Factorio Forums

TL;DR

Space platform 'weight' property should be renamed to 'mass'.

What?

The weight readout of space platforms should be renamed with mass. Additionally, any references to 'weight' in any sort of space/zero-gravity context should be replaced with 'mass'. No gameplay values need to be changed.

Why?

Mass is the scientifically accurate word when it comes to calculating thrust and force. Weight implies that there is a gravitational context (which doesn't exist in space). It's a minor change that just adds a bit more realism to the game.

Except that there is gravity in space! It's what causes your platform to be pulled to the nearest planet (at 10km/s) when it runs out of thrust. Unfortunately the rate you get pulled to the planet appears constant, and not dependent on mass, so it doesn't make sny physical sense anyway (see 122365 for more of a discussion about how the physics are all wrong).

Also, I'm curious how does the weight of a platform compare to the weight reported when sending the necessary materials up by rocket?

I agree with the initial poster. It should be 'mass'.

EpicPuppy613 wrote: Tue Oct 29, 2024 10:25 pm Weight implies that there is a gravitational context, which doesn't exist in space

Should be: "Weight implies that there is a gravitational context, which is (mostly, see orbital mechanics) negligible in space"

BraveCaperCat wrote: Sat Nov 23, 2024 11:09 pm Should be: "Weight implies that there is a gravitational context, which is (mostly, see orbital mechanics) negligible in space"

Not negligible in Factorio space! The planets are ridiculously close together.

IsaacOscar wrote: Sat Nov 23, 2024 11:25 pm

BraveCaperCat wrote: Sat Nov 23, 2024 11:09 pm Should be: "Weight implies that there is a gravitational context, which is (mostly, see orbital mechanics) negligible in space"

Not negligible in Factorio space! The planets are ridiculously close together*

*Subject to change.

BraveCaperCat wrote: Sat Nov 23, 2024 11:28 pm

IsaacOscar wrote: Sat Nov 23, 2024 11:25 pm

BraveCaperCat wrote: Sat Nov 23, 2024 11:09 pm Should be: "Weight implies that there is a gravitational context, which is (mostly, see orbital mechanics) negligible in space"

Not negligible in Factorio space! The planets are ridiculously close together*

*Subject to change.

Sorry for another comment, but I just realised that if the planets are cloee together, their gravity should mostly cancel out (whereas you get ±10km/s, even if you're equidistant from two planets) ... so I think the Factorio devs need a few physics lessons

IsaacOscar wrote: Sat Nov 23, 2024 11:31 pm

BraveCaperCat wrote: Sat Nov 23, 2024 11:28 pm

IsaacOscar wrote: Sat Nov 23, 2024 11:25 pm

BraveCaperCat wrote: Sat Nov 23, 2024 11:09 pm Should be: "Weight implies that there is a gravitational context, which is (mostly, see orbital mechanics) negligible in space"

Not negligible in Factorio space! The planets are ridiculously close together*

*Subject to change.

Sorry for another comment, but I just realised that if the planets are cloee together, their gravity should mostly cancel out (whereas you get ±10km/s, even if you're equidistant from two planets) ... so I think the Factorio devs need a few physics lessons

Yes, you're right - there are points near the bary-centre (weighted centre between two astronomical bodies) where gravity (between two bodies and an object at the bary-centre) is near 0, and that isn't taken into account in the space platform speed equation. Realistically, we'd want gravity (currently ±10km/s) to be purely dependent on distance between each body and their masses, instead of a constant(ish) term added to the equation.

BraveCaperCat wrote: Sat Nov 23, 2024 11:59 pm

IsaacOscar wrote: Sat Nov 23, 2024 11:31 pm

BraveCaperCat wrote: Sat Nov 23, 2024 11:28 pm

IsaacOscar wrote: Sat Nov 23, 2024 11:25 pm

BraveCaperCat wrote: Sat Nov 23, 2024 11:09 pm Should be: "Weight implies that there is a gravitational context, which is (mostly, see orbital mechanics) negligible in space"

Not negligible in Factorio space! The planets are ridiculously close together*

*Subject to change.

Sorry for another comment, but I just realised that if the planets are cloee together, their gravity should mostly cancel out (whereas you get ±10km/s, even if you're equidistant from two planets) ... so I think the Factorio devs need a few physics lessons

Yes, you're right - there are points near the bary-centre (weighted centre between two astronomical bodies) where gravity (between two bodies and an object at the bary-centre) is near 0, and that isn't taken into account in the space platform speed equation. Realistically, we'd want gravity (currently ±10km/s) to be purely dependent on distance between each body and their masses, instead of a constant(ish) term added to the equation.

The Problem with realism is that it can allow you to have your platform stuck somewhere with no fuel and/or thrusters and no way to get back (e.g. because asteroids destroyed your thrusters, or you ran out of uranium fuel cells for your power)

So the 10km/s doesn't bother me, it's the weird dependance on the platforms width that ought to be changed.

IsaacOscar wrote: Sat Nov 23, 2024 11:31 pm Sorry for another comment, but I just realised that if the planets are cloee together, their gravity should mostly cancel out (whereas you get ±10km/s, even if you're equidistant from two planets) ... so I think the Factorio devs need a few physics lessons

I get the impression this and some other related mechanics were added to foil casual attempts at accurate speed control without coming up with a way to do it that even NASA would be proud of .

IsaacOscar wrote: Sun Nov 24, 2024 1:44 am The Problem with realism is that it can allow you to have your platform stuck somewhere with no fuel and/or thrusters and no way to get back (e.g. because asteroids destroyed your thrusters, or you ran out of uranium fuel cells for your power)
So the 10km/s doesn't bother me, it's the weird dependance on the platforms width that ought to be changed.

Agreed.

IsaacOscar wrote: Sun Nov 24, 2024 1:44 am So the 10km/s doesn't bother me, it's the weird dependance on the platforms width that ought to be changed.

Yes that is curious, but again I think it is a mechanic to encourage a certain shape of ship. There is a lot of wierdness in the platform/thruster and fuel/efficiency/thrust relationships that seems very intentional from observing it. I never played the space exploration mod so I dont know if it a hangover from another purpose in that or whether they have a maths guru on the team who was looking for an excuse to go nuts with it...

I looked at renaming this and weight is used for space platforms, tiles, items, rocket capacity and vehicles. While it's doable to change the locale for all those places, that leaves the Lua API (and API docs) still using weight, which is quite confusing. Changing the Lua API is not viable since it's a breaking change.

All info I could find on this acknowledges that in common usages "weight" is used even when "mass" is meant, so I think we'll have to live with this not being the 100% physically correct name.

Mass is the value which is always the same, a property of the space platform. Weight depends on the gravitational forces working on the platform, the platform will get a certain weight relative to a planet as a function of the platform's mass and gravitational force from that planet.

Bilka wrote: Thu Jul 23, 2026 8:52 amWhile it's doable to change the locale for all those places, that leaves the Lua API (and API docs) still using weight, which is quite confusing. Changing the Lua API is not viable since it's a breaking change.

FFF-440 says:

Importantly, we plan to keep 2.1 as experimental over the whole summer (I.E, not mark it stable), so that mod authors will have plenty of time to update.

The entire point of 2.1 seems to be that it is the last opportunity to make breaking changes - and give mods sufficient time to adapt. I recognize that there would need to be an API change to rename/alias/deprecate the “weight” properties… and that this is unlikely to be worth it for the average user/modder.

But we can dream.

I strongly support the change of the label to mass. I don't think that changing the function names matters here at all though, keeping it as weight on the back end for compatibility reasons is understandable, but player-facing parts are another story.
I do not see weight in the description of any items in Factoriopedia (maybe I missed it though) and the only reference to it is the platform view, as on the screenshot in the original post.

When it comes to docs, it should not be very impactful to add a note that affected function/variable names refer to what is described as mass in-game. There's probably not that many things to confuse weight with there even if such a note was absent anyway.

We decided to change it to Mass only in the space platform GUI and leave the Lua API and vehicle weight, rocket payload weight limits etc (which are also called weight in-game) alone. The change will be in 2.1.13 (not in changelog).

Thank you!