Following Starship’s debut during Integrated Flight Test One (IFT 1), SpaceX is ready to improve on the vehicle’s objectives by employing a vast series of upgrades. Most of the enhancements have been made to the launch site and Booster 9, which, in turn, are waiting for final regulatory approval.
Changes to Booster
Booster 7 and 9 have several significant differences, starting with the changeover from Raptor 2 to Raptor 2.1, which uses electric TVC (Thrust Vector Control) over the previous hydraulic system. This removes two hydraulic power units (HPUs) from the booster’s aft.
Electric TVC uses electric linear actuators to move the center 13 raptors on a booster rather than with hydraulic actuators. This has multiple benefits; first off, SpaceX can get rid of the HPUs that were at the bottom of the booster, thus reducing weight, and secondly, electric TVC can allow for quick and smoother gimbaling action during flight.
Removing the need for the HPUs also helps reduce complexity and increase reliability, along with a mass of tubing inside the engine bay replaced by wire harnesses.
Booster 9 also had its Raptors and its valves upgraded after IFT 1, and the upgrades consisted of modifying the methane turbopumps and manifolds with new seals to reduce the amount of Methane leakage into the engine compartment. This had caused fires in B7’s engine compartment during the first flight test.
A possible reason why SpaceX has an issue with methane leakage compared to other rockets could be the high pressure that Raptor operates at in its Methane turbopumps, hot gas manifold, and the Main Combustion Chamber (MCC). This results in more pressure on the seals and causes leakage.
To help mitigate the methane buildup in the engine compartment, removal of the small chines on the side of the booster and replacing them with larger chines that include upgraded purge tanks have been employed.
These larger purge tanks will allow SpaceX to better control methane buildup within the engine compartment during flight and static fires. Part of this system is the addition of 18 vents to the engine section of Booster 9, which can be seen in action during static fire testing.
The gas used for this system is believed to be CO2, which is beneficial for extinguishing fires.
The engine shielding for Booster 9 has also been upgraded when compared to Booster 7. Unlike previously, where the it was retrofitted on the booster over time, Booster 9 has been designed with upgraded shielding from the start. SpaceX is slowly simplifying the design to make it easier to access engines and perform maintenance.
Booster 9 also has a major internal change over Booster 7, with a newly designed methane transfer tube after Booster 7’s imploded during a cryo test. The new transfer tube has many more reinforcement stringers than its predecessor.
After the flight termination system (FTS) on IFT-1 failed to destroy the full stack, SpaceX upgraded the FTS on Booster 9 by adding another explosive charge on the methane tank just above the common dome.
With this extra charge, SpaceX should be able to destroy the common dome and methane tank in such a way that mixes both the methane and liquid oxygen, which hopefully results in a larger explosion, thus destroying the entire booster.
Hot staging upgrade
One of the most obvious changes to Booster 9 was the addition of a hot stage vent ring on the top that will allow SpaceX to fire the ship’s engines while still attached to the booster. This simplifies the separation mechanism and allows the ship to always be under acceleration, thus allowing it to perform better and not incur losses due to gravity.
The dunes of Boca Chica beach provide nice foreground for Starship full stack photography. @NASASpaceflight
— Sean Doherty (@SeanKD_Photos) September 9, 2023
This ring has a steep dome with a flat top for shielding and is heavily reinforced under the shielded section. The steep dome allows for the exhaust gases from the raptor engines to be directed outwards and through the vented ring section to prevent buildup inside the interstage.
The hot stage ring attaches to the booster using the ship clamp system, allowing for easy installation and removal so technicians can access the grind fin motors and avionics located on the forward dome of Booster 9. In order for the ship to attach to the booster, the ring has a set of ship clamps on top.
Booster 9 has her crown and is ready to roll in the coming days.
— Chris Bergin – NSF (@NASASpaceflight) August 18, 2023
The ring was removed this week at the launch site, but is expected to be reinstalled in the coming days.
Changes to Ship
Ship 24 and Ship 25 had many upgrades over Ship 20, with the intro of Raptor 2s on a vehicle for the first time, a heat shield actually made out of tiles, and a payload bay – although it would be welded shut.
There are a few differences between Ship 24 and Ship 25, although they are basically sister ships. Both ships use HPUs for TVC, and they both have the same payload section compared to Ship 28, which appears to have a functioning payload bay door.
3 more engines for the meaning of life pic.twitter.com/nt7T2TPt05
— Elon Musk (@elonmusk) July 10, 2023
The main reason Ship 24’s and Ship 25’s payload section and door were welded shut was because SpaceX figured they might not survive flight loads, so they decided to weld those shut while they came up with a solution.
After Ship 25’s static fire, SpaceX removed all of the engine shielding and replaced it with thicker shielding to help protect the engines and ship during hot staging. This was added to the ship while parked in the rocket garden.
SpaceX has also added extra vents above the engine shielding “false floor” on Ship 25. This is for purging the engine skirt around the engines to prevent Methane buildup.
Two more vent lines have also been added to the engine section of Ship 25. However, it is currently unknown if these are related to the engine chill system, but these new lines don’t have pipe extensions like the engine chill lines on Ship 24.
Ship 25’s FTS received an upgrade just like Booster 9, with an extra charge just above the common dome.
With all these changes, SpaceX hopes to advance its objectives during the next flight. Reaching stage separation and ignition of the ship would be a big win for the program. Anything more than that would be icing on the cake.
(Lead image: Ship 25 and Booster 9 full stack. Credit: Mary for NSF)