Wet dress rehearsal
A key element to a successful launch is to make sure everything works as intended before an actual launch.
A wet dress test means bringing the vehicle to the launchpad, starting the countdown, initiate fueling and stop the countdown just before ignition (rocket engines will ignite for a few seconds and cutoff again). Solid boosters wont be ignited, as these cannot be controlled or turned off once ignited.
During this test everything will be monitored and tested.
This way potential leaks, or faulty units can be identified and the ground crew gets valuable training prior to the actual launch.
In space manager you can always perform a WDR on your vehicles, though its not mandatory, it does reduce the risk of having a failed launch, which is usually a very costly experience - so not mandatory, highly recommended. - Test flight launch window in 18 minutes. Perform a wet dress test or initiate fueling - Wet dress test started and vehicle fueled. Test test is now being performed to verify if the vehicle is flight ready - WDR summary. Test completed with no errors, and the vehicle is now ready for launch