Today’s the day—probably—for Relativity Space to attempt its first launch of the small-lift Terran 1 vehicle.

The three-hour launch window opens at 1 pm ET (18:00 UTC), and weather conditions at the company’s Cape Canaveral, Florida, launch site appear to be ideal. The biggest threat to a liftoff today, almost certainly, is some issue during the countdown with the vehicle or ground systems, as commonly occurs with new rockets.

If the rocket does lift off, then nominally, the Terran 1 will reach a 365 km by 373 km orbit at precisely eight minutes. But it’s very far from clear that the launch of the Terran 1 rocket, the majority of which was additively manufactured by large 3D printers, will go as planned. In recognition that this is purely a test flight, Relativity has put no customer payloads on the flight. And the mission has a lighthearted name, “Good Luck, Have Fun,” that acknowledges there is a bit of a hold-my-beer aspect to this test flight.