Deep Space Methalox Engines...Are Terrible

[Scarecrow71]

In my exploration game, I have recently unlocked Deep Space Methalox, which includes the Tuba, Trumpet, and Cornet engines.  The description on the Tuba includes the following statement:

Unlike its namesake, the LV-3000 "Tuba" is elegant and graceful and designed for superior performance in a vacuum.

Horse hockey.  The Tuba has an ISP of 385, but only pushes out 510.0 kN of thrust.  It also weighs 5 tons and has an impact tolerance of 6 m/s.  By comparison, the Skipper engine has an ISP of 322, but pushes out 600.00 kN of thrust, with a weight of 3 tons and an impact tolerance of 10 m/s.  I'd like to know exactly how the Tuba is better than the Skipper in this instance.  If you really want to compare apples to apples, take a look at the Trumpet (same size class):  ISP of 382, 160 kN of thrust, mass of 1.65 tons, and an impact tolerance of 6.0 m/s.

I spent all those science points for these lousy engines?  I can put multiple darts or vectors on something and get better results.  Heck, I can put 10 Twitch engines on something to get the same thrust, and only take up 1 ton of mass.

What is the purpose of the deep space methalox engines?  Is it to make you do 10 minute burns?  Did they just feel the need to suck 2800 science points away from you?  Like, can someone give me an honestly good reason why these engines even exist, and what the purpose is other than filling out the tech tree?

[The Aziz]

Didn't see you comparing TWR and dv for a given payload+fuel mass though. Thrust and ISP are barely values to determine the final results that actually matter.

[Scarecrow71]

1 hour ago, The Aziz said:

Didn't see you comparing TWR and dv for a given payload+fuel mass though. Thrust and ISP are barely values to determine the final results that actually matter.

There is no need to do that, though.  They are heavier and have less thrust than other engines in their class.  Yes, the slightly higher ISP would mean a bit more dV.  But the added weight and lower thrust would mean longer, less efficient burn times.

[Superfluous J]

I've not made it to the bigger LV engines yet but so far with the basic one I've been similarly unimpressed.

I make a ship with the LV, make it again with regular methalox engines, I get lower mass, higher TWR, and more dV.

I recall in KSP1 the nukes didn't get good until you were really pushing massive payloads around, so maybe I've just not built big enough yet.

[MechBFP]

1 hour ago, Superfluous J said:

I've not made it to the bigger LV engines yet but so far with the basic one I've been similarly unimpressed.

I make a ship with the LV, make it again with regular methalox engines, I get lower mass, higher TWR, and more dV.

I recall in KSP1 the nukes didn't get good until you were really pushing massive payloads around, so maybe I've just not built big enough yet.

They are essentially useless if you have a nuke, because similarly you need a large mass to make them useful, and it you have a large mass then nukes are superior in every way that matters at that point. 

[Scarecrow71]

8 minutes ago, MechBFP said:

They are essentially useless if you have a nuke, because similarly you need a large mass to make them useful, and it you have a large mass then nukes are superior in every way that matters at that point. 

I'm actually less impressed with the hydrogen engine than I am with the DSMs.  I only have the small H2 engine unlocked, but it is terrible.

I'm trying to build a craft to drop a rover on Tylo right now, and I'm just lacking in dV and TWR.  Need to rethink what I'm doing, primarily because all of these engines aren't very good.

[MechBFP]

5 minutes ago, Scarecrow71 said:

I'm actually less impressed with the hydrogen engine than I am with the DSMs.  I only have the small H2 engine unlocked, but it is terrible.

I'm trying to build a craft to drop a rover on Tylo right now, and I'm just lacking in dV and TWR.  Need to rethink what I'm doing, primarily because all of these engines aren't very good.

As long as you are using them for deep space purposes only (I assume you aren’t trying to land with them, but you did bring up their impact tolerance…) then they will be better than all other methalox engines for that same purpose. But it sounds like you aren’t using them for their intended role. 

Edited March 15 by MechBFP

[magnemoe]

3 minutes ago, MechBFP said:

They are essentially useless if you have a nuke, because similarly you need a large mass to make them useful, and it you have a large mass then nukes are superior in every way that matters at that point. 

The cornet is pretty nice for an heavy probe, use the trumpet for my Tylo probe lander.  But they are not very good for landing because of their length. Does not matter for my lander as I just tip it over and release the rover. 

Nuclear engines are for pushing heavy stuff to other planets. Stuff like multiple landers. Some has used the large one on landers but its an very heavy engine 

[steveman0]

Not sure why you so haphazardly gloss over the massive ISP difference. The tuba example compared to the skipper has nearly 20% more ISP. This translates to roughly 20% lower fuel consumption. This means if your rocket is carrying any more than 10t of fuel in the stage it will be more fuel efficient overall than the 2t lighter skipper and only gets better the more fuel you have. This can allow a reduction in total craft weight for a given dV budget enabling a better overall TWR than the skipper for a larger scale rocket.

[Presto200]

I also realized I haven't used the Tuba or Trumpet engines pretty much since the first week or two they were released, I hope the devs see this and make a couple tweaks. Their goal should be to make no engine "obsolete" and to make sure each one has a purpose and a time where the player would want to use it. They are cool to see animation wise but I wish I felt the need to use them more.

[Scarecrow71]

11 hours ago, MechBFP said:

I assume you aren’t trying to land with them, but you did bring up their impact tolerance…

I brought up impact tolerance only to show the differences in the engines.  I am in no way trying to land on them.  Now, there are engines I will try to use as landing gear, but not these.

9 hours ago, steveman0 said:

Not sure why you so haphazardly gloss over the massive ISP difference. The tuba example compared to the skipper has nearly 20% more ISP. This translates to roughly 20% lower fuel consumption. This means if your rocket is carrying any more than 10t of fuel in the stage it will be more fuel efficient overall than the 2t lighter skipper and only gets better the more fuel you have. This can allow a reduction in total craft weight for a given dV budget enabling a better overall TWR than the skipper for a larger scale rocket.

I am aware of the change in dV, and that, despite the added weight, the deep space engines all named after musical instruments do in fact give more dV.  However, the increase in dV does not equal an increase in efficiency, especially when attempting to use that fuel to slow down and orbit a celestial body.  For example, Jool (or one of its moons).  Coming in hot, I don't want to have to deal with a 10+ minute burn that will very likely not end with the circularization or even Ap/Pe I'm shooting for.  I'd rather have something far more efficient at slowing my craft down.  This really comes into play when you create maneuvers that can get you "free" encounters with the moons, such as when needing to go to Tylo.  That long burn from the DSM engines will most likely not work as well as the others.

This again falls into the category of "Expensive mid-game stuff that you are likely to never use but need to unlock to either complete the tech tree or unlock other nodes after it".  If the engines were to really be used in deep space, the thrust would be in line with paying for something that costs all those science points.  Regardless of the ISP, I will never use an engine that gives so little thrust unless I'm landing on Gilly or some other body that has a really low gravity/density.  For all other bodies, I'm going to take the higher thrust engines every single time.  And while I cannot speak for anyone else, I'm quite sure I'm not the only one.

[The Aziz]

The whole, entire point of deep space engines is that you don't need high thrust in the middle of nowhere. A tradeoff for increased efficiency.

I've been doing maneuvers around Jool moons and the planet itself using nothing but two basic hydrogen engines. Easy. Higher thrust? Yeah that's reserved for landing attempts, not orbital operations.

12 minutes ago, Scarecrow71 said:

However, the increase in dV does not equal an increase in efficiency,

Those two are synonyms.

13 minutes ago, Scarecrow71 said:

Coming in hot, I don't want to have to deal with a 10+ minute burn that will very likely not end with the circularization or even Ap/Pe I'm shooting for. 

That's on you then, no problem with the engine. Long burns can be quite accurate unless for some reason someone is still using the questionable KSP1 technique.

[Scarecrow71]

Just now, The Aziz said:

Those two are synonyms.

You took what I said out of context.  An increase in dV does not equal an increase in efficiency when burning said fuel.  Longer burns with more fuel do not necessarily equate to more efficient burns.

Just now, The Aziz said:

That's on you then, no problem with the engine. Long burns can be quite accurate unless for some reason someone is still using the questionable KSP1 technique.

I don't use the KSP1 technique in KSP2.  When the timer hits 0, I start the burn, aiming (mostly) at the maneuver marker on the SAS globe-thingy (is there an actual name for it?).  I do tend to slow down near the end of the burn timer, dropping from 100% slowly so as to not overshoot the burn or the fuel it says I need to use.  But longer burns are not better.  In my experience; your mileage may vary.

[MechBFP]

2 hours ago, Presto200 said:

I also realized I haven't used the Tuba or Trumpet engines pretty much since the first week or two they were released, I hope the devs see this and make a couple tweaks. Their goal should be to make no engine "obsolete" and to make sure each one has a purpose and a time where the player would want to use it. They are cool to see animation wise but I wish I felt the need to use them more.

I think their usage will be much more applicable once resources are in the game, as presumably nukes will be more difficult to obtain resources for. 

[MechBFP]

2 hours ago, Scarecrow71 said:

You took what I said out of context.  An increase in dV does not equal an increase in efficiency when burning said fuel.  Longer burns with more fuel do not necessarily equate to more efficient burns.

We would need a graph of single burns done at different attitudes between the two ships when capturing into an orbit to see if/when there is a trade off between the two.

I highly doubt that burning at a higher orbit (which reduces the Oberth effect but improves the maneuver efficiency) with the higher ISP engines would be worse in the majority of that graph.  I suspect that you would almost always be better off in the vast majority of that graph in fact. 

Edited March 15 by MechBFP

[Presto200]

1 hour ago, MechBFP said:

I think their usage will be much more applicable once resources are in the game, as presumably nukes will be more difficult to obtain resources for. 

Good Point, gotta think of the big picture

[Darta01]

4 hours ago, Scarecrow71 said:

An increase in dV does not equal an increase in efficiency when burning said fuel.  Longer burns with more fuel do not necessarily equate to more efficient burns.

The idea of longer burns being less efficient is wrong and comes from the inefficient way the maneuver node is computed. I'm sorry for the shameless self-promotion, but I wrote a post about this with Delta-V examples : Change the maneuver tool to compute the predicted path in the moving orbital frame

Basically, you can perform maneuvers with roughly the same Delta-V regardless of the TWR (except when the burn duration is critical of course, like landing phases), if you perform the maneuver well enough, which is NOT following the maneuver node. 

As was said by @The Aziz, the point of deep space engines is to maximize the Delta-V of your spacecraft, where you don't care about the TWR. There are well suited for lunar and interplanetary transfers, but not low orbit. Indeed nuclear engines may be more adequate, but hydrogen tanks are bulkier and don't use the same resources

Edited March 15 by Darta01

[The Aziz]

18 minutes ago, Darta01 said:

Indeed nuclear engines may be more adequate, but hydrogen tanks are bulkier and don't use the same resources

But are much, MUCH lighter. Same size hydrogen tank with a Nerv will give 3 times more dv than an efficient methalox engine. And will weigh few times less, allowing smaller launch vehicle. I pretty much switched to hydrogen for most deep space missions, except maybe Duna because the requirements for a there and back trip are so low.

[magnemoe]

47 minutes ago, Darta01 said:

The idea of longer burns being less efficient is wrong and comes from the inefficient way the maneuver node is computed. I'm sorry for the shameless self-promotion, but I wrote a post about this with Delta-V examples : Change the maneuver tool to compute the predicted path in the moving orbital frame

Basically, you can perform maneuvers with roughly the same Delta-V regardless of the TWR (except when the burn duration is critical of course, like landing phases), if you perform the maneuver well enough, which is NOT following the maneuver node. 

As was said by @The Aziz, the point of deep space engines is to maximize the Delta-V of your spacecraft, where you don't care about the TWR. There are well suited for lunar and interplanetary transfers, but not low orbit. Indeed nuclear engines may be more adequate, but hydrogen tanks are bulkier and don't use the same resources

This, also being able to do an capture burn inside the SOI but that is hardly an problem.  This require splitting the burn up into multiple parts. 
Been thrown stuff all day at Eve. an .3 twr nuclear engine looses less than 200 m/s over doing must of the burn on an mammoth 2 core stage. one single burn. 

For landing KSP 2 nodes give us an tool who can have you moving slowly at low attitude, make an braking burn but also with an up vector who end your burn 1-2 km above surface. Move at some speed as the Tylo moves you need to adjust for this at end of main braking burn. 
But again the tuba will loose against nuclear engines but it might be restrictions on them in future like radiation and getting uranium. But its not like you use up an nuclear thermal engine unless its designed for an short lifespan. You don't design jet engines for cruise missiles to last for thousands of hour  

[steveman0]

6 hours ago, Scarecrow71 said:

For all other bodies, I'm going to take the higher thrust engines every single time

This seems to demonstrate that you dom't know the value of isp for optimizing your rocket and mission. While a higher TWR can help in some cases, the extent of this is far less than you are thinking. Certainly far less than the benefit of 20% overall fuel efficiency especially since the increased fuel efficiency allows you to carry less fuel for a higher mission TWR. The example you originally cited with the skipper would have the skipper having far longer burn times because you'd have to carry more fuel (mass) for an equivalent journey. You can't look at engine thrust on it's own.

[Darta01]

13 hours ago, The Aziz said:

But are much, MUCH lighter. Same size hydrogen tank with a Nerv will give 3 times more dv than an efficient methalox engine. And will weigh few times less, allowing smaller launch vehicle. I pretty much switched to hydrogen for most deep space missions, except maybe Duna because the requirements for a there and back trip are so low.

I don't remember where they are placed in the tech tree, I guess there are further than deep space methalox engines, right? It would be the only way to balance it for now, since we don't have resource gathering nor radiators yet (nuclear engines should procude a lot of heat so your spacecraft would weigh more due to radiators)

I'd say it's very realistic: IRL nuclear engines are OP in terms of ISP compared to conventional rocket engines. The reasons why we don't use them are engineering difficulties, heat management and the risk at launch if the rocket explodes. These difficulties don't exist in KSP, except for heat management but it is pretty easy to do in the game.

[Scarecrow71]

15 hours ago, steveman0 said:

This seems to demonstrate that you dom't know the value of isp for optimizing your rocket and mission. While a higher TWR can help in some cases, the extent of this is far less than you are thinking. Certainly far less than the benefit of 20% overall fuel efficiency especially since the increased fuel efficiency allows you to carry less fuel for a higher mission TWR. The example you originally cited with the skipper would have the skipper having far longer burn times because you'd have to carry more fuel (mass) for an equivalent journey. You can't look at engine thrust on it's own.

I love that the simple answer anyone ever gets is "You are playing the game wrong".  In a game that is all but explicitly defined as being able to play any way you want, making a comment about what someone perceives in the game is simply playing it wrong.  Forgive me for not wanting to take 10 minutes to slow down, or that I'd like to have a higher TWR.  My bad for thinking that the DSM engines are pointless due to their low TWR.  I'm fully aware that a higher ISP in a vacuum means more dV.  None of that means I should blindly just agree that the engines are awesome and should be used.  I spent 2800 science points to get them; they should give me some benefit that makes me want to use them other than "You may get some fuel efficiency out of them, even though they are heavier and have lower thrust".

But, you know, I'm playing the game wrong.  

[Wheehaw Kerman]

Late to the party, but the Horn Section’s superior ISP may become very important when we have the rest of the game in place, and resource constraints in the hinterboonies make fuel efficiency paramount.

[MirageNL]

1 hour ago, Scarecrow71 said:

But, you know, I'm playing the game wrong.  

You're not necessarily playing the game wrong. If you want to put a Mammoth engine on everything because you want its superior thrust, then that's your call. You're just wrong to expect DSE's to provide sufficient thrust for tight orbital maneuvers. That's not what they're meant for: they're DEEP space engines, for long (fuel) efficient burns.

I think the problem is that DSE's are unlocked too late in the tech tree. They come way after the Nerv and only just before the Swerv. They then try to fill a niche between orbital and nuclear engines that isn't really there. Whenever resources, heat and maybe radiation become issues, that might change though.

[MirageNL]

19 hours ago, Darta01 said:

The idea of longer burns being less efficient is wrong and comes from the inefficient way the maneuver node is computed.

Well, burns are  more efficient the closer they are near periapsis (Oberth effect), so it's not entirely untrue. The fixed node direction just makes it  worse. However, I'm not sure at what point TWR would outweigh Isp in that regard.