This seems (to me) a more complicated procedure requiring more advanced hardware.
Not necessarily. Instead of thinking about "catching the booster with the arms", think about "the booster landing on the arms".
Imagine you take a Falcon 9 booster, but instead of putting the landing legs on the bottom, you put them on the top, and you dig a hole in the middle of the landing pad. That's kind of what we are talking about here.
The original idea was to land the booster directly back on the hold down clamps! Compared to that, the mechazilla catch sounds like a piece of cake.
The risk of extensive damage to ground-based structures in case of a failed landing also seems significantly higher.
Then don't fail the landing!
SpaceX has demonstrated more successful Falcon 9 landings in a row than most other launch systems even have total missions. We just had the 301st Falcon 9 landing, or the 318th, if you count Falcon Heavy center cores and side boosters, and the 244th consecutive successful landing (I lost count).
It will take a couple of tries, just like it did with Falcon 9, but practice makes perfect.
So presumably there is a good reason why the SuperHeavy booster would need to be captured upon landing rather than land on built-in struts. What is that reason?
Two reasons:
- Mass savings: landing legs are heavy. The actuation mechanism is heavy.
- Rapid turnaround: SpaceX wants the same booster to fly multiple times per hour. On Falcon 9, currently, it takes up to an hour to fold up the landing legs. In fact, on Falcon 9, the legs cannot fold up on their own, that can only be done externally. If you want to re-fly rapidly, the booster needs to be able to fold the legs up on its own – which again adds mass. And you pretty much have to land on or right next to the launch mount in order to enable such high cadence.
Remember:
- Every kilogram of mass on the second stage costs one kilogram of payload.
- Every kilogram of mass on the first stage costs roughly one quarter kilogram of payload.
- Mass on the ground equipment (what SpaceX likes to call "Stage Zero") is free.
In fact, those numbers are for expendable vehicles. For reusable vehicles, the penalties are higher, because you not only have to lift the extra mass up, you also have to boost it back, and land it (and add the fuel for lifting it up, boosting it back, and landing it, and add the fuel for lifting the fuel, and add the fuel for that, and so on).
