Greetings!

[Kaz]

Hello everybody! I'm Kaz, or as I decided when I started playing, Kerbal Avionic Zciences. Been playing KSP on and off for a year or so now, and decided to come to the forums here to join the community sort of.

Problem is I'm not that great at the game, mostly because I can't quite wrap my head around the process of deducing Delta-V and some of that other actual rocket science stuff. I poked around on the Wiki but I couldn't really grasp what information was there.

So, if anybody has a simpler guide to get me started on that kind of math I'd appreciate it! For Science!

[Freak80MC]

If your up to getting mods, there is a great one called Kerbal Engineer Redux that shows you calculations for Delta-V, TWR, mass, and stuff like that. It even shows this information for the different bodies in the Kerbol system, if you plan on your ship going to those bodies. It is a really great tool and I love using it as I don't need to keep guess and checking if my ship has enough fuel for my needs!

[Pecan]

KER, MJ and VOID are excellent information mods if you just want something to display those figures for you. Otherwise you'll have to work them out by hand, slide-rule, calculator or spreadsheet every time you make any change to your vehicle.

There are two numbers which you want to know: TWR (Thrust to Weight Ratio) and deltaV (potential velocity vector change).

TWR is dead easy - all you need to know is the total thrust of your engine(s) in any stage (which KSP gives you in the VAB/SPH part descriptions) and the total mass of the rocket, including any payload (including 'higher' stages) it has to carry. TWR is simply Thrust/Mass; if it comes out under 1 your engines aren't powerful enough to THRUST up against the WEIGHT of gravity pulling you back down - you can't liftoff and won't be going to space today. Ideally you launch with a TWR of 1.2 - 1.5.

deltaV is a bit trickier in that about the only word in "potential velocity vector change" that makes much sense is 'velocity'. That's a 'vector' though, in as much as if you're "going at 80mph" you must be going in some particular direction. You can burn fuel, using-up deltaV, to change that so you're going faster, slower and/or in a different direction - all depending on which way your engines are thrusting at the time. To calculate deltaV for a stage you need to know three things - engine Isp (which KSP tells you in the VAB/SPH part descriptions), the total mass of the rocket (including payload, etc) with all its fuel, wet_mass, and the total mass without fuel, dry_mass. The formula is: (Isp * 9.82) * LN(wet_mass / dry_mass) <- easy, isn't it ^^. It is actually ...

Isp = how efficient the engines are; the higher the better.

(9.82 is the gravity factor used in KSP).

wet_mass / dry_mass = what proportion of the rocket's mass is available to power the engines; the higher the better.

LN() = the natural logarithm function. Don't worry too much about it - you'll need logarithm tables or a calculator/spreadsheet to work it out anyway. What it means is that there are diminishing returns from adding more and more fuel, because that fuel itself has mass, which needs deltaV to push, so you use more and more of the fuel just to push the rest of the fuel. In Excel/LibreOffice Calc the function is written as "LN()"

Soooo ...

... (Isp * 9.82) [the more efficient the engines]

... * LN( [times diminishing returns from]

... wet_mass / dry_mass) [the greater the proportion of fuel available]

...= deltaV [the more you can potentially change your velocity vector]

(and it's all just 'potential' because you might not even use it!)

Edited December 30, 2014 by Pecan

[Kaz]

Thank you all for the greetings and advice! I look forward to poring over all that (and your helpful Exploring tutorial, Pecan) when I have the chance!

I might look into some mods for the future, to simplify things, but I'd like to have a firm understanding of how it works first- rather than just strapping my Kerbals into a rocket without knowing what I'm doing entirely. =p

Anyways, once again, thank you very much!