Help with MechJeb interplanetary transfers

[Nemesis1-1]

Hi, I'd appreciate it if someone could help explain how to perform a proper interplanetary transfer using Mechjeb. I've put in hours of work and I've never come close to another planet (Though I saw Sentar from really far away as I missed it). Only today I missed Dres by some margin, using Mechjeb.

Now I understand that you 'Transfer to another planet' and then once you get close you select 'Fine tune closest approach', but I'm still missing by some margin. I've exhausted all the science in the Kerbin system and need more.

Help would be very much appreciated, whether by telling me what to order mechjeb to do or something else,as this is getting frustrating.

[Technical Ben]

I tend to have to fine tune (trim) by hand on some journeys too. Depends on how/when I approach. Use the rendezvous planner and the closest approach reading and manually adjust your heading (via nodes or little spurts of rocket propulsion). Depending on your distance, you could even use some RCS to trim the final approach.

Hence I use MechJeb partly for automation, partly for info. I tend not to over do it on both.

[Nemesis1-1]

I've tried RCS before, didn't work unfortunately

[Hodo]

I can't say I have ever used MJ for interplanetary transfers. Always found it easier to manually do it.

[Nemesis1-1]

I can't say I have ever used MJ for interplanetary transfers. Always found it easier to manually do it.

Last time I plotted a transfer manually I missed Duna by several hundred thousand kilometers due to my lack of understanding of nodes, so I need Me chjeb.

[Technical Ben]

I can't say I have ever used MJ for interplanetary transfers. Always found it easier to manually do it.

Wobbling trajectories dues to gfx/rounding errors makes that too awkward for me. That and the zoom in not being close enough, so trimming constantly can get annoying. Mechjeb readouts (or other mods) allow for a bit more precision earlier on or a bit better view later.

[Nemesis1-1]

Right I've got it. I manually plotted a kerbin escape and then got mj to perform a hohmann transfer while in orbit of kerbol, then fine tuning closest approach, and I got to Eve, yay.

[Red Iron Crown]

Now I understand that you 'Transfer to another planet' and then once you get close you select 'Fine tune closest approach', but I'm still missing by some margin.

I think you may be doing your fine tuning too early or too late. Mechjeb can only change the craft's velocity to a certain precision in m/s; for a long initial transfer burn or early correction this margin of error can be the difference between an encounter and a miss. If you wait too long to do any fine tuning you may be too far off course to correct.

Basically, course corrections from further away cost less dV but are less precise, closer course corrections are more costly but more precise.

I usually do a course correction about halfway through the transfer, then another to refine it further once I enter the SOI of the target (especially important if you're planning on aerobraking).

Right I've got it. I manually plotted a kerbin escape and then got mj to perform a hohmann transfer while in orbit of kerbol, then fine tuning closest approach, and I got to Eve, yay.

This works, but costs more dV. Congrats on the encounter all the same, though.

Edited March 21, 2014 by Red Iron Crown