Why are tanks / srb's so heavy?

[Spanier]

I think the main reason, tanks are so heavy is, that it is assumed, they are filled with a substance similar to RP-1 and LO2, and since you have a fuel ratio of ~0.9/1.1 of two heavy substances, this makes the whole think a lot heavier, as if it would be filled with something like LH2/LO2, with LH2 being super-light and nearly needing no LO2. Therefore, the ISP of the engines is rather high for the fact they are burning RP-1 instead of the more efficient LH2.

Maybe we'll get a new type of fuel by the time, we get minable resources and tweakables for stock-parts.

SRB's are another story, in RL the SS-SRB has 80% more thrust than a F-1 engine, in KSP, the SRB has 80% less thrust then a Mainsail engine ...

[Aphox]

Done in one.

The scale is the reason.

This. What people seem to miss when they consider the physics in this game is the scale. From what I remember, Kerbin only has a diameter of 600,000 meters (6KM), while Earth has a diameter of 12,742KM. And Kerbin is something like 0.0089 Earth masses. Quite a big difference.

Also, weight is only relevant to gravity. Maybe stuff weighs more on Kerbin because VIDYA GAME PHYSICS

[SunJumper]

I actually really dislike the stock SRB's. Their ISP is so poor and they don't make enough thrust to be worth it. I hope they're cost-balanced when Campaign is introduced, otherwise liquid boosters will always be used. Solid Fuel is also substantially denser than liquid fuel, again making it worse.

The current balance is fine: 10% tankage may not be efficient compared to real-world analogues, but then again everything in KSP is lower quality than real life. I prefer 10% because it's just convenient to work out in my head as well.

The KSP parts are 11.1% non-fuel...

[RawChicken]

Kerbin is not the Earth and you cannot make comparisons between them. It is a game not a simulator. You can have mods with better thrust ratios and you can clearly see hoy they are overpowered.

[shand]

The scale is the reason. Kerbin and its star system are drastically scaled down, which makes some things much, much easier. On Earth, craft in low orbit might be traveling at Mach 25ish, so it's obviously a huge technical problem to transition from a Mach 3-5 hypersonic flight into even a suborbital trajectory. (Each Mach is ~330 m/s, for reference.) But on Kerbin, you can use your turbojets to get moving at Mach 5 without much effort, and you only need to double that to get a stable orbit. It's just a whole other experience, so you have to make things challenging in other ways to compensate.

You are confusing spaceplanes with SSTO. its much much much technically easier to SSTO then it is to MSTO, you have 1 engine, 1 fuel load, no explosive bolts (that you intend to use). the difference is in diminishing returns. its cheaper to have a second stage (including expensive rockets and decoupling systems and all the complexities) then it is to lump enough fuel on top of one rocket.

Titan first stage had the potential to be a SSTO with small payload, but it was cheaper (i imagine, dont have the numbers on me) to make a smaller MSTO.

further you can have a better suited rocket in the higher stages, like shape and fuel type. for example LOX is a great fuel for launching, but maybe a kerosine derivitive would be better suited to your upper stage mission profile.

Disclaimer:

This is of course assuming you have a rocket with high enough thrust and ISP to be able to reach the magic number. the deltaV tends to a limit as the additional mass of fuel decreases the benifit of each new tank.

[azazel1024]

The two pieces of rebalancing I'd like to see are, as someone mentioned, slightly higher TWR for SRBs. Not a huge amount more, but maybe 15-25% higher thrust, roughly the same Isp. So yeah, they'd burn faster, but harder. They are best for first stage lift off, which means you want the maximum thrust you can possibly get. As it stands, their heavy weight means that the thrust they do provide only helps "a smidge" for very heavy lifters and are much less efficient than a liquid fueled booster + engine...which I understand is the true reality, but it would be nice to either reduce the weight slightly, or increase the thrust slightly.

The other is, it would be nice if fuel tanks did not scale perfectly linearly. Since within reason, a fuel tank's weight is closer to the square of its size, but the volume it can hold is a cubed function (yes, I know, as you grow larger you also need thicker walls, but the wall and fuel vessel thickness does NOT scale linearly, probably closer to a square root function)...basically very large tanks are going to weigh less for the volume of fuel they can hold than small tanks.

I wouldn't want to see a huge scaling change in this, otherwise there would never be a reason to use small tanks if this scaling caused a big mass penalty for small tanks. However, if for instance the jumbo 1.5m tank held maybe 20% more fuel compared to its mass than the smallest 1.5m tank and the jumbo rockomax tank held maybe 20% more fuel compared to its mass than the smallest rockomax tank and more or less scale everything in between, I think it would add a scooche of realism as well as making very large rocket designs just a small amount easier.

I don't want "an easy button", but sometimes it can be rather time consuming and require rather intricate designs and/or massive designs to do something that shouldn't need to be quite so large and/or complex (like say, building a kerpollo style mission, which is not possible with stock pieces and resembling anything like the Saturn 5 or CSM/LM).

[Nobody_1707]

Real aerodynamics already gives SRBs a higher effective thrust to weight ratio on payloads where it matters because the drag stops being stupidly high. (Unless your rocket isn't aerodynamic.) Just install FAR and wait for them to implement real aerodynamics in stock KSP.