A dTon of hydrogen is a metric ton mass. The scout wants 40 metric tons of hydrogen, H2. Assume we're mining water ice: one ton per cubic meter, of which 89% (the oxygen) is unneeded. For each cubic meter they mine, they come away with 111 kilograms of hydrogen. You need about 360 cubic meters to fill the 40 dTon H2 tank.
How much energy you need to raise a ton of water ice to liquid temperature depends on the temperature of the ice. Assume -200C (temperature around Europa). One ton, a thousand kilograms, raised 200 degrees to melting point is 200 thousand kilocalories. A kilocalorie is 4.2 kilojoules, so 840 thousand kilojoules to turn a 1-ton block of water ice on Europa to liquid; then you suck it up. Your scout's 500 megawatt fusion plant puts out enough power to melt a ton of ice in a bit over a second and a half, so power isn't a problem - applying it to the desired location and reaping the reward without losing it to vacuum is your problem. That, and keeping the system small enough that you can say you have it without explaining why you're not allocating space specifically for it - it's a tiny part of the fuel system.
Technical problem is you're in vacuum, so your system needs to be able to deal with the ice in some manner as to prevent losing water to vacuum. Say, a large diameter semirigid hose (okay, flexible pipe if it makes people happy) ending in a head that's designed to press onto the ice and heat the surface covered by the head. Low power lasers or some other method can melt or vaporize the surface covered by the head - easier to vaporize in vacuum, water has a "triple point" at about 0C in vacuum, which means under these conditions the ice goes straight to vapor until enough pressure builds up under the head to support liquid water, which is just fine cause the vapor can be sucked up just as easily as it is produced.
Ice in space is unlikely to be just a block of water. You'll encounter other volatiles in ice form, most useful as sources of hydrogen, maybe they're mixed, I don't know. No reason to be picky. Run the vapor through the power plant, temps high enough to break down molecular bonds, turn the lot into a high temperature plasma, centrifuge the result, collect the lighter hydrogen and discharge the rest. Result isn't perfect, but it's good enough to call it an unrefined fuel.
For convenience and play balance sake, I'm going to say it takes a week to fill tanks that way: hoses with 500 kilowatt heaters operating constantly. A 500 Kw laser heating system is conveniently small and inexpensive by Striker design rules, you don't have to explain where the space or cash for it is coming from, and at that rate it's not an attractive method, not something to challenge canon, but it's doable if you can't or won't go to another fuel choice. Likely to be a lot faster in the polar zone of a terrestrial planet, where the temps aren't so radically low and you've got atmosphere - maybe one or two days. Antarctica sees lows down to -90 and lower but averages range from -10 to -55 depending on how close to the pole you are. Mars runs to a low of about -150C at the poles; ice temperatures there might be around -50C, though that's speculation. Ceres/asteroid belt runs to temps of about -30 to -120, and Europa -150 to -220. Likely to be a bit slower out in the Kuipers, where temps are in the -220C to -260 range; might take 8-10 days.
http://beforeitsnews.com/space/2012...mperatures-in-the-solar-system-2-2451130.html
You could of course go with a more powerful heating head, maybe chop time by a factor of 10.
