Hacker News Reader

Comment by LostLocalMan | Hacker News Reader

Sounds like they are not planning on testing the booster catch yet, I wonder what's stopping them

That's correct, there will be no catch attempt this launch. They're going to simulate a landing by attempting to do soft land it in the Gulf of Mexico.

The reason is pretty straightforward: this vehicle has never flown before and a lot can go wrong. There is a lot of ground equipment including propellant tanks very close to the launch tower. If anything goes wrong hundreds of tons of metal + propellant is going to cause a lot of damage, and they'd likely end up having to rebuild a large portion of their launch area. Best to see how the booster behaves first before risking all that infrastructure.

It can’t be that hard to not land it in your launch area right? Can’t they have a separate land and crash area (preferably separated by a few tens of kilometers)?

You would need to build a second tower with catch arms there. The booster does not have landing legs and will not touch down on the ground, the plan is to have it settle on the same "tower arms" that are used as a crane to stack the booster and the ship for launch, with engines still well above ground.

They managed landing legs and they decided to up the level of difficulty a few notches or something?

Pretty much. Catching it with the launch tower means in theory you can have much faster turnaround between flights, since you don't need to transport it from the landing site to the launch site.

It means less hardware/weight on the actual rocket.

And crucially more room to absorb shock.

It's true that SpaceX's previous landings have used legs, but that's either been Falcon boosters (much smaller/lighter than Starship boosters, AKA "Superheavies"), or for Starship's upper-stage (again, much smaller/lighter than Superheavy boosters).

The catching system looks crazy, but it might actually be easier than landing a Superheavy on legs. The ground is a larger target than the catching arms; but its maneuverability and shock-absorption are famously low.

Landing legs are heavy, because they need to absorb a big shock. They also need actuators. "The best part is no part"; if there is a way not to drag this extra weight from the sea level up to the stratosphere and back, it counts as an improvement.

It's a good question, and I don't have a great answer for you other than my understanding is that the ground space they have to work with in Boca Chica is not really that large. And there are a lot of environmental concerns (+ the chances of blowing up on landing is greater than blowing up on liftoff).

But I've heard speculation that they might build a dedicate landing tower around their Florida launch site for that reason. No idea how accurate that is though.

It's about weight. The landing legs on the Falcon 9 first stage make up 10% of the dry weight if I remember correctly. 10% is huge savings for a booster. They've already proven they can do pinpoint landings so moving the hardware to the ground makes a lot of sense. Also, the booster should be easier to control because it can hover (the Falcon 9 booster has to do a suicide burn because its near empty thrust to weight ratio is > 1 even with only one engine). They wouldn't want to hover because it's a big waste of fuel to rely on that but it is an option while they are still practicing the catch maneuver.

They are building a tower at the Cape (it's fully erected already) but people have noticed the arms on it are shorter leading some to speculate that it might not be used for catching.

Long term it’s better to have launch and landing on the same tower, if the goal is to rapidly reuse the rocket.

The falcon 9 did several "hover over water" landings in the ocean to prove out safe landing on... land, and also to alay fears that it might miss it's target and hit a population center. Even now, falcon 9 do a ballistic reentry that would hit the water, and then propulsively adjust the landing target towards land, after the engines have safely started.

Given how much larger, and how much additional fuel is onboard, it's not surprising that they're following a similar strategy this early in the program.

The hardware at the launch site is hundreds of millions of dollars (or more). They won't want to test that till they are sure they can fly the thing.

The Flacon 9 did a fair few simulated landing over water before they tried on land or risked and barge.

Need to verify that they can successfully launch and guide it back to a specific point before they aim a guided missile at US mainland.

Risk of damaging their only launchpad, I would assume.

They haven’t launched and recovered it at all yet, have they? Presumably they want to test out to sea where it won’t blow up the only launch tower if it comes in hot.

The booster has not yet flown, no. The closest it came was a all-engines static fire (during which 2 out of 33 engines didn't fire, but it was still enough of a success to continue with the program apparently).

Reply on news.ycombinator.com