To be fair, it's pretty common for "mature" organizations to reach orbit on the first try. SpaceX had three Falcon 1 failures before their first success, and a

To be fair, it's pretty common for "mature" organizations to reach orbit on the first try. SpaceX had three Falcon 1 failures before their first success, and a few other startups have shown similar numbers. On the other hand, the first Falcon 9 reached orbit. More directly relevant, Shuttle was a success on its first launch (good thing, too, with a pair of astronauts flying!). On the third hand, the first Ariane 5 failed 37 seconds into flight, for reasons discussed on HN every so often. I'd give SLS an 85% chance of reaching roughly the correct initial orbit, and only a small chance of leaving a smoking crater.