Reader Alex went skydiving the other day, and aside from taking his good self, packed an inflatable Portal turret to go with him.
Both then proceeded to jump out of a perfectly good aircraft at 13,000 feet.
Alex says that, thanks to air pressure, the turret was actually really tough to keep hold of, and it was only when they got to around 7000 feet that it deflated enough for him to only have to worry about not dying, instead of not dying and losing a Portal turret at 13,000 feet.