Why are the chopsticks so important after SpaceX already landed rockets?
In: Planetary Science
The bigger the rocket the bigger the legs you need. If you want to reuse the legs and not just crush them, you need to make them beefier.
The bigger the legs, the more fuel and performance you need just to get those legs into orbit and decelerated when landing.
When you’re building the most massive rocket ever built, you would need truly crazy legs in order to land. There’s also considerations like not destroying a pad (See the first integrated Starship test flight where they completely shredded the pad even launching off of a raised launch mount). So basically it would be completely infeasible to land a rocket that big on legs.
So beyond just the cool factor, you have the most massive rocket ever built – also reusable (pending further development, but good start). Which means much, much, much cheaper missions versus just tossing everything into the ocean.
Edit: Also, faster turnaround if you can literally just catch a rocket and set it right back on the launch mount, versus having it land on a separate pad or a droneship on the ocean. We’re obviously a ways away from that being a consideration, but that’s what Starship is designed to do when it’s fully operational.
Steel has a much higher tensile strength than compressive strength. In other words, steel is a lot stronger when you’re hanging something from it than when you’re trying to sit something on top of it.
The landing gear on the Falcon series of rockets adds a lot of weight to the overall rocket, which reduces the amount of payload or range you can get for the same amount of fuel. Changing the landing gear so that the rocket “catches” from the top and then hangs plays into the material properties of steel – you shift the steel from supporting the weight of the rocket by compression to supporting that weight by tension. Because steel is stronger in tension than compression, you get more carrying capacity out of the landing gear for the same amount of steel.
But why use the same amount of steel if your landing gear is stronger? A rocket doesn’t get bonus points for the landing gear being able to hold up twice the weight of the rocket. All it needs to do is to hold up the weight of the rocket. That means that you can now use less steel in the landing gear (and possibly throughout the rest of the rocket as well).
That, in turn, means that the rocket now weighs less. If the rocket weighs less, than you can get more payload capacity or range for any given amount of fuel. The entire point of the rocket is to maximize how much payload/range you get for a given amount of fuel.
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