The most powerful rocket in history launched on its second attempt Thursday, the first major step to making life multi-planetary. Liftoff of Starship from Starbase, Texas came after an uneventful countdown, with only a couple of short holds before roaring off the launch mount.
The vehicle lost several Raptors during first stage ascent before starting to rotate out of its trajectory before it was destroyed by the Flight Termination System (FTS). Clearing the launch site and gaining first stage data will provide vital data for the next flight with Booster 9 and Ship 26.
Flight background
From Starhopper’s 150-meter flight in August 2019 until now, SpaceX has been working through several vehicles to fully develop Starship. Test vehicles from serial numbers (SN) 1 through 6 were used to test Starship tank build quality, with SN5 and SN6 also helping gather early flight data.
Later vehicles from SN8 through SN15 were used by the company to test the extremely complex skydiving, flip, and landing burn maneuvers needed to turn Starship from horizontal to vertical as it comes for a landing. After several tries and one near-miss, a successful landing was finally achieved with SN15.
Around this time, the focus shifted, and the company started developing Super Heavy, the monster booster that makes up the first stage of Starship. Several iterations were made as teams figured out the best booster design to use for the first integrated flight of the system.
This iterative design approach also included decisions like not flying Booster 4 and Ship 20 after several months of working on the vehicles while being penciled in for the first test flight. Instead, SpaceX chose to go ahead and use Booster 7 and Ship 24 – each boasting substantial improvements over their predecessors – for this historic milestone of the program.
These vehicles were produced between late 2021 and early 2022, with Booster 7’s first rollout to the launch site occurring on March 31, 2022 – about a year ago. The booster’s test campaign suffered several issues – as is to be expected with development vehicles – but these were eventually resolved.
During a cryogenic proof test on April 17, 2022, Booster 7’s transfer tube was crushed and damaged, and teams had to roll it back to the production site for repairs. On July 11, Booster 7 performed a 33-engine spin prime test that ended in a sudden and violent explosion underneath it. This was later traced back to anomalous high concentrations of gaseous methane mixing with ambient air, which eventually found an ignition source and exploded.
Booster 7’s test campaign was also filled with success. It became the first vehicle to static fire while on the orbital launch mount (OLM) and eventually performed a 31-engine static fire test on Feb. 9, 2023.
Ship 24’s test campaign also had a mix of issues and successes. Its very first test, a pressure-proof test at ambient temperature, was cut short when a test setup error caused a pressure spike on a pipe inside its payload bay section which damaged part of the vehicle.
This ship was also the first to perform a six-engine static fire test while fitted with the more powerful Raptor 2 engines. This test would prove crucial in hindsight as structural reviews showed a potential weak point on the aft end of the vehicle. This aft section was later reinforced and design changes have been implemented on later vehicles to avoid this issue.
Ship 24 and Booster 7 are now in full stack configuration and will serve, once more, as test vehicles that will inform the future progress of Starship’s design and operations. SpaceX’s test, fail, fix approach to development will be used again during this flight.
Countdown and Flight
The launch attempt began with familiar milestones seen during previous tests, starting with the road closure.
Once SpaceX was ready, the sheriffs began clearing Boca Chica Beach and the surrounding area to ensure no unauthorized personnel were present in the area during the launch attempt. After this was completed, the Sheriffs blocked the road at a predetermined location along Highway 4 to ensure no one was able to pass.
SpaceX employees completed final work and checkouts ahead of the flight. Upon completion, all workers cleared the launch site and drove down Highway 4 to the other side of the roadblock put in place by the sheriffs.
After the pad was clear, SpaceX primed the tank farm ahead of the propellant load. Both the liquid oxygen (LOX) and liquid methane (CH4) sides of the tank farm spooled up and vented as the propellant systems began to chill down.
This is done to allow the various pipes, pumps, valves, etc. to slowly cool down to a temperature closer to that of both cryogenic propellants to avoid any thermal shock occurring to the systems.
During this period, the OLM and launch tower also began venting as the propellant lines running up to both the booster and ship quick-disconnect umbilicals (QDs) are chilled down.
At T-2:00:00 the launch director gave the go/no-go for propellant loading onto both vehicles.
Propellant loading began at T-1:39:00, with liquid oxygen and liquid methane flowing into Booster 7. Once loading began, frost started to form and continued to rise on both tanks as the amount of cryogenic liquid inside the tanks increased.
Ship 24 loading began at T-1:22:00 with liquid methane flowing into the ship’s fuel tank followed by liquid oxygen loading a short time later at T-1:17:00. Both of these events look similar to the booster as frost also forms on the outside of the ship.
During the first launch attempt, all was going to plan until the stuck valve came into play, resulting in SpaceX taking the opportunity to conduct a wet dress rehearsal while scrubbing the launch attempt.
For the second attempt, chill down of the Raptor engines on Booster 7 occurred at T-16 minutes and 40 seconds, with all the engines flowed a small amount of propellant through them to slowly cool them down to operating temperatures. This is done, much like with the tank farm and propellant loading systems, to avoid thermal shock and damage to the many components inside the engines.
At T-40 seconds, the fluid interfaces began their vent-down sequence. This saw propellant lines that connect both the booster and ship QDs vent any remaining propellant left in them in order to minimize damage during liftoff.
The Raptor engine startup sequence began at T-8 seconds, where all 33 Raptor 2 engines began in a staggered start before ramping up to flight thrust levels. During this test flight, the engines were not expected to run at 100% thrust but instead ran at a slightly lower ~90% thrust.
At this thrust level, Booster 7 officially became the most powerful rocket ever fired, producing approximately 67,000 kN (15,000,000 lbf) of thrust. The previous record was held by the Soviet Union’s N1 rocket, which had a liftoff thrust of 45,400 kN (10,200,000 lbf).
Then, the 20 hold-down clamps securing Booster 7 to the OLM released and the vehicles lifted off from the pad at T0.
Right as liftoff occurs, the Ship QD arm tasked with loading Ship 24 with propellant disconnected and immediately begin to swing away from the vehicle to avoid being impacted by the rocket, as well as protecting the arm from the booster’s exhaust.
A short time later, the vehicle cleared the tower and slowly start pitching downrange toward the Gulf of Mexico as the full stack begins its gravity turn.
Booster 7 started to lose Raptors, between five or six, during first stage ascent.
However, it did experience max-Q, the period of peak aerodynamic stress upon the rocket, approximately 55 seconds after liftoff. This was a major test of the overall structure of both Ship 24 and Booster 7.
A short time later, the vehicle began to spin, before being destroyed by the FTS.
Had it been a full mission profile, Booster 7 would have continued to burn until around two minutes and 49 seconds after liftoff. At this point, all 33 engines would have shut down in an event known as booster engine cutoff. If all remains nominal, would have occurred when the vehicle is at an altitude of approximately 64 km (~40 miles) and climbing rapidly.
Ship 24 would have then separated from Booster 7 around four seconds later and coasted away from the booster for five seconds. The ship would then attempt to ignite its three sea-level and three vacuum-optimized Raptor 2 engines located inside the aft skirt of the vehicle.
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If all six engines ignited successfully, Ship 24 would expect to perform an approximately six-minute and 23-second burn, assuming a nominal burn of all engines. Due to this being a very ambitious test flight, SpaceX has opted not to insert Ship 24 into a stable orbit but will instead fire its engines until just short of full orbital insertion. This would have lead the spacecraft on a trajectory to re-enter over the Pacific Ocean just northwest of Hawaii without any additional engine firings needed.
While Ship 24 would have performed its burn, Booster 7 would begin to flip around just after stage separation and reignite its inner 13 engines to perform the boostback burn a little over three minutes after liftoff. The boostback burn would have lasted approximately 55 seconds and put the vehicle on a course to splash down in the Gulf of Mexico approximately 31 km (~19 miles) off the coast of Texas.
LHAs for #StarShip 24 / SuperHeavyBooster 7 OTF mission from Starbase OLP-A, valid for NET 17 Apr 12:00 UTC, altern. 18 to 21 Apr based on issued NOTAM/NOTMARs. B7 boostback and splashdown expected ~32km downrange. S24 reentry/splashdown north of Hawaii. https://t.co/BpJZ15cY0J pic.twitter.com/nw5AsiggBr
— Raul (@Raul74Cz) April 16, 2023
Unlike Falcon 9, Booster 7 would not have performed an entry burn. Due to stainless steel’s higher temperate resistance compared to aluminum (which makes up Falcon 9), an entry burn was not required.
Booster 7 would have continued its descent using its four grid fins to help keep it oriented and steer toward the targeted landing zone in the Gulf of Mexico. The vehicle would have expected to go transonic around seven and a half minutes after liftoff with the final landing burn beginning ~10 seconds later.
The landing burn would have lasted around 23 seconds and used the vehicle’s three innermost engines with the booster expecting to impact the water at approximately 8.5 m/s (19 mph).
Ten seconds after splashing down, Booster 7 would have tipped over onto its side. In such an event where the tip-over does not cause the vehicle to break apart, the vent valves located on both propellant tanks would be commanded to open to allow water to ingress the vehicle in an attempt to sink it.
SpaceX’s ultimate goal is to fly Super Heavy boosters back to the launch site and use the large “chopsticks” mounted on the launch tower in order to “catch” the boosters as they come into land. This will hopefully allow for a rapid turnaround of the boosters as no recovery assets are needed and vehicles can be placed directly back onto the launch mount shortly after landing.
Had Ship 24 reached engine cutoff it would have coasted for a little over one hour, during which time the vehicle would vent all but nearly 14 tonnes of propellant (10 tonnes of LOX and four tonnes of CH4) in order to keep a correct amount of ballast during re-entry.
If the vehicle survives the nearly 10-minute-long re-entry phase of the flight, Ship 24 will go transonic just under one and a half hours after lifting off from Starbase.
For this flight, similar to Booster 7, no recovery of the ship would have been attempted. However, unlike the booster, Ship 24 would not perform a landing burn and was expected to impact the ocean at terminal velocity approximately one and a half hours after liftoff – had the mission gotten that far.
What comes next
The next phase of Starship and Super Heavy testing depends on the results of the first test flight.
Ship 24 and Booster 7 were transmitting live telemetry to the FAA’s Space Data Integrator system, which is used by the FAA to plan real-time airspace restrictions and releases. SpaceX had tracking assets, including the dishes at Starbase, working to downlink the telemetry.
Regardless of the result, SpaceX will be poring over the data obtained and learning how the vehicle actually performed during its flight. Workers at Starbase will also be installing a water deluge system beneath the orbital launch mount for use during future flights, and this work could take a few months to complete.
The next two flights of Starship at present will not be equipped to survive reentry, and the booster will be programmed to splash down into the ocean in a similar manner to the first Starship and Super Heavy test flight. Ships 26 and 27 are thought to be conducting these flights, along with Booster 9 and Booster 10.
Ships 26 and 27 are not equipped with flaps or heat shield tiles, so they would not be able to survive a reentry or land afterward. Super Heavy boosters from Booster 9 onwards will replace the hydraulic power units – featured on Booster 7 – with electrical power for engine gimbaling and other functions.
Other upgrades to both the ships and boosters likely will be tested, in line with SpaceX’s iterative design philosophy. The Starship that is operationally flying in a few years’ time will be very different from the one waiting for launch.
For the next two test flights, SpaceX has designated a zone 1,815 km southwest of Kauai where debris from the breakup of Ships 26 and 27 would fall. The ships will tumble during reentry until their breakup, which would occur around 50 to 70 kilometers in altitude.
The timing and objectives of the next two test flights will be informed by the results of the first flight and the condition of the orbital launch pad. Even in the best-case scenario, it will likely take several months before the second Starship test flight would be ready. Any serious damage to the orbital launch site likely would require considerable time to recover from.
Even if Ship 24 and Booster 7’s flight is a complete success, the system’s ability to go into a full low Earth orbit, restart its Raptor engines in space, and conduct a deorbit burn will need to be tested at some point. Payload deployment and in-space propellant refilling also await this on-orbit testing.
However, Ship 26 and Ship 27 seem to be currently planned to fly a similar profile to Ship 24. This means that neither ship would go into a full low Earth orbit. Ship 26 does not feature a Starlink deployer (nicknamed the “Pez Dispenser”). Ship 27 does feature such a mechanism, but there is no evidence of any plan to deploy satellites from it.
Sometime after the third test flight of the Starship system, depending on the results of the booster’s flights, the process to catch a booster with the Mechazilla’s “chopstick” arms will be tested. The recovery method of the Starship itself will be further developed, especially since landing legs will eventually be needed for the Starship-derived HLS lunar lander. Elon Musk has suggested using the chopsticks to also catch ships, however, this idea has not been heard in some time.
Success maybe, excitement guaranteed! https://t.co/LoDrBmHkQa
— Elon Musk (@elonmusk) April 14, 2023
Regardless of the result of the first Starship launch to space, humanity is on the brink of a new era of space exploration. Testing is about to begin on a space vehicle that is designed to become fully reusable, which could make things possible that we can only dream of today.
Photos from Nic (@NicAnsuini) and Jack Beyer (@thejackbeyer for NSF).
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