Perhaps just general use. In particular, once one is on course for a Lagrange point, how does one calculate delta V with respect to the point - so that you stay there after encounter?
I'll continue experimenting with it. Maybe I'll answer my own question.
Hi NukeET - it's very easy. Say you are in a standard orbit around Earth (as Jim Kirk world say), and you want to get out to Earth-Moon Lagrange 1, which is in line with Earth-Moon, about 80% of the way to the Moon. Just like doing any other altitude adjustment, you need to burn to create an elliptical orbit to reach up to the LP orbit (i.e. your apoapsis is at the LP altitude), and then when you are at the apoapsis, do a second burn to circularize your orbit on top of the Lagrange Point orbit.
As a quick example - open the Lagrange LEO to EML1 scenario from the Lagrange subdirectory. On the left, you'll see Lagrange, in ORBITmode. Blue blob up the top - that's Earth, and if you look carefully, a green orbit and a circle, representing our vessel. Down the bottom, you have the Moon in grey, and the E-M L1 point in purple.
Bring up Lagrange on the right MFD, and hit MOD twice to get to PLAN. You'll see that the plan is currently inactive, but there are values pre-set (i.e. Burn MJD at 51984.691869, for a 2935m/s prograde-only burn). Hit ARM. You will now see the ORBIT go red, and a path is plotted out to the Lagrange Point (actually, just overshooting, but good enough for a first burn).
Let's execute the burn: on the right MFD, hit MOD to bring up AUTOPILOT, and hit AB to set the Auto-Align and the Auto-Burn. You'll see that the burn start countdown has started, but it's 24,500 seconds away. Go ahead and hit T 3 times to warp up to 1000x. You'll see it automatically un-warp step by step as the time comes close. Also notice how the vessel has set to an absolute direction, which looks slightly inside the velocity vector on the start of the burn. This is normal, as by half way through the burn, we will be lined up on the velocity vector. Also notice as the burn is firing, we are back on a green line (live orbit) on the ORBIT display, so you are watching the progression of the live orbit out to the Lagrange point. As the calculation gets refreshed, you will see the encounter circles track across the orbits, as the integration engine constantly updates for a better orbit.
Once the burn is complete, you should have an orbit with an apoapsis fairly close to our target. On the right MFD, hit MOD three times to bring up ENCOUNTER. On my burn, it's predicting an encounter distance of 3.8Mm, with an encounter velocity of 650m/s. This means, if I don't do a 650m/s burn at the top of my orbit, I will fall down towards Earth again.
OK, let's lay in a second burn now. Press MOD, to go onto PLAN, where we have some more resolution on the encounter point. Mine shows:
Enc MJD ~= 51988.7007
Pro dV ~= -485
Out ~= 432
PlC ~= 0.05
Press MJD, then ENT, then enter the encounter MJD and press return. I suggest you take off 0.01 of a MJD, to burn at approx 1000 secs prior to the encounter point, so you can then do some approach course corrections.
Press TDV, then ENT, then delete the number and replace with 0, and press return. (Quick way to zero all the axis dV's).
Press PRO, then ENT and enter the desired dV to null out your Enc dV. E.g. for me, I'm entering +500 (as the number is rising all the time I am typing this).
Press OUT, ENT, then enter your outward correction.
Now hit ARM, and admire your handiwork on the ORBIT display. You should see the orbit go linearly out to the encounter (just before, actually), then turn a sharp left and track just inside the LP orbit. On mine, the orbit was a little bit short and a bit 'skittish'. To fix this, on the right MFD, hit MOD twise (to S4I), then RCT and enter 0.4. This tells the engine to take approximately 10x longer to work out the answer, so it works it out with 10x finer resolution than before. The range is set at 5 days, but hit RNG and enter 8d to extend it out to 8 days, which gives you a better length tail on the orbit plot now.
On the right MFD, MOD 3 x to get back to plan, and let's see if we can fine tune a bit more. On mine, the biggest position error is on the Outward (at -6Mm, with an encounter dV of -30m/s). So I start by selecting OUT and hitting ++ and -- a couple of times. I immediately see that the Coarse setting is very coarse for this burn, so I hit ADJ to get to Fine setting, and then ++/-- looks much nicer. Now add some outward until the red plot line falls nicely on the LP track. On mine, I am now down to 4.1Mm away.
Work on OUT, PRO, and PLC depending on which has the bigger error. Each time, you are looking to reduce the error in position, whilst leaving the dVel reducing the error (e.g. 1.05Mm pos error, with a negative dVel is a good thing). One piece of advice: DON'T GO CRAZY. 1Mm error at this stage is just fine. When you have a good solution, MOD to AUTOPILOT, AB to burn it, and T a few times to warp ahead. 1000x should be good ... so you can watch the orbit develop.
One thing - the off-axis burns are not as accurate as I would like for this v1.0 release. There's a host of technical reasons, but just treat it as 90% good, and you'll be fine. This is also why I recommend burning say 1000 secs before the encounter point, and not obsessing over the last 1 km of accuracy, as the burn will not live up to your expectations! However, successive mid-course corrections (MCC's) will chop down your encounter error, so after a couple of MCC burns, you can get very accurately to the target.
If you ever notice on an autoburn countdown that you have a residual alignment error, then this was because you changed warp mid-alignment. To fix it, come out to warp back to 1x, then select ROT RCS mode, and nudge the vessel with one tap of thrust to get it moving again. The autopilot will then correct things for you.
OK, we are now past the encounter burn. Mine got me to 669 km distance and 68 m/s from the target. This is a perfect first burn. I now recommend switching to manual thrusters. However, note that in this gravitational space, Orbiter has decided that as neither Earth nore Moon has dominat gravity, it selects SUN as the Orbit reference. Let's fix that: SEL Orbit MFD, REF Earth, and hit HUD. Then SEL Lagrange again. Manually rotate to the velocity vector (note that the Prograde AP is not your friend here, because of the weird gravity, so do it manually).
Once aligned with the velocity vector, switch to LIN thrusters, and experiment tapping some RCS thrust whilst watching the ENCOUNTER screen Enc. Pos. settings. Your goal is to reduce the Encounter Position to under 50 km. Work the biggest error axis successively until you achieve this goal. Once achieved, warp time until you are within say 1000 seconds of the encounter.
Now work on your Encounter Velocity. You goal is to get it to say 20m/s or less, with the velocity sign acting to reduce the enc. pos. error.
Once your actual relative position is under 100km, and your relative velocity is under 20 m/s, it is time for the Auto-Hold AP. Hit MOD to select AUTOPILOT, and hit AH for AutoHold. Then hit MOD and go back to the ENCOUNTER screen, to watch as the AutoHold reels in the target. I find setting the encounter pos and vel like this before engaging the AH gives the best results.
Feel free to assist the autopilot with your own LIN RCS thrust to get to the target.
Congrats - you are now at EML1. Have a look around outside!!
