This issue happened to me while playing pyanodons alternative energy https://mods.factorio.com/mod/pyalternativeenergy
Space Age was not enabled.
In the mod, there are items (tholins capsules) you launch into space in the same way you launch satellites in vanilla.
However the tholins capsules have a rocket capacity of 5 instead of 1 for vanilla satellites.
The "Send to orbit automatically" button does not wait for the rocket to be filled with 5 tholins capsules, and instead instantly launches when a single tholins capsule is inserted in the rocket silo.
In the screenshot below if i click the "Send to orbit automatically" button, the rocket will immediately launch.
There is also no circuit option to enable/disable the rocket silo or its launches so the only way to automatically launch full rockets are with simultaneous insertion of all 5 capsules, or using power switches.