The Real Reason SpaceX Built Mechazilla!

Let’s talk about the SpaceX Mechazilla - this is the giant, robotic launch and landing tower that will be literally catching Starship rockets out of the air with chopstick arms some time in the not so distant future. It’s an unprecedented and fantastical idea from Elon and the SpaceX engineers, but this isn’t about showing off, this is a purely functional decision for the company. 

And over the past year or so since Elon first tweeted that they were going to try and catch the Super Heavy Booster with the launch tower arm, we’ve had no end to the speculation over how exactly such a thing would even work. But things are starting to change, over the past few weeks, the Mechazilla has started to come alive and flex its muscles. And on top of that, Elon just released the very first official SpaceX render of what a booster catch will look like.

So, today we’re getting into the reasons why SpaceX is going through all of the trouble to build this crazy machine, if it will succeed and everything we know about how it works. Let’s get going.

Let’s start from the beginning by answering why SpaceX is even doing this robot catching thing in the first place. They’ve already figured out how to land the Falcon 9 rocket on legs, which is an accomplishment that remains unmatched by any other aerospace company, even years later. On December 21st, 2015, a Falcon 9 first stage made a successful landing on the ground at Cape Canaveral - something that had never been done before. And just a few months later, on April 8th, 2016, a Falcon 9 first stage landed for the first time on a ship in the ocean.

Why would SpaceX feel the need to take it to another level if they’re already at the top? Elon explained it all back on December 30th 2020 - through his Twitter replies, of course  - when someone asked him if the Super Heavy would descend to land the same way as a Falcon 9. Elon replied, “We’re going to try to catch the Super Heavy Booster with the launch tower arm, using the grid fins to take the load.”

Many assumed that maybe the Booster would be too tall and heavy for legs. But Elon clarified that, “Legs would certainly work, but best part is no part, best step is no step.” Basically saying that they could do it the easy way, but he’s choosing the hard way on purpose, and with good reason. Elon wrote, “Saves mass and cost of legs and enables immediate repositioning of booster on to launch mount — ready to refly in under an hour.”

So, if the Super Heavy were to come down onto the landing pad, the same way the first Starship tests did, then it’s actually going to take a lot of work to get it back on the launch mount - even if it’s not far away. First they’d need both a mobile crane and that giant, tank tread transport vehicle they use at Starbase for moving rockets. The crane would have to pick the booster up, place it on the transport, then move the whole situation over to the launch mount, then use the crane again to move the Booster back on the mount, and then drive both of the giant machines back to the hangar.

And, in addition to being heavy, expensive and complex, landing legs themselves can be very fragile and maintenance intensive. If we take the Falcon 9 for example, the rocket is light but it comes down with a lot of force that needs to be taken on by the legs. SpaceX don’t use shock absorbers in the Falcon legs, but they do use a sort of crumple zone to absorb the energy. SpaceX call these ‘crush cores’, they’re honeycomb style cartridges inside the legs that compress on landing. And these obviously have to be replaced after every landing. Now, there are a lot of things on Falcon that need to be refurbished between flights, mostly to do with the kerosene burning engine, so replacing crush cores is no big deal. But on the Starship and Super Heavy that demand rapid reusability and feature clean burning, methane engines, stopping to inspect and refurbish the legs is going to be too much. Particularly when we reach Elon’s ideal launch cadence for the Starship, which is three launches per day, per booster.

OK, so we have a pretty good idea why Elon is doing this. But now we get to try and figure out how it’s going to work – and that’s pretty fun.

We know that the core of the launch slash landing tower is a 145 meter tall, steel structure. And we also know that the tower has three mechanical arms - one is a quick disconnect arm that serves as an umbilical connection for propellant and acts as a mid-rocket stabilizer. The two remaining arms will work together to pick up and catch spaceships. This is how Elon described it last August, “SpaceX will try to catch the largest ever flying object with robot chopsticks. Success is not guaranteed, but excitement is!”

In this case, the chopsticks are 36 meter long, tubular steel beams. We know that mechanically, the arms are driven up and down along a rail track on the tower by a super heavy duty winch system, also called a draw work. The draw cables are powered by 4 giant electric motors that are mounted at the bottom of the tower and combine to produce 6,000 horsepower. This system is lifted directly from an oil rig, where it’s used to lower and retract drills from the bottom of the ocean. And the pinching motion of the chopsticks is controlled by hydraulic cylinders.

As for how the Booster and chopsticks will function together, Elon’s Twitter post on January 19th of a SpaceX digital render finally gives us a pretty good idea of the landing process.

So, the final landing burn begins at an altitude of about 1,800 meters - this is pretty much the same height that Falcon 9 starts its burn. And also like the Falcon 9, Super Heavy will be coming down at an angle, like a javelin, not straight up and down. The reason for this is to have more surface area of the rocket hitting the atmosphere and creating drag - or lift, depending on what term you want to use. And again, same as Falcon 9, the Super Heavy will be using grid fins to help stabilize the flight.

Unlike a Falcon, the Super Heavy will be using 9 engines at the top of its landing burn, and those will be attached to a motorized gimbal system that allows the engine nozzles to swivel around and steer the rocket as well.

At a height of about 800 meters, 6 of the engines will shut down, leaving just 3 Raptors that will gimbal to straighten out the rocket and bring it down for a controlled hover between the waiting arms of the Mechazilla. At this point, the arms of the tower will be shifted over to the side, away from the launch mount - SpaceX do not want the Booster coming down directly over top of the launch mount because it is very expensive and labor intensive to build - the boosters and ships are cheap, but the ground infrastructure is not supposed to be expendable. 

At about 65 meters above ground, the Super Heavy is hovering and two more engines cut off, leaving just one that will shut down as the chop sticks come up to grab two pins on the sides of the Booster, just underneath the grid fins.

This is a little bit different from the idea that most 3D artists had imagined previously, where the Booster would be coming down with force and the arms would cradle and absorb the energy. From Elon’s rendering, we are seeing the Booster come to a dead stop and hover for something like 5 seconds before being pinched by the chopsticks. According to this rendering, the sticks will move very little during the catch maneuver, they definitely won’t be sagging down like a shock absorber. We know that the catch rails on the chopstick arms have the ability to move up and down a few inches, and that’s probably all that would be needed to absorb the weight of the Booster - same deal as those crush cores in the Falcon legs.

We’re used to seeing the Falcon 9 come down pretty hard when it makes a landing - this is often referred to as a suicide burn - because if it’s too short, the rocket hits hard and explodes, but if it burns too long, the rocket will bounce off the ground and go back up, then tip over and explode - we’ve seen both cases happen to Falcons in the past. And the reason for this is, one, to use the least amount of fuel possible, hovering even for a few seconds requires a lot of fuel to be held in reserve. And two, an empty Falcon 9 is very light, only about 550 kilogra ms, while the Merlin engine is very powerful, so it’s actually not capable of throttling down enough to hover that booster.

This raises an interesting question to think about - is Super Heavy going to be capable of hitting such a narrow landing target? Yeah, it should be no problem really. And again, we can compare it to the Falcon 9 - that booster is able to land within a pretty small circle, even on a floating drone ship in the ocean. When Falcon boosters land on the ground, they almost always hit dead center on the pad. And the Falcon can only steer with the grid fins, it doesn’t have gimbaled engines and it doesn’t have the luxury of hovering. If we look at the Blue Origin New Shepard booster - that can make some incredibly slow and controlled ground landings with fins and the ability to hover, but still no control from gimbaled engines. So, with all of the advanced tech in the Super Heavy, the combination of grid fins, gimbaled engines and hovering, I can’t see any reason why it wouldn’t be able to literally land on a dime if it had to.

So, those are the reasons why Elon Musk is building the Mechazilla, it’s just his way of taking rocket engineering to the next level, and at the same time making the Starship even cheaper to build, even more reusable and even more efficient.

And this Mechazilla is just the first of its kind. There is at least one more of these towers going in at Starbase at some point in the next year. We know that SpaceX are building two more at their launch pad at Cape Canaveral Florida that will be even more capable than the Starbare towers. And then eventually, Elon’s goal is to build Mechazilla towers on Mars that would support the massive fleet of 1000 Starships that he imagines flying between our two planets. Eventually, a fully functioning Starbase on Mars with the ability to produce Super Heavy boosters would use their Mechazilla tower to launch fully stacked Starships on deep space missions to Saturn, Jupiter, Neptune or even places beyond our solar system. Which is pretty damn trippy.