Weight of ore

efreysson said:

I'm writing a space opera, in which starships use a fictional substances for the engines. One cargo ship gets stacked absolutely full of the stuff, to turn it into a giant bomb, but I realise I have no idea how much a cargo container of raw ore should weigh.

Can someone help me out?

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There's so much here. Should "weigh?" In.. space? Do you mean like how much you need to blow something up? It's an invented ore, so I dunno, nor do I know if or how they'd measure anything by weight in space.

In general Earth terms, there's no answer for that either, as you're talking about a fictional ore. The weight of an ore depends on what it is, as density varies considerably.

A quick google search reveals iron ore to be about 5,000 kg/m3. Obviously your fictional ore can be more or less than that. Water is 1,000 kg/m3. Anything less than that will float, more will sink.

Cornflake is right, that the ore doesn't really "weigh" anything. It does have mass which is greatly affect the ability of your spaceship to accelerate (including taking longer to slow down and turn).

One thing to note, for credibility purposes. Most fuel sources are highly engineered or controlled to only combust/fission/fusion in exactly the right circumstances at exactly the right rate. For instance, it is impossible, for all intents and purposes, to turn a nuclear reactor into a fission bomb.

High explosives and ammunition is similarly very stable and safe to transport. Not as safe as jelly beans, but not like the old westerns with a crate of nitro glycerin in the back of a stagecoach.

Likely your spaceship fuel would be under similar constraints - probably very difficult to impromptu turn into a bomb.

Then again, it could be as simple as hydrogen. We did blow up a space shuttle or two with that stuff. Whoops.

Edit: If these spaceships go any sort of meaningful distance (e.g >Earth-Mars distance) or near relativistic speeds, the energy density of your fuel is likely going to be very high (or you need a really, really big gas tank). Anything with a extremely high fuel density that goes easily boom in the wrong circumstances is pretty much suicide. Even taking the plastic explosive analogy (highly explosive, very stable, easy to detonate with the right equipment) - you wouldn't ship a cargo ship of the stuff across the galaxy without some extreme precautions, just like the military doesn't throw a truckload of c4 on the highway, high five the driver, and say good luck. Just food for thought on your bomb idea.

It really varies.

For example-- I hear about gold ore most often, in an anecdotal kind of way. It can take anywhere between 2 tons - 91 tons of ore to produce an ounce of gold. Obviously, you're not fueling your ship on gold... but it shows how much desirable stuff : other stuff the proportions can be.

"Ore" is a vague term in your context. However, on our planet, an ore is a naturally-occurring mineral substance or body of rock from which valuable commodities can be extracted at a financial gain. The latter phrase, of course, is the most pertinent to actual space mining, but we are dealing with fiction here. That said, most mineral ores of metals are either sulfides or oxides, and both tend to be pretty heavy. In a space context, you are dealing with mass, rather than weight, but mathematically that still matters. Moving a huge bulk of anything requires immense amounts of energy. Just getting to the place where the stuff is requires immense amounts of energy. Just find out where the stuff is requires immense amounts of energy.

Those last three sentences demonstrate my problem with pseudo-realistic space operas involving mining of "ores" I really like the first Alien movie, but the premise of a huge ore-bearing space ship still bothers me, from a reality standpoint.

caw

efreysson said:

I just need a number, as a character mentions just how much of the stuff has been loaded on the ship. And I don't have a good grasp of how much a lot of dense material weighs.

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No one in space would discuss it in terms of weight though, was my point.

cornflake said:

No one in space would discuss it in terms of weight though, was my point.

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This ^

You might find mass described as a weight with a caveat such as, 1,000 SEU kilos, (I made the SEU up to stand for standard Earth units).

efreysson said:

I just need a number, as a character mentions just how much of the stuff has been loaded on the ship. And I don't have a good grasp of how much a lot of dense material weighs.

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It would be helpful if you lookup "Tyranny of Rocket Equation." I looked for an easy-to-understand version, and they best is midway through this comic:

https://what-if.xkcd.com/38/

It’s what engineers call the tyranny of the rocket equation: As the amount that you want to change your speed (“delta-v”) goes up, the fuel required increases exponentially. The equation tells us that to turn the 720-kilogram Voyager around, we’re going to need at least 30 tons of fuel.

But to get that fuel out there, we need even more fuel. And to get that fuel, we need even more fuel. (This is where the tyrannical rocket equation gets its exponential term.) In fact, to rescue Voyager, we’d have to launch a fleet of—at minimum—60 New Horizons-sized spacecraft loaded with nothing but fuel.

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Basically what I'm saying if you have a spaceborne society that uses a fuel to go (I'm assuming) interstellar distances at faster than light speeds, they'll need that fuel to have an extremely high energy density. Not sure at which point relativity steps in to moderate this discussion, but we'll just hand-wave that away.

Point being, you could get away with a few tons, or even a couple hundred pounds. At this point, no one is really counting. The more massive the more unworkable it is from a logistical and navigational standpoint.

Now if you wanted a whole freighter payload of the unrefined stuff, the answer is as big as the freighter. The world's largest container ship is about 400K gross tonnage, so that's a good place to start. The trouble with an unrefined product is it really not plausible to detonate it. After all, dynamite doesn't grow on trees.

Another option would be an "oiler" of refined fuel. Also could put that in some multiple of 100K tons. That would be the most plausible in terms of having a high yield ship packed full of the stuff. But if I were the Vogans designing interplanetary shipping regulations, I would keep shipping volumes below planet-destroying level of energy.

cornflake said:

No one in space would discuss it in terms of weight though, was my point.

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I'm not so sure about that. Throw in a gravitational constant and it's basically the same thing. Most space faring people wouldn't be pedantic physicists. Europeans talk about weight in terms of kilograms, which is a normally considered a unit of mass. Weight and mass are commonly interchanged, in terms of vocabulary. I wouldn't find it so unbelievable if Earth conventions when speaking about shipping still held.

Actually, to that point, it's probably best to either talk in terms of mass, or in something more jargony related to nautical shipping, like gross tonnage. Lbs and stones would be a little odd.

It's complicated, even in nautical shipping. There's a marking called a 'Plimsoll Line' or 'International Load Line' showing how deeply a ship can safely be weighted down after loading, that includes options for various temperatures, water densities, type of cargo, dimensions of ship, etc.

A reference point: This gondola car is rated to carry 90 000 kg (90 t) of ore. How many tons are you expecting to load in a ship?

In space, ore used to power a spaceship would weigh about 360 rontos per cubic flagel.

Jeff

Are those metric rontos?

M.C.Statz said:

I'm not so sure about that. Throw in a gravitational constant and it's basically the same thing. Most space faring people wouldn't be pedantic physicists. Europeans talk about weight in terms of kilograms, which is a normally considered a unit of mass. Weight and mass are commonly interchanged, in terms of vocabulary. I wouldn't find it so unbelievable if Earth conventions when speaking about shipping still held.

Actually, to that point, it's probably best to either talk in terms of mass, or in something more jargony related to nautical shipping, like gross tonnage. Lbs and stones would be a little odd.

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I work in a field where one is picky about the difference between weight and mass, the same way an English teacher is picky about grammar and punctuation. It may not seem important to some but it is.

In SI units, the division between weight and mass is clear. Mass is a base unit, and weight (the Newton) is a derived unit. In Imperial units, weight is actually the base unit, and mass (the slug) is derived from it.

Note that in Imperial units, the statements "I weigh 220 pounds" and "my mass is 220 pounds" are not contradictory. The base unit of weight is the pound-force (lbf). There is a commonly used unit of mass called the pound-mass) which is simply a slug with the unitless number of 32.2 divided from it to make it numerically equivalent to a lbf in engineering calculations.

Would I have a cow about someone expressing their weight as 100 kg? No, but if they expressed a structural loading limit as 2,000 kg, they are going out the door, bags packed.

benbenberi said:

Are those metric rontos?

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Rontos are measured in base 18, and really should be related to dodecahedronal Phlobants, but to convert to metric Kwintessens is simply weight in Rontos times .555. Assuming you're using the decimal system, which would be the only reason to convert.

Bonus points for anyone that notices...

Jeff