Engine spin-up/spin-down and minimum throttles, and RCS

[HephaistosFnord]

KSP2 engines should probably have more realistic power-on sequence times, to differentiate engines like the Puff (instant-on, full throttle range, no lag) from say the Mammoth (probably at 60% thrust minimum and several seconds of spin-up time and a maximum throttle change of 10% per second or so).

Any engines that are sufficiently "instantaneous" (so all the monoprop some of the smaller methalox) should have the RCS "advanced controls" button so they can be tied to yaw/pitch/roll, lateral/dorsal/fore/aft, and forward throttle controls.

 

[The Aziz]

Nah, leave that to mods.

[Guest]

I like this! It would need careful tuning so it’s fun though!

[HephaistosFnord]

I can already anticipate most of the objections, but ultimately we need a reason for lower-performance engines to continue to exist, and the higher-performing engines already typically get used at mostly full throttle in most applications.

[The Aziz]

Lower performance as in ISP or thrust, or something else?

[GluttonyReaper]

Having messed with mods in the past that add similar mechanics... I'm kinda split on this. I like that it makes big lifter engines feel a lot more powerful when you have to let them spool up to full throttle before launching, but it does get a bit old after a while if you're launching a bunch of rockets, and I'm not really sure it fits the stock "vibe".

15 minutes ago, HephaistosFnord said:

I can already anticipate most of the objections, but ultimately we need a reason for lower-performance engines to continue to exist, and the higher-performing engines already typically get used at mostly full throttle in most applications.

Sure, but arguably KSP1 managed to let most engines exist pretty comfortably in their niches without this quite successfully - I'm not really sure it's worth restricting them even further just to justify the existence of manoeuvring engines. In general, I think that KSP should err on the side of generosity rather than tight restrictions, and this definitely feels it would start to walk down the path of "There is one objectively correct way to build you spacecraft, and any deviation will be heavily penalised". That said, I wouldn't be opposed to there being a minimum thrust limit on some engines at least... it was always a bit odd to me that KSP1's infinite thrust limiting meant you could theoretically use your lifting Mainsail for docking.

37 minutes ago, HephaistosFnord said:

Any engines that are sufficiently "instantaneous" (so all the monoprop some of the smaller methalox) should have the RCS "advanced controls" button so they can be tied to yaw/pitch/roll, lateral/dorsal/fore/aft, and forward throttle controls.

No opposition to this, though, if anything the game should let you tie any engine you want to RCS. The opposite would be great too, for smaller craft there's no real reason you couldn't tie your RCS engines to your main throttle instead of having any liquid fuel.

[HephaistosFnord]

32 minutes ago, GluttonyReaper said:

Having messed with mods in the past that add similar mechanics... I'm kinda split on this. I like that it makes big lifter engines feel a lot more powerful when you have to let them spool up to full throttle before launching, but it does get a bit old after a while if you're launching a bunch of rockets, and I'm not really sure it fits the stock "vibe".

Sure, but arguably KSP1 managed to let most engines exist pretty comfortably in their niches without this quite successfully - I'm not really sure it's worth restricting them even further just to justify the existence of manoeuvring engines. In general, I think that KSP should err on the side of generosity rather than tight restrictions, and this definitely feels it would start to walk down the path of "There is one objectively correct way to build you spacecraft, and any deviation will be heavily penalised". That said, I wouldn't be opposed to there being a minimum thrust limit on some engines at least... it was always a bit odd to me that KSP1's infinite thrust limiting meant you could theoretically use your lifting Mainsail for docking.

No opposition to this, though, if anything the game should let you tie any engine you want to RCS. The opposite would be great too, for smaller craft there's no real reason you couldn't tie your RCS engines to your main throttle instead of having any liquid fuel.

My phone isnt letting me reply point-by-point, but:

 

- "Skip Countdown" should just timewarp past the spool-up phase, so you dont have to sit through the process every time

 

- "fore by throttle" already lets you tie rcs to throttle, its pretty great

- "maneuvering engine" should definitely be a whole category, which includes all current RCS modules + the Puff + most of the radial methalox engines. All of them should get the full RCS advanced controls; other engines shouldnt.

 

(This also would let the Puff be used as a REALLY BIG linear RCS port)

32 minutes ago, GluttonyReaper said:

Having messed with mods in the past that add similar mechanics... I'm kinda split on this. I like that it makes big lifter engines feel a lot more powerful when you have to let them spool up to full throttle before launching, but it does get a bit old after a while if you're launching a bunch of rockets, and I'm not really sure it fits the stock "vibe".

Sure, but arguably KSP1 managed to let most engines exist pretty comfortably in their niches without this quite successfully - I'm not really sure it's worth restricting them even further just to justify the existence of manoeuvring engines. In general, I think that KSP should err on the side of generosity rather than tight restrictions, and this definitely feels it would start to walk down the path of "There is one objectively correct way to build you spacecraft, and any deviation will be heavily penalised". That said, I wouldn't be opposed to there being a minimum thrust limit on some engines at least... it was always a bit odd to me that KSP1's infinite thrust limiting meant you could theoretically use your lifting Mainsail for docking.

No opposition to this, though, if anything the game should let you tie any engine you want to RCS. The opposite would be great too, for smaller craft there's no real reason you couldn't tie your RCS engines to your main throttle instead of having any liquid fuel.

 

[GluttonyReaper]

2 minutes ago, HephaistosFnord said:

- "maneuvering engine" should definitely be a whole category, which includes all current RCS modules + the Puff + most of the radial methalox engines. All of them should get the full RCS advanced controls; other engines shouldnt.

They probably should, yeah - but I still feel like the convenience of them is enough to make them worthwhile without hobbling other engines, in a way that makes the game a fair bit more complex. I disagree on the RCS front... I'm a big fan of the game letting you make your own mistakes. Mainsails are obviously a terrible choice for RCS control, but that's something the player should find out themselves in a fun way, rather than the game arbitrarily deciding which engines "count". Plus, there's no actual reason that someone couldn't use Terrier engines as RCS thrusters on a really large craft, and that's definitely not something I want the game to stop people from doing.

[HephaistosFnord]

Just now, GluttonyReaper said:

They probably should, yeah - but I still feel like the convenience of them is enough to make them worthwhile without hobbling other engines, in a way that makes the game a fair bit more complex. I disagree on the RCS front... I'm a big fan of the game letting you make your own mistakes. Mainsails are obviously a terrible choice for RCS control, but that's something the player should find out themselves in a fun way, rather than the game arbitrarily deciding which engines "count". Plus, there's no actual reason that someone couldn't use Terrier engines as RCS thrusters on a really large craft, and that's definitely not something I want the game to stop people from doing.

Well yes, Terriers definitely should have RCS control.

 

The reason I object to the Mainsail in particular is that anything with a long spinup /spindown should be precluded from RCS, bc it simply wouldnt be able to respond in real-time.

 

Basically RCS capability for an engine should be a tradeoff against thrust, based on the size and design of the engine's turbopumps.

[The Aziz]

22 minutes ago, HephaistosFnord said:

- "Skip Countdown" should just timewarp past the spool-up phase, so you dont have to sit through the process every time

I never had the countdown on. It's just a waste of time, so is waiting for the engine to start.

[HephaistosFnord]

So, the proper additional values for an engine to have, which could easily be overridden by difficulty settings, are:

- flow minimum ("0% throttle" isn't "0% thrust" - if a rocket's flow minimum is half its flow maximum, then setting throttle to 0% means the rocket operates at half power)
- throttle inertia (if the throttle is currently at 25%, and you increase it to 100%, how many seconds does it take for the engine to throttle up to the new setting?)
- cold start time (the amount of time between activating an engine and it being ready to provide thrust)
- RCS-capable (boolean for whether the engine provides an "advanced controls" sub-panel that lets you tie it to RCS)
 

At low to medium difficulties, flow minimum and cold start time can both be 0, and throttle inertia can be set to infinity, duplicating the current settings.

At high difficulty, flow minimum, throttle inertia and cold start time can all be based on the engine's size and turbopump technology, so that engines like the Puff can be instant-on/instant-off with infinite no-worries restarts, and engines like the Mainsail can be "fire up on the pad, stay at near-100% throttle all the way into space, and then once it's shut down it's done for this mission".

RCS-capable should be based on flow minimum/throttle inertia/cold start time, but if difficulty settings disable those features the engine still keeps its RCS-capable boolean.

(Snip)

Edited December 17, 2023 by Gargamel
Portions redacted by moderator

[Bej Kerman]

On 12/15/2023 at 5:00 PM, HephaistosFnord said:

ultimately we need a reason for lower-performance engines to continue to exist

Ultimately they don't  need a reason to exist when you have better technology. How many times have you used a Commodore Amiga in the past week? They're obsolete and don't have a use in day-to-day life anymore - and yet we don't see laws being passed saying "we need a reason for obsolete computers to exist". You've asserted "we need a reason for x to exist" without explaining why.

If you really want to use low performance engines, play Science mode. Otherwise, they shouldn't be shoved down our throats.

[The Aziz]

2 hours ago, HephaistosFnord said:

"0% throttle" isn't "0% thrust" - if a rocket's flow minimum is half its flow maximum, then setting throttle to 0% means the rocket operates at half power

Great way to confuse players. 0 isn't 0.

 

[18Watt]

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