How to match satellite orbit

[daterxies]

Hey.. using mechjab and just cant figure out how to get this...

http://puu.sh/muZX7/551cbdcbdb.jpg <- Mission specifics... i was able to get the right AP and Pe and Inclination, but the longitude of ascending node was enough aparently to make it all messed up? I should took a screenshot at the time, i had the right orbit, just it w.as off of the purple path.. spend 45 mins trying to figure it out and ended up .♥♥♥♥ing it up, and eventually ran out of fuel


http://puu.sh/mv06F/d78574731c.jpg

So with Mechjab WHAT settings do i have .to set to get into that correct orbit., with the correct tilt and all?? Games so fun, but this is driving me nuts..

What i basically did was set. ascent to 2938km... once there .changed me AP and Pe to correc.t, same with the inclinations .32.3.. and it was way off still.. Couldnt figure out about the Ascending node because i would .put 97.9 deg in there and it .wouldnt match up to the purple line.

Any ideas .or tips?

Edit

http://puu.sh/mv1Em/1599207bc2.jpg This is what i always come up with.. dont understand what im doing wrong. I set all the settings i believe correctly.. but its not working out

[Wemb]

Okay - forget about MechJeb for a moment - it'll help in doing the burns, but it's really not necessary for this.

There are three things you need to do to get the orbits to match:

1- Get the Pe and Ap to match between your sat and the desired orbit - you can eyeball this easily enough in the map, and sounds like you've done this.

2- Get your planes to match - if you've done 1, then go back into the map and spin the display around and look where your orbit and the desired orbit's cross (the ascending or descending nodes) - you need to put a maneuver at one of these to adjust the 'up' or 'down' of your orbit so it matches the desired plane. Note - if you're orbit is on a wildly different plane to the desired orbit, this is probably going to be a very expensive maneouvour - you should try and launch such that you a) fly in the right direction, but also b) so that you're flying into the right direction at the right time.  Try popping your rocket on the pad, and then watching kerbal spin under time acceleration on the map - you should launch into the right direction when the KSC is right underneath the desired orbital path - otherwise, you'll be starting off in the wrong place entirely.

3- And the most annoying one that everyone has screwed up from time to time.  You need to be going in the right direction...  Look at the map - you should see dots flying around the desired orbit - that's the direction that your satelite needs to be travelling in.  If you're going the opposite way, you need to a perform a maneouver to do a 180 degree turn.  The amount of dV to do this should be twice what your current orbital velocity is (since you need to be going in the same orbit, but exactly opposite velocity) - it's cheapest to do this at the Ap. 

MJ can do all of these for you, but I'd try and have a go manually - you don't need to be horribly accurate for sat missions - eyeballing it is entirely good enough most of the time.

Wemb

Edited January 14, 2016 by Wemb

[HebaruSan]

The way I did specific orbit contracts was less efficient than Wemb's method but maybe easier for beginners:

1. Launch into an ordinary low equatorial orbit (easier than trying to time it right and eyeball the relative inclination on the map during a launch, and you can follow any launch tutorial verbatim)
2. Once in orbit, switch to the map screen and look for the relative ascending node (AN) and descending node (DN) of the target orbit
3. Whichever one has the target orbit farther away, set up a maneuver on the opposite side with enough prograde thrust to intersect the target orbit at the higher point
4. After that burn, place a maneuver at the intersection (which should also be your Ap marker now in addition to the AN or DN)
5. Drag the purple normal handles to match the orbit's inclination, the yellow prograde ones to raise the periapsis as needed, and the cyan radial ones to rotate, with the goal of moving your Ap and Pe markers to match the target orbit
6. Perform that burn once you get there, then fine tune as needed

This isn't the absolutely most efficient method, but I never ran out of fuel this way either, since most satellites can be built with very low mass and plenty of extra fuel.

[daterxies]

Thanks for the replies!  Im going to scrap MJ and learn how to do this stuff without it.  i ended up getting it last night by manually doing it.. but just accepted ANOTHER mission to place a satellite at like 5900ish km orbit.

[Wemb]

MJ is a really good learning tool - and I certainly would suggest it's worth using it (at least a few times) to do the actual burns so you can sit back, relax, and watch what it's doing from the map view and get a nice understanding of what it's doing, why, and how it does it. MechJeb is generally very good at performing discrete manoeuvres, and won't do what we've all done at some time which is occidentally mash the z key at the wrong moment, or have the ship pointing in entirely the wrong direction without realising it. It's timing is a lot better than mine too! 

I pretty much always fly with it onboard, not because I need it to tell me how to fly my ships, but because it's a lot better at more accurately performing the manoeuvres I need than I am. 

Well done on getting the satellite into orbit though - timed launches into a particular plane can often be a bit tricky.

Wemb

[Geschosskopf]

On ‎1‎/‎14‎/‎2016 at 10:55 PM, daterxies said:

.....

Any ideas .or tips?

For matching orbits with a satellite, MJ is of limited use, mostly just to execute burns.  But you pretty much have to set everything up by eye.

The general procedure I use is like this:

#1, and most important, BE SURE YOU KNOW WHICH WAY AROUND THE TARGET ORBIT IS GOING (as in prograde or retrograde).  You tell this by looking at the dots going around the target orbit in the map view.  If retrograde at Kerbin, be sure to launch heading west instead of east.  If retrograde at another planet, be sure to arrive there on inboard side, not the outboard side.  Otherwise, you're pretty much screwed from the get-go.

#2.  Having established which way I need to be going around the planet, the 1st parameter of the target orbit I go for is the inclination.  If you don't do this up front, it costs way more fuel than it should.  If the target orbit is at Kerbin, put the rocket on the pad, go to the map view, and warp until Kerbin rotates KSC directly under the target orbit's AN or DN, then launch directly into the target plane (remembering to go east or west as needed).  Problem solved.

#2A.  If, however, the target orbit is around another planet, things are a bit more complicated.  First, you do a mid-course burn to move your Pe at the planet above or below its equator to approximate the target inclination (and remembering to be on the inboard or outboard side of the planet as needed).  However, you're LAN will hardly ever be close to right so you'll have to finagle that after you capture.  So what you do is just BARELY capture into a highly elliptical orbit so the necessary plane change will be as cheap as possible.  Then rotate the map view until you're looking edge-on at both own orbit and the target orbit (both appear as single lines).  See where these lines cross---these are your AN and DN to move to the target orbit's inclination.  If one of these is far enough from the planet to make the burn cheap, put a node there and pull the up/down handles until you'll match planes.  But it often happens that both AN and DN are close to the planet.  In this case, put the plane-change node at your Ap.  This will either do the job or get you close enough that the real AN or DN is now far enough from the planet to use for the rest.

#3.  So now you're in the correct plane going around in the correct direct, all that's left is fixing your APe and setting your Pe and Ap to the correct values.  It's generally best to walk into the final configuration in steps.  First off, without worrying about your APe, just adjust your Ap and Pe so that your orbit is approximately the size and shape of the target but not quite.  Now pick a point about half way between your current Ap and Pe, place a node there, and pull the radial in/out handles.  This will slide your Ap and Pe around your orbit, IOW changing your APe.  Fiddle with this until your new Ap and Pe will like up with the target Ap and Pe.  It doesn't matter at this point if your Pe is next to the target Ap and vice versa because you'll fix that in a minute.   What you're doing here is getting your APe either correct (your Pe and the target Pe are on the same side of the planet) or 180^ off (your Pe is on the same side of the planet as the target Ap).  Once you've got your Ap/Pe on the same line as the target Ap/Pe, all that remains is adjusting your Ap and Pe to match the target's.  And when you do this, you'll swap your Pe/Ap to match the target's automatically if they didn't start that way.  So put nodes as needed at your Pe and/or Ap to change the altitude of the opposite side of your orbit.

#4.  Sit back for 10 seconds and watch the money roll in.

Edited January 15, 2016 by Geschosskopf

[Kryxal]

For orbits around another planet (and this applies to rescue missions too, they don't give you orbital data but we're not using it anyway), I usually try to execute capture and plane-change maneuvers at the same time.  I make a point of pretty well meeting the target orbit on the way in (a bit inside it to give nice clear distance markers) and try to meet the target on the next orbit.  I do far more rescues than satellites.  For satellites, it's a matter of eyeballing the plane, the ap/pe, and the POSITION of the ap/pe (or seeing where the orbit's inside the target and where it's outside, that's what you use radial to fix).

[Snark]

9 hours ago, Geschosskopf said:

#1, and most important, BE SURE YOU KNOW WHICH WAY AROUND THE TARGET ORBIT IS GOING (as in prograde or retrograde).  You tell this by looking at the dots going around the target orbit in the map view.  If retrograde at Kerbin, be sure to launch heading west instead of east.  If retrograde at another planet, be sure to arrive there on inboard side, not the outboard side.  Otherwise, you're pretty much screwed from the get-go.

+1 to this.  It's a very easy mistake to make, those little sparkly dots are subtle and lots of folks miss this.

FWIW, this is one thing that's due to get better with the upcoming release of 1.1.  They're redoing the orbits UI completely, and a few weeks back they posted some screenshots of what the new experience will look like.  It's gorgeous, and the orbit direction is a lot more obvious.  So hopefully this particular problem will get a lot better in a few weeks.