When a piece of equipment is in a zero g environment, gravity loads are zero, not '-1'.
There are two approaches to designing things for zero gravity, depending on exactly what you're doing.
Approach 1: design for mechanical robustness/stability against whatever your highest temporary loading condition is. For spaceflight hardware this is almost always going to be loads experienced during the launch. Loads experienced during orbital changes will almost always be quantitatively smaller than launch loads, but they may be off-axis from the launch load, in which case you need to account for that too. Then assume that if you're safe against 6+ g of launch load, you're safe with zero gravity load. This works most of the time.
Approach 2: design for mechanical robustness/stability against whatever your highest temporary loading condition is, BUT also determine what the exact response of the system will be to no gravity load at all. IE, if I have a frame holding widget x that weights 500kg under 1g, and under 1g widget x is 999mm from widget y, at 0 g that distance may become 1001 mm because of a lack of gravity induced deflection in the frame. This is necessary if you're designing VERY precise instruments- for example, the structures that hold the optics of orbital telescopes and downward looking cameras on satellites require very precise control of zero gravity dimensions.
In either approach you also need to make sure you understand and correctly account for thermal loads - they can be very large in orbit or transit between orbits.
