Maximun launch weight

[Juanfro]

Is there a top weight from which would be more efficient to launch another ship instead of adding more fuel and boosters?

Does this happens in real life?

[greg12]

Is there a top weight from which would be more efficient to launch another ship instead of adding more fuel and boosters?

Does this happens in real life?

I don`t know about a top weight limit. I never go higher then 200-400 tons.

I think in real life, they only has size limits. The size limit is what could fit under the fairings of their rocket.

[Red Iron Crown]

There is no upper limit in KSP that I'm aware of, you're more likely to be limited by the performance of your computer on high part count vessels.

In real life, the square cube law applies so rockets cannot be made arbitrarily large without losing efficiency.

[SpaceGremlin]

For a set amount of dV, your required rocket size increases linearly with payload. So a rocket that delivers 100 tons to LKO will be twice a large as one that delivers 50 (this is assuming that your rockets are identical in all other aspects such as their ISP).

As for real life, I think budget concerns usually dictate the mission profile. Its probably more cost efficient to do smaller launches (such as using the shuttle to build the ISS instead of Saturn V's), but in terms of raw tonnage it should work out to about the same.

[Streetwind]

KSP is less limited than real life because some laws of physics aren't fully modeled - for example aerodynamics and material strength. The one limit that KSP has is the size of the VAB. Trying clever ways to exceed it has a high chance to irreversibly corrupt the vehicle save file. Just ask Whackjob what the most difficult thing about buuilding large is.

Real life is more complicated than that. Individual stages are ultimately limited in how much dV they can pull (both in KSP and IRL), so you need to add extra stages in order to be able to lift more and/or fly farther. However, every additional stage you add to the bottom needs to be larger than the entire rest of the rocket above it - and quite a bit larger, too. This results in a rapid exponential growth of stage size and/or mass needed, and at some point the rocket simply ceases to be aerodynamic enough to fly and/or collapses under its own weight (or in the case of KSP, ceases to fit into the VAB).

But before you get there, you usually end up running into a different problem: because of the rapidly escalating mass, you'll eventually run out of thrust-weight-ratio because you don't have engines powerful enough. And XKCD showed us already what happens when you try to build outwards to get more thrust from running weak engines in parallel.

Edited March 28, 2014 by Streetwind

[SRV Ron]

For a set amount of dV, your required rocket size increases linearly with payload. So a rocket that delivers 100 tons to LKO will be twice a large as one that delivers 50 (this is assuming that your rockets are identical in all other aspects such as their ISP).

As for real life, I think budget concerns usually dictate the mission profile. Its probably more cost efficient to do smaller launches (such as using the shuttle to build the ISS instead of Saturn V's), but in terms of raw tonnage it should work out to about the same.

In theory, that will be true. In practice, it is difficult to get the right combo of parts, when the big fuel cans and engines needed, are not available in stock at present. Results are that either there is an overbuild with loss in efficiency, design becomes an issue due to bracing needed to keep things together, or that frame rate suffers.

For return to Earth flights with a payload that landed on an airstrip instead of having to be recovered at sea or some remote place on land, the Shuttle was most cost efficient. However, a Saturn 5 launcher would have been far cheaper in delivering large payloads as 70 tons of spacecraft would not have to be returned to Earth and completely overhauled for every 25 tons of payload placed in orbit. A Saturn 5 placed the converted third stage of some 100 tons, known as Skylab, in orbit.

Note that the Russians are still using the same 40+ year old throwaway rockets for lifting heavy payloads and astronauts to the ISS.

Edited March 28, 2014 by SRV Ron

[mellojoe]

Also, in real life, a main limiting factor is $$$$$. It just takes a lot of money to launch something, and the heavier it is, the more expensive it is due to the extra requirement of a larger launch vehicle and added fuel. Real life is driven more by funds availibility than anything else.

[R0cketC0der]

It actually gets more efficient the bigger you make your rocket.

Here's a simple example: imagine you launched two similar rockets side by side and then assembled their payloads in orbit. Now you could as well connect them by (weightless, not effected by aerodynamics) struts and you got essentially a bigger rocket which can lift two payloads of the original rocket into space, while maintaining the same efficiency. But we don't need to stop at strutting them together, we can also combine them into a bigger rocket with a bigger fuselage, which reduces drag and eliminates the need to take some components two time into space while you actually only need one.

So no, there is no limit where it gets more efficient to do multiple launches, it always is theoretically more efficient to launch everything in one go than to use multiple launches.

[Xavven]

My experience has shown there's a practical limit in KSP. If you're using all stock on v 0.23, try launching a 300 ton payload into Kerbin orbit. Even with thrust plates, I spent way more time trying to stop my rocket from falling apart on the launchpad or during ascent than it would have taken to just refuel the rocket in orbit with subsequent tanker launches.

I think my highest successful launch to orbit was a 450 ton payload, but the upper stages had strong shapes that made it possible. The same could not be said for my Eve return lander, which required 2 refuel missions in LKO to get its transfer stage back up.

If you're using Kerbal Joint Reinforcement or some other mod, I'm sure the practical limit increases. Of course, the next official patch has what's effectively joint reinforcement, less wobble, plus bigger tanks. So if anything, I can't wait to test my limits when that is released!

[maccollo]

My experience has shown there's a practical limit in KSP. If you're using all stock on v 0.23, try launching a 300 ton payload into Kerbin orbit. Even with thrust plates, I spent way more time trying to stop my rocket from falling apart on the launchpad or during ascent than it would have taken to just refuel the rocket in orbit with subsequent tanker launches.

I think my highest successful launch to orbit was a 450 ton payload, but the upper stages had strong shapes that made it possible. The same could not be said for my Eve return lander, which required 2 refuel missions in LKO to get its transfer stage back up.

If you're using Kerbal Joint Reinforcement or some other mod, I'm sure the practical limit increases. Of course, the next official patch has what's effectively joint reinforcement, less wobble, plus bigger tanks. So if anything, I can't wait to test my limits when that is released!

This is basically because of struts I think. Something happens when you get huge masses tugging on each other across the joint tree and things begin to randomly fail. I noticed this when playing around with the joint reinforcement mod. My rockets kept failing and I thought the mod didn't really help, until I removed all the struts and then everything worked like magic.

[Wooks]

This thing weights 2.985 tons on the launchpad (3002 parts, 36 stages), so far the heaviest thing I have ever launched into orbit. The video is a compilation of its failed launchs, this sunday I will upload the proper sucessful mission to Duna.

Edited March 29, 2014 by Wooks