Solid Rocket Motor Changes

[septemberWaves]

One of the things that has bothered me for a while in Kerbal Space Program is how little we can configure solid rocket motors. In reality, certain types of solid rocket motor can be set up to vary the thrust produced during flight (by altering the shape of the fuel prior to assembly), have the nozzle (and therefore the thrust vector) pointed in different directions, or have the length (and therefore fuel quantity and burn time) altered. None of these are doable in KSP, and I feel like the SRBs we have could use an improvement. I've made some of the following suggestions elsewhere in the forum on various topics, but I figured that it would be a good idea to collect them into one place and have a focused discussion.

Here are some things that I would like to have available for SRBs in the game:

1. Editable thrust/time profile for the burn duration of the rocket, unlockable either for advanced SRBs only, or as an upgrade to SRBs that can be researched in some way. Real solid rocket motors can have changes made to the thrust that is produced as they burn fuel, because the shape of the fuel determines the exhaust quantity produced at a given time and therefore the thrust. This is useful for limiting acceleration, which is now important for crewed launches as well as being a useful thing to control in the lower atmosphere where air resistance can be very detrimental.
2. Procedural segments containing solid fuel, usable by an advanced nozzle piece or pieces instead of having one single part that contains all the solid fuel. This way, solid rocket motors can have more configurable burn times, and can be adapted for more uses.
3. An advanced nozzle part that can have its thrust direction adjusted (within a reasonable limit) before flight. Anyone who's ever tried to mimic an Atlas V rocket or the Space Shuttle will understand why this is useful: it makes it far easier to ensure that the overall thrust vector of the vehicle points through the center of mass even with an unbalanced design. SRBs on the Atlas V are able to do this; the engines have good gimbal range, but the main reason that the rockets (particularly the variants with only one SRB) do not tip over is that the SRB nozzles are adjusted pre-flight so that the thrust acts through the center of mass. This is also another reason why changing the thrust/time profile is useful, because it can be altered to suit a changing center of mass (which is most commonly encountered on Space Shuttle designs).
4. Larger diameter SRBs. Not a high priority compared to the other suggestions, but it would be nice to have some 2.5m SRBs. And in fact, some 0.625m ones would be convenient as well for making cheap and small launch vehicles.
5. Nosecones containing a separation motor. This isn't directly related to SRBs, but as separation motors usually use solid fuel, it is still relevant.

[Magzimum]

If you add that in the stock game, please keep everything as it is, with a big checkbox clearly visible stating "Make Stuff More Realistic but also Moar Complicated". When checked, all the options you suggested can appear. But with it unchecked, the game should remain accessible for newbies, with such complex issues simply hidden away. (Some, or even a lot of) newbies suffer from an information overload already. 

[septemberWaves]

Procedural segments should be no more complex than fuel tanks for regular liquid fuel thrusters, only with the added power and mass of an SRB. The same goes for different diameters of SRB.

A preset gimbal on a nozzle is essentially the same as rotating a liquid fuel thruster to redirect the exhaust (like when building a space shuttle), which is simple enough to understand in theory but only actually ends up being used by advanced players anyway.

Editable thrust/time profiles are more complicated I agree, but perhaps they should fall under "advanced tweakables", since that encompasses various VAB tools that allow for more precise construction at the expense of a bit of added complexity.

Separation motors integrated into nose cones is basically identical to clipping a sepratron into a nose cone, except it uses a single part and will therefore be easier to place.

[Capt. Hunt]

yeah, vectored nozzles would be nice on SRBs, the Shuttles boosters had them.  One easy fix that i think would make solids more useful and more realistic, would be a shut off.  Some real SRBs have the ability to shut off on command, for more precise burns.  They just can't be restarted.  This would make solid PAMs more viable for inserting satellites into precise orbits.

Edited October 11, 2016 by Capt. Hunt

[Eklykti]

Procedural SRBs are in Procedural parts mod. Gimballing SRBs are also in KW Rocketry. Even thrust curves exist as a mod.

So you can just use mods and there's no need to wait for it in the stock.

[septemberWaves]

29 minutes ago, Capt. Hunt said:

yeah, vectored nozzles would be nice on SRBs, the Shuttles boosters had them.  One easy fix that i think would make solids more useful and more realistic, would be a shut off.  Some real SRBs have the ability to shut off on command, for more precise burns.  They just can't be restarted.  This would make solid PAMs more viable for inserting satellites into precise orbits.

Vectored nozzles wasn't actually what I had in mind, I was thinking more along the lines of a presettable nozzle direction that you don't have to re-angle the entire SRB for; the main thing that inspired that idea was my recent attempts to make Atlas V styled launch vehicles and having no choice but to rotate the entire SRB by quite a lot. However, some limited vectoring range would also be nice for an advanced rocket motor. Also, I like the idea of having a low-pressure-optimized SRB that can be cut off for a more precise burn.

11 minutes ago, Eklykti said:

Procedural SRBs are in Procedural parts mod. Gimballing SRBs are also in KW Rocketry. Even thrust curves exist as a mod.

So you can just use mods and there's no need to wait for it in the stock.

I know some of these things exist in mods. Lots of great things exist in mods, but it would be nice to have them in stock so that a) people who don't like to use mods can still have more variety, and b) they can be relied on being updated when the game is updated.

I use a lot of mods and I can see your point to some extent, but if every suggestion was countered merely by "they exist in mods anyway so there's no point making this suggestion" then this entire subforum of "Suggestions & Development Discussion" would be entirely pointless.

[Jonfliesgoats]

I like this idea, and I think it would be pretty intuitive and user friendly.  Either more tweakabkes could be added or modular SRBs could be employed as suggested by other folks here.  Each SRB nozzle module could be ground adjustable via existing controls in the VAB.  In flight gimballing of the nozzle should also be available with certain advancements.  The nozzle module would determine basic SRB thrust as a constant.  Each SRB fuel module could have a tweakabkes sliders regarding fuel consumption and thrust limiting coefficient applied to nozzle module thrust constant.  Basically, we should have as much control over our SRBs as we have with our sugar rockets in the shed.