Why is catching the SpaceX booster in mid-air considered much better and more advanced than just landing it in some launchpad ?
In: Planetary Science
If you want to launch again quickly, the arms can set it back on the pad, without needing to move the booster with heavy equipment from another pad
You don’t need to carry heavy landing hardware on the booster itself if it’s caught in mid-air, thus increasing overall rocket payload.
SpaceX have had some issues with their attempts at landing a rocket on a landing pad. The landing legs have to be very light because the weight margins of the rocket is already very tight and any mass in the landing legs will reduce the payload mass. Some customers have been paying SpaceX to not outfit their Falcon 9 rockets with landing legs so their satellites will fit, a full rocket is cheaper then a few extra tons of cargo to space. The light legs have collapsed in some landings. Building the legs stronger would make them heavier. Especially for the Starship rocket the legs would have to be very strong and heavy.
The second issue is that the landing pad have issues with the rocket exhaust. During a landing the rockets shoot out a huge amount of supersonic plasma directed straight at the pad. This can melt steel and even make concrete explode. For launches they raise the rocket up a bit and also carefully position it over a trench with a flame deflector made of steel and covered in water. But this is a hazard for the landing legs. And even then the launch pads is regularly damaged by flying pieces of the pad, a few times this have damaged the launching rocket as well. So this is a much bigger issue when the rocket is coming towards the pad instead of away and when the rocket comes much closer to the pad then during launch.
The “chopsticks” is an attempt at overcoming these issues. Firstly all the landing structure is on the ground and can be built very strong without sacrificing any payload mass. And secondly it can catch the rocket at a significant height above the pad so that there will be less damage and so that the rocket will not be hit by any debris.
The pad, while a small target for a rocket to land on using automated guidance, is very large compared to the opening for the catch arms on the tower. The booster also has to avoid the tower itself.
Its better because it helps reduce weight on the booster and reduces the chance of a catastrophic failure.
The booster’s landing gear is limited in strength. Every pound of material used to make it stronger is a pound of cargo less that the booster can carry (not exactly, but its that concept). By removing the complicated landing gear they can drop weight on the booster. It also doesn’t matter how heavy the tower is, so they can build it to be as strong as they want/need.
It’s better because you don’t add as much weight to the rocket adding landing legs.
It’s harder because you have to land much more accurately.
The rocket equation is a harsh mistress. Every gram saved at liftoff yields more delta-v downrange.
**1. Weight.** The booster is lighter without landing legs. This allows for greater thrust and power in allowing the payload to reach orbit.
**2. Rapid Reusability**. Catching it with the chopsticks allows them to lower it down to its launch mount quickly and easily, allowing it to launch again (ideally) within 24 hours.
Excellent question, excellent answers! Daring to pull such an inventive way of solving problems is extraordinary. “You catch it mid-air so you don’t need to have heavy legs attached, with the added benefit you don’t destroy the landing pas with supersonic plasma”.
Mind blown!
Nobody mentioned the rocket equation.
Imagine you have a toy rocket, and to get it into space, you need fuel. But here’s the tricky part: the more fuel you add to go higher, the heavier the rocket becomes. And because the rocket is heavier, it now needs even more fuel to lift all that extra fuel! It’s like a cycle where adding more fuel makes the rocket heavier, so you need even more fuel to lift the rocket.
This is where the rocket equation comes in! It tells us how adding weight (like more fuel) makes a big difference in how much fuel you need.
For every pound you save on the vehicle, you gain A LOT OF POUNDS in lift capabilities.
The legs don’t help it fly better, it’s dead weight and another thing that “could break in flight”.
This way it does not need legs.
There’s an engineering principle called KISS (Keep it Simple, Stupid) and this is like the definition.
Removing legs, is removing a failure point while adding more performance (Payload to Orbit)
Don’t have to carry legs up, which is a lot of extra mass you can have on the starship and not in the booster. But the issue is that one day the launch tower will go boom and those are slow to fix.
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