Landing legs are heavy and any mass you lift up lowers payload
Notably, the relationship is exponential, so lowers it more than you would expect.
The laziest possible search gives me 550,000kg for the rocket, 8,000 kg for payload, and 2,000kg for the landing legs, so 0.33% of total but an astonishing 25% of payload. Given the exponential relationship, even the 0.33% could have real impact, so 25% is somewhere between "holy shit" and "did lagrangian mess up the math and/or use poor data"?
Hard to find good data while they're still revising and testing. 550mT is probably high since a previous version was under 400mT for both stages put together, but they've beefed up both heat shield and booster a bit since and I dunno how much. Payload is probably around 40mT reusable right now but no telling for sure until they start doing real orbits. Landing legs on both stages would probably be 8% or so of dry mass, 32mT, but only mass on the upper stage trades off 1:1 with payload, so I'd guess they'd lose 40% of payload with v1 Starship, and maybe bring that down to 10 or 15% by v3.
Huh. That's actually not as bad as I'd have guessed. Either they're so good at guidance now that they consider the catch to be "easy", or they were afraid of losing even more mass budget during development (that 40mT is down from a 100mT goal), or they're really not kidding about their real goal for the catches being cadence.
Musk claims he wants to just set a booster back on the launch mount after a catch (as they just practiced late yesterday) and stack the next ship on to launch again an hour later (as they probably won't practice for years). Sounds crazy to me, but I though catching the giant rocket in more-giant robot arms was crazier, so what the hell do I know?
Musk claims he wants to just set a booster back on the launch mount after a catch (as they just practiced late yesterday) and stack the next ship on to launch again an hour later (as they probably won't practice for years). Sounds crazy to me, but I though catching the giant rocket in more-giant robot arms was crazier, so what the hell do I know?
I suspect that's one fight he'll lose on regulatory grounds. Space travel isn't quite regulated like the FAA, but aircraft maintenance requirements are no joke and no small part of why airline scandals become such a big thing, even as those same maintenance standards are why airline safety is so exception. The federal government is willing to accept some form of risk by SpaceX in the name of R&D, but if/when flights fail because of the complications of one flight compromise the next, maintenance delays can be enforced.
This is especially true if the inevitable accidents knock out a tower. One of the logistical issues of the catch-strategy is that it makes the towers a far more 'brittle' chokepoint. Previously, towers needed to just be able to set up the rocket in the first place, but the rocket could land more or less wherever that was a suitable pad. Now the rockets can only land in one place, and if a tower is damaged then no flights what-so-ever can land or launch from there until it is re-established. Which is to say, a single landing accident could take out a launch site for days / weeks / even months.
What that means for Musk is that the boosters will likely need to be re-inspected / re-certified. That would likely entail lowering them to the ground, driving them over to a maintenance facility, and otherwise doing more than an hour of work. The exception would be if a government was willing to provide a waiver for this requirement, say in time of conflict... but in such a conflict, an adversary who could justify a need to launch more payloads into orbit would also have the capacity to target the towers by various means, meaning, again, safety and reliability issues. And this, in turn, would bring the comparison of how governments regulate military aviation, which in some respects is more intense than civil regulations (because the government actually owns the expensive thing).
Now, don't get me wrong- it's all still very impressive- but this is one of those areas where the salesmanship and technical capacity starts to run against other actor interests.
A typical (so typical they did another two this morning and nobody paid attention) Starlink launch has the booster fire its engines, then shut them down, then fire them again for a reentry burn, then shut them down, then fire them again for the landing burn. For a return-to-launch-site mission like their two last month there's also a fourth startup and shutdown for the boostback burn.
There may be someone at the FAA who thinks four ignitions in a row (where the second ignition aims the rocket back at the coast of Florida!) without inspection is fine, but six ignitions in a row with only a brief inspection after the third is crazy, but I doubt it. The feds are pretty good about making distinctions between airline safety (where we're down to something like 1 fatal incident per million commercial flights and rightly proud of it) or astronaut safety (where NASA wants 1-in-250 or better) vs unmanned flight safety. In the most extremely opposite case, unmanned test flight safety, FAA rules have been as lenient as "yup, both halves of that Starship sure screwed up and exploded right where you warned us they might screw up and explode; carry on" after the 3rd test.
The FAA has rightfully cracked down on a bunch of Falcon 9 issues recently, and Starship shouldn't be any better, but it shouldn't be any worse. Not doing a return-to-landing-site or return-to-tower didn't save SpaceX from those crackdowns. Booster fails its 24th landing, on an unmanned ship, in the middle of nowhere, in a NOTMAR zone behind a "Beware of the Leopard" sign? Falcon 9 grounded for days. Second stage deorbit burn is 0.5 seconds too long and it burns up slightly short of where it was expected to burn up? Falcon 9 grounded for weeks. It doesn't matter whether there's a ship or a tower that might get damaged on a failed landing; they'd get grounded for an investigation of what led to any landing they didn't expect to fail, to find any root cause that might affect other phases of flight too.
The FAA hasn't been obviously right about how they license SpaceX flight plan changes lately (though it was nice that they finished the IFT-5 license as quickly as they did in the end), but that's a separate issue from incident investigations. And I did notice that they've been obviously wrong about not requiring an investigation for that last ULA Vulcan flight, where the rocket lost the nozzle of a solid rocket booster (an antiquated design in part because it can have no "off" switch, only a "kaboom" switch) mid-ascent. Considering that case makes me worry a little more about political adversaries than military ones. The contrast between "I want to build cities in space" Bezos speeches versus "you can't launch that often!" Bezos protests is particularly sad.
You're welcome. It is an argument, though, to be fair, not a proof. I have to admit I felt better about seeing them attempt the tower catch after they finished stacking the second Texas launch tower, and I would have felt better still if they had the second tower operational already.
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Notes -
Notably, the relationship is exponential, so lowers it more than you would expect.
The laziest possible search gives me 550,000kg for the rocket, 8,000 kg for payload, and 2,000kg for the landing legs, so 0.33% of total but an astonishing 25% of payload. Given the exponential relationship, even the 0.33% could have real impact, so 25% is somewhere between "holy shit" and "did lagrangian mess up the math and/or use poor data"?
Hard to find good data while they're still revising and testing. 550mT is probably high since a previous version was under 400mT for both stages put together, but they've beefed up both heat shield and booster a bit since and I dunno how much. Payload is probably around 40mT reusable right now but no telling for sure until they start doing real orbits. Landing legs on both stages would probably be 8% or so of dry mass, 32mT, but only mass on the upper stage trades off 1:1 with payload, so I'd guess they'd lose 40% of payload with v1 Starship, and maybe bring that down to 10 or 15% by v3.
Huh. That's actually not as bad as I'd have guessed. Either they're so good at guidance now that they consider the catch to be "easy", or they were afraid of losing even more mass budget during development (that 40mT is down from a 100mT goal), or they're really not kidding about their real goal for the catches being cadence.
Musk claims he wants to just set a booster back on the launch mount after a catch (as they just practiced late yesterday) and stack the next ship on to launch again an hour later (as they probably won't practice for years). Sounds crazy to me, but I though catching the giant rocket in more-giant robot arms was crazier, so what the hell do I know?
I suspect that's one fight he'll lose on regulatory grounds. Space travel isn't quite regulated like the FAA, but aircraft maintenance requirements are no joke and no small part of why airline scandals become such a big thing, even as those same maintenance standards are why airline safety is so exception. The federal government is willing to accept some form of risk by SpaceX in the name of R&D, but if/when flights fail because of the complications of one flight compromise the next, maintenance delays can be enforced.
This is especially true if the inevitable accidents knock out a tower. One of the logistical issues of the catch-strategy is that it makes the towers a far more 'brittle' chokepoint. Previously, towers needed to just be able to set up the rocket in the first place, but the rocket could land more or less wherever that was a suitable pad. Now the rockets can only land in one place, and if a tower is damaged then no flights what-so-ever can land or launch from there until it is re-established. Which is to say, a single landing accident could take out a launch site for days / weeks / even months.
What that means for Musk is that the boosters will likely need to be re-inspected / re-certified. That would likely entail lowering them to the ground, driving them over to a maintenance facility, and otherwise doing more than an hour of work. The exception would be if a government was willing to provide a waiver for this requirement, say in time of conflict... but in such a conflict, an adversary who could justify a need to launch more payloads into orbit would also have the capacity to target the towers by various means, meaning, again, safety and reliability issues. And this, in turn, would bring the comparison of how governments regulate military aviation, which in some respects is more intense than civil regulations (because the government actually owns the expensive thing).
Now, don't get me wrong- it's all still very impressive- but this is one of those areas where the salesmanship and technical capacity starts to run against other actor interests.
A typical (so typical they did another two this morning and nobody paid attention) Starlink launch has the booster fire its engines, then shut them down, then fire them again for a reentry burn, then shut them down, then fire them again for the landing burn. For a return-to-launch-site mission like their two last month there's also a fourth startup and shutdown for the boostback burn.
There may be someone at the FAA who thinks four ignitions in a row (where the second ignition aims the rocket back at the coast of Florida!) without inspection is fine, but six ignitions in a row with only a brief inspection after the third is crazy, but I doubt it. The feds are pretty good about making distinctions between airline safety (where we're down to something like 1 fatal incident per million commercial flights and rightly proud of it) or astronaut safety (where NASA wants 1-in-250 or better) vs unmanned flight safety. In the most extremely opposite case, unmanned test flight safety, FAA rules have been as lenient as "yup, both halves of that Starship sure screwed up and exploded right where you warned us they might screw up and explode; carry on" after the 3rd test.
The FAA has rightfully cracked down on a bunch of Falcon 9 issues recently, and Starship shouldn't be any better, but it shouldn't be any worse. Not doing a return-to-landing-site or return-to-tower didn't save SpaceX from those crackdowns. Booster fails its 24th landing, on an unmanned ship, in the middle of nowhere, in a NOTMAR zone behind a "Beware of the Leopard" sign? Falcon 9 grounded for days. Second stage deorbit burn is 0.5 seconds too long and it burns up slightly short of where it was expected to burn up? Falcon 9 grounded for weeks. It doesn't matter whether there's a ship or a tower that might get damaged on a failed landing; they'd get grounded for an investigation of what led to any landing they didn't expect to fail, to find any root cause that might affect other phases of flight too.
The FAA hasn't been obviously right about how they license SpaceX flight plan changes lately (though it was nice that they finished the IFT-5 license as quickly as they did in the end), but that's a separate issue from incident investigations. And I did notice that they've been obviously wrong about not requiring an investigation for that last ULA Vulcan flight, where the rocket lost the nozzle of a solid rocket booster (an antiquated design in part because it can have no "off" switch, only a "kaboom" switch) mid-ascent. Considering that case makes me worry a little more about political adversaries than military ones. The contrast between "I want to build cities in space" Bezos speeches versus "you can't launch that often!" Bezos protests is particularly sad.
This is a fair argument, and I appreciate you taking the time to make it.
You're welcome. It is an argument, though, to be fair, not a proof. I have to admit I felt better about seeing them attempt the tower catch after they finished stacking the second Texas launch tower, and I would have felt better still if they had the second tower operational already.
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