Premise: Spare synthmorph (from Gatecrashing) modified with Internal Rocket (from Transhuman).
(... Am I the only one who's all too amused by the mental images of a fork-happy fellow sending hordes of customized, large-squirrel-sized robots tootling across the solar system, without bothering putting them in something as large as a spaceship?)
Starting Numbers: A standard Spare weighs 2 kg; Internal Rocket creates 0.25 gravities of thrust for 90 minutes; according to this thread, metallic hydrogen drives have an ISP of 1,600.
Calculations: That acceleration for that time provides a total delta-v of 13,230 m/s, which is reasonably nifty. Assuming that the 2 kg figure counts as the payload mass, then the rocket equation concludes that the morph, plus fuel, weighs a total of 4.65 kilograms. Assuming there's a bit of slack in that 2 kg number, enough that it includes the structural support and the equipment to keep the metallic hydrogen from immediately evaporating, that's over five and a half pounds of MH attached to a morph that's usually the size of a frisbee...
... So just how many ways would there be for a PC to void any warranties, and have fun with the stuff? :)
As the most obvious example - the rocket normally has a mass-flow rate of around half a gram a second; how explosive would the results be if it was all released at once, such as by being in the middle of a firefight?
The density I get for MH via Google is 0.6 g/cm^3, so the tanks for the modified Spare adds about 4.4 litres to the morph's volume. If all that hydrogen were converted into ordinary gas, that would be 29,483 litres, something like 6,675 times its previous volume. Put another way, that's enough to inflate a 10x10x10 foot balloon at standard pressure... or to double the air pressure in a 10x10x10 foot sealed room, which seems likely to rupture a few important gadgets (or biomorph organs), or even cause a blowout. And that's without even considering hydrogen gas's famous flammability.
How expensive do you think a gadget to create fresh metallic hydrogen, to refuel emptied tanks, would be to nanofacture, and/or to run? How fast would it work? Is there any reason water electrolyzed into its component elements couldn't be used as feedstock? How expensive would MH be to buy in random places? (One possibility - if local water is already being split to create breathable oxygen for biomorphs, then the hydrogen might be little more than a waste product.)
What are conditions inside the MH tanks like? For example, would it be possible to hide an object within that would be nigh-impossible to notice until the tanks were emptied, without significant damage? I found a note that MH can't be stored long at Venus's surface; what other sorts of environmental conditions might PCs venture into that would affect MH tanks?
Is there any way to deliberately make MH tanks unsteady, or MH more volatile, ala the ultra-high-pressure versions of Things I Won't Work With?
What other evil ideas come to your mind?
Thank you for your time,