Lego SRBs

[Nich]

I know it would take a lot of rework but why don't we separate SRB motors from there fuel like LFO.  This way you can build your own SRBs as you would like.  If this mod already exists please let me know as I feel it is not worth the devs time to add to stock if it has already been done in a mod

[Red Iron Crown]

Needs a new resource flow mode, which can't be added by mods afaik. Would be interesting to be able to set the number of propellant segments.

[Nich]

Hhhmmm..... You could use air breathing so it drains tanks evenly but if you can't restrict fuel flow to the stack then it would require an honer system to not do cheaty designs

[max_creative]

How would that work though? Would there be different types for different systems? How would adding more effect the burn time, efficiency, and thrust? 

[Red Iron Crown]

11 minutes ago, max_creative said:

How would that work though? Would there be different types for different systems? How would adding more effect the burn time, efficiency, and thrust? 

To my mind, it would work similarly to LF/O engines now, you add the engine at the bottom (which determines thrust/Isp) and add solid fuel segments (like LF/O tanks) above. The main differences would be lack of throttling/shutoff, no crossfeed/fuel lines, and no refueling.

@Nich might have other ideas, though.

[Nich]

Nope you nailed it perfectly only thing I would add is they burn evenly out of each fuel segment. Although the this is not the exact answer as heat and flowrate at the bottom causes more to burn on the bottom. Please feel free to correct me but I believe the effect is called erosion

Edited April 18, 2016 by Nich

[Alshain]

Can you flesh out exactly what this would add?  Solid fuel is, well solid.  Powder really, but it doesn't go flowing through fuel lines like a liquid would.  So at most you would be stacking a bunch of solid fuel blocks on a motor.  Perhaps that gives you the ability to customize the size of the SRB, but the problem we have now is they don't have a big enough diameter, I don't think the height is the issue.  Plus, I feel like this could lead to impeccably bad balance.  SRB's are cheap, so if I can just build a massive SRB and use tiny little engines for a little control, then why would I ever spend money on an LFO lifter?

[Nich]

Career pad weight limits on hard pretty much require an all LFO for first mun flyby, orbit until you unlock the terror. Otherwise you should be using SRBs off the pad combined with minimal vectored LFO for control

Edited April 18, 2016 by Nich

[Alshain]

11 minutes ago, Nich said:

Career pad weight limits on hard pretty much require an all LFO for first mun flyby, orbit until you unlock the terror. Otherwise you should be using SRBs off the pad combined with minimal vectored LFO for control

That really doesn't answer the question though.  What advantage would this give over what we have now?  All I see it as is adding a bunch of extra parts to the game to recreate exactly what we have now.

[HebaruSan]

10 minutes ago, Alshain said:

That really doesn't answer the question though.  What advantage would this give over what we have now?  All I see it as is adding a bunch of extra parts to the game to recreate exactly what we have now.

I have seen a new user stack SRBs vertically based on what they saw others do with LFO tanks. It's a not quite fair "gotcha" for one to work and not the other (though it did make for quite a hilarious launchsplosion). Practically, I suppose the point would be to be able to add more fuel to the SRBs that we have, for payloads where the current configuration is overkill for initial TWR.

[Nich]

14 minutes ago, Alshain said:

That really doesn't answer the question though.  What advantage would this give over what we have now?  All I see it as is adding a bunch of extra parts to the game to recreate exactly what we have now.

Actually you are right I can get less thrust longer using thrust limiting and I can get more thrust shorter by using half full kickbacks.  I guess using half full SRBs makes me sad. Guess I just need to install spacey parts to get bigger SRBs.

[Alshain]

Ok, well I guess we just play differently then.  I've never really had a need to adjust the fuel in my SRB's except maybe first or second launch in a new career.  But I guess I'm not really opposed to it either.

[MaxL_1023]

Thrust-limiting a large SRB sacrifices delta-v (if you are using a booster + sustainer setup) as you carry solid fuel longer. The sustainer would barely notice if you increase SRB thrust to full, but add more solid fuel to keep your pad TWR identical. 

 If you use a pure-solid first stage, you are alright with thrust-limiting, but the lack of gimbals (or very narrow ones) plus the very high acceleration curve (a SRB stage will often pull 4 or 5 g's just before burnout due to the low ISP) makes a soild stage difficult to execute effectively. 

Right now almost all of the SRBs are 1.25m in diameter - a stackable solid fuel tank to add fuel to existing boosters (they keep the same thrust/isp/etc.) would help - perhaps unlock it along with the hammer in tier 2 so you can make somewhat customizable boosters. The tech tiers could then be devoted to unlocking more powerful and efficient engines (defined by the base booster type, thumper, kickback, etc.). 

[Capt Snuggler]

I would love for SRBs to handled this way.

1. Basic nozzle
2. gimballing nozzle
3. Solid Fuel core large
4. Solid fuel core small

On 4/18/2016 at 5:33 PM, Red Iron Crown said:

To my mind, it would work similarly to LF/O engines now, you add the engine at the bottom (which determines thrust/Isp) and add solid fuel segments (like LF/O tanks) above.

I'm not so sure. Don't think its right for it to behave exactly like the LFO engines.

SRBs have a hollow core running up the middle right? Isn't it the surface area of the solid propellant that determines the thrust? the surface of the propellant burns expands and shoots out the bottom. therefore stacking more cores on top should increase surface area and thrust. (offset by the increase in mass)

also changing the core shape has an effect.

*edit: also propellant grain size apparently.

Edited April 19, 2016 by Capt Snuggler
using words instead of werds

[Red Iron Crown]

@Capt Snuggler That would require a more extensive rework (though I would certainly approve of it). 

[Knaapie]

@Capt Snuggler Shouldnt nr 5 slightly increase in thrust over time ?

Hehehe forget i mentioned that.. I like the idea! Even seen someone mod it on youtube. It will help a lot for not going too fast at the end of the SRB burn

[Nich]

number 4 would never work, you would burn through your sidewall very quickly or keep your pressure/temp very low/inefficient.  Fuel is needed to provide isolation to structural parts.

[Hobbes Novakoff]

A sort of From The Depths-esque SRB (or even LFO engine) would be very cool. However, From The Depths achieves its high degree of modularity by confining everything to a voxel system. With the free-form placement of KSP, that becomes a bit more difficult. Not to mention, it requires finely tuned balancing, otherwise within three seconds someone will have figured out the optimal way to do everything for every situation and everything will start looking exactly the same. 

[kujuman]

On 4/18/2016 at 11:50 AM, Red Iron Crown said:

Needs a new resource flow mode, which can't be added by mods afaik. Would be interesting to be able to set the number of propellant segments.

It's doable via mods, but the fuel flow isn't "official" (so the game doesn't know it's flowing fuel...it's...hacky lol), so I had to write a custom engine module, and things like KER and MechJeb don't know how to calculate the dV for them.

On 4/18/2016 at 11:41 AM, Nich said:

I know it would take a lot of rework but why don't we separate SRB motors from there fuel like LFO.  This way you can build your own SRBs as you would like.  If this mod already exists please let me know as I feel it is not worth the devs time to add to stock if it has already been done in a mod

It's been done as a mod, but not updated for 1.1 yet. AdvSRBs (check my sig) didn't appear to ever get the support I felt warranted the upkeep put into the project.

 

I still think I got SRBs the way they "should" work but without being able to work natively with KER and MechJeb using them took a little more effort by hand than they were ever worth, except for perhaps shuttles.

[Nich]

@kujuman Advanced Solid Rocket Boosters!  link is broken and development thread only points to a kerbal stuff link that is no longer active.