I found this paper online:
https://thephysicsofspacex.wordpress.com/wp-content/uploads/2016/07/isp-upper-limits.pdf

Hence, the upper limit for a stochiometric methalox mixture ratio is:
Isp = 458.7s

(By the way, “stochiometric” means that the combustion is not fuel rich or oxygen rich, so all the molecules burn and turn into the exhaust molecules (CO2 and H2O), producing the maximum amount of energy.)

The Raptor engine gets a specific impulse (Isp) of about 380s in vacuum, so it looks like there is room for 17% improvement.

I hear you asking already: “But wait. Musk said in an interview, I think with the Everyday Astronaut, that the Raptor gets 99% of the energy out of the fuel and oxidizer, so shouldn’t the Isp be much closer to 454 seconds?

If SpaceX were to use electric turbo-pumps, like Rocket Lab’s Electron does, would they get a higher Isp? Yes. So maybe what we need is a low weight battery, like lithium ion, without the high flammability of lithium ion.

Following acceptable levels of reliability of course.

By the way, I can’t claim to really understand ISP, but is there a theoretical max ISP for a MethaLOX engine, and if so, how close to it are we?

By the way my back of the envelope calculations for the rotational speed of the Earth’s surface at various points are:
Wallops Island: 1317 km/hr or ~4.7% orbital velocity
Cape Canaveral: 1467 km/hr or ~5.2% orbital velocity
Starbase: 1504 km/hr or ~5.4% orbital velocity
Puerto Rico: 1583 km/hr or ~5.7% orbital velocity
Guiana Space Centre: 1663 km/hr or ~ 5.9% orbital velocity
Equator: 1670 km/hr or ~ 6% orbital velocity

So to move from Starbase to Puerto Rico, you gain a whopping 80 km/hr. Oh well…

People like to ignore me when I suggest Mobile, but I could see something like mulberries leading out to a launch site with methane right out of an off shore well.

We have stainless steel plants on the coast–and Birmingport in central Alabama–far from hurricanes.

The SLS pathfinder was built not far from me in West Jefferson County.

I think Elon needs to build even wider, taller vehicles–with 50 Raptors.

Easier to float and stand up if made where it can lay on its side.

I still consider Starship too small for what Elon wants to do.

Ray Van Dune: Considering that Puerto Rico’s power grid went down today (reminiscent of Cuba’s recent problems), combined with its government’s corruption and inability to fix the damage from hurricanes, I strongly suspect there has been little interest in approaching them at all.

Of course, this only highlights the problems a citizenry causes to itself when it chooses its leaders badly.

As things stand now, they’ve applied for pads at LC-39A and SLC-37 (with an alternative location a km north of 37 if that doesn’t clear). Those two sites are large enough to accommodate two Starship pads each, and it’s widely speculated that this is what they’ll do. Combined with Boca Chica, that would give them six pads, hopefully operational by 2027 (the big hangup is the EIS for each site, now underway) and that ought to be sufficient to undertake the initial Artemis missions and a decent cadence of Starlink V2 launches. In the long run, they will need more pads. I think they’d prefer more pads at the Cape.

I think the bigger issue is obtaining sufficient quantities of LOX and liquid methane. The quantities needed are, uh, enormous. That is going to require a lot more infrastructure at both places….though I don’t doubt that SpaceX will figure it out.

Given the size of Starship, it is arguable that it can only be efficiently launched, recovered, and serviced from a locale immediately adjacent to where it is developed and built. That means a Starship facility would necessarily be quite extensive and generate massive local benefits, probably putting the Brownsville case to shame.

Imagine a Starbase, but with a half-dozen towers, and the industrial infrastructure to keep them launching continuously at the rates Elon has projected. That’s what it seems like it will take, in say a decade!

Ray Van Dune: My guess is that the Puerto Rican government has probably been the main reason there is a lack of interest in setting up launch facilities there.

Given the island’s US territorial status, proximity, latitude and the Roosevelt Roads harbor and inactive naval facilities, any ideas why it wouldn’t make sense?