Half million ships, call it an average of 50 dtons each, is 25 million dtons.
Call it 340 million cubic meters of hydrogen
Or 0.34 cubic kilometers.
11 to one density shift for Water to LHyd, so multiply by 11 ...
Gives 3.74 or so Cubic kilometers water per year.

http://hypertextbook.com/facts/2001/SyedQadri.shtml
Table 1.
Lakes alone are 242,000 cubic kilometers.

Looks like just the lakes would give us about 64,000 years...

On Thu, Aug 28, 2014 at 10:15 AM, John Geoffrey <xxxxxx@gmail.com> wrote:
> Ok, i might be overthinking this, but wouldn't half a million ships per year
> need a LOT of hydrogen? Wouldn't this amount of ships impact the environment
> quite negatively?
> Half a million scout ships would need 20 million tons of fuel each year. And
> this fuel would mostly be spent in space (for the jump-bubble). Would this
> not lead to a lot of hydrogen loss over a few years?
>
>
> On 28 August 2014 16:04, Jeffrey Schwartz <xxxxxx@gmail.com>
> wrote:
>>
>> Or deliver... Or both.
>>
>> But, yeah.
>>
>> Using those numbers, I can see where the Imperium doesn't need
>> Megafreighters and can operate with just the small book ships.
>>
>> The problem then becomes the large number of ships per year....
>>
>> Let's ballpark a half-million ships per year.
>> That's about 1400 per day.
>>
>> But is landing the ship at a single starport and lugging stuff all
>> over the planet the best way of doing things?
>> How about various "local ports" ?
>> What if we were to spread this over the world's top 50 airports and
>> top 50 container ports?
>> That comes out to 14 ships per day, per port.... which in a
>> player-local-view begins to sound like a Traveller 'feel': a ship
>> lifts or lands about every hour or two, providing background noise for
>> the players activities.
>>
>> If you spread it out more, then you could get to were the T5 numbers
>> start to seem right... per _port_, not for the whole system.
>>
>>   *** THERE MAY BE MATH ERRORS HERE, FEEL FREE TO PICK APART ***
>>
>> Once out in space, then figure 80% the ships are going either up or
>> down the main, and the rest are going 'across the grain' elsewhere in
>> the subsector. That'd put the high traffic area around 560 ships,
>> about 23 per hour.
>> At one G, 800,000km (100d) is about 5 hours...
>> The Earth's moving around the sun at about 300km/sec, or about 1 million
>> km/hour
>> That'd scatter 115 ships over a arc 5 million km wide by 0.8mkm
>> deep.... in the busy direction.
>> Call it around 40kkm apart, on average, or about an hour push at 1G to
>> meet each other.
>>
>>
>> That's sparse enough for Exciting Play, I think.
>> The Type-A having a serious malfunction could be 2 hours travel time
>> away from the other Merchants, but only 40 minutes away from a Type-S
>> who can come to the rescue at 2G.
>>
>> On the "across the sector" low traffic arcs, there'd only be about a
>> quarter as many ships, so the above would be as much as 8 hours vs 90
>> minutes
>>
>>
>> On Thu, Aug 28, 2014 at 9:32 AM, Ian Whitchurch
>> <xxxxxx@gmail.com> wrote:
>> > And because a vanilla type S - not refitted as a belter - has 4dtons of
>> > cargo space, they'll be looking for 400kdtons of cargo a year to take
>> > back
>> > to try and cover their costs, right ?
>> >
>> >
>> >
>> >
>> > On Thu, Aug 28, 2014 at 11:05 PM, Jeffrey Schwartz
>> > <xxxxxx@gmail.com> wrote:
>> >>
>> >> On Wed, Aug 27, 2014 at 5:57 PM, Ian Whitchurch
>> >> <xxxxxx@gmail.com> wrote:
>> >> > Its like you show people a game mechanic, and their brains turn off.
>> >> >
>> >> > If a world with a billion people, then it has roughly 20 million 18
>> >> > year
>> >> > olds. If it has 1/6th of them go join the IISS, and that world doesnt
>> >> > have a
>> >> > IISS base, then thats 3 million people a year we need to move off the
>> >> > world,
>> >> > every year.
>> >> >
>> >> > Theres your need for megafreighters, right there.
>> >> >
>> >>
>> >> The flip side of that is there's, at a guess, 100k people a year who
>> >> are on "Detached Duty" from the IISS, who have brought their "S" home
>> >> for vacation.
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