Thrust scaling with atmosphereic pressure, instead of Fuel Flow rate. Yay!

[NecroBones]

Here: http://kerbaldevteam.tumblr.com/post/110666185425/devnote-tuesday-point-sharp-end-towards-space

Aside from the input revision, I’ve also gone over the Engines code, and tweaked them so that now throttle regulates the fuel flow rate, instead of the final thrust. That means fuel flow stays constant, and as Isp changes as you leave the atmosphere, thrust output increases (as opposed to thrust staying constant and fuel consumption changing).

Not only will this add to the realism, but it will probably help with the atmospheric balancing they're probably having to do after adding the new aerodynamic model.

[CalculusWarrior]

That's one of the most major features I've seen! It seems like KSP is starting to take the 'realism crowd's' suggestions!

[SpenSpaceCorp]

i am so excited to see the implementation of a better atmosphere model and its implications approaching!

[flightmaster]

I'm not sure I understand what ramifications this will have. Will it make it harder, easier, or just change the way it works?

[metl]

Can someone explain to me how this will actually affect gameplay? I'm confused on that part as twr currently increases going up in the atmosphere. So fuel efficiency will remain constant now? It didn't before? I know turbo jet engines were more fuel efficient higher up, but I never noticed a difference with rocket engines. What am I missing?

[NovaSilisko]

Very glad to see this change being made.

[RobotsAndSpaceships]

It's about time. I'm surprised no one had done this with a mod before.

[NovaSilisko]

It's about time. I'm surprised no one had done this with a mod before.

Pretty sure several mods have done it before. I know it happens in realism overhaul.

[RobotsAndSpaceships]

Pretty sure several mods have done it before. I know it happens in realism overhaul.

True, besides RO, it hasn't been done.

[Daze]

I think that with this implementation there's no need to "nerf" too much the vertical ascent from a planet with atmosphere + new aero

[Dunbaratu]

Looks like people using kOS will probably have to redesign the logic of some of their scripts. (not that it's a bad thing). Currently, the knowledge that, say, 30% throttle means you get 30% of your max thrust has made certain calculations a lot simpler than they realistically would be.

[Seshins]

im with the others here, what does this mean exactly? less fuel consumption in vacum vs atmo?

[:D​]

As it currently is (or was, I'm not clear on if this was implemented yet), ISP (engine efficiency) increases linearly with atmospheric pressure - which decreases exponentially with height. This means at very low altitudes, the engine uses a value close to the atm ISP, while it very quickly uses higher ISP as it gets above 15k.

In the actual physics code, though, the current ISP controls how much fuel is used per unit of force - in effect, the fuel flow rate. This is governed by the following equation:

dm = T/(((IF-II)*atm-IF)*G);

where 'dm' is the instantaneous change in mass of the rocket, T is thrust, IF is ISP final, II is ISP initial, atm is current atmospheric pressure, and G is 9.82.

This will change. Instead of fuel flow changing, the rocket will just be able to generate more thrust. However, they are basically isomorphic.

Edited February 11, 2015 by :D​

[Yellowburn10]

Can someone explain to me how this will actually affect gameplay? I'm confused on that part as twr currently increases going up in the atmosphere. So fuel efficiency will remain constant now? It didn't before? I know turbo jet engines were more fuel efficient higher up, but I never noticed a difference with rocket engines. What am I missing?

As most of us know, ISP is the fuel efficiency of an engine. The higher, the better. In the real world, a rocket engine can produce more thrust in a vacuum because it can burn the same amount of fuel more efficiently than if it were in an atmosphere. In current KSP, as you enter space, the thrust doesn't change, but the fuel consumption is lowered, giving you the effect of a more efficient engine.

(If anything here is wrong, please feel free to correct it.)

[NovaSilisko]

For those not understanding what this change means, allow me to explain.

The current behaviour of engines in KSP is that, as you leave the atmosphere, the rate of fuel consumption changes as a function of your desired thrust (via throttle) and specific impulse (which changes with atmospheric pressure). This is not how real spacecraft work.

The change here is making the engines work like the real thing - throttle sets a desired fuel consumption value, and then thrust is set as a function of that and your specific impulse (which still changes with atmospheric pressure). This is because the exhaust can expand much more effectively in a vacuum than in an atmosphere, and thus can impart more energy to your spacecraft.

Balance-wise, this won't affect much, but it will make engines kick a bit harder in vacuum, so landers of the same design may have higher TWR than they used to.

Now what we need are realistic exhaust plume particle effects to reflect the expansion of exhaust in vacuum, the current ones aren't anything like what real rocket engines look like.

Edited February 11, 2015 by NovaSilisko

[Merinsan]

Can someone explain to me how this will actually affect gameplay? I'm confused on that part as twr currently increases going up in the atmosphere. So fuel efficiency will remain constant now? It didn't before? I know turbo jet engines were more fuel efficient higher up, but I never noticed a difference with rocket engines. What am I missing?

It means as your altitude increases, your thrust will increase. Currently, the fuel consumption drops.

The only reason the TWR increases as you go up at the moment is because fuel is being used. If you use the cheat menu and activate unlimited fuel, the TWR remains constant currently. With this change, the TWR will increase as you get higher.

[Stargate525]

So the question then becomes, are all of our engines getting a nerf at sea level, or a boost in space?

[Bill Phil]

So the question then becomes, are all of our engines getting a nerf at sea level, or a boost in space?

Both.

The engines are getting nerfed all around, but this feature might actually counter act that a bit once in space...

[FlowerChild]

True, besides RO, it hasn't been done.

I believe it was first done in Arcturus Thrust Corrector, and also appears in KIDS and BTSM. I suspect there are some other mods that also do it I'm not aware of.

So, really, it's been done plenty before. Just not by Squad

So the question then becomes, are all of our engines getting a nerf at sea level, or a boost in space?

I think with the changes in the aero model, all bets are off with regards to previous balance, so what qualifies as a nerf is entirely up in the air because we have no basis of comparison anymore. I think Squad has even stated that we're essentially going to be playing a whole new game.

Edited February 11, 2015 by FlowerChild

[Randazzo]

Can someone explain to me how this will actually affect gameplay? I'm confused on that part as twr currently increases going up in the atmosphere. So fuel efficiency will remain constant now? It didn't before? I know turbo jet engines were more fuel efficient higher up, but I never noticed a difference with rocket engines. What am I missing?

Currently, engines burn less fuel at higher ISPs. For example, The LV-909 has an atmospheric ISP of 300 and a Vacuum ISP of 390(I think, this might be too high. Maybe 350.). It will burn fuel faster in the atmosphere than it will in space. With this change, it will burn fuel at the same rate, but generate more thrust in a vacuum. The end result will be overall less Delta V but higher TWR. It's making it more "realistic". Subjectively speaking, harder.

KSP strikes a wonderful balance between fun and reality, pushing the boundary too far in either direction narrows their potential audience.

[kujuman]

This is, of course, fantastic news. This will make Eve even more of a pain And give us a great reason to use SRBs again! Oh happy day!

True, besides RO, it hasn't been done.

Not sure about mods the change the stock engines, but I can think of one for SRBs that has always had thrust controlled by Isp.

[RobotsAndSpaceships]

Will the ISP nerf be atmospheric or universal? I wouldn't be a huge fan of a universal one.

[Whirligig Girl]

This wasn't even part of the realism crowd. I wanted this change. I don't think anyone really wanted the Isp to work like it does now.

- - - Updated - - -

Now what we need are realistic exhaust plume particle effects to reflect the expansion of exhaust in vacuum, the current ones aren't anything like what real rocket engines look like.

http://forum.kerbalspaceprogram.com/threads/92764-90-Stock-Part-Revamp-Update-1-7-2%21?p=1702382&viewfull=1#post1702382

Just had to plug this.

[Thomas988]

Well, as glad I am to hear KSP will start making sense, I'm getting quite nervous. I mean, with all these huge changes such as the ISP and aerodynamics I'm sure we'll all have to relearn flying one way or another.

[hoojiwana]

This wasn't even part of the realism crowd. I wanted this change. I don't think anyone really wanted the Isp to work like it does now.

- - - Updated - - -

http://forum.kerbalspaceprogram.com/threads/92764-90-Stock-Part-Revamp-Update-1-7-2%21?p=1702382&viewfull=1#post1702382

Just had to plug this.

You should probably be plugging Smokescreen instead since that's what actually allows for expansion FX.