After a lot of talk and rumors over the last few weeks about booster 4 being
moved to the Orbital Launch Mount, it was moved today. While it's easy
to expect them to start doing the static testing that's a barrier to trying an
orbital launch, this is the third time that booster has been on the OLM and
there are no guarantees this isn't some sort of test fit that will be followed
by dismounting B4 soon. Still, Elon Musk said he hopes to do the first
attempt at orbit "early in January" and that's less than three weeks
away. If they're going to make it, those tests must become high
Screen capture from Lab Padre. As it says.
As we've said dozens of times, the first boosters will have 29 Raptor engines. That helps make this launch pad among the most complex the world has ever seen. If not the most complex launch mount. Eric Ralph at Teslarati supplies some details.
... By all appearances, Super Heavy hold-down clamps – mechanical devices designed to hold the booster to its work stand or keep it immobile on the launch mount during a variety of test – work by reaching inside the lip of the booster’s aft ‘skirt,’ which sports a very sturdy ring of steel that 20 Raptor Boost engines mount to and push against. The 20 clamps fit precisely between each of those 20 outer Raptors and grab onto Super Heavy from the inside.
Just before liftoff, all 20 hold-down clamps will rapidly retract back into the orbital launch mount. So will another 20 small quick-disconnect umbilical panels designed to supply every single Raptor Boost engine with the gases they need to ignite. The primary booster quick-disconnect – which connects Super Heavy to power, communications, and propellant supplies – will also retract into a hooded enclosure at some point during the process. Finally, a giant, swinging arm located about halfway up Starbase’s ‘launch tower’ will retract a similar quick-disconnect panel for Starship fueling, retract two claw-like support arms, and swing back for liftoff.
Eric goes on to say that there are probably even more than those just described. Every Starship launch will require at least 44 separate devices to
actuate in rapid and precise succession – 41 for Super Heavy and
at least 3 for Starship. It's my impression that a lot of this hardware was borne out of the idea that was first talked about earlier this year: to move as much infrastructure as possible out of the vehicle and onto what Elon called, "Stage Zero" - the OLM. All in an effort to minimize the mass of the booster and maximize its payload. That complicated the design of the OLM and seems that it must have contributed delay to getting the OLM ready for testing.
As of now, the Cameron County road closure page for SpaceX shows the next round of closures starting Wednesday 12:00 p.m. to 8:00 p.m., with "secondary" (backup) days of Thursday (same time) and Friday 8:00 a.m. to 2:00 p.m.. It's probably wishing a bit too much to hope they'll do any testing of B4 this week.