Would you like reducing the thrust of the new engines?

[Ravenchant]

My 2 cents: The new parts seem overpowered compared to the other parts in the game. They make getting to places easier. And it doesn't bother me one bit. Why?

They are in the last tier of the tech tree. Meaning that realistically, the player already has unlocked most of it, maybe even all of it. Which means that the only thing he/she is playing for is FUN, not unlocking stuff for "completion". And at that stage, he/she has probably launched dozens of rockets and done an interplanetary transfer or two- repetitive things, you might notice. So if the new parts make those easier- great! That leaves more time to work on the actual mission.

And imposing your own restrictions is half the fun anyway. This is coming from a guy who never used a Mainsail or a LV-N

[luizopiloto]

and if you use that real size kerbin mod, this engines will help a lot...

[Rakaydos]

My 2 cents: The new parts seem overpowered compared to the other parts in the game. They make getting to places easier. And it doesn't bother me one bit. Why?

They are in the last tier of the tech tree. Meaning that realistically, the player already has unlocked most of it, maybe even all of it. Which means that the only thing he/she is playing for is FUN, not unlocking stuff for "completion". And at that stage, he/she has probably launched dozens of rockets and done an interplanetary transfer or two- repetitive things, you might notice. So if the new parts make those easier- great! That leaves more time to work on the actual mission.

And imposing your own restrictions is half the fun anyway. This is coming from a guy who never used a Mainsail or a LV-N

"Parts shouldnt be balanced for sandbox, even if they're unlocked so late in the game carear might as well be sandbox."

[UberFuber]

I would like to keep tossing this out.

1. Don't reduce thrust of new part.

2. Tweak the Isp profile of new part for what they're designed for, which is lifting heavy stuffs off Kerbin.

In that vein, keep the current thrust and Isp profile for atmospheric flight, but heavily nerf the vacuum Isp.

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

Rocket engines, specifically those with a bell-shaped nozzle, are designed with a specific atmospheric pressure in mind. Leave that specific atmospheric pressure, efficiency starts to go down. Our new SLS engine can be balanced by making its Isp in vacuum fairly horrible (say, 180 or 210). You still get quite a lot of benefit for SLS (that initial kick into LKO), but it would not be feasible to keep using it for the majority of your mission.

Come to think about, I remember hearing something from the KSP dev that the new SLS rockets are supposed to do just that, a distinct Isp profile that makes them fairly bad at vacuum but phenomenal as 1st stage kicking.

[Jouni]

Our new SLS engine can be balanced by making its Isp in vacuum fairly horrible (say, 180 or 210). You still get quite a lot of benefit for SLS (that initial kick into LKO), but it would not be feasible to keep using it for the majority of your mission.

The problem with that approach is that Isp currently scales linearly with air pressure. At 3500 m altitude, the Isp is around halfway between atmospheric and vacuum values.

[sal_vager]

I just want to remind you guys that even that is broken, in real life the thrust scales with air pressure, not the isp :/

[Red Iron Crown]

I just want to remind you guys that even that is broken, in real life the thrust scales with air pressure, not the isp :/

Both, actually. Fuel consumption stays constant, thrust and Isp increase as air pressure decreases.

[purpletarget]

I just want to remind you guys that even that is broken, in real life the thrust scales with air pressure, not the isp :/

Actually it's both. The ISP increases inverse to the air pressure, and that results in greater thrust, because IRL engines generally maintain a constant fuel mass flow throughout their operation (with a few notable exceptions)

[sal_vager]

Ahh right, thanks, I thought it was isp, but yeah it's fuel flow.

[WindShieIds]

I personally don't find it too overpowered, let's compare it to KW rocketry for example

[Rakaydos]

I personally don't find it too overpowered, let's compare it to KW rocketry for example

Lower thrust, but crazy high Thrust to weight and ISP?

[KASASpace]

As many have said, engines should fill a niche roll.

KR-2L: Upper Stage, generally meaning lower thrust (I'm thinking in between Mainsail and Skipper thrust) and good Isp (which it has)

KS-25 x4: First stage, generally meaning higher thrust (Lower it by about 250 KN is all I ask) and LOW Isp, like a Mainsail's or even less

That LRB: Booster, generally high thrust and low Isp (in between Skipper and Mainsail for thrust, and less than Mainsail Isp)

Anyways, those are my thoughts.

[Jouni]

As many have said, engines should fill a niche roll.

KR-2L: Upper Stage, generally meaning lower thrust (I'm thinking in between Mainsail and Skipper thrust) and good Isp (which it has)

KS-25 x4: First stage, generally meaning higher thrust (Lower it by about 250 KN is all I ask) and LOW Isp, like a Mainsail's or even less

That LRB: Booster, generally high thrust and low Isp (in between Skipper and Mainsail for thrust, and less than Mainsail Isp)

Anyways, those are my thoughts.

The KR-2L, the KS-25x4, and the LFB KR-1x2 are SLS parts, so it would make sense that they perform in a similar way as their inspirations.

The proposed liquid boosters using F-1A engines are about 66 m tall and 5.5 m wide. If we scale them down to 2.5-meter scale, we can simulate them with the LFB, two orange tanks, and a nosecone. The F-1A is a low-Isp first-stage engine (it's Isp is actually lower than Mainsail's), so it would make sense to reduce the Isp of the LFB. The real booster has TWR a bit over 1.6 at liftoff, which we could achieve with 1800-1900 kN of thrust, assuming that engine mass stays at 6 tonnes. So maybe the LFB part should provide 1900 kN of thrust with Isp 270/320.

The SLS first stage uses high-Isp engines with moderate thrust. The engines are actually so weak that the first stage can't even lift itself. With the same 1:2.2 scaling, we can build the first stage as a stack of 3 big fuel tanks, the KS-25x4 engine cluster, and a decoupler. The stack has a total mass of bit over 250 tonnes, meaning that the thrust should be no more than 2400 kN. The vacuum Isp of real LOX/LH2 engines goes up to around 460 s, while KSP engines peak at 390 s. This suggests a scaling factor of 1.18, leading to Isp 310/380 in KSP.

Now, I'm not sure what the KR-2L engine is supposed to be. It looks like the J-2X engine, but while the SLS upper stage will use 3 engines, the KR-2L is one big engine. Assuming that it should have similar performance to the cluster of 3 smaller engines, its vacuum Isp is about right. The engine, one big fuel tank, an ADTP-2-3 adapter, and a Rockomax decoupler make a reasonable imitation of the upper stage, with a total mass of around 90 tonnes. As the SLS upper stage should have initial TWR a bit over 1.1 without payload, we can reach it with 1000 kN of thrust.

There is some need for fine tuning, as the boosters are now very lightweigth compared to the core, and the entire rocket can barely lift off with 40 tonnes of payload. In the real SLS, a single booster has roughly the same mass and twice the thrust of the first stage, which we can't really replicate with stock fuels. This perhaps justifies the higher thrust values of the first-stage engines, as well as lowering their Isp. So, if we want to balance the SLS engines with the existing engines, while keeping the SLS feel, I would suggest the following changes:

KR-2L: Thrust 1000 kN.

KS-25x4: Fine as it is. Maybe lower Isp to 300/360 (or to 300/350 to match the Skipper).

LFB: Lower Isp to 270/320 or even to the real 270/300 values.

Edited April 7, 2014 by Jouni

[Whirligig Girl]

No, I would not reduce their thrust, and I think it's fine to be able to put a lot of mass into space with fewer parts.

What I would do is reduce the TWR, and by doing that, reducing the Delta V cap at TWR > 1, buff the total thrust a bit to compensate. What this means is that you would still be able to push a similar amount of mass to orbit with a single column + boosters.

The difference would be that you couldn't single stage a good fraction to orbit, because currently the size 3 engines can single stage the same fraction as other engines can if they ARE staged.

I mean... the KR-2L... what would the real world analog for this engine be? Like an kerosene engine with the ISP of a hydrolox engine? That'd be some pretty magical stuff.

It's only efficient is space, and it's thrust isn't great compared to the KS-25 4x Cluster. It's meant to be an F-1 and a J-2 engine, I think, but using 5 mainsails actually works better than the KS-25 Cluster.

[KASASpace]

The KR-2L, the KS-25x4, and the LFB KR-1x2 are SLS parts, so it would make sense that they perform in a similar way as their inspirations.

The proposed liquid boosters using F-1A engines are about 66 m tall and 5.5 m wide. If we scale them down to 2.5-meter scale, we can simulate them with the LFB, two orange tanks, and a nosecone. The F-1A is a low-Isp first-stage engine (it's Isp is actually lower than Mainsail's), so it would make sense to reduce the Isp of the LFB. The real booster has TWR a bit over 1.6 at liftoff, which we could achieve with 1800-1900 kN of thrust, assuming that engine mass stays at 6 tonnes. So maybe the LFB part should provide 1900 kN of thrust with Isp 270/320.

The SLS first stage uses high-Isp engines with moderate thrust. The engines are actually so weak that the first stage can't even lift itself. With the same 1:2.2 scaling, we can build the first stage as a stack of 3 big fuel tanks, the KS-25x4 engine cluster, and a decoupler. The stack has a total mass of bit over 250 tonnes, meaning that the thrust should be no more than 2400 kN. The vacuum Isp of real LOX/LH2 engines goes up to around 460 s, while KSP engines peak at 390 s. This suggests a scaling factor of 1.18, leading to Isp 310/380 in KSP.

Now, I'm not sure what the KR-2L engine is supposed to be. It looks like the J-2X engine, but while the SLS upper stage will use 3 engines, the KR-2L is one big engine. Assuming that it should have similar performance to the cluster of 3 smaller engines, its vacuum Isp is about right. The engine, one big fuel tank, an ADTP-2-3 adapter, and a Rockomax decoupler make a reasonable imitation of the upper stage, with a total mass of around 90 tonnes. As the SLS upper stage should have initial TWR a bit over 1.1 without payload, we can reach it with 1000 kN of thrust.

There is some need for fine tuning, as the boosters are now very lightweigth compared to the core, and the entire rocket can barely lift off with 40 tonnes of payload. In the real SLS, a single booster has roughly the same mass and twice the thrust of the first stage, which we can't really replicate with stock fuels. This perhaps justifies the higher thrust values of the first-stage engines, as well as lowering their Isp. So, if we want to balance the SLS engines with the existing engines, while keeping the SLS feel, I would suggest the following changes:

KR-2L: Thrust 1000 kN.

KS-25x4: Fine as it is. Maybe lower Isp to 300/360 (or to 300/350 to match the Skipper).

LFB: Lower Isp to 270/320 or even to the real 270/300 values.

I know about the SLS design, but I mentioned in general.

Really, the Core acts as a quasi-upper stage (Once Boosters detach).

Those kinds of changes are suitable.

[Nemoricus]

As an aside, would it be possible for someone to make charts like these that include the new engines and tanks? It might add another perspective on the current situation.

[GusTurbo]

The KR-2L, the KS-25x4, and the LFB KR-1x2 are SLS parts, so it would make sense that they perform in a similar way as their inspirations.

The proposed liquid boosters using F-1A engines are about 66 m tall and 5.5 m wide. If we scale them down to 2.5-meter scale, we can simulate them with the LFB, two orange tanks, and a nosecone. The F-1A is a low-Isp first-stage engine (it's Isp is actually lower than Mainsail's), so it would make sense to reduce the Isp of the LFB. The real booster has TWR a bit over 1.6 at liftoff, which we could achieve with 1800-1900 kN of thrust, assuming that engine mass stays at 6 tonnes. So maybe the LFB part should provide 1900 kN of thrust with Isp 270/320.

The SLS first stage uses high-Isp engines with moderate thrust. The engines are actually so weak that the first stage can't even lift itself. With the same 1:2.2 scaling, we can build the first stage as a stack of 3 big fuel tanks, the KS-25x4 engine cluster, and a decoupler. The stack has a total mass of bit over 250 tonnes, meaning that the thrust should be no more than 2400 kN. The vacuum Isp of real LOX/LH2 engines goes up to around 460 s, while KSP engines peak at 390 s. This suggests a scaling factor of 1.18, leading to Isp 310/380 in KSP.

Now, I'm not sure what the KR-2L engine is supposed to be. It looks like the J-2X engine, but while the SLS upper stage will use 3 engines, the KR-2L is one big engine. Assuming that it should have similar performance to the cluster of 3 smaller engines, its vacuum Isp is about right. The engine, one big fuel tank, an ADTP-2-3 adapter, and a Rockomax decoupler make a reasonable imitation of the upper stage, with a total mass of around 90 tonnes. As the SLS upper stage should have initial TWR a bit over 1.1 without payload, we can reach it with 1000 kN of thrust.

There is some need for fine tuning, as the boosters are now very lightweigth compared to the core, and the entire rocket can barely lift off with 40 tonnes of payload. In the real SLS, a single booster has roughly the same mass and twice the thrust of the first stage, which we can't really replicate with stock fuels. This perhaps justifies the higher thrust values of the first-stage engines, as well as lowering their Isp. So, if we want to balance the SLS engines with the existing engines, while keeping the SLS feel, I would suggest the following changes:

KR-2L: Thrust 1000 kN.

KS-25x4: Fine as it is. Maybe lower Isp to 300/360 (or to 300/350 to match the Skipper).

LFB: Lower Isp to 270/320 or even to the real 270/300 values.

I like these changes. They would seem to balance things better.

[Jouni]

KR-2L: Thrust 1000 kN.

KS-25x4: Fine as it is. Maybe lower Isp to 300/360 (or to 300/350 to match the Skipper).

LFB: Lower Isp to 270/320 or even to the real 270/300 values.

I forgot one point: KSP rockets lift larger payloads than real rockets. In SLS Block 2, the upper stage is roughly twice the size of the payload, making the combined TWR around 0.65-0.70. Considering that my SLS-style launcher lifts around 100 tonnes comfortably, and lowering the Isp of first stage engines would drop its capacity to around 90 tonnes, the upper stage engine would need 1200 kN of thrust for similar TWR. The KR-2L would still be clearly weaker than the Mainsail, while being useful as an upper stage engine for large payloads.

Generally I don't care too much about sandbox balance, but I won't complain, if we get balanced engines by basing them on some real engines.

[Dodgey]

As an aside, would it be possible for someone to make charts like these that include the new engines and tanks? It might add another perspective on the current situation.

Here you go.

[Nemoricus]

Here you go.

The tables and graphs in that thread aren't like the ones in my link, which shows the most efficient engine for a given payload mass, delta-v, and thrust-to-weight ratio.

[Dodgey]

They are the only ones I have seen floating around the forums.

[John FX]

Tweakables, that is all.

[Dodgey]

Tweakables, that is all.

That's as good of an argument as "just edit your config files" is. That is to say a very lously one.

[Muzza]

I strongly agree. The new parts make the game WAY to easy: on my first launch with them, I got an escape with 6Km/s... with what was meant to be the final stage of the launcher... The new parts easily put 200 tons in to orbit.

When I was launching, I was getting about 32 MN of thrust. In reality, the Saturn V had around 34 MN of thrust. The new parts are far to similar to real life parts. Which in most games would be great, as it is realistic. The big problem is that Kerbin isn't similar to earth. Low Kerbin satellites orbit at around 2.2 Km/s. This value is around 8 Km/s for Earth. That is more than 3.5 times greater. So why do the new parts not put real life parts to shame, yet achieving Kerbal orbit is a third easier? It is ridiculous!

Now, we don't have to use any of the old engines: we can get to the Moon with the KR-2L. What happened to the Poodle? We can get to Eeloo with the KR-2L. What happened to the Atomic rocket? It is madness!

I welcome the new parts. But there needs to be changes to the actual game, as in, making transfers take a greater amount of ^V. Then we have perfection.

Edited May 21, 2014 by Muzza

[Jouni]

The new parts made this possible.

I'm not complaining.