How do you plan your dV for your return trip (without the maths)?

[Oddible]

Currently using the KSP Wiki's Cheat Sheet for most of my transfer dV planning. Curious how people plan the dV for their return without busting out the scientific calculator? Just did a Duna landing and return and cut it very close with 7200 dV (I'm not the most efficient pilot and had my parachutes attached to my pod which necessitated using engines for slowing things way down without breaking it from the return vehicle).

How do YOU calculate your return dV? Just read the wiki cheat sheet backwards?

[Boosterspice]

Calculate....

I use Mechjeb while building my rocket to check the delta-v and TWR of each stage, making sure that it's enough for getting where I want. Sometimes I just build by feeling, and usually I get back. Delta-v of my final stage is always important to me, cause that is my "there and back again" stage, usually.

[Kasuha]

I don't calculate dV. I just guess number of orange tanks the mission will take and add some Nervas and a lander piece.

Then I fly there, leave the fuel reserve in orbit, land and return, re-attach fuel and fly home.

The most fuel I used so far was five tanks for Eeloo mission. And I think it was unnecessarily much. Three sufficed for all my Jool missions. My recent Moho mission used three as well but it was quite on the edge, I depleted them before I parked at Moho and had to use Eve slingshot to get home.

[Oddible]

Calculate....

I use Mechjeb while building my rocket to check the delta-v and TWR of each stage, making sure that it's enough for getting where I want. Sometimes I just build by feeling, and usually I get back. Delta-v of my final stage is always important to me, cause that is my "there and back again" stage, usually.

Well, that's not really what I was asking. The part of your reply that I'm asking about is the "making sure that it's enough". How do you know how much is enough? I use MechJeb and Engineer to know how much dV my rocket can do, I need to know if that is enough to return from where ever I'm going. I use the wiki's cheat sheet to get me TO my destination but my question is how to know how much it will take to get home?

[numerobis]

Curious how people plan the dV for their return without busting out the scientific calculator?

I bust out a python shell instead.

Sometimes I bust out my cell phone and fire up the scientific calculator app, but usually that's not convenient for doing the necessary calculations.

[Oddible]

I bust out a python shell instead.

Imagining you setting up for a launch...

[silent_prtoagonist]

How do YOU calculate your return dV? Just read the wiki cheat sheet backwards?

Reading the delta-v maps backwards works just fine. Just remember that those maps are only approximate and very optimistic. I usually figure on adding 50% to whatever number they give you for a relatively low-stress flight.

[Boosterspice]

Well, that's not really what I was asking. The part of your reply that I'm asking about is the "making sure that it's enough". How do you know how much is enough? I use MechJeb and Engineer to know how much dV my rocket can do, I need to know if that is enough to return from where ever I'm going. I use the wiki's cheat sheet to get me TO my destination but my question is how to know how much it will take to get home?

Ah

I take it on the feel depending on where I'm going, and what I'm doing there. Capsule to Duna orbit and back? Couple of nervas and three-four FL-T 800 tanks.

Lander to one of Jool's moons? Orbital Engine-Fuel and Lander module rendezvous, and then off I go. Land, get back to the Engine-Fuel module and head home.

[Specialist290]

For my "milk runs" to the Mun and Minmus, I've pretty much done them so often that I can almost wing it simply from past experience. As silent_prtoagonist mentions, reading the delta-v numbers for landing and establishing orbit backwards works well enough; you don't have to worry about Kerbin --> Mun / Minmus transfer delta-v, since you can dispose of that cheaply enough while passing through Kerbin's atmosphere if you get a low enough periapsis in your Kerbin orbit.

For interplanetary trips out and back to Kerbin, I typically have alexmoon's Launch Window Planner open to see when my next transfer window is, and how much delta-v it will take.

Edited October 27, 2013 by Specialist290

[Stochasty]

If you are using a tool like alexmoon's Launch Window Planner, you can just ask it to plot the return trajectory. Otherwise, here's a good rule rule of thumb: your insertion delta-v on arriving at your target will be roughly the same as your ejection delta-v when leaving. Likewise, your takeoff delta-v will be roughly the same as your landing delta-v. So, simply add the insertion and landing delta-vs, and that's how much extra you should budget to get home.

For a case like Duna, you obviously will be using aerobraking to save fuel on the insertion and parachutes to help with the landing. That's fine; just try to figure out how much delta-v you'd be spending if you decided not to aerobrake (and how much it'd cost to land if Duna were airless) and add that to your budget. (Typically, this will come to a little less than 2 km/s delta-v, so the total trip budget is about 3 km/s starting from LKO. Most Mun craft are also capable of Duna return.)

[maccollo]

I just eyeball it. Sometimes I'm not so correct in my predictions, but recently I've had this strobe of luck where the rockets I built for Tylo, A tour of the Jool system, Eeloo and Moho all ended up with me having less than a third of the fuel left in the final stage when I finished my intercept burn with Kirbin.