Threaded alternative to MMCX connectors which mates to RG-316/U
The other option is to simply glue or pot the connector in place. I couldn't speak for space applications, but for military stuff that had shock/vibe requirements we often pot through hole components like big caps and certain connectors to stop them shaking apart.

For an MMCX you could also try solder blobs on the connector body shield down to a ground plane on the PCB.

Failing that, try a different connector more suited to high vibration. Avoid SMPM (GPPO) if you can, the connector locates using the contact pin and has a tendency to deform it with every mate cycle.