UI/UX Broken DeltaV with multiple engines and/or with side tank attached [fuel tank placement order messes up dV calculations]

[Niko_Dragovich]

Reported Version: v0.2.0 (latest) | Mods: none | Can replicate without mods? Yes 
OS: Windows 11 Pro | CPU: i5 13600KF | GPU: RX 7900 XTX | RAM: 32GB DDR5 6000 CL32

 

Hi.

It's very complicate for me to explain this bug. I'll try to explain it with screenshots in the video below. When I have 2 engines or more and/or with a radial tank, the deltaV of my stage is broken.

This video explain the bug on the VAB, you can stop the video to read the text.

Now, the problem in my mission in exploration mode. I add 8 radial tank and 8 engine behind them. So my deltaV is broken. I have ~3600m/s for a ~1100m/s manoeuver but I use all my hydrogen before I finish my manoeuver.

 

 

Included Attachments:

Edited December 22, 2023 by The Space Peacock

[Flush Foot]

On 12/23/2023 at 10:45 AM, HebaruSan said:

It's clearly not just leaving out the additional mass, because that would give the same delta V, not greater. Maybe it (also) thinks the exhaust velocity increases with the increasing thrust?

I would have to do some serious testing / investigating to know for certain, but my hypothesis is that the game says (using hypothetical numbers):

25t of fuel through one 0.5t engine = 2,000 m/s delta-v

25t of fuel through three 0.5t engines = 5,700 m/s delta-v (it recognizes increased engine mass BUT it believes each engine gets to run through the whole 25t of fuel, not 1/3 of 25t each)

[Scarecrow71]

Reported Version: v0.2.1 (latest) | Mods: Micro-Engineer; MapView Focus and Targeting; Maneuver Node Controller; Flight Plan; K2D2 | Can replicate without mods? Yes 
OS: Windows 11 | CPU: AMD Ryzen 9 3900 12 core | GPU: GeForce RTX 2060 Super | RAM: 32 GB

Created a craft to try and get to Duna.  Craft has a central stack of 2 X200-64 Methalox tanks sitting atop 2 Mainsail engines.  Radially attached to this are 4 X200-64 Methalox tanks, all 4 of which are topped with an RS-AD 800, and powered by a pair of Mainsail engines.  Fuel lines flow FROM radially attached tanks TO central stack.  All engines (2 central, 8 radial) are in Stage 1, with the decouplers for the radial tanks in Stage 2.  dV calculated on Stage 1 as 2558 m/s at 0 altitude in Kerbin atmosphere, but the dV calculated for Stage 2 is 0 even though there should be fuel/dV remaining in the central stack after separation of the radial tanks.  This calculation stays the same in the VAB and on the launch pad.  Images in the spoiler:

Spoiler

Removed the fuel lines, separating the 8 radial engines and the 2 central engines into their own separate stages.  dV recalculates as having 2562 m/s in Stage 1, with 1739 m/s in Stage 2.  This is at 0 km altitude on Kerbin.  Images in the spoiler:

Spoiler

 

Included Attachments:

TutankhamenI.json

[DibzNr]

@Scarecrow71Merged your report with this post

[Scarecrow71]

Reported Version: v0.2.1 (latest) | Mods: Most notable mods are Flight Plan, MapView Focus and Targeting, and K2D2 | Can replicate without mods? Yes 
OS: Windows 11 | CPU: AMD Ryzen 9 3900 12 core | GPU: GeForce RTX 2060 Super | RAM: 32 GB

I have a craft in LKO (~100km) that is supposed to be bound for Duna.  I'm using a medium hydrogen tank, with 6 radially attached small hydrogen tanks, and each small tank is outfitted with 2 small hydrogen engines.  According to the dV readout on the right side of the screen, this stage has 2329 m/s of dV remaining.  I created a maneuver to go to Duna, which is to end with a Pe of ~90km (which is pretty standard, at least for my flights).  According to the maneuver thing on the bottom of the screen, this maneuver should take 1121 m/s of dV, which should then leave me with over 1000 m/s of dV to circularize and maneuver so I can start the landing process.

However, the burn takes up all of the available fuel in the stage (all 2329 m/s), and the maneuver isn't finished being executed.  To complicate matters further, the burn timer shows that there is still 16 seconds remaining, with no indication of how much more fuel is needed to complete the burn.  If the maneuver calculation was correct, and the craft really did have 2329 m/s of dV/fuel when I started the burn, the maneuver should be done accurately.  Fuel consumption, maneuver burning, calculations...all wrong.  The video I attached shows this all happening.

Apologies in advance forthe length of the video (>1 minute, < 2minutes), but I do not use time warp while burning, and I wanted to show the entirety of what happens with this issue.

Included Attachments:

Ksp22024_02_02-07_59_18_01.mp4

TutankhamenI.json

[Spicat]

@Scarecrow71, merged your bug report.

[Anonymous Bug Reporter]

Reported Version: v0.2.1 (latest) | Mods: none | Can replicate without mods? Yes 
OS: Windows 11 | CPU: i9 13900k | GPU: Nvidia RTX 4080 | RAM: 64GB DDR5 5600MT/s

When in the VAB building a craft, only rarely does the game display the DeltaV or TWR of any of the stages, let alone all of them. I would say 90% of the time I have to guess. This doesn't make the game unplayable, but it certainly makes it a lot more difficult, feeling like the early days of KSP1 early access. It does sometimes carry over into flight, but usually only with crafts constructed in orbit from more than one launch. I have noticed sometimes the deltaV displayed is not correct even in flight though. Not sure exactly what causes it because it seems random to me.

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[Anonymous Bug Reporter]

Reported Version: v0.2.1 (latest) | Mods: none | Can replicate without mods? Yes 
OS: Microsoft | CPU: amd5080 | GPU: nividia 3080 | RAM: 32 gigs corsair

The Delta-V and Thrust to weight ratio displayed in the VAB under the engineering report are the wrong numbers. I made a rocket with a 1.4 thrust to weight ratio and it wouldnt even leave the launch pad.

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[Aiurwarrior1]

Reported Version: v0.2.1 (latest) | Mods: BepInEx, UITK, SpaceWarp, Community Fixes, Flight Plan, K2-D2, Kerbal Headlamp, Maneuver Node Controller, Node Manager, Orbital Survey, Patch Manager, Premonition, Wayfarers Wings | Can replicate without mods? Yes 
OS: Windows 10 Home | CPU: Intel i5-10600K @ 4.10Ghz | GPU: NVIDIA GeForce GTX 3060 | RAM: 16 GB
 

Severity: Low (Can be worked around) Frequency: High (Can reproduce consistency with and without mods, with different combinations of parts)

Description: When using multiple engines in a stage with multiple fuel tanks, delta-v calculates differently based on the order and size of the fuel tanks in the stage.

I was building a Falcon-9 style recoverable first stage, and was adding tanks to give more delta-v for recovery when I noticed that it was not reaching the expected delta-v. I'd added a "X200-32" to the top of a stack of "x200-64" tanks, noted the additional Dv, and then swapped it out for an X200-64. To my surprise the Dv went down instead!

I tested multiple fuel tank combinations and found that the Dv calculates wrong when there's a smaller tank below a larger tank, or two of the same size tank. However, when there are smaller tanks above larger tanks it calculates correctly (or at least gives a higher Dv result)! I also tested with single engines vs multiple, and the bug does not appear to occur with single engine builds.

 

Included Attachments:

Spoiler

Edited March 1 by The Space Peacock

[The Space Peacock]

@Aiurwarrior1 merged your report

[magnemoe]

I wonder if wrong dV values after undocking my lander at Duna is related. 
Lander with over 2800 m/s dV shows up as having only 1139 m/s so less than half, tanks are full so this is an miss calculation, more so that doing an 120 m/s burn reduces my dV with less than 60 m/s. 
Burn indicator indicates much shorter burn than needed so it looks like it think lander is much lighter than it is, micro engineer report correct full and dry weight but same dV. 

Lander dock with mothership to refuel from metalox tanks and then undock, mothership uses nuclear engines but has to stagable metalox engines to burn off leftover fuel going home. 
Bug is permanet, restarting the game, trying to undock again and it does not solve it. its also consistent, transferred the monoprop in lander to mothership and dV went up a bit. 

I did not have this bug at Ike, but did only one docking, first landing was an decopling and the second landing was with reduced fuel as it was an single landing. 
 

[magnemoe]

Reported Version: v0.2.1 (latest) | Mods: K2-D2, Micro Engineer, Maeuver Node Controller, Node Manager, orbital survey. | Can replicate without mods? Yes 
OS: Windows 10 | CPU: AMD Rysen 9 5950X | GPU: 3070ti | RAM: 64 GB

Doing an series of landing at Duna to farm science.  Lander who has over 2800 m/s vacuum dV show up as having less than 1200 m/s.

Her after deorbit and landing.  It appear that the game believe craft has much less fuel than it has as burn times is far to short. This is visual only but consistent, an 120 m/s dV burn just used less than 60 m/s.  Interesting K2-D2 calculate correct burn time, disabling mods does not change dV readings. 

This happened after I docked with mothership and moved from Ike to Duna. Here is lander and mothership at Ike, has docked and partially refueled lander and undocked again. 

 Has performed multiple landings and docking around Duna but this bug persist. I disabled the engine on lander for Duna transfer. Tried to not enable engine after first undocking at Duna, also staging engine and so on. Mothership has spare metalox for lander and also none active metalox engines for burning off reminding metalox if this is an reason. 

The low dV values shown is mostly confusing and can cause issues trying to make an circulation burn as it typically show 400 m/s then I get into space again. 

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[Spicat]

@magnemoe, merged your bug report.

[magnemoe]

32 minutes ago, Spicat said:

@magnemoe, merged your bug report.

Ok so this is an known issue  

[allanp11]

I had a similar/related issue yesterday (17/03/24 in case you're reding this in the future!).

My interplanetary stage, consisting of a double stack of medium hydrogen tanks with a double stack of 8 small hydrogen tanks around the outside, with a total of 9 NERV engines on the bottom, plus it's payload on top) had just over 4000 deltaV, but when I did a roughly 1000 deltaV burn it used up just over half of my 4000 deltaV. I wondered if the VAB was giving me the wrong DeltaV figure but when I calculated it myself using the rocket equation (would be nice if the VAB stage info showed the end mass, not just the start mass), I got roughly the same deltaV figure, so the VAB actually gave me the correct number in this case, but still, most of my fuel was used up when it shouldn't have been. I also had the issue where burning the full length of the maneuver plan produced a result that was quite far off the intended, meaning I had to burn a bunch more fuel, and I noticed that during flight the DeltaV figure would rapidly change up and down.

If you're wondering, I did manage to get Jeb and Bob back from a Duna polar orbit (seriously, that Duna monument mission is tough for a first interplanetary mission!) with only about 1000 DeltaV with a maneuver node that took a painfully long time to get right (fine tuning can't come soon enough) and 3 aerobrake attempts!

[Anonymous Bug Reporter]

Reported Version: v0.2.1 (latest) | Mods: none | Can replicate without mods? Yes 
OS: Win 11 | CPU: AMD 5900HX | GPU: RTX 3080 | RAM: 32GB

DeltaV for initial stages is calculated correctly

Once we get to the third stage (Hydrogen engines) it reads out zero (0) dV and zero thereafter despite setting it as "vacuum" - this gives an incorrect reading of only ~4400 dV despite the craft having 10k dV in orbit

Included Attachments:

12kmohofinalalmost.json