I only just noticed...

[Foxster]

...this...

Wonder why only ore tanks get this rather handy facility?

[Snark]

47 minutes ago, Foxster said:

Wonder why only ore tanks get this rather handy facility?

Yeah, that one's been around for quite a while.  I've wondered about that question, myself

I would imagine because they're the ones that need it the most.  Suppose you have a ship with loaded, heavy ore tanks.  Ore is really heavy.  The ship might be in a situation where it doesn't have anywhere near the dV that it needs, and it has no way to shed the load-- it could be the difference between losing a ship and saving it.

Compare that with fuel tanks, where, 1. the fuel is something you can actually use, generally, and 2. even if you do need to empty a fuel tank... there's at least some way to ditch the mass (just burn the fuel!), even if it's not necessarily as convenient or ideal as having a "jettison contents" button.  I've never been in a situation where I found myself wanting to jettison fuel, but if I did, I expect I'd just improvise and Apollo-13 my way out of it. 

And other than ore and fuel... I'm hard-pressed to think of any other resource that has enough mass that I'd ever care about wanting to jettison it.

Certainly, I would really prefer not to have a "jettison contents" button on my fuel tank:  can you imagine the hideous consequences of hitting that button by accident?  My guess is that "people who get bitten by accidentally hitting the button" would outnumber "people who get helped by being able to jettison fuel deliberately" by several orders of magnitude.

Would be interesting to see how that's implemented internally.  I'm not in front of a KSP computer right now, so I can't check this at the moment, but hopefully the "show 'jettison' or not" would be something defined in config (either for the resource, or for the part), rather than hard-coded.  If that's the case, then if you want it for everything, you could add it with just a snippet of ModuleManager config.

[Guest]

*insert post complaining about clickbait-y title here*

[Daniel Prates]

There is a "jettison and burn fuel contents" mod available! But it is a very crude mod. I don't use it.

I too would like to have the option of jettisoning contents. For landing overwheight spaceplanes, for instance. Think of space shuttles. They differ from normal planes as their landing gears only have to whitstand empty weight, not a full takeoff weight, allowing some weight-saving design choices. But what happens if you return home with too much unburnt fuel or monopropelant? Dumping it would be an excelent option!

Edited February 18, 2017 by Daniel Prates

[Ty Tan Tu]

They have often been used as blast for submarines. Maybe that has something to do with it. But in general, they are the only tanks that starts out empty, and ore is heavy, so maybe it is just a means of returning the tanks to their default state to make it easier to jettison any remaining ore before launching something like a return ship.

[Gaarst]

You can actually jettison the contents of a fuel tank: through an ingenious process involving mixing several unwanted fuels you can turn them into magical fire and expel them away really fast. (Side effects are possible)

[Cunjo Carl]

2 hours ago, Ty Tan Tu said:

They have often been used as blast for submarines....

Along those lines, I'm rather pleased with this use of ore Jettisoning from the Kerbal Atlantis challenge.

http://imgur.com/a/CQrzm

As for why they have the jettison option, if your spaceship has its own ISRU facilities onboard, it's indispensable to be able to dump leftover ore once the fuel tanks are topped up and it's time to launch. I kinda figured that was the devs original intent, but as with anything in KSP we make all kinds of silly use beyond the initial intent!

Speaking of which, good luck with your ISRU ship, @Foxster! If you happen to be new to them, the ISRUs and drills will warm up while in rails-time-warp after you turn them on, which is also downright indispensable.

[Blasty McBlastblast]

8 hours ago, Gaarst said:

"Side effects are possible"

Also forward effects! 

It's interesting to try to think about how the liquid in a partially filled tank might be directed to a pump suction port while in micro gravity, without using ullage motors or otherwise changing course. Perhaps the craft could spin the fuel to the outer edge of the tank, or maybe some cleverly shaped channels and baffles could use surface tension to draw the liquid to where it's needed. I wonder how (or if) it's done in real life?

[swjr-swis]

18 hours ago, Snark said:

hopefully the "show 'jettison' or not" would be something defined in config (either for the resource, or for the part), rather than hard-coded.  If that's the case, then if you want it for everything, you could add it with just a snippet of ModuleManager config.

 

This is the part that does it. Should be easy to add for MM users.

MODULE
{
	name = ModuleFuelJettison
}

 

A quick test with cloned parts shows it works for any tanks containing Ore, Liquid Fuel, Oxidizer, Monopropellant, Xenon Gas, Ablator (heatshields), and even Electric Charge (batteries). All of them, when the above text is added, show the 'Jetisson Tank Contents' button, which when clicked empties the container.

(I just realized I forgot to test 'Intake Air' and 'EVA Propellant' as well, but there's no reason to assume they'd be any different, although intake air would need to be set back to 'visible' in the resource.cfg to see it.)

Obligatory pics-or-it-didn't-happen:

Spoiler

All components radially attached to or on top of the large probe core were cloned and had the ModuleFuelJettison edited into their part cfg. They started out with full resources, the above screenshot was taken after clicking their newly-acquired and fully functional 'Jettison Tank Content' button.

 

Edited February 18, 2017 by swjr-swis
tested, screenshot

[Jestersage]

I am gonna assume some mods have a "Jettison fuel content and convert to wet workshop"?

[ExtremeSquared]

10 hours ago, Blasty McBlastblast said:

Also forward effects! 

It's interesting to try to think about how the liquid in a partially filled tank might be directed to a pump suction port while in micro gravity, without using ullage motors or otherwise changing course. Perhaps the craft could spin the fuel to the outer edge of the tank, or maybe some cleverly shaped channels and baffles could use surface tension to draw the liquid to where it's needed. I wonder how (or if) it's done in real life?

Won't all potential components of rocket fuel boil at ~0 atm? Just poking two symmetrical holes in a fuel tank should eventually allow them to gradually boil off naturally, unless I'm missing something. Oxygen can have odd properties around 0atm/0K I think...

[Guest]

13 hours ago, swjr-swis said:

SNIPPITY SNIP™

One does not simply "jettison" electric charge.

Unless you also made the battery heat up, which would simulate resistors melting your electricity away and contributing to the heat death of the universe, but then why would you want to throw away electric charge?

[swjr-swis]

32 minutes ago, Aperture Science said:

One does not simply "jettison" electric charge.

Maybe one (in the Real Universe) does not, but the game (in the Kerbal Universe) does. EC is treated exactly as every other resource (including solid fuel, which I now noticed I also forgot).

One does not 'simply jettison' anything in a micro-gravity environment, but there hasn't been much outcry over why mining vessels don't fly off Gilly after instantaneously emptying highly massive excess ore; I wonder if we could run some nrs on the potential TWR of that ore jet.

And if we are really worrying about conservation laws, having a few piddly electrons disappear without trace is several orders of magnitude lower on the violation scale than having tonnes of massive ore vanish into thin air, I would say.

Anyway, the question I set out to respond was whether the Jettison button could be made to appear and work for, and I quote, "everything". The answer is yes. That's all.
 

[samstarman5]

22 hours ago, Blasty McBlastblast said:

Also forward effects! 

It's interesting to try to think about how the liquid in a partially filled tank might be directed to a pump suction port while in micro gravity, without using ullage motors or otherwise changing course. Perhaps the craft could spin the fuel to the outer edge of the tank, or maybe some cleverly shaped channels and baffles could use surface tension to draw the liquid to where it's needed. I wonder how (or if) it's done in real life?

It is a tricky process indeed.  The crew of Apollo 13 had to retain their bodily waste for fear ejecting it would send the wounded craft too far off course.

[Snark]

12 hours ago, samstarman5 said:

It is a tricky process indeed.  The crew of Apollo 13 had to retain their bodily waste for fear ejecting it would send the wounded craft too far off course.

"Whoever ejected it, collected it."

(sorry, couldn't resist)

[Blasty McBlastblast]

henceforth the Specific Impulse of any liquid waste ejection system should be written as I_spee     

a separate annotation may be needed for "number 2 stage jettison"

[Cubfan]

The Jettison button is pretty handy for the "Deliver ore to such and such contracts". After delivery, you just dump the extremely heavy ore and move on. It's also useful for mining rovers. It's nice to be able to dump the ore when you want to maneuver quicker. Braking takes a long time with tons of ore on board.

[Corw]

On 19.02.2017. at 0:13 AM, Aperture Science said:

One does not simply "jettison" electric charge.

Unless you also made the battery heat up, which would simulate resistors melting your electricity away and contributing to the heat death of the universe, but then why would you want to throw away electric charge?

Technically, Samsung did