how to calculate Payload to Orbit

[Kroslev Kerman]

i have been developing the Kerman(i could not think of another name k?) Series of Heavy payload rockets but i wanna know how much payload they can actually bring into a low kerbin orbit(or where ever else)

[Kerbalstar]

2 minutes ago, Kroslev Kerman said:

i have been developing the Kerman(i could not think of another name k?) Series of Heavy payload rockets but i wanna know how much payload they can actually bring into a low kerbin orbit(or where ever else)

Do you have KER or MJ? If so, make a payload that weighs x tons and put it on top of your rocket. To get to LKO it should have roughly 3200m/sec of D/V in atmo, and 1.20 TWR in vac.

[Kroslev Kerman]

i have MJ. But in RORSS people know how much they can actually lift into orbit(i dont have RORSS but i want it kinda like that)

[Kerbalstar]

There's also a mod called Kerbal NARP that allows you to generate procedural test weights. 

36 minutes ago, Kroslev Kerman said:

i have MJ. But in RORSS people know how much they can actually lift into orbit(i dont have RORSS but i want it kinda like that)

I'm almost sure my previous post is how they do it.

Edited November 10, 2018 by Kerbalstar
Clarifying.

[Kroslev Kerman]

it worked Thx

[Kerbalstar]

1 minute ago, Kroslev Kerman said:

it worked Thx

You're welcome.

[Loskene]

Yeah I test launcher payload capacities by just sticking tanks full of ore on top of them and seeing if they make it. Ore's quite dense so it makes for good test weights that'll always fit inside the fairing. If they have spare deltaV left over I add more ore or use it to deorbit spent upper stages, if it falls short I take some off. When finished testing my naming scheme for launchers includes their payload tonnage to a 450km 50 degree inclined orbit, to guarantee it'll always put at least that much into orbit from any launch site with some margin left over when flying to lower/uninclined orbits. 450km makes for a 1 hour orbital period meaning your original launch site will pass under it once a Kerbal day, which is handy for testing shuttles.

You could just take the KER/MJ deltaV readouts as gospel but since the actual performance depends heavily on flight characteristics and ascent trajectory, I prefer to just use those readouts as my starting point for testing before I find out how much they can really lift.

[MR L A]

I know there's the mathematical way to work this out which involves doing the rocket equation in reverse...

Is anybody good at maths willing stick it in a spreadsheet and share it with the community?

I know it gets pretty complicated when we start calculating for staged launch vehicles too, so it would somehow need to have an option for selecting the number of stages and then inputting their dV and TWR etc... hmmm, sticking weights on rockets and testing is beginning to sound a lot easier now. 

[magnemoe]

3.2 or safer 3.4 km/s is an good figure, don't have to low initial TWR, moar boosters in this case, this doubles if using mechjeb for launches as it hates slow rockets. 
Add a bit more if your rocket look as an mushroom because of fairing. 
 

[Deddly]

Sounds like a Gameplay Question to me. Moved it for you