On 17 Feb 2016 at 11:54, Greg Chalik wrote:

> However, it seems to me that following a misjump what the ship will
> lack is fuel, assuming a misjump will consume 100% of stored fuel.
> But, space is full of potential fuels, though perhaps not as
> efficient as purpose-designed fuels.
> So I'd say that the SOP would be to deploy massive scoops to start
> accumulating that matter to serve as fuel.
> Since hydrogen is the most abundant element in space, and judiciously
> is the canon jump fuel in liquid form.
> It seems to me then that the SOP for ANY ship in misjump is to
> 1. Deploy hydrogen scoops
> 2. when there is a sufficient quantity scooped, commence operation of
> the hydrogen liquifier converion unit (HLCU)
> 3. When the HLCU has acheived sufficient volume, commence transfer to
> fuel tanks
> 4. When there is enough liquid hydrogen in the fuel tanks, try for
> another jump.
>
> Is there a problem with this?

Yes. At ordinary speeds you won't accumulate hydrogen at useful
levels *ever*. Remember, you are operating in a hard vacuum. Hydrogen
atoms may be as high as a dozen per cubic meter.

Avogadro's number is the number of molecules in a mole. A mole of
hydrogen atoms would be one kilo.

Avogadro's number is 6.0221409e23.

So at 6 atoms per cubic meter, you'd have to run the scoops thru
100,000,000,000,000,000,000,000 cubic meters of space to get one kilo
of fuel.

That's 100,000,000,000,000 cubic kilometers. For one kilo. For a
tonne of fuel, it'd be 100,000,000,000,000,000 km^3. That's a cube
464,159 km on a side.

You'd be scooping for a very, *very* long time.

Bussard ramjets (which turn out to not be workable) were supposed to
use magnetic fields hundreds of km across, and they'd need to be
moving at at least a few percent of c to scoop enough fuel.

alas, it turns pout that drag from the scoops won't let them get up
to a velocity that'd gather as much fuel as they'd need to run.

Only practical way to refuel in an "empty" hex is to find an icy body
and mine the ice. Neither of which is at all easy.

--
Leonard Erickson (aka shadow)
shadow at shadowgard dot com