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[1.7.3, 1.8.x] Modular Segmented SRBs


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Gene looked at the reports and sighed. How did it come to this... again???
Gathering everything together, he stomped into the main briefing room, looked around coldly at everyone, then slammed the pile of reports onto the table, sending papers flying all across the room.
"The budget projects for the next project are out of sight.... Again!!!"
"It's those darned SRBs, they're too big..." Bill replied meekly.
"They're still cheaper than making complete rockets" Bob continued even more softly...
Gene just glared...
"I have an idea," von Kerman raised his hand, and all eyes turned on him. "Why don't we make the SRBs the same way we make rockets; in parts"
Gene looked exasperated. "Because rockets use LIQUID FUEL!!!"
Werhner took a deep breath and smiled slyly....
"So?"
Gene rolled his eyes, "How do you intend to fuel the SRBs on the pad???  They ARE solid, you know!"
von Kerman just smiled and continued unphased.
"Why don't we make standard sized modules, fill them with the solid propellant, and then stack them together. Just like we stack the liquid tanks"
Gene took a deep breath.  Everyone shrank back, expecting an explosion.  No explosion happened, other than Gene turning a bit greener.
"Ummm, explain yourself", Gene grumbled, then sighed in resignation. "Please".
"The thrust of an SRB is determined by how long it is." Von Kerman explained  "So, we stack segments to get the desired length... and Voila'"
Everyone watched amazed as Gene's eyes crisscrossed a few times, then slowly focused back on von Kerman.
"You have a week to make it happen..." 

Reviewed by Kottabos

Features

  • SRB segments, 2, 4 and 8 meters long.  One part for each diameter using PartVariants
  • 3 different engine styles, two parts for each engine, PartVariants used to scale engine to different sizes
  • Nosecones with built in parachutes and sepratrons, two parts, PartVariants used to scale engine to different sizes
  • Visual alarm in editor if SRB stack is too tall, outsized SRB stack gets highlighted
  • Abort mode, nosecones separate from stack, causing thrust be cancelled out by gases spewing from open stack
  • Failure modes if SRBs are made too long
  • Thrust directly relates to height, taller = more thrust
  • Two thrust models, one which matches stock thrust, one which matches BetterSRBs (about double stock)
  • Dev/test mode for testing, enables actions and PAW event to trigger engine failure
  • Audible alarm when engine failure occurs
  • SRB stack experiencing engine failure gets highlighted

Parts

There are two types of parts, each uses the PartVariant in a different manner.

Segments (aka tanks).  There is one part for each of the 4 diameters available.  Each part can be either 1 segment long, 2 segments long or 4 segments long.  The length of a segment depends on the diameter of the part:

 

Diameter Segment Length
0.625m 1m
1.25m 2m
1.875m 3m
2.5m 4m

End parts, including NoseCone and Motors.  There is one part for each, the PartVariants for these scale the part to the different diameters available.

A word of explanation.  The parts are set up this way to minimize the number of parts in the mod.  There are currently 12 parts in the mod.  If I were to have a nosecone for each size, that would add an additional 6 parts for no real benefit.  Same goes for the motors

Fuel

Currently there is only one type of solid fuel available.  In a future release, there may be an additional one or two fuel types added

Usage

Segments can be stacked on each other, and the part variant selected even while stacked together.  Be sure to put a motor on the bottom, and something on top, either a nosecone or something else

Thrust vs Duration

SRBs generate thrust by the burning of the solid fuel.  The more surface area is exposed inside the SRB, the more will burn and the end result will be greater thrust.
The duration of the burn, however, will depend on how thick the amount of fuel is.  So, to get a longer burning SRB, you need to make it fatter.  
Additionally, fatter SRBs will end up with a larger exposed surface on the inside, so a fatter SRB will actually have  more thrust than a skinny one of the same length.


Important Information about mass and dV

Solid fuel by definition does not flow.  In order to make this work properly, I've had to create two resources.  They are both hidden, but knowing what they are is necessary to understand some odd behaviour.
In order to allow vessels to be designed correctly, the fuel has to be in the tank segment .  In order to calcualate the dV correctly, the fuel has to be in the motor.
So what happens is that in the editor, all fuel is normally put into the motor.  When the CoM marker is shown, the fuel is moved into the tank segments,

In the flight scene, the fuel is in the tank for proper balance.  Because of this, at this time, the ISP, Thrust, TWR and Burn time are not correct in either the KSP info, MechJeb or KER.  When the SRB is running, the ISP, Thrust and TWR will be correct


Models have been made by @SuicidalInsanity
Consultative services provided by @OhioBob

Availability:

Dependencies

 

Edited by linuxgurugamer
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It appears that you don't have a nose cone, or something else on top, so the exhaust of the SRB is able to escape upwards as well as downwards..

 

If not, please provide the craft file for me.

 

2 hours ago, OhioBob said:

Congratulations on the release.  I'll have to check it out.

(edit)  I'm experiencing the same issue as described by @ddavis425.

 

Craft file, please

2 hours ago, OhioBob said:

Congratulations on the release.  I'll have to check it out

well, it is only a beta :-)

 

Edited by linuxgurugamer
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While I won't be able to confirm this, I suspect that you may have a part on top which might be confusing.

One think I think I need to add is a SRB cap, which would cap the top of the SRB and allow other parts to be placed on top. What may be happening is that the mod doesn't see a recognizable top (ie:  nosecone) and is making the mistake of assuming that the top is open

You can confirm this (or not) by putting on one of the nosecones

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14 hours ago, ddavis425 said:

I just downloaded and made a test rocket with a 1.25m diameter, 8m long fuel segment and a Minuteman nozzle and the engine does not appear in the staging, and upon launch the rocket is firing smoke upwards into the air and cannot be activated.

b78668f672.png

 

2 hours ago, OhioBob said:

Congratulations on the release.  I'll have to check it out.

(edit)  I'm experiencing the same issue as described by @ddavis425.

 

Please install the dependency I forgot to list:

Dependencies

 

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1 minute ago, linuxgurugamer said:

Please install the dependency I forgot to list:

Dependencies

Hopefully that will fix it.  Because I just ran a test and was about to report that the problem is the same with or without a nosecone.  I'll test again with the dependency.

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@linuxgurugamer, I just ran a bunch of tests and most things seem to be working.  As long as something is attached to the top it works fine; with nothing the exhaust escapes from both top and bottom.

Here are some issues that I see:

  • The long nozzles are suppose to include an integrated fuel section, but I see no difference between long and short.  The in-flight KER readout shows the same mass and thrust with either.
  • When using the long nozzle, the in-flight KER readout shows a specific impulse of 0.0s.
  • Some of the exhaust plumes seem to be off a bit.  They generally look to me like they start too high up on the booster.

 

Edited by OhioBob
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I'll look into the integrated segments, thanks

Same for the in-flight KER, might be related to the above.

Re. the exhaust plumes.  I've been trying to keep the number of parts at a minimum, but to fix this, I'll have to change the part variants for the motors from size to length, and then have one part of each for each size.

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The exhaust plumes are the least of my concerns, but I thought I'd mention it.  The integrated segments, however, needs a look.  I did see the thrust change in the KER readout when swapping nozzle in the VAB, but not in flight mode.  And I don't think the mass changed in either VAB or flight mode.

I also did a flight test with both nozzles and saw no difference in performance between them.

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  • 2 weeks later...

Testing this out, I've found a few bugs
-Reverting to launch has a tendency to instead switch focus to the next vessel in flight, in my case, a discarded lander in orbit around Duna; this tends to happen more often than not following a crash or RUD, ratherthan simply resetting while in optimal flight or on the pad.
-Parachutes don't work. This comes in two flavors. 1) They don't generate any braking force when deployed; 2) the fuel segment variants animation breaks.*
-1.875m STS is not properly scaled, it still has 1.25m scaling.
-Motor-with-fuel-segment variants engine nozzles cannot be adjusted.*
* This is due to the Stock part variant system only grabbing animation info for the first model loaded. Since these models weren't originally created with jamming them together via partVariant in mind, I'll see about converting them, either to work with the stock variant system, or B9 PartSwitch.
Now, admittedly, the following are from deliberately trying to break things and likely outside the 'average' user purview:
-Placing 2 SRMs on a stack - (e.g. placing a fuel segment, placing a motor on the bottom as usual, then placing a second motor, upside down, on top to burn the candle at both ends), when launched, causes the game to jump to an ethereal Otherspace dimension. (there a name for this? Void Kraken? SubSpace Kraken?)Empty starfield, map doesn't work. Game can be reverted to launch or VAB, subsequent launches result in all textures being see through. Log is spammed with 'look rotation viewing vector is zero', if that helps.
-Placing a motor on a vessel without a fuel segment above it, if staged, also summons the SubSpace Kraken like above.

Also, question from a gameplay PoV: when a stack is sundered and fire starts spewing out from every exposed fuel segment node, should that be producing SRM levels of thrust? There's no nozzle/combustion chamber focusing and directing the gas expansion of the fuel deflagration, wouldn't any generated thrust be lower? Alternatively, shouldn't that result in a reduction of thrust from the SRM, due to sudden loss of pressure?

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17 hours ago, SuicidalInsanity said:

Reverting to launch has a tendency to instead switch focus to the next vessel in flight, in my case, a discarded lander in orbit around Duna; this tends to happen more often than not following a crash or RUD, ratherthan simply resetting while in optimal flight or on the pad.

Strange.  Nothing like what I was testing.  I'll have to place some other vessels around and test that

17 hours ago, SuicidalInsanity said:

-Parachutes don't work. This comes in two flavors. 1) They don't generate any braking force when deployed; 2) the fuel segment variants animation breaks.

I wonder if both flavors are related to the following:

17 hours ago, SuicidalInsanity said:

* This is due to the Stock part variant system only grabbing animation info for the first model loaded. Since these models weren't originally created with jamming them together via partVariant in mind, I'll see about converting them, either to work with the stock variant system, or B9 PartSwitch.

Worst case, I can split them into two parts.  I'm trying to avoid using another mod, if possible.

17 hours ago, SuicidalInsanity said:

1.875m STS is not properly scaled, it still has 1.25m scaling

Easy enough, thanks.

17 hours ago, SuicidalInsanity said:

Placing 2 SRMs on a stack - (e.g. placing a fuel segment, placing a motor on the bottom as usual, then placing a second motor, upside down, on top to burn the candle at both ends), when launched, causes the game to jump to an ethereal Otherspace dimension. (there a name for this? Void Kraken? SubSpace Kraken?)Empty starfield, map doesn't work. Game can be reverted to launch or VAB, subsequent launches result in all textures being see through. Log is spammed with 'look rotation viewing vector is zero', if that helps.

I assume both SRMs were in the same stage?  I'll see if I can replicate, and then, if I can, will try the same thing with liquid engines.  

17 hours ago, SuicidalInsanity said:

Also, question from a gameplay PoV: when a stack is sundered and fire starts spewing out from every exposed fuel segment node, should that be producing SRM levels of thrust? There's no nozzle/combustion chamber focusing and directing the gas expansion of the fuel deflagration, wouldn't any generated thrust be lower? Alternatively, shouldn't that result in a reduction of thrust from the SRM, due to sudden loss of pressure?

Yes.  I was having some issues with it, so figured that it was a disaster anyway, and that somewhat minor details like that weren't too significant.  In reality, the way I tried to set it up, the open top would have about 70% of the thrust of the bottom.  I was also concerned with fuel flow and rate, was trying to keep the final burn times of the damaged boosters roughly the same.

Thank you for testing and these excellent reports

Edited by linuxgurugamer
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17 minutes ago, linuxgurugamer said:
18 hours ago, SuicidalInsanity said:

Placing 2 SRMs on a stack - (e.g. placing a fuel segment, placing a motor on the bottom as usual, then placing a second motor, upside down, on top to burn the candle at both ends), when launched, causes the game to jump to an ethereal Otherspace dimension. (there a name for this? Void Kraken? SubSpace Kraken?)Empty starfield, map doesn't work. Game can be reverted to launch or VAB, subsequent launches result in all textures being see through. Log is spammed with 'look rotation viewing vector is zero', if that helps.

I assume both SRMs were in the same stage?  I'll see if I can replicate, and then, if I can, will try the same thing with liquid engines

I know what's going on here.  Both motors are competing for the same resources.  Interestingly enough, this doesn't happen if you use the motor variant which has the attached fuel segment.  I'll have to think about how to handle this, it's an edge case I hadn't thought of.

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22 hours ago, SuicidalInsanity said:

-1.875m STS is not properly scaled, it still has 1.25m scaling.

Minuteman had the same issue.

This dual engine thing is weird, going to take a little bit of digging to figure it out.  I found that it's only one engine which is causing it, so far in my testing it was the top engine, but that may just be the way I added the parts.

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On 10/8/2019 at 8:52 PM, SuicidalInsanity said:

Reverting to launch has a tendency to instead switch focus to the next vessel in flight, in my case, a discarded lander in orbit around Duna; this tends to happen more often than not following a crash or RUD, ratherthan simply resetting while in optimal flight or on the pad.

This is odd.  I'm trying to replicate, but so far, no luck.

Can you be a bit more specific?  Save file would help, I suppose.  Also some specifics about the rocket in question.  A craft file would also be helpful.

I've just finished crashing about 20 vessels, in one form or another and haven't seen that happen.

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On 10/8/2019 at 8:52 PM, SuicidalInsanity said:

-Placing 2 SRMs on a stack - (e.g. placing a fuel segment, placing a motor on the bottom as usual, then placing a second motor, upside down, on top to burn the candle at both ends), when launched, causes the game to jump to an ethereal Otherspace dimension. (there a name for this? Void Kraken? SubSpace Kraken?)Empty starfield, map doesn't work. Game can be reverted to launch or VAB, subsequent launches result in all textures being see through. Log is spammed with 'look rotation viewing vector is zero', if that helps.
-Placing a motor on a vessel without a fuel segment above it, if staged, also summons the SubSpace Kraken like above.

Found and fixed this problem.  There was a divide-by-zero, causing the vessel to instantly attain an infinite amount of speed, etc.

On 10/8/2019 at 8:52 PM, SuicidalInsanity said:

Reverting to launch has a tendency to instead switch focus to the next vessel in flight, in my case, a discarded lander in orbit around Duna; this tends to happen more often than not following a crash or RUD, ratherthan simply resetting while in optimal flight or on the pad.

It's possible the same error (and fix) for the SubSpace Kraken listed above was causing this.  Please try the new beta I'll be releasing in a few minutes

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New Beta, 0.0.0.2

  • Fixed missized Minutman and STS engines
  • Fixed duplicated crashTolerance in nosecones
  • Fixed typo in crashTolerance in segment_0625 and segment_125
  • Fixed following edge cases, caused by a divide by zero error:
    • Placing 2 SRMs on a stack - (SRM + segment + SRM (upside down)) when launched, causes the game to jump to an ethereal Otherspace dimension. (there a name for this? Void Kraken? SubSpace Kraken?)Empty starfield, map doesn't work. Game can be reverted to launch or VAB, subsequent launches result in all textures being see through. Log is spammed with 'look rotation viewing vector is zero', if that helps.
    • Placing a motor on a vessel without a fuel segment above it, if staged, also summons the SubSpace Kraken like above.
  • Added Known-Issues.txt file
  • Added new subdirectory called Ships, will contain sample ships.  Currently has Kerbal-X with SRBs

You can get it here:

https://github.com/linuxgurugamer/ModularSegmentedSRBs/releases/tag/0.0.0.2

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New beta, 0.0.0.5

https://github.com/linuxgurugamer/ModularSegmentedSRBs/releases/tag/0.0.0.5

  • More part model updates
  • Fixed missing sepratrons in nosecone
  • Fixed missing transform topNode in the MinuteMan motor (was preventing top thrust after damage)
  • Fixed configs for 1.875 & 2.5m nosecones
  • Fixed top node of MinuteMan motor
  • First stab at fixing the thrust of open ends and motor ends, seems to be mostly working
  • Fixed all node sizes
  • Adjusted position of thrust effects for many motors
  •  

Open Issues

Issue:    Reverting to launch has a tendency to instead switch focus to the next vessel in flight, in my case, a 
        discarded lander in orbit around Duna; this tends to happen more often than not following a crash or RUD
        rather than simply resetting while in optimal flight or on the pad.
Status: Unable to replicate, requested more information

Issue:  When stack is broken, open end is spewing same thrust (?) as motor end
        Motor continues to spew same thrust
Status: Work in progress
 

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New beta, 0.0.0.6

https://github.com/linuxgurugamer/ModularSegmentedSRBs/releases/tag/0.0.0.6

  • Fixed issue when sometimes during a RUD, the top end of a SRB stack would spew thrust while the motor shut down
  • Replaced effects of open ends
  • Replaced all Destroy(this) with part.RemoveModule(this)
  • Reorganized all part configs to make them all have the same format
  • Merged the multiple EFFECTS stanzas in each file
  • Added flameout stanzas to the effects for the open ends
  • Added reasonable cost values
  • Made the additional items in nosecone optional
  • Fixed missing crashTolorance fields 
  • Added code for thrust variability, but disabled at present
  • Cleaned up a log of disabled code

 

Known issues

  • Cost values for the 1.875 and 2.5 have not yet been completed
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  • 3 weeks later...

Final Beta, first release candidate, 0.0.0.7

https://github.com/linuxgurugamer/ModularSegmentedSRBs/releases/tag/0.0.0.7

  • Added code to refresh PAW window.  Will need to be updated when compiled for 1.8 (3 locations)
  • Added 3.75m parts
  • Configured all costs for 1.875, 2.5 and 3.75m parts to be consistant
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