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There are several advantages: - Turnaround time is a major one for SpaceX. They want to stack a new Starship on top of it and launch the booster again in hours

by Aaargh20318 2y ago

There are several advantages: - Turnaround time is a major one for SpaceX. They want to stack a new Starship on top of it and launch the booster again in hours, not weeks. By catching the booster they can simply lower it back onto the launch mount, refuel and relaunch. - No need for landing legs. The legs add significant weight, especially on something as large as Super Heavy. Leaving these out means more usable payload to orbit.

carabiner 2y ago
If the chopsticks are catching the rocket by the grid fins, doesn't that mean the grid fins (and associated structure) have to be strengthened (weight added) to support the entire weight of the vehicle? That would negate some of the weight savings of removing the legs. Does this end up being more efficient because more of the loading is in tension instead of compression?
- deleted 2y ago
  [deleted]
- Teever 2y ago
  Sort of. They need to lift the rocket to put it in place on the launch structure so that is already built into the design.
- rockemsockem 2y ago
  The chopsticks actually don't catch the booster by the grid fins, there are little struts that stick out from the rocket that don't stick out nearly as far. I thought the same thing before the first catch, if you go look at the catch footage you can see the booster resting those on the chopsticks.
  - carabiner 2y ago
    So the struts (plus supporting structure) are lighter than the legs? Why is that?
    - ceejayoz 2y ago
      They’re much smaller and don’t have to move/deploy.
    - krisoft 2y ago
      The legs would need to be much longer (because you can’t push the engine nozzles all the way into the ground and still hope for good things.) Longer structure means more mass, but also larger torque which need to be handled with the support of the structure. Legs need to move to deploy. The struts are just there, static things are much simpler. Simpler things weigh less. Legs need to contain shock absorbers. With the struct solution the shock absorber is in the chopsticks. It doesn’t matter how much the shock absorber weighs when you don’t need to carry it up with you.
      - adolph 2y ago
        It was pretty neat how Bezos explained to Everyday Astronaut how they were using 6 legs so the legs weren’t as long. On the whole, pad catch is the way to go for non-expeditionary vehicles. For orbital uses each booster basically becomes a pyrotechnic elevator.
      - avmich 2y ago
        It would be good to see the numeric analysis of variants here. Legged landings are surely possible - say, with longer legs (twice as long as struts?), possibly static (legs are always deployed, even when launching), with shock absorbers which aren't that heavy... Would be good to see good and bad qualities next to each other.
        rockemsockem 2y ago
        I think it all just comes down to weight. If you can trim mass on the vehicle then you should do it.
    - deleted 2y ago
      [deleted]
    - mhio 2y ago
  - eichin 2y ago
    One of the things that came up in one of the livestreams was that some of the changes to the starship heat shielding were to test a couple of different spots for those struts - because the booster doesn't do orbital-speed reentry, starship itself does, so to catch that, you need to avoid burning off the struts...
- pseudosavant 2y ago
  I thought it was the grid fins initially too until I saw that there are actually just two pins that the entire thing rests on. Check this clip around 19:30. https://youtu.be/dpxB1S-ohEU?si=yozlCWmDCNeEFO4B&t=1169 https://youtu.be/dpxB1S-ohEU?si=yozlCWmDCNeEFO4B&t=1169
- coderjames 2y ago
  > If the chopsticks are catching the rocket by the grid fins The chopsticks don't catch the rocket by the grid fins. There are dedicated supports (pins) sticking out the sides of Super Heavy that support the load. It does negate some of the savings from removing the legs, but by returning not only near the launch site like Falcon 9 but literally to the launch tower itself, they can save a whole bunch of time on transporting the stage back to where it will be launched again. They want to launch these things at such a rapid pace that every hour they can save in the refurb / repair / refuel part after landing matters.
- jcims 2y ago
  This is a pic of the top of the booster. You can see the landing lugs between the grid fins. https://x.com/TrainOfError/status/1846030879602209054 https://x.com/TrainOfError/status/1846030879602209054
jojobas 2y ago
[flagged]
- recursive 2y ago
  If you think of a way to make that happen, I guess you should do it then.
  - talldayo 2y ago
    Apparently a good start is promising to build $25,000 EVs, raising capital and tax subsidies stock value, and then bailing on the promise entirely. You might even be able to afford two or three submarines with that kind of money.
- notfish 2y ago
  If you had spacex’s budget you could make all of these things happen
  - jojobas 2y ago
    Didn't they already burn through their Starship development budget?
    - malfist 2y ago
      They're a private company funded personally by the richest man in the world. What makes you think there is such a thing as a "starship development budget" and that it's limited?
      - jojobas 2y ago
        Musk's interplanetary delirium aside, HLS is the customer for Super Heavy/Starship. They've reported spending all of the NASA's 3 billion and delivered very little of contracted capability so far. SpaceX filings show $3.8B of funding from various mostly undisclosed investors, Musk's own stake can't exceed that can it? The richest man wouldn't be so rich if he didn't watch his money.
whaaaaat 2y ago
I've never understood this, because the economics of hourly launches just don't make sense. There's not nearly enough demand, even assuming they drive prices down and induce demand. Today, there are about ~1,100 metric tons of satellites launched into orbit annually. Starship is aiming for $100/kilogram cost per kilo to orbit. Let's get absolutely wild and assume that Starship takes over the entire world's launches. It would earn what, 1,100 tons * 1000 kilos/ton * $100/kilo = $110,000,000. $110M is... not a tremendous amount of money. It's definitely not enough to be building a fleet of rockets up. Only about 20% of satellite costs are due to launch (and that was found in a pre-SpaceX era), so it's not likely satellite builders are going to optimize solely on cost. It's not an order of magnitude cost savings for builders. So SpaceX will have to find other means to compete -- reliability, capability, etc. The US puts up <100 orbital launches per year. Even if Starship took all of those (and it won't), they'd need to have 10x the number of launches for an hour level restack and refuel to make a difference. And that's not even counting the differences in payload capacity. Add several whole integer multipliers to account for that. For starship to need an "hours-scale" relaunch time, you'd need something like 50x+ the number of launches we currently have AND every launch in the nation to be on the platform. It's a cool engineering target, but it's total nonsense for now.
- martyvis 2y ago
  I think they have a "build it and they will come" attitude. While their own Mars goals will need 100s if not 1000s of launches they also see new customers that would want launch and even recover much larger payloads than what are feasible today
  - whaaaaat 2y ago
    I think that's a reasonable attitude to a point, but like, it doesn't scale infinitely. Build it and it will come to 50-100x today's launch capacity? And Mars is still a laughable pipedream. Doing 100s of launches will cost SpaceX so much more than they are making selling launches to the rest of the world, it simply makes no sense. And like, I'm a space enthusiast. I think we should be out mining asteroids and setting up space living quarters. I just... hourly starship launches don't make any sort of logical sense. What they do make sense as is a marketing gimmick for Elon to get on stage to appeal to emotions of investors and nerds online. It's a gorgeous dream! I want it to be! But it's just a clever emotional appeal to get you to not think too hard or too critically.

carabiner 2y ago

If the chopsticks are catching the rocket by the grid fins, doesn't that mean the grid fins (and associated structure) have to be strengthened (weight added) to support the entire weight of the vehicle? That would negate some of the weight savings of removing the legs. Does this end up being more efficient because more of the loading is in tension instead of compression?

deleted 2y ago
[deleted]
Teever 2y ago
Sort of. They need to lift the rocket to put it in place on the launch structure so that is already built into the design.
rockemsockem 2y ago
The chopsticks actually don't catch the booster by the grid fins, there are little struts that stick out from the rocket that don't stick out nearly as far. I thought the same thing before the first catch, if you go look at the catch footage you can see the booster resting those on the chopsticks.
- carabiner 2y ago
  So the struts (plus supporting structure) are lighter than the legs? Why is that?
  - ceejayoz 2y ago
    They’re much smaller and don’t have to move/deploy.
  - krisoft 2y ago
    The legs would need to be much longer (because you can’t push the engine nozzles all the way into the ground and still hope for good things.) Longer structure means more mass, but also larger torque which need to be handled with the support of the structure. Legs need to move to deploy. The struts are just there, static things are much simpler. Simpler things weigh less. Legs need to contain shock absorbers. With the struct solution the shock absorber is in the chopsticks. It doesn’t matter how much the shock absorber weighs when you don’t need to carry it up with you.
    - adolph 2y ago
      It was pretty neat how Bezos explained to Everyday Astronaut how they were using 6 legs so the legs weren’t as long. On the whole, pad catch is the way to go for non-expeditionary vehicles. For orbital uses each booster basically becomes a pyrotechnic elevator.
    - avmich 2y ago
      It would be good to see the numeric analysis of variants here. Legged landings are surely possible - say, with longer legs (twice as long as struts?), possibly static (legs are always deployed, even when launching), with shock absorbers which aren't that heavy... Would be good to see good and bad qualities next to each other.
      - rockemsockem 2y ago
        I think it all just comes down to weight. If you can trim mass on the vehicle then you should do it.
  - deleted 2y ago
    [deleted]
  - mhio 2y ago
- eichin 2y ago
  One of the things that came up in one of the livestreams was that some of the changes to the starship heat shielding were to test a couple of different spots for those struts - because the booster doesn't do orbital-speed reentry, starship itself does, so to catch that, you need to avoid burning off the struts...
pseudosavant 2y ago
I thought it was the grid fins initially too until I saw that there are actually just two pins that the entire thing rests on. Check this clip around 19:30. https://youtu.be/dpxB1S-ohEU?si=yozlCWmDCNeEFO4B&t=1169 https://youtu.be/dpxB1S-ohEU?si=yozlCWmDCNeEFO4B&t=1169
coderjames 2y ago
> If the chopsticks are catching the rocket by the grid fins The chopsticks don't catch the rocket by the grid fins. There are dedicated supports (pins) sticking out the sides of Super Heavy that support the load. It does negate some of the savings from removing the legs, but by returning not only near the launch site like Falcon 9 but literally to the launch tower itself, they can save a whole bunch of time on transporting the stage back to where it will be launched again. They want to launch these things at such a rapid pace that every hour they can save in the refurb / repair / refuel part after landing matters.
jcims 2y ago
This is a pic of the top of the booster. You can see the landing lugs between the grid fins. https://x.com/TrainOfError/status/1846030879602209054 https://x.com/TrainOfError/status/1846030879602209054

jojobas 2y ago

[flagged]

recursive 2y ago
If you think of a way to make that happen, I guess you should do it then.
- talldayo 2y ago
  Apparently a good start is promising to build $25,000 EVs, raising capital and tax subsidies stock value, and then bailing on the promise entirely. You might even be able to afford two or three submarines with that kind of money.
notfish 2y ago
If you had spacex’s budget you could make all of these things happen
- jojobas 2y ago
  Didn't they already burn through their Starship development budget?
  - malfist 2y ago
    They're a private company funded personally by the richest man in the world. What makes you think there is such a thing as a "starship development budget" and that it's limited?
    - jojobas 2y ago
      Musk's interplanetary delirium aside, HLS is the customer for Super Heavy/Starship. They've reported spending all of the NASA's 3 billion and delivered very little of contracted capability so far. SpaceX filings show $3.8B of funding from various mostly undisclosed investors, Musk's own stake can't exceed that can it? The richest man wouldn't be so rich if he didn't watch his money.

whaaaaat 2y ago

I've never understood this, because the economics of hourly launches just don't make sense. There's not nearly enough demand, even assuming they drive prices down and induce demand. Today, there are about ~1,100 metric tons of satellites launched into orbit annually. Starship is aiming for $100/kilogram cost per kilo to orbit. Let's get absolutely wild and assume that Starship takes over the entire world's launches. It would earn what, 1,100 tons * 1000 kilos/ton * $100/kilo = $110,000,000. $110M is... not a tremendous amount of money. It's definitely not enough to be building a fleet of rockets up. Only about 20% of satellite costs are due to launch (and that was found in a pre-SpaceX era), so it's not likely satellite builders are going to optimize solely on cost. It's not an order of magnitude cost savings for builders. So SpaceX will have to find other means to compete -- reliability, capability, etc. The US puts up <100 orbital launches per year. Even if Starship took all of those (and it won't), they'd need to have 10x the number of launches for an hour level restack and refuel to make a difference. And that's not even counting the differences in payload capacity. Add several whole integer multipliers to account for that. For starship to need an "hours-scale" relaunch time, you'd need something like 50x+ the number of launches we currently have AND every launch in the nation to be on the platform. It's a cool engineering target, but it's total nonsense for now.

martyvis 2y ago
I think they have a "build it and they will come" attitude. While their own Mars goals will need 100s if not 1000s of launches they also see new customers that would want launch and even recover much larger payloads than what are feasible today
- whaaaaat 2y ago
  I think that's a reasonable attitude to a point, but like, it doesn't scale infinitely. Build it and it will come to 50-100x today's launch capacity? And Mars is still a laughable pipedream. Doing 100s of launches will cost SpaceX so much more than they are making selling launches to the rest of the world, it simply makes no sense. And like, I'm a space enthusiast. I think we should be out mining asteroids and setting up space living quarters. I just... hourly starship launches don't make any sort of logical sense. What they do make sense as is a marketing gimmick for Elon to get on stage to appeal to emotions of investors and nerds online. It's a gorgeous dream! I want it to be! But it's just a clever emotional appeal to get you to not think too hard or too critically.