As to whether catching the booster adds risk - I'm not sure it does.
First, to the extent the booster is out of position in the x (sideways) direction, the chopsticks can move to accomodate error. But actually I think this dimension is the easiest of the three, as the booster has plenty to time to null any error in this dimension.
In the y direction (direction of travel towards the tower), the rails on the chopsticks can cope with the booster touching down along quite a long distance. But importantly, they appear to be smooth, so the pins can initially skid along them and then the booster can swing if it has not fully nulled any horizontal movement.
In contrast, if the booster used legs and has not yet fully nulled any horizontal motion at touchdown, there is a greater risk of breaking a leg or simply tipping over.
And in the z direction, it should be possible for the chopsticks can absorb more vertical motion than legs can absorb, because you can easily build in huge springs/dampers/etc into the ground equipment without concern about mass.
Catching also puts the booster in tension rather than compression - it's easier to be rigid in tension than compression.
Finally, if legs were used, the engines would have to get close to the ground during landing, so reflected shock from the ground could cause damage. I know Falcon 9 does this, but the area of the base of Starship is much greater, so there's effectively less room for the reflected energy to escape. Catching completely removes this risk.
On balance, I think they would have better chance of success for each mission by catching. The main downside would be if you fail to catch, you may need to build a new tower, whereas a flat pad would be cheaper and easier to repair.
I am really curious what the maximum wind speed allowed for a booster landing will be. Upon landing, it has a lot of windage and not nearly as much mass as during take-off.
I have experience with docking large boats and it does seem to be a bit similar. In the case of boats, wind is a big deal, and the booster has nothing "below the waterline" to slow down the effects of wind.
Not because wind wouldn't affect an empty booster; it certainly would.
But since the booster returns within 8 minutes of the launch, the weather in which a booster lands is restricted to the weather in which they will launch a rocket.
The value of what is going up (which includes the booster) will be greater than the value of the empty booster. Factors of safety would be based on the launch rather than the catch. In other words, if it's deemed safe to launch the calculation for safe to land is easier to pass. Especially when you are taking passengers on launch. Wind is already a significant factor in launch.
That's true, except it neglects the cost of the launch tower itself. If you botch a catch and need to rebuild the launch tower, that could get very expensive, both in immediate costs of rebuild, plus in opportunity cost of missed launches. So in the end, whichever has the lowest wind limit, launch or landing, will likely determine whether they fly.
Ah, excellent point! They wouldn't ignore one hazard because another is less severe. And you are correct, I wasn't considering hazards to the launch tower itself. I think you are absolutely right, either would cause a flight to be scrubbed. I wonder if the two wind limits would be different.
That value is unlikely to be significantly different than safe takeoff conditions. Yes the booster is lighter at landing, but launch is way more dangerous with larger error margins and more conservative condition requirements.
Definitely not, and I am not trying to be a doomsayer here. It's just interesting. Now that I think about it more, I believe a Falcon 9 Starlink launch was once delayed due to weather conditions at the drone ship.
The most challenging axis in my opinion is the roll axis of Super Heavy, if there is a roll angle error, the pins could not sit properly on the chopsticks and the whole booster slides off.
Might as well chuck a full size engine on the side pointing in the yaw direction to be safe. I mean as long as you tie enough magical struts and cables to it I'm sure you are fine /s
First, to the extent the booster is out of position in the x (sideways) direction, the chopsticks can move to accomodate error. But actually I think this dimension is the easiest of the three, as the booster has plenty to time to null any error in this dimension.
In the y direction (direction of travel towards the tower), the rails on the chopsticks can cope with the booster touching down along quite a long distance. But importantly, they appear to be smooth, so the pins can initially skid along them and then the booster can swing if it has not fully nulled any horizontal movement. In contrast, if the booster used legs and has not yet fully nulled any horizontal motion at touchdown, there is a greater risk of breaking a leg or simply tipping over.
And in the z direction, it should be possible for the chopsticks can absorb more vertical motion than legs can absorb, because you can easily build in huge springs/dampers/etc into the ground equipment without concern about mass.
Catching also puts the booster in tension rather than compression - it's easier to be rigid in tension than compression.
Finally, if legs were used, the engines would have to get close to the ground during landing, so reflected shock from the ground could cause damage. I know Falcon 9 does this, but the area of the base of Starship is much greater, so there's effectively less room for the reflected energy to escape. Catching completely removes this risk.
On balance, I think they would have better chance of success for each mission by catching. The main downside would be if you fail to catch, you may need to build a new tower, whereas a flat pad would be cheaper and easier to repair.