This concerns the Live build on Steam "ONI - Spaced Out" Build EX1-445739
Not sure if this can be considered a bug, as you seem to be in process of redesigning the space travel gameplay, but I found no information on how this should work otherwise: the gantry is missing from the rocketry building menu, and/or is not accesible through any research topic. It is still mentioned by the in-game encyclopedia though.
Without the grantry, it's hard to construct and access rocket modules that are a few tiles above the rocket pad.
- Built a rocket platform
- Observe that there are no build or research options to place a gantry