Oberth vs Ions

[viktor19]

Having recently researched Ion engines in my SETI career and realizing their potential for Minmus contracts (and interplanetary missions aswell), I was wondering what's the "region" of TWR when it's more efficient to do more burns than one due to Oberth.

Edited October 17, 2015 by viktor19

[ajburges]

As long as you don't change SoI it is always more efficient to do multiple burns.

The efficiency loss you are alluding to is your choice of sub-optimal prograde burns away from Pe or cosine losses with an averaged burn. Peak efficiency is prograde exactly when velocity is highest. It is all about compromise. I've heard 1/6 an orbital period quoted and that seems a fairly reasonable compromise between cosine losses and burn time.

[Red Iron Crown]

1/6th of an orbit is a good rule of thumb as ajburges mentions (about 5 mins in LKO, longer in higher orbits). It's not about TWR alone, but also how much dV must be expended to eject. E.g. a ship might not need to split burns to go to Eve but the same ship might need to for an ejection to Jool.

You can check out the tutorial in my sig if you'd like to get a bit more precise with split burns.

[viktor19]

1/6th of an orbit is a good rule of thumb as ajburges mentions (about 5 mins in LKO, longer in higher orbits). It's not about TWR alone, but also how much dV must be expended to eject. E.g. a ship might not need to split burns to go to Eve but the same ship might need to for an ejection to Jool.

You can check out the tutorial in my sig if you'd like to get a bit more precise with split burns.

So, the verdict is: burns longer than a sixth of orbital period are more efficient if split. Thanks for the advice, guys.

Red Iron Crown, I have already looked at the link in your sig just out of curiosity. I'm going to give it some more attention in the future.