SpaceX is working on Starship, which is afaict about as close to being finished as the aforementioned competitor rockets, and when it is finished it’ll should provide somewhere between $15/kg and $150/kg.
Does some independent analysis exist that goes through the calculations to come up with those performance numbers for the Starship design, and maybe estimate how far Starship development is from commercial viability? My impression is that at this point no claims by SpaceX/Tesla should be given any credence, given their abysmal track record with those. (Red Dragon Mars 2018? Starship Mars 2022? Tesla FSD?) On the other hand, it can be easy to overcompensate because of this, just because many of their claims have no basis in reality, does not automatically mean that their technology is bad. Hence, it would be nice to see someone do a thorough analysis.
Starship can launch something like 150 metric tons to orbit iirc. So that’s 150,000kg? So to get to $15/kg it would need to cost a bit more than $2M dollars per launch. Or to get to $150/kg, it would need to cost a bit more than $20M dollars per launch.
IIRC the cost to build an entire Starship + Superheavy is something like $100M. It’s made of steel, so the materials themselves are pretty cheap, and the few dozen Raptor 3′s are like half a million each, and the manufacturing cost will go down a lot due to returns to scale as they start pumping out a ship a day at the Starfactory. (And eventually, several ships a day; perhaps the limits on efficiency are reached when they are producing hundreds per day like a car factory assembly line)
Falcon 9′s already get reused 30+ times, and Raptor 3 is supposed to be much more reusable than the Merlin engines. Seems plausible to me that Starship, once it matures over the course of a decade or so, will be doing hundreds or even thousands of flights. (main uncertainty IMO is the heat tiles...)
So the amortized cost of building the ship won’t prevent it from hitting the $15/kg milestone, and the $150/kg milestone should be almost trivial to hit.
what about the fuel and propellant costs? LOX and liquid methane. Both are super cheap as fuels go but still IIRC the cost of a fully fueled stack is like $2M just for the fuels? Maybe that’s where the $15/kg estimate comes from, maybe it’s a lower bound set by the price of the fuel.
I wonder though if the price of the fuel can be brought lower over time… for example, by producing it on-site at massive industrial scale, and taking advantage of the falling cost of solar panels and the bountiful sun of Texas to get unusually low energy prices to power the whole thing.
How’s that? It’s possible I hallucinated some of those numbers.
Starship can launch something like 150 metric tons to orbit iirc.
Well this is one of the main assumptions I am doubting. We haven’t seen Starship carry anything close to that. AFAIK none of the flights so far were done with a mass simulator, the most it carried was a couple of starlink satellites, which I don’t think would weigh more than like 1 ton.
Also, to what orbit? Low earth orbit, geostationary orbit, or an interplanetary transfer trajectory are completely different beasts. (But I guess for most of the examples you list for economic impact you mean LEO.) And with what reuse profile? Both booster and upper stage reuse, or just booster, or nothing? That obviously factors massively into cost, for the lowest cost you want full reuse.
Upper stage reuse in particular is completely new and unproven tech, they promised that with the Falcon 9 too but never delivered.
I would be interested in e.g. seeing a calculation of a LEO launch with booster return to launch site, and with upper stage landing on a drone ship. (Idk what equations you need here, or if you need some simulator software, the extent of my knowledge is the basic rocket equation, and that I have played Kerbal Space Program. In particular aerodynamics probably complicates things a lot, both for drag on ascent, and for braking on descent.)
What is the claimed specific impulse of the raptor engines, and what might be the actual figures? (And also keep in mind that the vacuum engines of the upper stage will be less efficient at the sea level landing, though probably that does not matter much as you burn most of your velocity via aerobraking.) How much fuel are you carrying in which stage, and what reserve do you need for the landings?
At least seeing these numbers check out, without anything physics defying would already be a plus, without even getting into any of the engineering details.
main uncertainty IMO is the heat tiles...
Agree, in particular I don’t see how they will be fully reusable? (AFAIK right now they are ablative and have to be replaced.) I remember years ago there was some presentation that the ship will be “sweating” liquid methane to cool itself on reentry, this being tossed in favor of a non-reusable solution does not instill confidence in me.
what about the fuel and propellant costs?
I agree that the exact fuel price does not matter much, once you get to the point where it’s the main driver of cost you have already reached the level for transformative economic impact.
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.
Yeah good point re: heat shields & upper stage reuse being hard. They’ve experimented with reusing Dragon heat shields but still they mostly just replace them each time.
Thinking aloud… suppose they never solve Starship reuse, but the Booster basically works great (as it seems to already be working pretty great). So the booster gets reused like 100 times but the Starship has to be scrapped each launch.
...In this world, the Starship could maybe be cheaper due to using old, worn-out engines retired from the boosters (don’t need to be super reliable since it can still complete the mission if a couple blow up, none of them are coming back anyway) and not needing a heat shield or wingflaps. Apparently right now the majority of the cost is the engines, the hull itself is cheap. And again a full stack booster+starship costs $100M. So the starship (having far fewer engines) is probably like… $25M or so right now? And price could drop further due to the aforementioned effects plus simply normal returns to scale… let me see how much does a car cost per kg and how much does starship weigh? Apparently starship dry mass is 85,000 kg. Tesla model 3 is 1600kg and costs like $36,000. So $22/kg. So if they can produce starships for the same cost per kg as model 3 cars, then the cost would be less than $2M. So yeah, obviously they won’t get there immediately but that’s the price they would naturally trend towards.
So that means even if they don’t reuse the upper stage at all, if they use old engines they would have retired anyway then they could get the price down to maybe $30/kg eventually. Assuming they have 150 tons to orbit payload of course, which is unproven. If they use new engines, maybe they can only get to $100/kg.
Also, as a fun bonus, if they are building a space station in LEO, then they can use the hulls of the single-use starships as material for the space station! That’s a free 85,000 kg of steel in LEO with every launch, in addition to the payload! And it already comes formed into a spacious pressure vessel!
Does some independent analysis exist that goes through the calculations to come up with those performance numbers for the Starship design, and maybe estimate how far Starship development is from commercial viability? My impression is that at this point no claims by SpaceX/Tesla should be given any credence, given their abysmal track record with those. (Red Dragon Mars 2018? Starship Mars 2022? Tesla FSD?) On the other hand, it can be easy to overcompensate because of this, just because many of their claims have no basis in reality, does not automatically mean that their technology is bad. Hence, it would be nice to see someone do a thorough analysis.
From memory, real quick:
Starship can launch something like 150 metric tons to orbit iirc. So that’s 150,000kg? So to get to $15/kg it would need to cost a bit more than $2M dollars per launch. Or to get to $150/kg, it would need to cost a bit more than $20M dollars per launch.
IIRC the cost to build an entire Starship + Superheavy is something like $100M. It’s made of steel, so the materials themselves are pretty cheap, and the few dozen Raptor 3′s are like half a million each, and the manufacturing cost will go down a lot due to returns to scale as they start pumping out a ship a day at the Starfactory. (And eventually, several ships a day; perhaps the limits on efficiency are reached when they are producing hundreds per day like a car factory assembly line)
Falcon 9′s already get reused 30+ times, and Raptor 3 is supposed to be much more reusable than the Merlin engines. Seems plausible to me that Starship, once it matures over the course of a decade or so, will be doing hundreds or even thousands of flights. (main uncertainty IMO is the heat tiles...)
So the amortized cost of building the ship won’t prevent it from hitting the $15/kg milestone, and the $150/kg milestone should be almost trivial to hit.
what about the fuel and propellant costs? LOX and liquid methane. Both are super cheap as fuels go but still IIRC the cost of a fully fueled stack is like $2M just for the fuels? Maybe that’s where the $15/kg estimate comes from, maybe it’s a lower bound set by the price of the fuel.
I wonder though if the price of the fuel can be brought lower over time… for example, by producing it on-site at massive industrial scale, and taking advantage of the falling cost of solar panels and the bountiful sun of Texas to get unusually low energy prices to power the whole thing.
How’s that? It’s possible I hallucinated some of those numbers.
Well this is one of the main assumptions I am doubting. We haven’t seen Starship carry anything close to that. AFAIK none of the flights so far were done with a mass simulator, the most it carried was a couple of starlink satellites, which I don’t think would weigh more than like 1 ton.
Also, to what orbit? Low earth orbit, geostationary orbit, or an interplanetary transfer trajectory are completely different beasts. (But I guess for most of the examples you list for economic impact you mean LEO.) And with what reuse profile? Both booster and upper stage reuse, or just booster, or nothing? That obviously factors massively into cost, for the lowest cost you want full reuse.
Upper stage reuse in particular is completely new and unproven tech, they promised that with the Falcon 9 too but never delivered.
I would be interested in e.g. seeing a calculation of a LEO launch with booster return to launch site, and with upper stage landing on a drone ship. (Idk what equations you need here, or if you need some simulator software, the extent of my knowledge is the basic rocket equation, and that I have played Kerbal Space Program. In particular aerodynamics probably complicates things a lot, both for drag on ascent, and for braking on descent.)
What is the claimed specific impulse of the raptor engines, and what might be the actual figures? (And also keep in mind that the vacuum engines of the upper stage will be less efficient at the sea level landing, though probably that does not matter much as you burn most of your velocity via aerobraking.) How much fuel are you carrying in which stage, and what reserve do you need for the landings?
At least seeing these numbers check out, without anything physics defying would already be a plus, without even getting into any of the engineering details.
Agree, in particular I don’t see how they will be fully reusable? (AFAIK right now they are ablative and have to be replaced.) I remember years ago there was some presentation that the ship will be “sweating” liquid methane to cool itself on reentry, this being tossed in favor of a non-reusable solution does not instill confidence in me.
I agree that the exact fuel price does not matter much, once you get to the point where it’s the main driver of cost you have already reached the level for transformative economic impact.
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.
Yeah good point re: heat shields & upper stage reuse being hard. They’ve experimented with reusing Dragon heat shields but still they mostly just replace them each time.
Thinking aloud… suppose they never solve Starship reuse, but the Booster basically works great (as it seems to already be working pretty great). So the booster gets reused like 100 times but the Starship has to be scrapped each launch.
...In this world, the Starship could maybe be cheaper due to using old, worn-out engines retired from the boosters (don’t need to be super reliable since it can still complete the mission if a couple blow up, none of them are coming back anyway) and not needing a heat shield or wingflaps. Apparently right now the majority of the cost is the engines, the hull itself is cheap. And again a full stack booster+starship costs $100M. So the starship (having far fewer engines) is probably like… $25M or so right now? And price could drop further due to the aforementioned effects plus simply normal returns to scale… let me see how much does a car cost per kg and how much does starship weigh? Apparently starship dry mass is 85,000 kg. Tesla model 3 is 1600kg and costs like $36,000. So $22/kg. So if they can produce starships for the same cost per kg as model 3 cars, then the cost would be less than $2M. So yeah, obviously they won’t get there immediately but that’s the price they would naturally trend towards.
So that means even if they don’t reuse the upper stage at all, if they use old engines they would have retired anyway then they could get the price down to maybe $30/kg eventually. Assuming they have 150 tons to orbit payload of course, which is unproven. If they use new engines, maybe they can only get to $100/kg.
Also, as a fun bonus, if they are building a space station in LEO, then they can use the hulls of the single-use starships as material for the space station! That’s a free 85,000 kg of steel in LEO with every launch, in addition to the payload! And it already comes formed into a spacious pressure vessel!