Nah, doesn't work like that. Weight and inertia aren't the same thing. Weight is a measure of gravity affect on something, inertia is it's resistance to a change in velocity. All matter has inertia proportional to it's mass all the time. In fact, mass is basically a measure of inertia.
To say the least, if no gravity meant no inertia, the second you went into zero gravity you'd either cease to exist or be converted into energy in a truly magnificent explosion. Neither would be amenable to space travel, and sattelites would be a very, very bad idea.
The Iceni doesn't have to overcome the force of gravity, but it does have to overcome it's own inertia to make any change in velocity.