What was SpaceX’s Starship SN8?
SN8 was an early prototype of SpaceX’s Starship spacecraft, the second stage of the Starship Super Heavy launch vehicle. SN8 was the eleventh Starship test article, including test tanks, prototypes, and the infamous Starhopper.
Starship development in the Boca Chica, Texas area started about a year and a half before SN8’s construction began. A small team of SpaceX engineers began building proof of concept designs out in the middle of a dirt field – A very different development process from conventional programs. This led to the coverage of Starship’s development to become extremely popular, with 24/7 livestreams keeping a watchful eye on SpaceX.
The goal for SN8 was to be the first to conduct a high-altitude test to gather flight data. Secondly, SN8 was to verify both the Starship and new Raptor engine designs in flight. If it landed, it would be a plus. Even if it made it a kilometer into the sky, it would be a win.
Why did SpaceX fly SN8 if they knew it might fail?
SpaceX wanted to fly SN8 in the name of data precious flight data. While many companies spend years in offices designing a rocket, making sure everything will work before prototyping begins. SpaceX chose to go with an iterative design process. Breaking things early and learning from failures.
SN8’s test flight was one of many steps to mature Starship from an idea to a working launch vehicle just with real hardware instead of on paper and in simulations.
Starship SN8’s famous flight
After weeks of hopeful launch attempts that led to scrubs or delays, the stars finally aligned on a December afternoon. The rocket was fueled with just enough liquid methane and oxygen to make the 12.5 km hike. When venting occurred from the “tri-vents,” a helpful tip used by Starship watchers to know when something was about to happen, everyone in the Cameron County area kept an eye on the shiny tower on the horizon.
It’s been a long time since I saw a launch bring so many people to an area to watch it. We met people not just from around Texas but around the country. Even with the scare of a global pandemic, people felt like they needed to come to watch SN8’s flight.
Slowly, extremely slowly, SN8 began to rise from its test stand. All three Raptor engines were firing beautifully, forming a slightly translucent tail behind it. As SN8 burned off, fuel SpaceX began to throttle down then shut off individual engines to keep a constant speed. After a short hover, the final Raptor engine shut off, and SN8 began to pitch over and start its “belly flop” descent.
What caused SN8’s explosive landing?
SN8 suffered from lower pressure in one of its four propellant tanks. While most rockets use only two tanks, one fuel and one oxidizer, Starship is designed with four, two fuel and two oxidizers. The extra tanks are “header tanks” and are much smaller than the main ones. The header tanks are used during landing. These help keep the vehicle horizontal during descent and provide air bubble-free fuel and oxidizer to the Raptor engines when relit.
The fuel header tank suffered from lower pressure which didn’t let all the engines fully ignite appropriately on landing. As a result, while the rocket was able to return to verticle, it could not slow itself down before contacting the landing pad.
Implications of SN8’s flight
SpaceX launched four more high altitude Starship test flights, although only to 10 km. After SN8’s flight, the FAA got way more involved with the approval of SpaceX’s test launch license after being ignored before SN8. Now SpaceX must have an FAA safety inspector at Boca Chica before flights to approve the launch.
The flight data from SN8’s launch helped SpaceX verify its design and loaned a hand in the company successfully landing a Starship vehicle just a few months later, something many thought would never happen. So now SpaceX is moving on to launch Starship to orbit as soon as the first quarter of 2022.
