SpaceX Starship: The Continued Evolution of the Big Falcon Rocket

by Phillip Gaynor

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SpaceX announced the predecessor to Maezawa’s flight on February 27, 2017.  It would have featured a Crew Dragon six day circumlunar flight launched on a SpaceX Falcon Heavy rocket for two paying passengers.  Those plans were later shelved, and on September 17, 2018, SpaceX announced that Yusaku Maezawa and a group of six to eight artists would circle the Moon on the Big Falcon Rocket by 2023.  To put that in perspective, Apollo 17 last flew astronauts around the Moon in December 1972.

SpaceX CEO Elon Musk said that the Japanese tycoon had been one of the potential customers for the Falcon Heavy flight. However, he had chosen to upgrade from the Falcon Heavy to be able to bring more artists on his voyage.  In the Dear Moon presentation, Musk said the estimated cost of the overall BFR development was “roughly 5 billion dollars”. He added that Maezawa’s contribution to the cost of the mission “will actually have a material effect on paying for the cost of the development of BFR”.

On November 17, 2018, Elon Musk hinted that his rocket company was making more changes to the design and no longer looking to upgrade the existing Falcon 9 rocket’s upper stage to be reusable.  Instead, SpaceX was speeding up work on the Big Falcon Rocket, which would be fully reusable and thus potentially cheaper.  Musk tweeted that the design had changed in a “delightfully counter-intuitive” way.

In a series of tweets on November 19, 2018, Elon Musk announced the fourth different name of the rocket.  The upper stage would be renamed ‘Starship’, while the booster stage would be renamed ‘Super Heavy’.  Musk had previously used the name in April 2018 during the run-up to the Falcon Heavy’s first flight, when he mentioned the possibility of a Falcon Super Heavy.  This would have been a Falcon Heavy with two extra boosters.  The rocket’s original name, when Musk first discussed it in 2007, had been Big Falcon Rocket.  Musk later mentioned that this name had been inspired in part by the BFG from the Doom video game series.

Carbon fiber tooling at the Port of Los Angeles with a Tesla for scale – via SpaceX

SpaceX announced in April 2018 that it had approval to develop its BFR rocket and Starship at the Port of Los Angeles.  By this stage, approximately 40 personnel worked on the design and a tent there, housing the massive carbon fiber tooling SpaceX had ordered to construct the BFR.

SpaceX’s plans called for the launch vehicle to be assembled at the Port of Los Angeles and then transported by barge via the Panama Canal to its Cape Canaveral, Florida launchpad.  However, with a sudden tweet from Musk on December 8, 2018, that the design had changed from all carbon fiber to metal, these plans were cast in doubt.

On December 22, 2018, Elon Musk confirmed in a tweet to NSF that a radically re-designed engine would be ready to fire the next month.  The next day, following a trip to SpaceX’s Boca Chica, Texas launch site, Musk announced that the first test article Starship had been under construction there for several weeks.

On the 24th, he announced that Starship would be made of stainless steel.  This vehicle would fly with three of its seven planned Raptor engines, with a first flight no earlier than March 2019.  By January 10, 2019, the primary structure of this test article was complete.

Starhopper in the early era of SpaceX Boca Chica – via Nomadd for NSF

Among the reasons stated for the radical design change included stainless steel’s mirror-like thermal reflectivity and its superior ability to handle extreme heating, which meant it could end up requiring less heat shielding than carbon fiber.  Winds damaged the nose of the test article on January 23, which SpaceX decided not to replace.

On February 1, 2019, Musk unveiled a picture of the first completed full-scale Raptor engine.  He also noted that the rocket’s Super Heavy booster’s early test flights would likely feature fewer than 31 engines (later refined to probably around 20).  The change was possible because initial test flights would not need the design’s full capacity.  This would have the added advantage of lessening testing costs.

SpaceX finished the construction of its Starhopper prototype in April 2019.  Shaped a bit like a flying water tank, it was constructed with stainless steel and featured a single Raptor engine.  It was meant to test elements of the Starship design.  The company conducted two seconds-long tethered tests on April 3 and April 5.  During May 6 to 7, technicians installed cold gas thruster pods from a mothballed Falcon 9 on the Starhopper in preparation for untethered test flights.  An untethered test followed on July 25, when the vehicle rose 18 m (59 ft.) off the ground.  A final flight on August 27 saw it rise to 150 m (492 ft.) and move sideways to a different landing site. The Starhopper was retired from flight afterward.

A rendering produced by NASA’s Goddard Space Flight Center (GSFC) on April 11, 2019, showed that the Starship cargo hold could carry both variants of the planned LUVOIR space telescope, which is one of the four planned options for the successor to the James Webb Space Telescope.  The same day, it was announced that SpaceX was conducting another 500 million dollar funding round to help fund SpaceX’s simultaneous development of their Starlink satellite constellation and Starship/Super Heavy.

Credit: NASA Goddard Space Flight Center

On May 14, NSF member Zpoxy spotted a second Starship under construction in Cocoa, Florida.  This was shortly thereafter confirmed by Elon Musk, who mentioned that two competing teams would be constructing Starship prototypes.  They would share design details with one another but not be required to follow the other’s design, potentially speeding up Starship and Super Heavy’s development.

Each will feature three Raptor engines and are notably constructed in the open, a departure from almost all rocket construction.  In the run-up to SpaceX’s September 28, 2019 update, the construction of Starship Mark 1 (Texas) and Mark 2 (Florida) made rapid progress.  The Mark 2 prototype had its nosecone and main cylinder constructed, but they were not welded together.  The Mark 1 prototype had its nosecone mounted on top of its main cylinder.

The September 28 update showcased the 11th known version of the vehicle.  Elon Musk also announced that they hoped to achieve orbit with a more advanced Starship prototype in six months.  These prototypes would feature the full six Raptor engines as well as single seam welding.  The full launch Starship vehicle would follow, and construction of its Super Heavy stage would be heavily dependent on the pace of Raptor engine construction.

Following the announcement, the Starship Mk 1’s canards and wings were removed and then reinstalled, while the lower part of the vehicle was transported to the launch site pedestal.  Further details were announced regarding a launch pedestal, which would allow the higher thrust design to be launched at LC-39A.  Musk additionally mentioned the possibility of a non-gimbaling, simplified Raptor engine producing 300 tf (2,942 kN/661,400 lbf) of thrust on a future version.

On November 20, 2019, Starship Mark 1 (MK1) suffered a tank rupture at its Boca Chica test site in southern Texas.  During a test of the vehicle’s propellant tanks, this failure occurred when cryogenic liquid nitrogen was loaded.

The tank rupture occurred partly because the company was testing higher than normal pressurization.  This prototype was originally planned to fly the first 20 km test flight in the Starship test program.  Although the failure slowed SpaceX’s testing plans, the Mark 3 prototype’s construction was already well underway at Boca Chica.

On December 5, 2019, SpaceX announced they were pausing much of their Starship construction work at their Florida site.  Workers there would instead be transferred to work at either the Boca Chica, Texas site, or SpaceX’s Cape Canaveral locations.

On January 10, 2020, SpaceX suffered a liquid oxygen tank test failure, which failed at 7.1 bar, not reaching its 8.5 bar target.  It followed this up with a successful header tank test with liquid nitrogen on January 24, 2020.  On January 28, 2020, SpaceX again tested a liquid oxygen tank, this time successfully, with the tank being destroyed after passing its pressurization target.

Starship Liquid Oxygen tank during cryogenic testing – via Mary (@bocachicagal) for NSF

In January 2020, the Los Angeles Times learned that SpaceX was once again interested in building the Starship factory at the Port of Los Angeles.  This was followed by news on February 6, 2020, that a header tank test was tested to destruction but had passed its pressurization requirements.  On February 26, 2020, the Los Angeles City Council approved SpaceX’s use of the 5.0 hectare (12.4 acre) site.  A day later, SpaceX activated the third and first vertical Raptor test stand.

The Starship Mark 3 prototype was renamed SN1, which was subsequently destroyed in a pressurization test on February 28, 2020.  While being pressurized with cryogenic liquid nitrogen, it suffered a catastrophic structural failure when liquid nitrogen leaked out violently.  The cause of the error was a poorly designed “puck”, where the three engines are mounted to the base of the liquid methane tank.  At Boca Chica, a test fuel tank was created with a newly designed puck called SN2.  It passed its critical tank pressurization test on March 8, 2020.

On March 16, 2020, Elon Musk confirmed that the Starship design had further changed, resulting in the 12th known version of the design.  The company suffered yet another failure on April 3, 2020, when the SN3 prototype suffered a critical failure during pressurization testing, leading to its destruction.  Data would point to a test configuration issue as the cause.  With the SN3’s failure and the US struggling through a pandemic, SpaceX’s aggressive testing timeline had been pushed back.

The SN4 prototype featured one of the Raptors meant to be added to SN3.  The first Raptor firing on the SN4 prototype followed on May 5, 2020.  SN4 did not last long, for on May 29, 2020, it was destroyed shortly after its fifth engine test, when a large amount of propellant was spilled by a malfunction and caught fire.  The issue was caused by a fault in the ground support equipment’s (GSE) quick disconnect system rather than a Starship design issue, as was the case with prior failures.  While repairing the damage, the Los Angeles Times reported on June 8 that SpaceX would re-abandon the Port of Los Angeles as the Starship’s factory site.  Expansion at the Boca Chica site has continued unabated in the meantime.

Test tank prototype SN7 was pressure tested to failure on June 23, 2020.  It was a testbed for a new, more malleable stainless steel alloy called 304L, which has better ductility (is more malleable) at cryogenic temperatures, allowing less violent structural failures.

SpaceX performed liquid nitrogen pressure testing with its next prototype, SN5, on June 30, 2020.  It made a successful first 150 m (492 ft.) hop flight on August 4, 2020.  This was followed by a hop of the SN6 prototype on September 3, 2020.  In the meantime, SpaceX continues making rapid progress on prototypes SN7.1 (a 304L stainless steel test tank), SN8 (which will feature 3 Raptor engines, a nose cone, and aero surfaces), SN9, and SN10.  It has also begun preparing for the construction of the first Super Heavy inside the new high bay.

Conclusion

The Starship program is unique and one of the most ambitious in the history of rocketry.  The design has now gone through at least twelve known versions and four different names!

Its first version was a single or triple-core rocket back in 2013, which has evolved into the single-core stainless steel Starship design under construction today.  Even as the design’s size has fluctuated dramatically, its repertoire of missions and roles has expanded.

A comparison render by NSF member Lamontagne.

It started out as a rocket meant to colonize Mars but now is envisioned as an all-purpose carrier rocket to replace the Falcon 9 rocket family.  It is expected to launch satellites into Earth orbit, fly people point-to-point on Earth, ferry cargo and crew to and from the Moon, in addition to its original role as a Mars colonization vehicle.

The vehicle’s push towards flight has made rapid progress since the decision to ditch an all-carbon-fiber design in 2018.  Despite the setback of the Starship Mark 1, SN1 and SN3 tank ruptures, and the SN4 ground support equipment accident, further rapid progress seems likely, despite the financial strain of its development.

The combination of stainless steel construction, A/B prototyping, and iterative testing are allowing an accelerated development timeline.  It is possible that it will beat several competitors’ rockets to orbit despite being both much larger and in development for a shorter period.  It builds on visions of colonizing Mars dating back to Wernher von Braun’s Mars plans after World War II.

If this vehicle does bring about an era of rapidly reusable rocketry, a new spaceflight era may dawn.  Perhaps most encouraging is the fact that it all started as nothing more than the dreams of a young boy in South Africa.

Special thanks to the NSF Design Team for helping me to craft this article.  I’d also like to thank NSF community members Bocachicagal and Nomadd for their tireless work, which has greatly benefited our understanding of Starship’s design evolution.

Lead phot via Mary (@bocachicagal)

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