The 100 − 150 ton numbers that SpaceX has offered over the years are always referring to the fully-reusable version launching to LEO. I believe even Falcon 9 (though not Falcon Heavy) has essentially stopped offering expendable flights; the vision for Starship is for them to be flying full-reusable all the time.
That said:
I forget where I got this impression (Eric Berger reporting, possibly?), but IIRC right now they’re not on track to hit their goal numbers; the first reliably-working version of Starship might be limited to more like 50-70 tons, because the ship came in heavier than expected (all those heat tiles! plus just a lot of steel.) and the Raptor engine, while very impressive, has perhaps not fully achieved the nigh-miraculous targets they set for themselves.
if you want to take 100 tons, not to LEO, but to Mars (which is the design goal of the system) then you have to use many starships to ferry fuel to refuel other starships, gradually boosting their orbit until you have a fully-fueled ship in a highly elliptical earth orbit, and then you can finally blast off to Mars. For the moon it’s even worse, you need maybe 20 refueling flights to land 1 starship on the moon with enough fuel to come back.
Agreed with you that the heat shield (and reusable upper stage in general) seems like it could easily just never work (or work but only with expensive refurbishment, or only from returning from LEO orbits not anything higher-energy, or etc), perhaps forcing them to give up and have Starship become essentially a big scaled-up Falcon 9. This would still be cheaper per-kg than Falcon 9 (economies of scale, and the Raptor engines are better than Merlin, etc), but not as transformative. I think many people are just kind of assuming “eh, SpaceX is full of geniuses, they’ve done so many astounding things, they’ll figure out the heat shield”, but this is an infamously hard problem (see Shuttle, Orion, X-33...), so possibly they’ll fail!
Some other tidbits:
Raptor’s claimed vacuum ISP is 380; I don’t think they’re just, like, making this up (they have done lots of tests, flown it many times, etc—it’s not a hypey future projection like “Starship will cost $4m per flight”), but I also don’t know where I’d go if I wanted to prove to myself that the number is legit (wikipedia just cites an Elon tweet...).
Apparently those Starlink mass simulators actually weigh about 2 tons each?? So flight 7, which carried 10 Starlink simulators, actually put 20 tons of payload in orbit.
The first reliable version of Starship will very likely fall short of its intended 100 ton goal (i mean… unless it takes them a really long time to make Starship reliable, lol). But they also plan to stretch the rocket, refine the engine, maybe someday make the whole thing wider, etc. So I expect that they’ll eventually hit 100 tons. (The first version of Falcon 9 could only lift 10.4 tons to LEO; the current version can lift 17.5 tons AND land the first stage on a drone ship for reuse!) But of course if you make the whole ship bigger, some of your launch costs are gonna go up too.
Personally I’m doubtful that they ever hit the crazy-ambitious $20/kg mark, which (per Thomas Kwa) would require not just a reusable upper stage (very hard!) but also hyper low-cost, airline-like turnaround on every part of the operation. But $200/kg (1 OOM cheaper from where Falcon 9 is today, using the rumored internal cost of $30m/launch and 17.5 ton capacity) seems pretty doable—upper stage reuse (even if somewhat ardurous to refurbish) probably cuts your costs by like 4x, and the much greater physical size of Starship might give you another almost 2x. Cheap materials (steel and methane vs aluminum and RP1) + economies of scale in Raptor manufacturing might take you the rest of the way.
Raptor’s claimed vacuum ISP is 380 [...] I also don’t know where I’d go if I wanted to prove to myself that the number is legit (wikipedia just cites an Elon tweet...).
The Isp of a closed cycle rocket engine with a given propellant mix is largely a function of its chamber pressure and expansion ratio, so one can use a program like RPA to plug in known numbers and see what other claims are consistent with an Isp of 380. Example (for SL variant) in this tweet.
My guess is that 380 is achievable if they close the throat and use a large enough nozzle, but they’ll opt for slightly lower in order to cram 9 engines into the upper stage. With Starship staging at record low velocities, reducing gravity losses through higher thrust might matter more than a 1% efficiency gain.
The 100 − 150 ton numbers that SpaceX has offered over the years are always referring to the fully-reusable version launching to LEO. I believe even Falcon 9 (though not Falcon Heavy) has essentially stopped offering expendable flights; the vision for Starship is for them to be flying full-reusable all the time.
That said:
I forget where I got this impression (Eric Berger reporting, possibly?), but IIRC right now they’re not on track to hit their goal numbers; the first reliably-working version of Starship might be limited to more like 50-70 tons, because the ship came in heavier than expected (all those heat tiles! plus just a lot of steel.) and the Raptor engine, while very impressive, has perhaps not fully achieved the nigh-miraculous targets they set for themselves.
if you want to take 100 tons, not to LEO, but to Mars (which is the design goal of the system) then you have to use many starships to ferry fuel to refuel other starships, gradually boosting their orbit until you have a fully-fueled ship in a highly elliptical earth orbit, and then you can finally blast off to Mars. For the moon it’s even worse, you need maybe 20 refueling flights to land 1 starship on the moon with enough fuel to come back.
Agreed with you that the heat shield (and reusable upper stage in general) seems like it could easily just never work (or work but only with expensive refurbishment, or only from returning from LEO orbits not anything higher-energy, or etc), perhaps forcing them to give up and have Starship become essentially a big scaled-up Falcon 9. This would still be cheaper per-kg than Falcon 9 (economies of scale, and the Raptor engines are better than Merlin, etc), but not as transformative. I think many people are just kind of assuming “eh, SpaceX is full of geniuses, they’ve done so many astounding things, they’ll figure out the heat shield”, but this is an infamously hard problem (see Shuttle, Orion, X-33...), so possibly they’ll fail!
Some other tidbits:
Raptor’s claimed vacuum ISP is 380; I don’t think they’re just, like, making this up (they have done lots of tests, flown it many times, etc—it’s not a hypey future projection like “Starship will cost $4m per flight”), but I also don’t know where I’d go if I wanted to prove to myself that the number is legit (wikipedia just cites an Elon tweet...).
Apparently those Starlink mass simulators actually weigh about 2 tons each?? So flight 7, which carried 10 Starlink simulators, actually put 20 tons of payload in orbit.
The first reliable version of Starship will very likely fall short of its intended 100 ton goal (i mean… unless it takes them a really long time to make Starship reliable, lol). But they also plan to stretch the rocket, refine the engine, maybe someday make the whole thing wider, etc. So I expect that they’ll eventually hit 100 tons. (The first version of Falcon 9 could only lift 10.4 tons to LEO; the current version can lift 17.5 tons AND land the first stage on a drone ship for reuse!) But of course if you make the whole ship bigger, some of your launch costs are gonna go up too.
Personally I’m doubtful that they ever hit the crazy-ambitious $20/kg mark, which (per Thomas Kwa) would require not just a reusable upper stage (very hard!) but also hyper low-cost, airline-like turnaround on every part of the operation. But $200/kg (1 OOM cheaper from where Falcon 9 is today, using the rumored internal cost of $30m/launch and 17.5 ton capacity) seems pretty doable—upper stage reuse (even if somewhat ardurous to refurbish) probably cuts your costs by like 4x, and the much greater physical size of Starship might give you another almost 2x. Cheap materials (steel and methane vs aluminum and RP1) + economies of scale in Raptor manufacturing might take you the rest of the way.
The Isp of a closed cycle rocket engine with a given propellant mix is largely a function of its chamber pressure and expansion ratio, so one can use a program like RPA to plug in known numbers and see what other claims are consistent with an Isp of 380. Example (for SL variant) in this tweet.
My guess is that 380 is achievable if they close the throat and use a large enough nozzle, but they’ll opt for slightly lower in order to cram 9 engines into the upper stage. With Starship staging at record low velocities, reducing gravity losses through higher thrust might matter more than a 1% efficiency gain.