Using a series of small burns.

[liquidis54]

I saw on a post a while back someone was asking how they were supposed to use nuclear engines to reach other planets if the burn would take 30 minutes. The answer they got was to split it into 3 smaller burns. This is something I've been wondering about for awhile now. I installed a mod with several ion engines and tanks but the TWR is sooo low that it'll take me an hour or 2 to get to just Duna. Can someone explain to me how to split the burn into smaller parts and still get the timing right? or maybe a better solution to the problem? I'd like to use the ion engines to send small probes to all the planets instead of building big, long probes using standard engines. Thanks in advance!

[Dkmdlb]

Burn for 5 minutes before and after the maneuver node. going interplanetary, it shouldn't mess anything up too bad, because a series of 5 or 6 burns will take you maybe 1 day - not long enough to screw up your transfer window.

Just set your maneuver node, and then burn each time you come around in your orbit. You may have to do a small course correction once you are halfway there, but it shouldn't be too outrageous.

What's your TWR, anyway?

[Claw]

You can also spit the maneuver into multiple parts by doing one burn at your PE to get into an elliptical orbit. Do another lap around that elliptical orbit, and when you are back at PE do another burn to actually eject from the SOI. You might need to do a third burn after that to set up your transfer with the interplanetary approach that you want.

Splitting it this way allows you to harness more Oberth effect. I'm not sure if that's what you saw previously, but that would be one major advantage to splitting up the burn for a low TWR craft.

Here's a video that demonstrates what I'm talking about (and includes some discussion about gravity assists which is irrelevant to your question). In this case, using multiple burns saved about 7% on the fuel requirement.

Edited April 30, 2014 by Claw

[cantab]

Pick some length of time, say 3 minutes. Set up your manouevre node as normal. Start burning 3 minutes before, keep burning until 3 minutes after then stop. Note down (or memorise) the delta-V remaining. You should now be in an elliptical orbit with periapsis at your manouevre node. Advance the node one orbit and reduce the delta-V to what was left to do from last time. Repeat as many times as needed, and watch out for the Mun interfering!

[BudgetHedgehog]

In my KSP, if a burn takes more than 3 minutes to complete (no matter the target), it's poorly designed and I need to increase TWR. It's why I've recently started doubling up on LV-Ns for almost any interplanetary mission (used to have 2, now have 4) - sure, it's possible to split up a burn into several smaller ones and is more efficient (i.e. the most efficient way is with just one LV-N), but I find that it creates more problems than it solves - it's a lot simpler and easier to just send a refuelling probe in the same window.

[Claw]

In my KSP, if a burn takes more than 3 minutes to complete (no matter the target), it's poorly designed and I need to increase TWR. It's why I've recently started doubling up on LV-Ns for almost any interplanetary mission (used to have 2, now have 4) - sure, it's possible to split up a burn into several smaller ones and is more efficient (i.e. the most efficient way is with just one LV-N), but I find that it creates more problems than it solves - it's a lot simpler and easier to just send a refuelling probe in the same window.

That's the beauty of this game. There are so many ways to play and so many ways to decide how to get your goals done.

[mellojoe]

I find that I end up making a new maneuver node after each successive burn. Make your original burn. It shows 30 minute burn time. YIKES! Set up about 5 minutes before, start burning full throttle. Keep burning until about 5 minutes after. Delete that node. Go back and make a new node. It will show about a 20 minute burn time. Rinse. Repeat.

[Kasuha]

I had a few 40-minute burns in my early KSP days but later I did not go over some 15 minutes. Even that can bite somewhat off the Oberth effect and it has tendency to send you in wrong direction if you just follow the maneuver indicator on Navball so I learned to not follow it and rather to match the Kerbin SOI escape.

Burn splitting is decent if your intermediate orbit does not go past Mun - longer orbital periods may make you miss your transfer window. And even with orbit all the way to Kerbin SOI boundary you're still only halfway through the ejection when going to Jool or Moho so you got to burn straight and compensate for the error anyway.

It's simpler to just let the ship burn and go have a snack or coffee, then return and issue a few corrections. Unless you want or need to be super effective.

[Zaeo]

What I do, is for probes, find a healthy delta-V (12,000 for interplanetary missions for my Solar 1 rocket, capable of launching 3 ton payloads all the way into polar joolian orbit) And then use the mun as a velocity slingshot into solar orbit. From there, I finetune my target approach via a 2/1 orbit ratio, That is for every two orbits the space craft makes, the planet makes 1 orbit. I then put a maneuver node at apoapsis, which is where the intersection meets, and click "Next orbit" And until i get a SOI interaction, I keep pressing next orbit. You will eventually get an interaction, and should only need ~ 1000 d-V to make the maneuver into orbit.

This method will take a LOT of time in max timewarp to get it in orbit, but it will work, every time.

Note: if I'm not going to the outer planets, I have about 6000 d-V remaining after all the burns. The only ones that need all 12,000 is polar jool orbit, Dres, Eeloo, and a select few joolian moons.

Edited May 1, 2014 by Zaeo

[EtherDragon]

The only part of any mission that may require you to split your burn is the Ejection Burn from a planetary SOI. The reason is because the burn is prohibitively long, otherwise. So, as others suggested, for instance when leaving Kerbin for interplanetary space, do three burns at your burn point - once for each fly by at 10 minutes.

Once you are out of Kerbin's SOI - 30 minute burns are no biggy at all because of the extreme time-frame you are now working with.