Calculating maximum payload to orbit

[Bartybum]

This question is mainly for those who post lifters to the Spacecraft Exchange. Is there a mathematical way or a mod that can calculate your maximum payload to e.g. 80km, or does it all involve just trying for yourself? The reason that I'm asking is because I'd like to upload a lifter series to the Exchange, but I don't know their payload capacities.

[UmbralRaptor]

It's ambiguous. You can make some rough approximations based on ÃŽâ€V (4400 - 4700 m/s stock, depending on orbit and ascent profile, mind the changing Isp) and TWR with various payloads, but testing will give the clearest results.

[Bartybum]

How would you do it using the rough approximations?

[DaveofDefeat]

It takes 4500 m/s of delta v to reach orbit. slap kerbal engineer on your lifter with payload and see how much it gets.

[UmbralRaptor]

You have to make some assumptions about Isp for each stage, though. Engines that burn all the way to orbit can be treated as being in 0.2 atm. Anything that starts burning above ~10 km can be treated as having vacuum Isp more or less. For first stages, it depends on how many the craft has.

[Bartybum]

It takes 4500 m/s of delta v to reach orbit. slap kerbal engineer on your lifter with payload and see how much it gets.

Any random payload?

EDIT: BRAINFART. I just understood it. thanks

Edited October 7, 2013 by Bartybum

[blizzy78]

Wouldn't you rather go and design a lifter that is able to lift a specific payload, given its mass? I'm curious as to why you need to find out how much mass your lifter can lift after it's being designed.

[Lojik]

I built a lifter last night at 1am for the first section of my Space station (bad idea) was unable to achieve orbit with its payload, If you use Flight Engineer Redux be aware that the Delta V shown on the right hand side of each stage is the total of the Delta V including that stage and not each stages Delta V, I made this mistake and was not able to achieve orbit, you can see my total for the lift stage only reaches 3189 delta v and including my orbit stage it is only 4128

Edited October 8, 2013 by Lojik

[Specialist290]

A small correction on that: The first delta-v number is the stage's delta-v. The second number is the combined delta-v of that stage and all stages that fire before it.