Appearances are misleading.My understanding is that most of the time spent in building a launchpad has to do with getting the earth beneath it to settle in order to create a solid foundation. This involves things like piling a big mound of dirt on the site and leaving it to sit for a few years while its weight slowly compresses and drives the water out of the earth below to make a nice solid foundation. But they've already done this at Boca Chica!Once the ground is finally prepared for the foundation, the rest of the construction can go quite fast. A flame trench is just a big trench in the ground with concrete sides. The service tower is a heavy duty scaffolding with pipes running up it. Tanks, trenches for pipes, lightning rods, launch clamps... None of this is likely to take very long to install once the ground is ready to support it.The foundation is everything. It has to support thousands of tons of fueled up rocket, and then nothing shortly afterward. This sort of dynamic load flexes and cracks and is in general much harder on the foundation than a building which just peacefully sits there. And all this is on top of land that started out as marshy unstable coastland.
The foundation is everything. It has to support thousands of tons of fueled up rocket, and then nothing shortly afterward. This sort of dynamic load flexes and cracks and is in general much harder on the foundation than a building which just peacefully sits there.
Quote from: Keldor on 04/02/2019 10:39 pmThe foundation is everything. It has to support thousands of tons of fueled up rocket, and then nothing shortly afterward. This sort of dynamic load flexes and cracks and is in general much harder on the foundation than a building which just peacefully sits there.I'm curious how SeaLaunch handled this dynamic load during/after launch. It looks like they used a semisubmersible with a minimal waterline. The small waterline means that big waves don't kick the platform around much. But it also means that large changes in load, requiring large changes in displacement, will cause the platform to lurch vertically in the water.I'm also curious about how a jack-up platform deals with dynamic loads. It has some sort of foundation: whatever the interface is between those vertical trusses and the sea floor. Is it typical to just hammer piles into the sea floor and let the friction between the piles and the clay handle the dynamic loads? Piledrivers don't work overnight but they don't take months either, and it does seem that you could decouple from underwater pads to tow the barge into dock, and then recouple to those same underwater pads later.Decoupling/recoupling to an underwater LOX and LNG pipeline seems more risky, but it also seems you could have a permanent abovewater terminal for those, to which a jack-up rig and barge for carrying the SS could dock.
It finally occurred to me that they already have almost everything they need right in front of us at 39A. In fact, they have too much equipment! The answer is that Boca Chica is the initial testbed not only for building a Starship, but also for transporting it to a launch facility and launching it. The one facility lacking at BC to launch the full stack is the flame trench, so they will transfer the whole launch procedure to Florida and use the existing trench for further testing!
A major reason for assuming that they needed a new pad was the assumption they wanted to implement the full rapid reuse system including landing SH on the launch mount. That wouldn’t be accepted at 39a, and any mods to require it would interfere with the F9/FH use of 39a. If they put legs on SH and land both it and SS at the regular LZ that’s not a problem.Doing it this way means giving up the ambition for very rapid reuse at first but I’m sure that’s secondary to getting it flying ASAP. Working on both sites gives them an alternative if they hit obstacles.
It is clear that the Hopper will be launched from the concrete pad at Boca Chica, a la Grashopper.As the orbital prototype is under construction at Boca Chica also, it is generally assumed that it will be launched from the same pad, without a flame trench. This is surprising, because the SS is supposed to have around 1000 ton fueled mass, more than 3x heavier than a Soyuz rocket. Well, SS is supposed to be launched without a flame trench from Mars, also. However, as somebody explained in one of the many discussions here, there is no acoustic problem in the thin air of Mars.
I don't see any particular reason they couldn't start restricting F9/FH to LC-40. They'd have to expand or replace their service tower for crewed flights, but that's not really a show stopper. I don't think even NASA could find a reason to drag their feet over the safety of a simple tower with an elevater and an access arm. I mean, they do have that zip line system on LC-39B, and the associated bunker, but an escape method like this on a rocket with fueling once the astronauts are inside and the ground crew evacuated and an launch escape system having any sort of practical use is pretty far fetched.They can keep the clamps and tooling for F9 and FH nearby and ready in case LC-40 gets fragged. Reinstalling them to convert LC-39B back to use with the Falcon rockets should be finished sooner than the fleet is ungrounded.Since LC-39B is so historic, SpaceX wants to use it for their most prestigeous flights. Right now that means FH and crew Dragon. But SH/SS will overshadow that.Eventually they will want redundancy in case something gets blown up. They might also want more rapid launch cadence with Starlink and all. This means a Boca Chica pad in likely to happen in the future.If permitting drags on to the point where SpaceX has a rocket ready and it's causing delays, I wouldn't be the least bit surprised to see an executive order come down the pipe to get their butts in gear. Permitting and associated regulations are done by the Executive branch, and the launch facilities are overseen or outright run by the feds, again Executive branch. The president would be completely within his rights here. Even with Boca Chica, federal law overrides state law, and the feds are the authority for launches.
LC-39A is Spacex, LC-39B is SLS and LC-39C is unused.