KSP Math

[7499275]

Hey guys back once again! Trying to improve myself as a player and be less dependent on mods...

How does the math of vehicles work? Like the mass? What does 0.3 mass equal? I'm assuming once I know the mass of objects I can use an equation based on the Kn of thrust an engine provides to determines if that engine can lift that total mass? Also how to determine the Delta V of a stage and of the entire rocket.

I hope you guys understand what I'm getting it. Its aggervating not knowing the true weight in tonnage and not knowing the lift capabilties of a stage! So if you guys can point me in the right direction on the math I'd appreciate it! thanks!

[UbioZur]

Mass is in Tons in KSP.

And most of the math you need is available on the wiki

[7499275]

so the mk1 pod's mass is 0.8 so in tons that would be...?

And the wiki will take some time to break down into my understable range but thank you. Will look at it and give it a go!

[aNewHope]

Also it's good to know, that that 1 unit of liquid fuel / oxidizer mix weights 5kg or 0.005 t.

If you want to find out your vessels mass, just switch to map view and click on the button to the right.

[capi3101]

The Mass of the Mk 1 is .8 metric tonnes = 800 kilograms. You'll sometimes see this also as 0.8 megagrammes; correct but hard to wrap your head around if your country doesn't regularly employ the metric system. All the units in the game are metric. Except for temperature - nobody knows what scale is being utilized there.

Thrust-to-Weight Ratio: this equals your total stage thrust divided by the quotient of the mass of the rocket and the gravity of the world from which it is being launched. If TWR is greater than one, your rocket can take off; if not, it won't.

Delta-V is determined via the Tsiolkovsky Rocket Equation: dV = ln(M/Md) * 9.81 * Isp, where dV is delta V, M is the total mass of your rocket, Md is the dry mass of your rocket (how much it weighs after it runs out of fuel), and Isp is the specific impulse of the rocket's motors (i.e. their efficiency). The equation works on a stage-by-stage basis, so for a multi-stage rocket you just add up the delta-V of all the individual stages.

Edited October 21, 2013 by capi3101

[capi3101]

The Cheat Sheet is a good resource for mission planning. I'd also suggest looking at the Advanced Rocket Tutorial; it's a bit heady but supplements the Cheat Sheet nicely. And the general Stock Parts table contains crucial information.

[7499275]

Ah damn metric system... I thought it used American or Imperial tons not Metric tons... That is good to know correctly now.

And okay the delta V is really throwing me for a loop... I apologize I am only learning geometry ( only had algebra in the past ) and I stuggle with math as it is lol.

So with that equation that capi301 provided I think I can figure it out and get used to it but the TWR.

How do I know the total stage thrust? Is that the "power" in the VAB?

[SRV Ron]

Consider the mass to be measured in metric tons since distance is in meters.

As far as calculating thrust and delta V, just do what the kerbals do, go to the school of hard knocks or what can be called trial and error. Build something and observe how it performs. Then, tweak the design and see if it performs better or worse.

[Sirrobert]

Ofcourse it's metric tons, what else would it use?

Good science always uses metric

[Specialist290]

So with that equation that capi301 provided I think I can figure it out and get used to it but the TWR.

How do I know the total stage thrust? Is that the "power" in the VAB?

Maximum thrust per engine is indeed the value under the (wrong) label "Max Power" in the VAB.

As for the weight you'll be thrusting against, that's the total starting mass of the craft, multiplied by standard surface gravity (9.8 m/s^2). You divide the total thrust by the craft's weight, and if it's greater than 1, you'll actually be able to lift off the pad the moment you fire up the engines.

[capi3101]

Total stage thrust (i.e. total stage power) is simply the sum of the thrust of all of your engines at full throttle (where most folks run them anyway). For example, an LV-T30 has a thrust of 215 kN and an LV-T45 has a thrust of 200 kN (kilonewtons, 1000 Newtons, 1,000 kgm/s² - again we're metric, and that's a unit of force). If your booster has one -45 and two -30s, your stage thrust is 630 kN (200+215+215).

From that you can get the total maximum allowable mass of your rocket for a certain thrust-to-weight ratio. TWR = T/M_o*g_o, where T is your thrust, M_o is your initial mass and g_o is the surface gravity of the world you're taking off from; for Kerbin, that's standard gravity at 9.81 m/s². Simple algebra therefore indicates that M_o = T/TWR*g_o

So you just plug in the numbers:

At Thrust = 630 kN

TWR = 1.9, M_o=33.80009657 Mg

1.8, 35.67787971

1.7, 37.77657852 - generally considered optimal for asparagus.

1.6, 40.13761468

1.5, 42.81345566 - minimum you want for asparagus, good for onion.

1.4, 45.87155963

1.3, 49.40014114

1.2, 53.51681957 - optimal for a one stage-to-orbit (SSTO) rocket

1.1, 58.38198499

1.0, 64.22018349 - the limit; that thruster set can lift no more more than this.

[7499275]

Ah thank you guys for all the help you have provided I really appreciate all of it!