Solid Rocket Motor Improvements

[CoreI]

In my opinion, solid rocket motors in KSP 1 are very difficult to use. This is primarily due to their thrust profile being constant (AKA once you light them, they produce a constant amount of thrust). Setting the thrust limiter lower means having a low initial TWR, defeating the purpose of the SRB. Keeping the thrust limiter high mean having a massive TWR late in the burn, resulting in higher velocities deeper in the atmosphere, causing large ΔV losses due to drag. Additionally, the constant thrust makes off-center SRB's (think Space Shuttle) extremely finicky and difficult.

Fortunately, this is not how SRBs work in the real world. Motors which are used on real rockets have different shaped fuel grains which allow them to have a varying thrust profile over time (see bottom of post for examples). For example, here's the plot of the Space Shuttle SRB's thrust over time:

So, my suggestion is to implement varying thrust profiles for SRBs in KSP 2. Of course, the thrust profile of a booster can't be changed once it rolls out to the pad, because the fuel grain is still a solid. There are a few ways I can see implementing this, going from most complicated and least new-user friendly to vice versa.

1. Custom fuel grains: Let players draw their own SRB fuel grains to achieve exactly the thrust profile they want. Now, this probably isn't the best idea, since it requires players to have decent knowledge of how SRBs burn fuel.

2. Custom thrust profiles: Let players graph their own thrust profiles, within the bounds of what is possible through SRB grain shapes. I'm thinking a graphing system similar to KSP 1's robotics controller. This still isn't very new-user friendly because it requires players to plan timing during their launches fairly meticulously.

3. Preset grain shapes/thrust profiles: This is probably the most realistic implementation. Have a few grain shapes and their corresponding thrust profiles already in the game, and allow players to switch between them like how they switch through variants of a part in KSP 1. This will allow players to have flexibility with how the SRB burns, while keeping things fairly simple for new players. Perhaps in career/science mode, new grain shapes can be unlocked gradually by researching technologies, giving new players an easier learning curve.

Here are some examples of grain shapes and their corresponding thrust profiles:

[AtomicTech]

That would be great!

It would add a whole 'nother level of complexity and design!

Spoiler

Number One's my personal favorite!

 

[GuessingEveryDay]

There is a mod that lets you do this in KSP1, by the great @OhioBob

Unless you're on console, you'll have a great time with this.

[AtomicTech]

2 minutes ago, GuessingEveryDay said:

There is a mod that lets you do this in KSP1, by the great @OhioBob

Unless you're on console, you'll have a great time with this.

I can't wait to use it!

(Hi btw )

Edited January 7, 2022 by AtomicTech

[Benzo Kerman]

This would be a great implementation into KSP2. I like the 3rd idea of having different grains for the player to chose from, and allowing new grains to be researched in the r and d.

[Tundra]

I think this could be a good idea, but with a slightly different implementation.

 

___________________________________________________________________________________________________________________________________________________________________________________________________________

WARNING:  Below is a personal opinion and can be wrong/just down right stupid.

 

I think there should be a staring level of SRB (Number 1 for example) but as you unlock more tech nodes you get more SRB patterns.   At a certain point, you will gain the ability to use "Computers" to help you design grains.    You can tell the computer what you want your TWR to look like over your ascent (Taking into account your non-SRB engines too) and it will try to find a grain that could help you get the TWR you need.   This might feel little to modded, but I think you could make it a latter game item until it feels balanced.

 

!!!Personal opinion passed!!!

___________________________________________________________________________________________________________________________________________________________________________________________________________

 

Edited January 7, 2022 by Tundra

[darthgently]

4 hours ago, CoreI said:

In my opinion, solid rocket motors in KSP 1 are very difficult to use. This is primarily due to their thrust profile being constant (AKA once you light them, they produce a constant amount of thrust). Setting the thrust limiter lower means having a low initial TWR, defeating the purpose of the SRB. Keeping the thrust limiter high mean having a massive TWR late in the burn, resulting in higher velocities deeper in the atmosphere, causing large ΔV losses due to drag. Additionally, the constant thrust makes off-center SRB's (think Space Shuttle) extremely finicky and difficult.

Fortunately, this is not how SRBs work in the real world. Motors which are used on real rockets have different shaped fuel grains which allow them to have a varying thrust profile over time (see bottom of post for examples). For example, here's the plot of the Space Shuttle SRB's thrust over time:

So, my suggestion is to implement varying thrust profiles for SRBs in KSP 2. Of course, the thrust profile of a booster can't be changed once it rolls out to the pad, because the fuel grain is still a solid. There are a few ways I can see implementing this, going from most complicated and least new-user friendly to vice versa.

1. Custom fuel grains: Let players draw their own SRB fuel grains to achieve exactly the thrust profile they want. Now, this probably isn't the best idea, since it requires players to have decent knowledge of how SRBs burn fuel.

2. Custom thrust profiles: Let players graph their own thrust profiles, within the bounds of what is possible through SRB grain shapes. I'm thinking a graphing system similar to KSP 1's robotics controller. This still isn't very new-user friendly because it requires players to plan timing during their launches fairly meticulously.

3. Preset grain shapes/thrust profiles: This is probably the most realistic implementation. Have a few grain shapes and their corresponding thrust profiles already in the game, and allow players to switch between them like how they switch through variants of a part in KSP 1. This will allow players to have flexibility with how the SRB burns, while keeping things fairly simple for new players. Perhaps in career/science mode, new grain shapes can be unlocked gradually by researching technologies, giving new players an easier learning curve.

Here are some examples of grain shapes and their corresponding thrust profiles:

Agreed.  But in Career mode, I think there should be a one-time cost to altering a profile as that would be equivalent to an engineering change, though the cost shouldn't be as high as I would propose for something like a TweakScale engineering change.  And yes, something like TweakScale, with a tool-up cost, should be part of stock KSP 2

Edited January 7, 2022 by darthgently
corrected "should" to "shouldn't"

[OHara]

KSP1 has the capability for option 3 in the top post, thrust profiles.

No stock SRBs use them, but players have written configuration files to do so (link link).

The interact in the simplest possible way with the fuel-fraction and thrust-limiter sliders in KSP1.  The thrust-limiter reduces thrust by the requested fraction across the whole burn.  The fuel-fraction acts as if the booster was loaded with fuel in the same pattern as it has when fuel has burned to that level.  

The interface is a bit awkward because it works in terms of fuel remaining, so you type the curve in reverse order.  I  like this profile, similar to picture '3' in the top post, for limiting the g-forces  late in the booster phase:

@PART[*]:HAS[@MODULE[ModuleEngine*]:HAS[@PROPELLANT[SolidFuel]]] {
    @MODULE[ModuleEngine*] {
        %useThrustCurve = true
        %flameoutBar = 0
        %thrustCurve {
            key = 0.00 0.4 0.0 1.2
            key = 0.60 1.0 0.0 0.0
            key = 0.98 1.0 0.0 0.0
            key = 1.00 0.5 -40 0.0
} } }

[Thundrevv]

I think there is a mod for KSP 1 that adds that capability (for example, 4 choices, one sets it for thrust to be 130% average for first 20% of the burn, then 90%, and then 60% the last few)

I don't remember what it is, but i think it's waterfall

[AtomicTech]

41 minutes ago, Thundrevv said:

I think there is a mod for KSP 1 that adds that capability (for example, 4 choices, one sets it for thrust to be 130% average for first 20% of the burn, then 90%, and then 60% the last few)

I don't remember what it is, but i think it's waterfall

It's not waterfall, that's for sure. 

[RKunze]

1 hour ago, Thundrevv said:

I think there is a mod for KSP 1 that adds that capability (for example, 4 choices, one sets it for thrust to be 130% average for first 20% of the burn, then 90%, and then 60% the last few)

I don't remember what it is, but i think it's waterfall

No. Waterfall adds great exhaust effects to everything except SRBs. The mod you are looking for is probably  

 

[Thundrevv]

On 1/19/2022 at 9:39 PM, RKunze said:

No. Waterfall adds great exhaust effects to everything except SRBs. The mod you are looking for is probably  

 

Yeeah, I remember having BetterSRBs at the time. That is most probably it

 

[Bej Kerman]

On 1/19/2022 at 7:08 PM, Thundrevv said:

I don't remember what it is, but i think it's waterfall

Waterfall is a graphics mod?

[AtomicTech]

8 minutes ago, Bej Kerman said:

Waterfall is a graphics mod?

Kinda

[shdwlrd]

12 minutes ago, Bej Kerman said:

Waterfall is a graphics mod?

It's a better looking version of real plume.

[AtomicTech]

1 minute ago, shdwlrd said:

It's a better looking version of real plume.

Correction: It's a MUCH better looking version of real plume.

It doesn't even use particles!

(Save for the RAPIER's Jet Mode)

[shdwlrd]

5 minutes ago, AtomicTech said:

Correction: It's a MUCH better looking version of real plume.

It doesn't even use particles!

(Save for the RAPIER's Jet Mode)

I wouldn't know, I don't use visual mods. In games I prefer performance over looks.

[AtomicTech]

3 minutes ago, shdwlrd said:

I wouldn't know, I don't use visual mods. In games I prefer performance over looks.

I've heard HebaruSan, I think, suggest that with Waterfall, you can get better performance than the stock particle plumes.

[Bej Kerman]

56 minutes ago, shdwlrd said:

It's a better looking version of real plume.

Ik, I use it myself with Near/Far Future and it's wonderful. Hence the confusion when someone links it to SRBs.

[BekfastDerp13]

On the grain shapes, I think number 6 would fare the best for KSP due to Kerbin's small size