3.75 meter upper stage engine.

[SubzeroSpartan7]

We need a new engine for the 3.75 meter stacks, an upper stage. The KR-2L may be efficient in vacuum, but it is overpowered as an upper stage. Plus we only have two 3.75 meter engines to work with, so I kind of just want more engines to work with there.

[JPmAn]

I agree

10 char

[Frozen_Heart]

agreed as well

[Red Iron Crown]

What would the specs of such an engine be? In my experience, vacuum Isp is by far the most important spec for an upper stage engine, and the KR-2L is quite good in that respect. I'm not sure what is meant by "overpowered" here as higher TWR is better, all other things being equal.

[sal_vager]

If the engine is too powerful you can right click it and reduce the thrust limiter

[Bill Phil]

It is big for an upper stage engine... Maybe a smaller one similar to the Skipper but with a 3.75 meter attachment point. Or just add an upside down adapter that can run fuel too.

[King Arthur]

Last I checked, adapter parts have fuel lines running through them.

[Bill Phil]

Last I checked, adapter parts have fuel lines running through them.

The ones that you flip upside many last don't. Or did they fix that? It's like a one way fuel line.

[FishInferno]

i think that we should get a single KS-25 engine (from the 4-egine cluster) as a surface-attachable engine like those in AIES

[MKI]

The SLS parts are designed as a launch system, not much more.

There's a pretty small need for a 3.75 "lander"engine, and as you said the KR-2L is already efficient, just very strong. So you want a low weight, high efficiency 3.75 sized upper stage engine thats NOT the KR-2L. It sounds like to much of a niche item to want and not something dire necessary compared to other engine designs still missing.

[mattinoz]

Instead of an additional engine. What if the automatic engine farings sized themselves to match the part above and below them?

Then you could use one of the 2.5m engines in the upper part of the stack.

[Red Iron Crown]

Instead of an additional engine. What if the automatic engine farings sized themselves to match the part above and below them?

Then you could use one of the 2.5m engines in the upper part of the stack.

That would be amazing, and would make a lot of designs much more aesthetic. NecroBones has made some progress with resizable engine fairings in his SpaceY pack.

[SubzeroSpartan7]

If the engine is too powerful you can right click it and reduce the thrust limiter

Yeah I know. However the engine is huge and weighs quite a bit however it makes up for it in raw thrust. Reducing thrust will work, however size and weight and aesthetic is the biggest problems for me. Theoretically we only need one engine in the game that we can limit the thrust of but that isn't any fun.

[DancZer]

If the engine is too powerful you can right click it and reduce the thrust limiter

Reducing the thrust limiter and not the engine size/weight isn't the effective way of building rocket.

[Red Iron Crown]

Reducing the thrust limiter and not the engine size/weight isn't the effective way of building rocket.

When you come down to it, neither is a 3.75m upper stage. The inferior mass ratios of 3.75m tanks make them a poor choice for orbital craft; 2.5m parts are better in this regard. The 3.75m parts are designed for lifting heavy loads, the high TWRs and poor tank ratios are less of a penalty in lifters than they are in orbital craft.

[Slam_Jones]

I use the KR-2L all the time. Just lower the thrust so it's not such a ridiculous TWR

Edit: Didn't see the other replies >.>

[SubzeroSpartan7]

Instead of an additional engine. What if the automatic engine farings sized themselves to match the part above and below them?

Then you could use one of the 2.5m engines in the upper part of the stack.

Actually I would prefer that alternative highly. I'm not sure how that would work but if it can there would have to be a redesign of that feature completely.

[Jouni]

It's better to think upper stage engines in terms of mass instead of thrust, as excessive thrust can always be tweaked down.

For 1.25 m upper stages, we have three basic options: the LV-909 (0.5 tonnes), 2x-6x 24-7S (0.18-0.54 tonnes), and the LV-T30/45 (1.25/1.5 tonnes, depending on whether thrust vectoring is needed). An intermediate engine at 0.8-0.9 tonnes could be a useful addition, especially if you don't like the 6x 24-7S option.

For 2.5 m upper stages, we have a lot of options: 4x-6x 24-7S (0.36-0.54 tonnes), the Poodle (2 tonnes), the Skipper (3 tonnes), and sometimes even the Mainsail (6 tonnes). The main gaps where new engines could be useful are at 1 tonne and at 4-4.5 tonnes.

For 3.75 m upper stages, we only have the KR-2L (6.5 tonnes). It's good for burning an entire S3-14400 fuel tank quickly, but a 4-4.5-tonne engine could be useful for smaller upper stages.

If the game remains as it is, it needs one new 1.25 m engine, two 2.5 m engines, and one 3.75 m engine. On the other hand, if engine fairings and, even more importantly, connection nodes resized themselves to match the decoupler, we could do with just one new engine and changes to several existing engines:

• Increase the mass of the 24-77 to 0.1 tonnes.
  
• Reduce the thrust of the 48-7S to 20 kN and the Isp to 250/300 s.
  
• Add a new relatively low-profile 1.25 m engine with 100 kN of thrust, 0.8 tonnes of mass, and Isp between the LV-909 and the LV-T30/45.
  
• Make the LV-T45 a bit shorter than the Poodle.
  
• As the LV-T30/45 can now replace the Poodle in small 2.5 m upper stages, we can inrease the size of the Poodle to 2.5 tonnes / 300 kN.
  
• The size of the Skipper can also be increased to 4 tonnes / 900 kN.
  

[zekes]

We need a new engine for the 3.75 meter stacks, an upper stage. The KR-2L may be efficient in vacuum, but it is overpowered as an upper stage. Plus we only have two 3.75 meter engines to work with, so I kind of just want more engines to work with there.

Dependa on what you're using them for... I have thirteen of them on my Cira VI's upper stage