[newbie] Mothership burning issues

[mk1980]

a correction burn is probably best done somewhere in the middle of the transfer. in my case, the descending node happened to be roughly halfway to duna, so i put the maneuver node there. time to node was something like 90 days or so (i set it up right after ending the burn in LKO)

after placing the maneuver node, i focus on duna and look around where the current (pre-correction) trajectory is. then mouse over the vector-manipulation thingies (don't know how they are actually called ) and use the mousewheel to increase / decrease the burn components. dragging the vector thingies is too inaccurate.

if the current trajectiory is above/below the planet, the pink axis (normal/antinormal) can shift your projected course up/down. if it's too far "inside" or "outside" the orbit line, you can add prograde or retrograde to shift it inwards or outwards.

if duna's moon (ike) gets in the way, you can add a bit of radial or anti radial to the burn (which also tends to shift the trajectory in/out) and correct it back with more pro/-retrograde. that last bit probably sounds weird, but what it does is - adding (or removing) velocity in anti/-radial direction will make you arrive a few hours earlier or later, and by correcting the distance from the planet via pro/retrograde velocity, your ship will still arrive at roughly the same spot (relative to duna), but at a different time (a few hours more or less should be enough to avoid ike if it gets in the way)

long story short - put a maneuver node somewhere in the middle of the transfer focus on duna, rotate the camera so you can see duna, your projected course and the node, and use fine input via mousewheel to gently add/remove speed from the 3 axes until the flyby looks good.

a trial-and error approach works fine, you'll figure out which vector does what fairly quickly. if you mess it up completely, just delete the node and start from scratch. you have all the time in the world. it will take 100 days or whatever until your ship actually reaches the node.

 

as for executing the burn: using RCS is fine. if you don't have RCS, you can also use the main engine(s) of the ship. it will be a delicate high precision burn, so it's probably a good idea to right click the engines and set their thrust limiter very low (so you have better fine control over the exact amount and avoid overshoot).

if you used the thrust limiter, don't forget to toggle it back to full thrust after the correction (otherwise you might forget and then zoom past duna wondering why you barely slow down. that happened to me a friend of mine and i he felt like an idiot. ahem

 

[sdj64]

Splitting into multiple burns at periapsis is the generally accepted way of doing things because it's most efficient.  However your ship seems to be quite low TWR to even do that - you'll probably need 3 or more burns and it will throw off the timing of leaving Kerbin.  It has lots of extra Delta V so going to high orbit (halfway to Mun) first is not a bad choice.

Getting within 800 Km is fine with this first maneuver.  Once you're on your way to Duna put another maneuver node (correction burn) at your Ascending or Descending node (whichever occurs before you reach Duna) and fiddle again to get closer.  If you can't seem to get your intercept closer, move the node closer to Duna and try again.

 

Edit: hold down Alt and timewarp to get physics warp outside of atmosphere, that way you can do the burn in a shorter time.  If you have a very big ship, watch out for bending when you do it...

Edited September 5, 2017 by sdj64

[GuyWithGlasses]

Hello everybody!

Yesterday I was able to dedicate one hour to this job.

I did the third burn in Kerbin SOI, after this, a correction burn when the ship leaves Kerbin influence and the final correction burn when the ship enconuntered Duna (bad done, I did it too much near at the encounter's periapsis, but before the inyection burn).

I was able to reach a (more o less) good orbit without wasting a lot of fuel, around 2400 m/s of deltaV in all the burns I had to do in the way. One screenshot: https://imgur.com/yXtMN2C

I hope this weekend  I'll have enough time to test again the landers...

 

Best Regards!