With Flight 9 set to liftoff in a few days on the 27th, SpaceX has been busy preparing both the first booster set to be reused, along with an upgraded Starship upper stage. In a recent report from the company, they went into more detail about each of the changes made and what separates the vehicle from past flights.
If successful, we’ll see a launch that ends with the upper stage completing a landing burn and flip, followed by a soft splashdown in the Indian Ocean.
Starship Upgrades
There are two main categories of upgrades made to both the ship and the booster. One group is comprised mainly of specific changes and fixes meant to address past issues, for example, harmonic response or a hardware failure with a Raptor engine. The other group is general upgrades, as SpaceX works to improve the vehicle as a whole and test different features.
Starting with the booster, in order to achieve its first-ever reflight, the company highlighted that extensive inspections took place following the booster’s first launch to assess hardware health and identify where maintenance or replacement hardware was needed. Known single-use components like ablative heat-shielding were replaced, but a large majority of the booster’s hardware will be flight-proven, including 29 of its 33 Raptor engines. SpaceX was quoted saying, “Lessons learned from the first booster refurbishment and subsequent performance in flight will enable faster turnarounds of future reflights as progress is made towards vehicles requiring no hands-on maintenance between launches.”
There are also some booster-related upgrades based on Flight 8’s performance. In that case, multiple engines failed to relight during the boostback burn as well as the landing burn. SpaceX determined that “The most probable cause for engines not relighting was due to torch ignition issues on the individual engines caused by thermal conditions local to the igniter.” In response, they added additional insulation as mitigation.
As for the upper stage, a lot of the focus is on the heat shield. The Flight 9 “test includes several experiments focused on enabling Starship’s upper stage to return to the launch site. A significant number of tiles have been removed from Starship to stress-test vulnerable areas across the vehicle during reentry. Multiple metallic tile options, including one with active cooling, will test alternative materials for protecting Starship during reentry”. Since Flight 7, SpaceX has been trying to get some data during an actual reentry but the early end to both the last two flights has stopped that from happening, at least as intended.
“On the sides of the vehicle, functional catch fittings are installed and will test the fittings’ thermal and structural performance.” Assuming Flight 9 is successful, SpaceX is not too far from attempting to catch the upper stage back at the launch site, especially with the second tower almost complete. These catch pins in that case would be very important and need to survive Earth reentry without any significant damage.
We also haven’t seen the new flaps truly put to the test since they were altered with Starship V2. In this case, the current version of Starship has the forward flaps shifted leeward, meaning they were moved toward the back of the vehicle relative to reentry. This is meant to help improve reliability, ease of manufacturing, and payload to orbit. It’s also meant to withstand reentry heating much better than what we’ve seen so far on earlier flights that made it to that mission milestone. In those examples, we saw burn through and more heating than SpaceX was hoping for. Even on flight 6, where the upper stage made it in one piece for a soft splashdown, the buoy camera helped showcase how charred the vehicle was, with reentry likely putting more stress on the vehicle than ideal.
In relation to that, as an upgrade, “The entire ship’s tile line also received a smoothed and tapered edge to address hot spots observed during reentry on Starship’s sixth flight test.”
The final main ship upgrades have to do with the engine failure on Flight 8. Specifically, they identified that hardware failure in one of the upper stage’s center Raptor engines resulted in inadvertent propellant mixing and ignition. For flight 9 engines on Starship’s upper stage have received additional preload on key joints, a new nitrogen purge system, and improvements to the propellant drain system.
In addition, after flight 7, SpaceX made hardware changes to the fuel feedlines to vacuum engines, adjustments to propellant temperatures, and a new operating thrust target. To address flammability potential in the attic section on Starship, additional vents and a new purge system utilizing gaseous nitrogen were added to the current generation of ships with the goal of making the area more robust to propellant leakage. These are just some of the main changes SpaceX has made in order to improve the vehicle and keep the Starship program developing. In reality, there are likely hundreds of other small changes and upgrades the company has made but hasn’t talked about.
Flight Profile
Thanks to the booster being reused for the first time, the flight profile has a similar end goal as past missions, but with quite a few changes in between launch and splashdown. For context, the upcoming flight test marks the first launch of a flight-proven Super Heavy booster, which previously launched and returned on Starship’s Seventh Test Flight.
In a statement, SpaceX said, “The booster on this flight test is also attempting several flight experiments to gather real-world performance data on future flight profiles and off-nominal scenarios. To maximize the safety of launch infrastructure at Starbase, the Super Heavy booster will attempt these experiments while on a trajectory to an offshore landing point and will not return to the launch site for catch.”
“Following stage separation, the booster will flip in a controlled direction before initiating its boostback burn. This will be achieved by blocking several of the vents on the vehicle’s hotstage adapter, causing the thrust from Starship’s engines to push the booster in a known direction. Previous booster flips went in a randomized direction based on a directional push from small differences in thrust from Starship’s upper stage engines at ignition. Flipping in a known direction will require less propellant to be held in reserve, enabling the use of more propellant during ascent to enable additional payload mass to orbit” they said.
They then highlight, “After the conclusion of the boostback burn, the booster will attempt to fly at a higher angle of attack during its descent. By increasing the amount of atmospheric drag on the vehicle, a higher angle of attack can result in a lower descent speed which in turn requires less propellant for the initial landing burn. Getting real-world data on how the booster is able to control its flight at this higher angle of attack will contribute to improved performance on future vehicles, including the next generation of Super Heavy.”
“Finally, unique engine configurations will be demonstrated during the Super Heavy’s landing burn. One of the three center engines used for the final phase of landing will be intentionally disabled to gather data on the ability for a backup engine from the middle ring to complete a landing burn. The booster will then transition to only two center engines for the end of the landing burn, with shutdown occurring while still above the water, and the vehicle expected to make a hard splashdown,” they said.
It’s clear based on these quotes that SpaceX doesn’t mind losing the booster and, in turn, will be trying a bunch of different things from hot staging to a relatively violent splashdown.
This contrasts significantly with the upper stage, which SpaceX would love to keep in one piece. Starship will again target multiple in-space objectives, including the deployment of eight Starlink simulators, similar in size to next-generation Starlink satellites. The Starlink simulators will be on the same suborbital trajectory as Starship and are expected to demise upon entry. A relight of a single Raptor engine while in space is also planned.
The payload deployment should happen around T + 18 minutes into flight, and the Raptor engine relight around T + 38 minutes. If everything goes well, it will end with a landing burn, flip, and soft splashdown with a high degree of accuracy.
Recently, the FAA approved Flight 9 saying, “With the Starship vehicle return to flight determination, Starship Flight 9 is authorized for launch. The FAA finds SpaceX meets all of the rigorous safety, environmental and other licensing requirements.”
They go on to say, “The FAA is expanding the size of hazard areas both in the U.S. and other countries based on the updated flight safety analysis and because SpaceX intends to reuse a previously launched Super Heavy booster rocket for the first time. The Aircraft Hazard Area (AHA) for Flight 9 covers approximately 1,600 nautical miles and extends eastward from the Starbase, Texas, launch site through the Straits of Florida, including the Bahamas and Turks & Caicos Islands. For Flight 8, the AHA covered approximately 885 nautical miles. To minimize disruption to U.S. and international airspace users, the FAA required the launch window to be scheduled during non-peak transit periods” they said.
Conclusion
SpaceX is only a few days away from Flight 9 of Starship. After the early end to the last two flights, the company has made quite a few upgrades both to the ship and booster with the goal of completing the flight profile and keeping both vehicles in one piece.