Why are tanks / srb's so heavy?

[Fel]

While checking the 'realism' of some of the numbers I noticed how poor the fuel / weight ratios of these devices seem in comparison to their earth counterparts. For a game that has serious micromanagement in weight ratios; it feels counterproductive to make things heavier.

Just wondering if there is a balance trade off or something.

[Temstar]

Just wondering if there is a balance trade off or something.

It only costs 4500m/s to reach LKO as opposed to 9300m/s to reach LEO. In order to not make things like SSTOs too easy Squad make tanks and engines perform worse than their real life counterparts.

Even then rocket SSTO to LKO is quite simple where as its never been achieved here on Earth, despite Earth having a lot better rocket parts.

[drakesdoom]

It probably could be done here on earth but why would you, you have to pay to build the rocket here.

[tavert]

People have paid, big money, to try for many decades. Hasn't worked yet, but Skylon looks like it stands the best chance of being the first to really happen. Still lots of money away, we'll probably see SpaceX recovering their boosters before Skylon flies SSTO.

[Fel]

While I can understand the engine balances...

I feel tanks should better reflect reality. Take the toroid tank, now that is nothing more than foil and it is still heavier than the regular tanks!

Of course, impact, heat, exit and re-entry tolerance of a 'foil tank' would be non-existent.

I feel like if I'm going to bring a tank up for assent and then let it burn up in the atmosphere... I really want it to be light as hell.

But if I want that tank to survive impacts I'd like it re-enforced and heavier.

*Feels picky about trying to balance the balances.

[Spatzimaus]

It only costs 4500m/s to reach LKO as opposed to 9300m/s to reach LEO.

Done in one.

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.

Now, I'm not suggesting they rescale the game to reflect reality; I LIKE that the current setup makes it easy for us to try unconventional designs. But you have to acknowledge that with the current sizes, "realistic" fuel tanks and engines would be horrendously overpowered; you'd be able to get to orbit just by parking Jeb on a lawn chair on top of a standard NASA-surplus SRB. That doesn't make for a very good game.

[magnemoe]

It makes sense that the small tanks has worse dry mass / fuel ratio than large ones however mostly it scales linearly, my main issue is that engines has so low twr, would prefer ligher engines and heavier fuel, however this would make SSTO rockets even easier.

[Nexustrimean]

Its because this is not a sim, its a game, Some things have been changed to make things more fun/challenging.

[Qumefox]

It makes sense that the small tanks has worse dry mass / fuel ratio than large ones however mostly it scales linearly, my main issue is that engines has so low twr, would prefer ligher engines and heavier fuel, however this would make SSTO rockets even easier.

Actually all fuel tanks in KSP have the exact same fuel/dry mass ratio. The only benefit to using larger tanks is to reduce part count.

The current balance is set to not make things too easy, nor too hard(despite what some people may think).

That being said. If you don't like it, you're perfectly welcome to edit the .cfg files for all the engines/tanks in your install to set the ISP's and masses to whatever you personally think they should be.

[Wait- Was That Important?]

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.

[(An Original Name)]

Um... where did the delete post button go? I cant seem to find it

Edited April 29, 2013 by (An Original Name)

[(An Original Name)]

While nobody has made a true SSTO yet, we certainly have the technology to make one. A (nonreusable) SSTO could have been made even in the 1960's, since something like the Titan II first stage had the d/v to get to orbit with a small payload.

While nobody has made a true SSTO yet, we certainly have the technology to make one. A (nonreusable) SSTO could have been made even in the 1960's, since something like the Titan II first stage had the d/v to get to orbit with a small payload.

[TwoHedWlf]

Also keep in mind that the game's setting is a bunch of incompetent aliens with no sense of self preservation building rockets using bits of garbage they've found lying in ditches.

[Rhomphaia]

Actually all fuel tanks in KSP have the exact same fuel/dry mass ratio. The only benefit to using larger tanks is to reduce part count.

The very small tanks (Oscar-B and ROUND-8) don't.

[Spatzimaus]

Actually all fuel tanks in KSP have the exact same fuel/dry mass ratio. The only benefit to using larger tanks is to reduce part count.

More than that. Three reasons large tanks are better than using multiple small tanks:

1> You don't deal with the structural strength issues you have when you try to connect multiple smaller tanks together. A single large tank is really convenient as the center of a large station, especially if you experience high stresses during launch. It's not just about reducing part count; a single tank CAN'T warp, no matter how much stress it undergoes.

2> Tanks expend fuel in a different mass distribution. A series of small tanks will drain the frontmost tank first before expending anything from the aft tanks, which very quickly results in your mass being concentrated at the back of the vessel. Depending on what you intend to do, this can be either a really good thing (trying to land a brick on Duna) or a really bad thing (trying to take off with a spaceplane). Larger tanks drain in a more uniform way.

3> When you're transferring fuel around between multiple tanks (like when you're refilling your ship's tanks at a space station), you can only pick one start and one end tank. Refilling a dozen small tanks is just a pain, whereas refilling a single large tank is easy. Also, big tanks transfer fuel more quickly, although this isn't a big deal in practice. Now, if/when we get a more robust fuel transfer system, this one will go away; all we really need is the ability to select "Out" or "In" on a single tank and have it transfer to/from all other tanks on the same vessel (minus the ones you've explicitly blocked from being used by engines, like on lifeboats), and we'll have a much easier time.

[Sathurn]

Ok I get the arguement that, kerbal is scale to make "Easy", so real world tanks would be over powered. I get that this is "kerbal" rocket science.

Yet, I agree with the op on the SRBs. The SRB need a boost. I don't use them because the don't seem to help. In fact it seems to me they barely lift there own weight when compared to LFR. (totally personal opinion, I don't feel like doing the math for a game) Only SRB I use are the serptrons to get the parts away before they can hit my rocket.

[willneu97]

I actually really dislike the stock SRB's. Their ISP is so poor and they don't make enough thrust to be worth it.

But they do look cool

[foamyesque]

Done in one.

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.

Now, I'm not suggesting they rescale the game to reflect reality; I LIKE that the current setup makes it easy for us to try unconventional designs. But you have to acknowledge that with the current sizes, "realistic" fuel tanks and engines would be horrendously overpowered; you'd be able to get to orbit just by parking Jeb on a lawn chair on top of a standard NASA-surplus SRB. That doesn't make for a very good game.

Quite right. I .cfg'd up a Saturn V... it got all the way into orbit on the first stage.

[Francesco]

In fact it seems to me they barely lift there own weight when compared to LFR. (totally personal opinion, I don't feel like doing the math for a game) Only SRB I use are the serptrons to get the parts away before they can hit my rocket.

you're right in saying it's your personal opinion: SRB actually have a pretty high TWR in this game - try putting a probe on top of RT-10, fire it and you'll see.

besides, that is not a fair comparison.

SRB are pre-built, while you can build liquid fuel boosters of any size and thrust.

[Sathurn]

besides, that is not a fair comparison.

SRB are pre-built, while you can build liquid fuel boosters of any size and thrust.

your right, but on a heavy lift the srb just don't seem to make that much of a difference. but I'm a noobie.

Just succeeded in an Apollo style Mum mission. 3-man comand module, two man mun lander. docked to the top at lift-off. My first stage had 5 jumbo tanks and 21 motors (lv-t30). Which worked better than 5 mainsails. Although without asus I could of never flown the thing off the pad with the lag on my laptop (157 total parts)

[Endeavour]

Before Nova joined the team, the main lifting engines had ISPs over 500s, and the decouplers were heavier. It was actually easier to do an SSTO than a staged rocket. The current balance has been refined to the point it is now.

[Nobody_1707]

Ok I get the arguement that, kerbal is scale to make "Easy", so real world tanks would be over powered. I get that this is "kerbal" rocket science.

Yet, I agree with the op on the SRBs. The SRB need a boost. I don't use them because the don't seem to help. In fact it seems to me they barely lift there own weight when compared to LFR. (totally personal opinion, I don't feel like doing the math for a game) Only SRB I use are the serptrons to get the parts away before they can hit my rocket.

Install FAR.

Enjoy useful SRBs.

???

Profit!

[Fel]

It makes sense that the small tanks has worse dry mass / fuel ratio than large ones however mostly it scales linearly, my main issue is that engines has so low twr, would prefer ligher engines and heavier fuel, however this would make SSTO rockets even easier.

The large tanks are made out of swimming pools... the toroidal tank is foil (or an inner-tube with pretty gift wrapping). It is a strength to weight trade off without the actual "weight" trade off.

That being said. If you don't like it, you're perfectly welcome to edit the .cfg files for all the engines/tanks in your install to set the ISP's and masses to whatever you personally think they should be.

Thing is, I'm quite hesitant to.

I understand the need to balance the game due to Kerbin being much smaller than earth... but I can FEEL the tanks dragging me down; the whole diminishing returns aspect.

Also keep in mind that the game's setting is a bunch of incompetent aliens with no sense of self preservation building rockets using bits of garbage they've found lying in ditches.

Yes... until you wonder how that fully operation rocket part got there to begin with. ("It must have come from one of our rockets that exploded","But how did it get on your rocket to begin with","Well, we found it!")

your right, but on a heavy lift the srb just don't seem to make that much of a difference. but I'm a noobie.

Just succeeded in an Apollo style Mum mission. 3-man comand module, two man mun lander. docked to the top at lift-off. My first stage had 5 jumbo tanks and 21 motors (lv-t30). Which worked better than 5 mainsails. Although without asus I could of never flown the thing off the pad with the lag on my laptop (157 total parts)

SRB's offer "That Small Boost" that you need... of course they're too heavy to be better than throwing out expensive engines... but they're also PRETTY and good at making neat rocket trails!

Also was working on a moon lander... but I wanted mine to be a little more "Practically Launched." Ended up splitting into two rockets; 11Mg lander with a probe launcher [Guess what most of that weight is -__-] and a behemoth to get a 25Mg 'Mk3 FuelTank (and Command Module)' up. As much as I try to keep things sensible... I ended up having to start slapping on aerospikes and LV's. (At least it was only ~200Mg at launch, which is decent by my standards).

*And aside from getting extremely pissy because even though my self-launch went perfectly (eventually) and I was predicted to arrive 30km ahead of the target vehicle; the lack of 'finer' controls (and me removing rotpower, forgetting to add rcs in, and now relying on a 2.0 vectored engine for all navigation) cause my final burn to be a little too hard to control and screwed my inclination up by something like 15deg. (Good news was, I still managed to sync orbits enough so that *cough*infinite fuel*cough* put things back on track.) [And the joys of docking when you cannot rotate XD!]

[Temstar]

See the thing is the ideal ascent profile for any Kerbin rocket calls for the rocket to reach local terminal velocity (100m/s at sea level) ASAP. Then the thrust should be reduced to keep TWR at around two so the rocket hugs the local terminal velocity curve on its way up.

Which engines give you a burst of very high acceleration at lift off then can be quickly jettisoned once terminal velocity is reached? SRBs. That's why they're so useful for heavy rockets - they allow large rockets to have very high TWR at lift off followed by a quick "throttle down" in the form of staging.

[rkman]

Its because this is not a sim, its a game,

According to squad, it is both.