Woah, it's today, in less than 12 hours. Not sure if I'll watch this live, because it's going to blow and I'm not ready for that kind of suspense.
Elon gives it 67% chance of success, which I find unrealistically low. The worry is the interaction of the three F9 cores and 27 Merlin engines, which has never been tested in flight (kind of obvious, since that's the only thing that's new). But fixing that issue has been why they have been delaying the Heavy until now. I don't think they would fly if they weren't confident that had fixed any known troubles with that – if they haven't, no amount of good telemetry from a test flight will solve them for the ArabSat 6A launch, which is ‘early’ this year.
So I presume the 33% chance of failure Elon gives is about unknowns they didn't foresee in their simulations, and other shortcomings of those simulations or the static fire as a source of data. But that means he doesn't know the actual chance, and if it is 33% and we don't blow, they may not even notice the issue until a future rocket blows, which doesn't seem reasonable.
And I don't think they would be risking damage to the pad if the chances were really this low.
Doesn't the worry here also apply to their future Mars rocket, which has even more engines that are way bigger? I guess they might be willing to blow up some Heavy rockets to get the BFR right, but that sounds far-fetched.
I think the flight will be successful, but I still won't watch. Call me when SpaceX are actually confident they can fly this thing.
