Ability to define a thrust envelope for solid rockets

[John FX]

In RL solid boosters are tuned by adjusting the width of the gap in the centre of the solid fuel so that their thrust can vary during the burn time. This allows engineers to tune them so that they provide appropriate thrust at various times during launch. Increasing it after 55 seconds for throttle up for example.

It would be good to be able to do that in KSP. Obviously this could only be changed in the VAB as opposed to an SRB having a throttle.

A quick google for images came up with this one for (I assume) the shuttle solid boosters. I would imagine the dip at 52 seconds might be Max Q.

[passinglurker]

We probably don't need something so complex as the thrust curves of the real world but it would be easier to control an all solid first stage if the thrust tapered off a little as it emptied instead of just letting the TWR escalate out of control. The means are already in the code for such thrust curves they just aren't definable in the vab.

[fourfa]

Agreed this would be a worthy addition

[Mr. Peabody]

Such an addition would be a great Delta V saver and would also make SRBs much easier to control after liftoff. Perhaps the width of the gap in the centre of the SRB could be adjusted in the VAB similarly to how the thrust limiter is used to control max thrust on liquid fueled engines? (Right click on SRB then adjust a slider to control the SRB gap width.)

[John FX]

Even if we could pick the amount of seconds before the thrust tailed off that would be a start although having the ability to properly set a thrust envelope would be far better and not much more complex for the user. Obviously not setting any points means a SRB acts as it does now.

Just initial thrust, time of min thrust, time of max thrust, which would also be the time thrust fade started. If it was a graphical interface you set start thrust, drag one point down to set min thrust and time, another up to set max thrust and time. That`s it.

Any simpler and I am not sure it is worth it.

[Shadowmage]

This capability already exists in the stock code + configs; stock SRBs fully support adding a thrust-curve to their config file.  All it takes is a simple patch to add the thrust-curve data into the part config files.

Now.. changing in the VAB / editor -- that runs afoul of the stock 'no complex GUIs' mantra.  Absolutely doable (I have a setup for exactly that in SSTU), but not without adding additional fairly complex GUIs, which is something stock KSP seems allergic to.

[John FX]

Just now, Shadowmage said:

This capability already exists in the stock code + configs; stock SRBs fully support adding a thrust-curve to their config file.  All it takes is a simple patch to add the thrust-curve data into the part config files.

Now.. changing in the VAB / editor -- that runs afoul of the stock 'no complex GUIs' mantra.  Absolutely doable (I have a setup for exactly that in SSTU), but not without adding additional fairly complex GUIs, which is something stock KSP seems allergic to.

Not everything that is a mantra is a good idea too.

Squad could do with adding a bit more function to the game. As I say above, the interface would be as simple as a GUI could get and still be called such. Not much more complex than a tweakable at all.

As you say, they seem to be allergic to going that last bit to make the game polished, they seem happy to just have it work.

[Leafbaron]

workaround, set thrust on SRB in VAB and reduce fuel by half. add a second set of SRB's with half fuel and a new thrust setting. when first SRB's run out stage the second ones with new lower thrust to account for the weight reduction from burning the first set of SRB's. Simple, clunky, and nowhere near ideal thrust envelope. 

[passinglurker]

39 minutes ago, Shadowmage said:

This capability already exists in the stock code + configs; stock SRBs fully support adding a thrust-curve to their config file.  All it takes is a simple patch to add the thrust-curve data into the part config files.

Now.. changing in the VAB / editor -- that runs afoul of the stock 'no complex GUIs' mantra.  Absolutely doable (I have a setup for exactly that in SSTU), but not without adding additional fairly complex GUIs, which is something stock KSP seems allergic to.

There was a simple mod that boiled it down to two thrust limiter sliders one for the thrust at the start and one for the thrust at the end (the curve inbetween is linear)

[John FX]

4 hours ago, passinglurker said:

There was a simple mod that boiled it down to two thrust limiter sliders one for the thrust at the start and one for the thrust at the end (the curve inbetween is linear)

Even that would be something.