How do the v1.4 & DLC engines rank against our old favorites?

[Cunjo Carl]

  While I intend this to be a general place to beam/gripe/talk/ponder about the new engines, my spark to the conversation is some pretty charts that show how the new engines compare to the rest. Ultimately, these new engines will be like new golf clubs in our caddy, which is exciting! Let's see how exactly these new engines will fit into our day to day rocket building.

  How do the DLC engines rank against our old favorites?
 
  There's a lot to choosing a rocket engine, like cost, gimbal, size... But at the end of the day, our choice will typically boil down to: "How well does it push?". In other words, for a required TWR, what's the most mass efficient engine? And does it happen to be one of the new ones ??? The following charts answer that question using a handy value called effective ISP. If you're not feeling in the mood for math, the bottom line is BIGGER IS BETTER! If you do want some math, effective ISP takes all the complicated bits out of the rocket equation, so deltaV = Isp_Eff*g₀*ln(m_payload/m_wet). This effective Isp is a direct measurement of the stage's mass efficiency, and conveniently your whole rocket's mass efficiency is just the weighted average of the stages' . (Rocket Mass Efficiency = sum(Isp_Eff,i*X_i)/sum(X_i) where X_i = ln(m_Payload,i/m_wet,i) ) . Bigger is better .
 
  On to the action! Here's our old favorites, sorted by size.  (Values measured in vacuum)

         
 
  And here's the new engines shown with a couple old ones as a backdrop for reference.
Note the NEW values from, which have come with the DLC release! The old plot is in the below spoiler for continuity reasons.

Edit: Alright, Cheetoh gets to be a Cheetah now. It's had a notable TWR buff! Most of the engines are quite similar their prerelease values the vacuum TWR and ISP department, which means we'll actually get to use the wildly powerful Skiff and Wolfhound! There's been one additional change which doesn't show up on the chart, and that's Mastadon's TWRs have been changed from (ASL,Vac) (265,290) to (280,290), which means it will be THE engine for Eve assent. Looks like there's an atm curve defined for Mastadon which makes it not very helpful for Eve ascent... Aww man... Lastly, there's one new radial engine named Cub! It's cute, and has saving for its cost has very nice stats for a radial engine. While much more expensive than Thud or Twitch, it's also vastly superior with a slight downside of its gimbal meaning you'll need 3+ for proper gimballed control.
 

Spoiler

 

Pre-release engine stats

Definitely not a misspelling on cheetoh there.  Holy heck though, Wolfhound and Skiff blow everything out of the water!
I hope it stays that way long enough for us to try them out .

 

 To get these efficiencies, your stages need to be the right size. How big is shown in the following charts...

Spoiler

 

With either chart, divide your required TWR by your engine's TWR to get the value on the x-axis. You can use the chart on the left to size the stage by its deltaV (using a resource like KER) by multiplying the chart value by your engine's Isp. Note, this is where the '2000m/s per stage' design rule comes from! Alternatively, you can use the chart on the right to pick the masses of your payload fuel and engine using either of the 2 sets of lines. The sizing doesn't need to be exact because the optimum is nice and broad. So as long as you're anywhere close you'll be fine. That said, if you need to be way different, it's better to be on the side of higher deltaV or in other words smaller payload fraction. SRBs and Twinboar are exceptions to this, so let me know if you're interested in those!

      

  Generally, using stages sized for maximal efficiency will give you the most mass efficient rocket, but there is 'one weird trick' (tm) to help low efficiency stages not drag back your rocket as much as they normally would. An example might be a rocket that goes terrier -> spiders, or vector -> thuds. It turns out you can eke a bit better rocket efficiency by making the less efficient stage a little smaller than their optimum size (~~100m/s less deltaV), and the more efficient stages a bit bigger than their optimum size (~~150m/s more deltaV). Perhaps not that weird of a trick "get more of the good stuff".

 

 

Part2:  It's a new dawn for ion propulsion thanks to new lighter Xenon tanks!

The Xenon tanks in v1.4 now have much lower drymass, which provides a nice advantage for ion based rockets. The real win for this is that the lower drymass makes ions much more tenable for use in SSTOs! As a note, the Dawn engines in the above chart are assumed to each be paired with .075tons of energy storage+production, which is a low but reasonable ammount.

 Right now the DLC engine values are from Scott Manley's video. I suspect the values will move around a bit, and I'll do my best to keep the chart updated. For the moment, our only conversation option is "pining", but hey the release is only a few days away!

EDIT: Direct download link for the pictures used here.

Edited March 14, 2018 by Cunjo Carl

[Ty Tan Tu]

The Skiff could be my new Poodle.

[Gaarst]

The Wolfhound is a 400kN, 412s Isp, better looking Poodle... obscenely overpowered.

Edited March 9, 2018 by Gaarst

[F3ARSTUNTS]

They made my precious ion engine less overpowered by lowering the fuel capacity in the tanks. Oh well. 

[Cunjo Carl]

45 minutes ago, Gaarst said:

The Wolfhound is a 400kN, 412s Isp, better looking Poodle... obscenely overpowered.

I was also pretty surprised by the 412 Isp. I'm wondering if it'll make it to the final release? It's possible they balanced it with a specific rocket or mission in mind... Here I'm thinking an Apollo to the Mun story mission, or something to that effect. If it does make it in, I think a lot of challenges will need to make separate categories for DLC vs non-DLC like we've been doing for stock vs mod. As a speed runner though, I have to say, I could really use an over powered poodle. That would be just dandy!

 

44 minutes ago, F3ARSTUNTS said:

They made my precious ion engine less overpowered by lowering the fuel capacity in the tanks. Oh well. 

Great news, it's actually the other way around! Ion engines are much better now thanks to the new tanks. The tanks all have just a smidge more fuel, and their drymass has gone from 44% (Yuck, ewww, ack!) to 25% which will let ion crafts go dramatically faster and farther. I should mention, your current ion craft won't be automatically updated. The new tanks are technically new parts, and so you'll need to go through your crafts in the VAB/SPH and swap out the tanks to get the upgrade. Out with the old, in with the new!

[F3ARSTUNTS]

Just now, Cunjo Carl said:

Great news, it's actually the other way around! Ion engines are much better now thanks to the new tanks. The tanks all have just a smidge more fuel, and their drymass has gone from 44% (Yuck, ewww, ack!) to 25% which will let ion crafts go dramatically faster and farther. I should mention, your current ion craft won't be automatically updated. The new tanks are technically new parts, and so you'll need to go through your crafts in the VAB/SPH and swap out the tanks to get the upgrade. Out with the old, in with the new!

Wow! I just downloaded the update and didn't know this! Many thanks!

[Gargamel]

12 hours ago, Cunjo Carl said:

I could really use an over powered poodle.

I may be 40, but I still giggled like a 13 year old at that. 

[Archgeek]

On 3/8/2018 at 10:09 PM, Cunjo Carl said:

Ion engines are much better now thanks to the new tanks. The tanks all have just a smidge more fuel, and their drymass has gone from 44% (Yuck, ewww, ack!) to 25% which will let ion crafts go dramatically faster and farther.

Holy crap!  I can't wait to see how vastly this improves my 100km/s monstrosities.

[Frozen_Heart]

Depending on the form factor of some of these engines, but they might work as a Vector replacement in some of my capital ships.

[klesh]

I found it odd that alot of the preview players on youtube claimed they needed to remove fuel from some of their tanks in order to get their Saturn V mock-ups in the air.  Perhaps they were overbuilding them.

[Temeter]

On 9.3.2018 at 3:59 AM, Gaarst said:

The Wolfhound is a 400kN, 412s Isp, better looking Poodle... obscenely overpowered.

IMO the Poodle was always a bit underpowered, even after the buff. Sure it makes a solid orbital engine, but IMO the poodle should rather be an upper stage launcher engine. Think a 2.5m stack, the lower stage a Mainsail, the upper stage a Poodle. Sounds natural, doesn't it? Smart design to teach beginners how to do rockets.

But no! I've went through much experimenting, and there is just not way to use for a poodle upper stage without wasting a bunch of money/weight. Kerbins circularization burns are just too short to support something with thrust that weak; and the Skipper is obviously too heavy and powerful for an upper stage.

So a Wolfhound might finally be an engine that you can put above a 2.5m lifter stage and not feel silly.

On 9.3.2018 at 5:09 AM, Cunjo Carl said:

I was also pretty surprised by the 412 Isp. I'm wondering if it'll make it to the final release? It's possible they balanced it with a specific rocket or mission in mind... Here I'm thinking an Apollo to the Mun story mission, or something to that effect. If it does make it in, I think a lot of challenges will need to make separate categories for DLC vs non-DLC like we've been doing for stock vs mod. As a speed runner though, I have to say, I could really use an over powered poodle. That would be just dandy!

It's the J2-type engine, isn't it? Was 421 Isp in real life. Hard to truly balance without H2 and boiloff systems.

[Tyko]

It looks like your attachments have disappeared from your original post?

[Gaarst]

1 hour ago, Temeter said:

It's the J2-type engine, isn't it? Was 421 Isp in real life. Hard to truly balance without H2 and boiloff systems.

It's an SPS analogue... The "actual" J-2 has something like 340s Isp, I know it's stupid.

As for the Poodle, I personally find it sometimes too powerful as an orbital engine and not enough as an upper stage engine. Plus it's ugly; so I usually end up using Terriers or boosting my first stage/boosters so that it does most of the work to orbit, and use an orbital stage with abysmally low TWR once up there. It's not the most efficient way to get to orbit, but I prefer my rockets looking nice (ie realistic) than to cling to a few more decimals in my payload fractions.

Edited March 12, 2018 by Gaarst

[Hans Dorn]

58 minutes ago, Tyko said:

It looks like your attachments have disappeared from your original post?

Weird.

 

I still can see them.

[Temeter]

3 hours ago, Gaarst said:

It's an SPS analogue... The "actual" J-2 has something like 340s Isp, I know it's stupid.

I've just checked. The actual J-2 is actually a weaker engine, strangely enough.

J-2 Skiff is 1 ton, 330 ISP and 300kn. Sounds like a case for the ablancing team^^'

LV91 also looks a bit weak. Very low thrust for minimally better ISP compared to normal 1.25m engines, straightup downgrade from an aerospike. Otherwise balancing looks fine.

Quote

As for the Poodle, I personally find it sometimes too powerful as an orbital engine and not enough as an upper stage engine. Plus it's ugly; so I usually end up using Terriers or boosting my first stage/boosters so that it does most of the work to orbit, and use an orbital stage with abysmally low TWR once up there. It's not the most efficient way to get to orbit, but I prefer my rockets looking nice (ie realistic) than to cling to a few more decimals in my payload fractions.

IMO the Aerospike makes both an excellent upper stage and orbital engine, it's become a real powerhouse after it's buff. Also much easier to place and make artificial shrouds via payload bays.

Edited March 12, 2018 by Temeter

[KerikBalm]

I don't like this "effective Isp" calculation. I think its much better to present maximum dV for a given minimum TWR, assuming a 9:1 wet:dry mass for the tanks (For the LFO engines)

[Cunjo Carl]

7 hours ago, Tyko said:

It looks like your attachments have disappeared from your original post?

Could be that your system doesn't like my image host, Postimage? I don't know why that would be, but I'll be updating the pictures tomorrow, so if they're still missing after that I'll host a direct download link to the pictures too.

 

9 hours ago, Archgeek said:

Holy crap!  I can't wait to see how vastly this improves my 100km/s monstrosities.

Right? Imagine something like turbopumped's 100km/s ion sundive run again in v1.4! Of course I wouldn't dream of this, but it's also possible to use this extra efficiency to make the mega rockets smaller....

 

8 hours ago, Temeter said:

IMO the Poodle was always a bit underpowered, even after the buff. Sure it makes a solid orbital engine, but IMO the poodle should rather be an upper stage launcher engine. Think a 2.5m stack, the lower stage a Mainsail, the upper stage a Poodle. Sounds natural, doesn't it? Smart design to teach beginners how to do rockets.

But no! I've went through much experimenting, and there is just not way to use for a poodle upper stage without wasting a bunch of money/weight. Kerbins circularization burns are just too short to support something with thrust that weak; and the Skipper is obviously too heavy and powerful for an upper stage.

It's the J2-type engine, isn't it? Was 421 Isp in real life. Hard to truly balance without H2 and boiloff systems.

For simple single stack rockets I totally agree, it's tricky to squeeze the poodle in unless you were planning to use it for some interplanetary/KSO burns as well. I was very surprised though in one of the more recent cost-to-LKO competitions, there was a 2 stage kickback->Poodle craft that narrowly edge out the more standard kickback->twinboar and kickback->skippers. So, I guess the answer is moar (tm) boosters.

For the Wolfhound (J2-Type), it would be kinda fun to mimic boiloff by having the engine constantly leak fuel like probes constantly use power.  I think in practice it would probably drive me nuts, though...

 

3 hours ago, Temeter said:

LV91 also looks a bit weak. Very low thrust for minimally better ISP compared to normal 1.25m engines, straightup downgrade from an aerospike. Otherwise balancing looks fine.

Agreed, with any luck it will be a very low tech engine.

 

2 hours ago, KerikBalm said:

I don't like this "effective Isp" calculation. I think its much better to present maximum dV for a given minimum TWR, assuming a 9:1 wet:dry mass for the tanks (For the LFO engines)

I also like the maximum dV calculation! It's a great first order look at rocket efficiency, and can be calculated just by typing formulas into google. Effective Isp is a quite similar but second order look which accounts for one additional detail, which is payload. While I present it kinda slapdash here ('cause it wasn't the main focus), effective Isp does have a mathematical underpinning I could share if you wanted. Anyways, the maximum dV calculation is equivalent to a single stage rocket without a payload, but our actual rockets have payloads, and so they need more thrust (=engines) than the maximum dV calculation accounts for. This means in real rockets, engine TWR is a little more important than the maximum dV calculation shows. Just like any first and second order analysis, the difference between the two techniques is generally not very great.

 

10 hours ago, klesh said:

I found it odd that alot of the preview players on youtube claimed they needed to remove fuel from some of their tanks in order to get their Saturn V mock-ups in the air.  Perhaps they were overbuilding them.

I also find that surprising. Relative to the Mamoth, the F1 equivalent Mastadon looked a little anemic on TWR, but not that badly.  Maybe it's the huge fuel tanks they're trying to push like you say. I remember hearing stories that SaturnV gently meandered off the launch pad relative to many modern rockets, so perhaps the DLC isn't far from the truth!

[Archgeek]

1 hour ago, Cunjo Carl said:

Right? Imagine something like turbopumped's 100km/s ion sundive run again in v1.4! Of course I wouldn't dream of this, but it's also possible to use this extra efficiency to make the mega rockets smaller....

HEH, yes, yes, that was cool, but I've had a brachistochrone Eve transfer in the offing for a while now.  My pre-1.4 designs breach 100.2km/s in 22 stages and 170 tonnes using ~4500m/s stages, but only really need ~60km/s for the mission, which they can overshoot by 3.3km/s in 13 stages for for only 28 tonnes.

I'm guessing the new tankage numbers aren't on the wiki yet.  Where might I find them?  I look forward to seeing by how much they beat the old .44 ratio.

[Renegrade]

2 minutes ago, Archgeek said:

 Where might I find them?  I look forward to seeing by how much they beat the old .44 ratio.

They are extracting it from a Scott Manley video.  I haven't seen it yet, but I'm sure he hovers over the stat panes for a moment to look at the engines or such and they scribbled the numbers down...

[Cunjo Carl]

27 minutes ago, Archgeek said:

HEH, yes, yes, that was cool, but I've had a brachistochrone Eve transfer in the offing for a while now.  My pre-1.4 designs breach 100.2km/s in 22 stages and 170 tonnes using ~4500m/s stages, but only really need ~60km/s for the mission, which they can overshoot by 3.3km/s in 13 stages for for only 28 tonnes.

I'm guessing the new tankage numbers aren't on the wiki yet.  Where might I find them?  I look forward to seeing by how much they beat the old .44 ratio.

Tada! @Renegrade is correct for everything except this, which we happen to have in ksp 1.4 already. The old masses are .413 empty, .938 full. And, the new masses are .19empty, .76 full.

 

 
       Version 1.3 Xenon tanks (44%) vs...                                Version 1.4 (25%)

 

[Archgeek]

6 minutes ago, Cunjo Carl said:

Tada! @Renegrade is correct for everything except this, which we happen to have in ksp 1.4 already. The old masses are .413 empty, .938 full. And, the new masses are .19empty, .76 full.

 

 
       Version 1.3 Xenon tanks (44%) vs...                                Version 1.4 (25%)

 

Holy heck, not only is that a better ratio than before, that's .05 more tonnes of xenon per tank!  With no changes to the spreadsheet other than to the big xenon tank (were the other two likewise improved?), those two monsters achieve 116km/s and 68.3km/s respectively, or 103.4km/s in 19 stages for 92.7 tonnes and 63.4km/s in 12 stages for only 20.6 tonnes.  Numbers that no doubt get a lot scarier if I optimize and move the S10 engines down a few stages.

[Cunjo Carl]

4 minutes ago, Archgeek said:

 (were the other two likewise improved?)

Yep, the other two were improved in step with the big tank, at least in terms of drymass/fullmass. I need to break some bad news to you though, the tanks don't automatically update in v1.4. You'll need to go through and swap them all out for the new ones. It makes sense they did this for compatibility reasons. If you're doing a re-optimization anyways, perhaps not that big of a deal. So, brachistochrone to Jool?

Oh, also I was poking in my calculator to pull up the fuel values anyways, so I ran the mass optimal stage sizings, and it looks like v1.4 stages are ~40-50% more deltaV than the old v1.3 ones for most reasonable TWRs and asparagus-levels. Might be a good starting place to check in your reoptimization? Best of luck! I'm curious to see this thing when you get it going again.

[KerikBalm]

4 hours ago, Cunjo Carl said:

I also like the maximum dV calculation! It's a great first order look at rocket efficiency, and can be calculated just by typing formulas into google. Effective Isp is a quite similar but second order look which accounts for one additional detail, which is payload. While I present it kinda slapdash here ('cause it wasn't the main focus), effective Isp does have a mathematical underpinning I could share if you wanted. Anyways, the maximum dV calculation is equivalent to a single stage rocket without a payload, but our actual rockets have payloads, and so they need more thrust (=engines) than the maximum dV calculation accounts for. This means in real rockets, engine TWR is a little more important than the maximum dV calculation shows.

I still don't see how you're arriving at "effective Isp" (which is a term I'm familiar being used for jet engine specific impulse, and a related effective exhaust velocity).

The Isp is fixed. Engine TWR is fixed. Payload is variable. More importantly, Payload as a fraction of total dry mass is variable. dV required for the payload is variable. You're going to have to give a more detailed mathematical explanation, because I really have no idea what you're trying to show here. You haven't given a rigorous definition of "effective Isp".

 

Edited March 13, 2018 by KerikBalm

[Renegrade]

4 hours ago, Cunjo Carl said:

Tada! @Renegrade is correct for everything except this, which we happen to have in ksp 1.4 already. The old masses are .413 empty, .938 full. And, the new masses are .19empty, .76 full.

 

 
       Version 1.3 Xenon tanks (44%) vs...                                Version 1.4 (25%)

 

Oh yeah, 1.4 has some of the changes in it.

Just beware that there are some other issues with tanks at present.  So it's possible the new tank values might be wrong

[Frozen_Heart]

Which engine is the Skiff from the DLC?