Thrust in space! ;)

[Arugela]

I was in a thread I made about a vehicle I was making. Someone mentioned that now ISP is the only thing to change. Is this how it will work from now on?(I'm assuming he meant thrust remains the same and fuel guzzling changes now) Does this mean that I should always balance my thrust to weight the same for space and ground now? What happened to those values that say max thrust at Seal level are different than space. Is that going away now.

I'm not certain the person who told me was correct or that I understood what he meant... The game shows ISP changing thrust. So shouldn't my thrusters get more efficient in space. And why don't I see this affect when I get into orbit.<- Why I am believing him but not understanding it. It seems as if I get no more out of the thruster in space. Which I was counting on for my designs. Or is this all a glitch that has to be settled later in a patch? I'm a bit confused. What is the current state of thrust in space?!

Edit: BTW, I came away from what he said like it was some temporary fix so I'm not sure if tutorials would help. I'm trying to find out what it is supposed to be, what it is now, and what they are going to do with it. I'm pretty confused as to my ship design atm because of it. I was designing on one concept, that the thrust increases once and as you get in orbit. But I'm not sure that is happening now or why.

Edited September 27, 2015 by Arugela

[Alshain]

Not correct. Thrust to Weight ratio depends on weight. Weight is a function of the force of gravity and if the force of gravity is less, TWR is less EDIT: more (as opposed to mass which the strength of gravitational attraction and remains unchanged). So the further you get from gravity's center, the less you weigh. As you ascend you get further from Kerbin's center of gravity.

The only way that would change is if Squad decided to abandon physics.

Edited September 27, 2015 by Alshain

[Arugela]

So Is the information on the engines still correct as to how they function?

[Alshain]

So Is the information on the engines still correct as to how they function?

What information on the engines?

[Arugela]

The information in game when you right click on them.

[FungusForge]

Pre-1.0 pressure changed how much fuel engines consumed. So the Ion Engine for example would be stupid inefficient on Kerbin at sea level. Now an engine's thrust changes (like it would in real life) so taking the Ion Engine for example again, it now produces minimal thrust on Kerbin ASL while consuming the same ratio of fuel it would in space.

If you right click on an active engine it should tell you the current thrust. If you run an engine on the launchpad and run the engine in space there should be a thrust increase. Out of all the engines however, the Aerospike is the least effected, much like how a real aerospike rocket has minimal change in ISP.

Unless you are using asymmetrical engine setups then this shouldn't really make any difference on the rocket. If you are using asymmetrical engine setups then there will be some noticeable effect on the CoT and may cause minor instability.

[Alshain]

Oh, yes of course that is accurate. That data is directly populated from the parts config so it is pretty much impossible to be wrong.

[xtoro]

ISP is your engine's efficiency, like Miles per Gallon. Having good or bad MPG has nothing to do with how powerful the engine is.

Thrust changes in space because of the design of the engine's nozzle. Which depending on its shape, can be optimized for sea-level, high altitude, vacuum, and everything in between. But if an engine is optimized for low altitude launches, it will be less efficient in a vacuum, and vice versa. There is also the presence or lack of external pressure outside the engine nozzle which also affects its thrust. Thrust is always measured by a force such as newtons.

https://en.wikipedia.org/wiki/Rocket_engine_nozzle

Don't confuse ISP with thrust, or TWR, and don't confuse weight with mass. These are all different things. Mass never changes, but weight does, depending on the gravitational forces being applied to the ship/object. This is why TWR changes. But it's still important to know when wanting to launch/land on a planet or moon because you need a ratio of more than 1:1.

Edited September 27, 2015 by xtoro

[Foxster]

...Mass never changes...

Unless you are going pretty quickly

[GoSlash27]

arugela,

I think I understand what you're getting at. It used to be that thrust was constant and fuel flow varied with Isp. That changed with the 1.0 update. Now fuel flow is constant and thrust varies with Isp. If you check the info on the parts you will see 2 figures for thrust and 2 figures for Isp.

This unnamed other poster is mistaken.

Best,

-Slashy

[Corw]

Mass never changes, but weight does, depending on the gravitational forces being applied to the ship/object. This is why TWR changes. But it's still important to know when wanting to launch/land on a planet or moon because you need a ratio of more than 1:1.

This is half-true, because the mass of the vehicle changes as it expends fuel. Shedding fuel mass is main factor in TWR change during flight.

[xtoro]

This is half-true, because the mass of the vehicle changes as it expends fuel. Shedding fuel mass is main factor in TWR change during flight.

Well of course. Just like the mass is reduced after you drop off cargo, but I assume 99% of people are aware that spent fuel equal lost mass and it's not worth mentioning. What I meant was that an object retains the same mass whether it's in microgravity or under the influence of 10x earth's gravity...