How Did SpaceX’s New Pad Hold Up Against Starship’s Second Launch?
After around 7 months of building, testing, and waiting for approval, yesterday morning Starship lifted off for a second time. While the launch itself was very exciting, a lot of people’s attention shifted to the pad right after the mission had ended. This has to do with the fact that the pad was damaged quite severely on the first launch which took up time in a few different ways.
Since then, SpaceX put a lot of time and effort into creating a new pad protection system meant to not only withstand one launch, but many. This consists of a massive water-cooled steel plate positioned under the 33 Raptor engines of Super Heavy.
At this point, comments from SpaceX along with pictures of the pad suggest that it held up very well to this second attempt. Here I will go more in-depth into the current state of the pad, what damage if any it suffered, what to expect in the coming weeks, and more.
Pad Aftermath
As you can imagine, 33 Raptor engines firing that close to the ground create a challenge when trying to withstand the created forces. In reality, the mount is about 18 meters or 60 feet high. That proximity to the bottom of Super Heavy exposes whatever material is placed under the pad to extremely high pressures and temperatures.
Not long after the mission had finished we began receiving images of the pad and Stage 0. Stage 0 is the main pad infrastructure that supports the Starship launch and catch operations. This includes the launch tower, orbital launch mount, propellant tanks, and any other ground system helping Starship complete a launch. All of which are in close proximity to the pad and vulnerable if things start flying in every direction. This being said, images highlighted that both the Orbital Launch Mount, and the steel plate itself seem to be in very good condition. Besides being charred from the Raptor’s exhaust, they are in one piece and don’t look to have suffered any significant damage. This was supported by a tweet from Musk saying, “Launch pad is in great shape”.
In addition, looking at the footage of yesterday’s launch, one of the best signs of an intact pad we saw was the lack of flying debris. In a slow-motion video of the launch released by SpaceX, you can’t see any debris flying in the air or impacting the surrounding water or structures. Compare this to the first launch when both large chunks of concrete could be seen in the air near the tower and also tons of material splashing in the ocean hundreds of meters away. That was the first sign that the pad on this second launch had done a much better job of at least staying in one piece. To add to this, the plume cloud produced by the Raptor’s exhaust was also very white as a result of it hitting the water. The first launch created a massive dark cloud of dust and debris when firing directly onto the concrete.
With all this in mind, the question becomes how much time will SpaceX need to repair or alter pad infrastructure including the steel plate to prepare for another launch. Based on images and comments from Musk, it seems like very little time is necessary and the system is practically ready for another mission. This is an extremely important aspect of Starship’s future because the goal is to launch the rocket again and again. A core factor in frequent missions is a launchpad that can easily hold up to a launch and be ready in just days for another.
In relation to this, it’s important to point out that this steel plate has already been exposed to multiple partial thrust static fires in addition to yesterday’s launch. Back in August, SpaceX conducted two separate Super Heavy static fires on the same water-cooled steel plate. While not full thrust, they held up great and demonstrated that this system is strong enough to withstand a launch and have a quick turnaround.
Finally, one other factor influencing the pad and how it held up was the length of time it took Starship to get off the ground. On the first flight, Starship took significantly longer to get in the air which exposed the pad to a lot more stress. Before yesterday’s mission, Elon Musk was quoted saying, for the next flight, “we’re going to start the engines faster and get off the pad faster.” From engine start to moving Starship “was around 5 seconds, which is a really long time to be blasting the pad.” Going to try to cut that time in half” he said. This change was obvious on yesterday’s launch as the time between engine ignition and liftoff was quite a bit faster.
Why The Steel Plate Works
On the last launch, SpaceX just used a special concrete for the pad named Fondag. Fondag is a type of concrete designed to be resistant to fire, abrasion, corrosion or thermal shock. Its formulated using specific aluminum oxide binders and synthetic aggregates. In other words, it’s a much stronger and more capable concrete mixture. Considering it held up decently for a few partial thrust static fires, the company thought they could get away with using it for just one full Starship launch. This ended up not being the case as it destroyed the pad and caused a handful of problems.
Around that time, Elon revealed that they had already been working on a steel plate but wanted to launch Starship as soon as possible. He was quoted saying, “3 months ago, we started building a massive water-cooled, steel plate to go under the launch mount. Wasn’t ready in time & we wrongly thought, based on static fire data, that Fondag would make it through 1 launch” he said.
Dr. Phil Metzger, a planetary scientist with quite a lot of experience, highlighted the benefits of a steel plate. He commented that he used steel plates for some of the Morpheus launch locations so that they weren’t tied down to places with concrete. He analyzed the heating of the sheet and showed that the heat would redistribute fast enough that it would not locally melt on the surface, and that the steel plate was large enough to take the heat of the entire launch event without melting.
In reference to using this method for Starship, he was quoted saying, “For such a large rocket that much steel would be excessive. And ablative would not be enough to solve this, either. Would the ablative need to be 3 feet thick? He continued by saying, “But he said it will be water-cooled, which is an awesome idea. The water will be taking heat out of the steel in realtime so it won’t melt. Simple, and it should be effective.” This would also allow SpaceX to use much less steel as it won’t be needed to distribute the heat” he said.
He also went on to highlight the importance of not only the steel plate, but the addition of water. Here he commented, “The very first “sound” that happens on launch is the shockwave from engine ignition. It bounces off the pad then runs up the sides of the vehicle, stressing everything. At NASA it is called the “Initial OverPressure” or IOP. To put in perspective the power of this, the IOP almost ruined the 1st Shuttle launch.
This is why the steel plate will need to be complemented by a significant water deluge system at Stage 0. On the first Space Shuttle launch the IOP deflected the elevons— the control surfaces on the wings — so far that the engineers were worried they could have snapped. So they added the water deluge system to absorb and break up the IOP shockwave” he said. Based on yesterday’s launch, the combination of the two seemed to have complimented each other very well.
For SpaceX, this marks an important milestone as they needed to come up with a somewhat innovative pad protection system. Usually within the industry, you see large flame trenches or structures designed to redirect the engine’s exhaust. For example, the Space Shuttle used a flame trench built with concrete and refractory brick that bisected the pad at ground level. It was 490 feet long, 58 feet wide and 42 feet deep. The flame deflector system includes an inverted, V-shaped steel structure covered with a high-temperature concrete material five inches thick that extends across the center of the flame trench. One side of the “V” receives and deflects the flames from the orbiter main engines; the opposite side deflects the flames from the solid rocket boosters. There are also two movable deflectors at the top of the trench to provide additional protection to shuttle hardware from the solid rocket booster flames.
In terms of SpaceX using a similar design, the area has a very high water table. The water table is an underground boundary between the soil surface and the area where groundwater saturates spaces between sediments and cracks in rock. Creating a massive trench would complicate this process significantly. That is part of the reason they went for a lower-profile deflector positioned directly under the engines.
Over the next few weeks, we can expect to hear even more from SpaceX on the exact condition of the pad and its surrounding structures. This being said, Stage 0 looks to be in great shape thanks to the new water-cooled steel plate. A change that should support more frequent launches as SpaceX continues to manufacture and innovate the Starship vehicle.
Conclusion
Yesterday SpaceX launched Starship for a second time and the pad was exposed to the full thrust of 33 Raptor engines. This time however SpaceX was much more prepared and knew that concrete alone would not be sufficient. We will have to wait and see how it progresses and the impact it has on the space industry.