UFO's

[Anomalocaris]

Uh, >>90% of the water in our solar system is not on earth.   If our understanding of the process of planetary formation is correct, then most planetary systems would contain many times more water than present on earth, many of these would have them concentrated on large outer planets and moons.

Apologies for being unclear, what I was stating in a rather vague roundabout way is, why does a starship need water?

Water may indeed be a valuable resource for an interstellar spaceship, growing petunias or whatever but as a reaction mass for a propulsion system then that is one piss poor starship drive they have.

Edit:

Other than water what does planet Earth have that they can't find in the millions of planets much closer to their home world?

Yes I see your point. My bad.

Water as reaction mass for a propulsion system may not seem nearly science fictiony enough for an future age we are told that would be populated by warp factors and Alcubierri drives,  but there seems to be no reason why such reaction propulsion systems can not form the basis of interstellar civilization.

Right conceited yokels we would seem if several hundred years in the future, we are still stuck on this planet pining away for faster than light technology, and scrappy adventurous aliens in chemical rockets a century or two behind our own technology curve come down and demand to see our leaders.

[Gawdzilla Sama]

And we can't be that interesting to a space-faring race. Maybe for battle royals, perhaps.

[Succubus]

Water as reaction mass for a propulsion system may not seem nearly science fictiony enough for an future age we are told that would be populated by warp factors and Alcubierri drives,  but there seems to be no reason why such reaction propulsion systems can not form the basis of interstellar civilization.

Science fictiony or not, if ET is using water as a reaction mass then they will never leave their home system.

The Tyranny of the Rocket Equation.

[Anomalocaris]

And we can't be that interesting to a space-faring race. Maybe for battle royals, perhaps.

Who knows, may be we are interesting, and unbeknownst to us, we already live inside a terrarium for giant trans dimensional aliens,  and only yesterday a holographic sign invisible from the inside was posted on the outside of the terrarium saying “don’t tap on the force field!”

[Gawdzilla Sama]

And we can't be that interesting to a space-faring race. Maybe for battle royals, perhaps.

Who knows, may be we are interesting, and unbeknownst to us, we already live inside a terrarium for giant trans dimensional aliens,  and only yesterday a holographic sign invisible from the inside was posted on the outside of the terrarium saying “don’t tap on the force field!”

"The True Man Show".

[Anomalocaris]

Water as reaction mass for a propulsion system may not seem nearly science fictiony enough for an future age we are told that would be populated by warp factors and Alcubierri drives,  but there seems to be no reason why such reaction propulsion systems can not form the basis of interstellar civilization.

If ET is using water as a reaction mass then they will never leave their home system.

The Tyranny of the Rocket Equation.

There is no real difference between using water as reaction mass or using some gas like helium as reaction mass.   You can build very efficient ion propulsion by vaporizing, dissociating water, and ionizing the oxygen and hydrogen and use them as reaction mass using electric propulsion.

Ion drive can be much more efficient than chemical propulsion.  

We’ve already sent probes out of our solar system using chemical propulsion.

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Science fiction writers seem to imagine the first alien to come to our system would be much more advanced than we are, and can easily squash us like bugs.   That probably is a statistically reasonable assumption.

However, I think it is more interesting to speculate the reverse, taking a cue from Ming and Qing dynasty China.    What happens if the first alien who comes to us are technologically more backwards and poorer then we are, like the Europeans were technologically more backwards than Ming and early Qing dynasty China, and far poorer and less productive than the mogul empire in India, but they are far more ruthless and enterprising than we are?

We fantasize that we are mean little buggers, and even if we are not technologically competitive, we are just good at fighting, hence all the fantasy novel of human mercenaries serving technologically superior aliens.    but what if we’ve not compare to them?  We are rich, fat, complacenct buggers compare to the real carnivores of the universe?

We think discovery of extraterrestrial intelligence will instantly unite humanity.  I think not.  We will each seek to enlist the aliens to help overmatch our fellow men.   In the end the aliens will find it effortless to divide and conquer us.   They hardly need to break out the fancy hardware and clouds of wicked looking machines. They just drip feed some offers of help in our fight against our fellow humans and we will trip over ourselves to do their biddings, just as a few tens of thousands of brits hardly had to conquer much of India by force to completely subjugate the entire subcontinent of four hundred million.

[Succubus]

If ET is using water as a reaction mass then they will never leave their home system.

The Tyranny of the Rocket Equation.

There is no real difference between using water as reaction mass or using some gas like helium as reaction mass.   You can build very efficient ion propulsion by vaporizing, dissociating water, and ionizing the oxygen and hydrogen and use them as reaction mass using electric propulsion...

I see no net gain in chucking ionised water (for want of a better term) out the engine nozzle as opposed to chucking out superheated steam.

[Anomalocaris]

There is no real difference between using water as reaction mass or using some gas like helium as reaction mass.   You can build very efficient ion propulsion by vaporizing, dissociating water, and ionizing the oxygen and hydrogen and use them as reaction mass using electric propulsion...

I see no net gain in chucking ionised water (for want of a better term) out the engine nozzle as opposed to chucking out superheated steam.

You can only add so much energy to steam before they stop being steam and become ions anyway.   Also, it’s much more efficient to use a magnetic field to chuck stuff out at high energy and speed than to try to do it using heat.  To do so the stuff being chucked out needs to be charged.

[Succubus]

<Much snipped for focus> What happens if the first alien who comes to us are technologically more backwards and poorer then we are...

How would they get here?

[Anomalocaris]

<Much snipped for focus> What happens if the first alien who comes to us are technologically more backwards and poorer then we are...

How would they get here?

Solar sails?  Chemical rockets?   This is several centuries in the future,  they can have stuff we can’t imagine today, and still be a technological behind where we would be then.   The Chinese had far better ships and technology overall in the 1400s, but it was the Europeans who made much better use of inferior ships and discovered America, and reached China, instead of the other way round.w

Maybe they are more advanced than we are in one area, but we are more advanced in several others.   So the Europeans had better ships and better astronomy than the Indians in the early 1700s, but the Indians were still competitive or superior in many areas of farming and metallurgy, and arguably some aspects of military technology as well.    Yet queen victoria became the empress of India, while no india prince ever became emperor of British isles.