't really waste that much just using the same one for the low-dV contracts.

Your video is out of date the isp for the engines have changed, so you don't get near as much Dv on this build now.. it is still very useful though..

[Superfluous J]

Your video is out of date the isp for the engines have changed, so you don't get near as much Dv on this build now.. it is still very useful though..

Out of date!? I uploaded it 3 days ago! It's in 0.90 in an almost completely stock build. The only mods I have are there to make the visuals better (And Kerbal Engineer to show the stats in the VAB).

Edited January 7, 2015 by 5thHorseman

[MacroNova]

You're not missing anything. The descriptions of the contracts imply you need to place your periapsis at a certain place, and your apoapsis at a certain place, and have them be all exact. The player gets out into space and trying to tweak all these things together is like a Rubik's Hypercube. You can't even figure out how to change one thing and by trying to do it, end up messing up all the other things.

Eyeballing the orbits and just making a maneuver node to get close is 100% assured to work and 1000% easier than even GLANCING at the particulars in the contracts window.

That's how I do it too. The original FinePrint mod gave a percentage deviation instead of using cryptic terms like "moderate" or "minimal." When the apoapsis is 8,000,000m, a 3% deviation ends up being a pretty generous amount, and smart players will recognize that right away. Shoot, I remember getting credit for contracts when I felt like I was still pretty far off; while I was setting up my maneuver node I got the notification.

[MoridinUK]

Out of date!? I uploaded it 3 days ago! It's in 0.90 in an almost completely stock build. The only mods I have are there to make the visuals better (And Kerbal Engineer to show the stats in the VAB).

I have nothing but kerbal engineer installed, as you did and you also had the enhanced nav ball on. I noticed that your lv-909 engines have 390 isp, mine read 300 and the boosters have 240 where as mine are just 225. Unless I've missed something else? My deltaV read out isn't nearly as high as your own, and the rocket struggles to maintain speed after the first lv-909 starts at about 11k up. (I'm playing normal mode and your video you said it was on easy? Could that be it or could I have miss something else?) I did not mean to offend or anger you.

Edit: I have it, I had kerbal engineer with the atmosphere up, and perhaps you had it set to a vacuum? I guess my problems flying are all my own! Sorry..

Edited January 8, 2015 by MoridinUK