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SpaceX Starship booster’s ‘hot gas’ thrusters make first public appearance
‘Hot gas’ thrusters meant to boost the efficiency of SpaceX’s Starship spacecraft and Super Heavy boosters have been spotted in public for the first time.
On the evening of June 21st, spaceflight photographer Brady Kenniston – on assignment for NASASpaceflight – caught the first glimpses ever of what amounts to the newest rocket engine designed and built by SpaceX. As yet unnamed, SpaceX CEO Elon Musk has consistently referred to the new engine as a “hot gas thruster” for several years, though virtually no concrete details have ever been shared.
The reason behind the lack of major visible progress is simple enough: until Starship is ready for serious orbital testing, hot-gas thrusters just aren’t necessary. Instead, SpaceX has relied on tried and true cold gas thrusters derived – or quite literally taken, in the case of Starhopper – from those used on Falcon 9 and Falcon Heavy boosters to maintain attitude control in space and safely land back on Earth.
For Starhopper and Starships SN5 and SN6, all three of which focused on simple hop tests, those cold-gas thrusters primarily augmented Raptor’s thrust vectoring capabilities by fine-tuning vehicle rotation and attitude. On Starships SN8, SN9, SN10, SN11, and SN15, cold-gas thrusters played a more substantial role in their more complex medium-altitude test flights, flipping each ship horizontal at apogee, helping to maintain stability during skydiver-style freefalls back to Earth, and augmenting three Raptor engines during the final landing flip and landing burn.
By all appearances, the thrusters did their jobs perfectly on all nine test flights. However, those eight suborbital prototypes could all afford to expend large portions of their mass budgets on a plethora of pressure vessels filled with tons of nitrogen gas. More importantly, empty Starships and their Super Heavy boosters are expected to weigh anywhere from 10-50 times more than Falcon 9’s booster and upper stage, and SpaceX’s suborbital prototypes have also required much less performance (delta V) than operational ships and boosters will need.
-->Cold gas (nitrogen) thrusters are too inefficient and the exponential aspects of rocket engineering too cruel for what works on Falcon to efficiently meet the needs of Starship and Super Heavy. SpaceX’s long-planned solution has been the development of a bipropellant thruster that would borrow from Raptor expertise and use the same methane and oxygen propellant – albeit in their high-pressure gaseous forms. If properly realized, such a thruster could offer around five times the efficiency and thrust of a similarly-sized cold-gas system – a boon for maneuvering and manipulating massive 100-250 ton (~250,000-550,000 lb) ships and boosters in space.
In theory, moving from nitrogen to methalox thrusters also means that Starship could refuel its thrusters using a tiny fraction of the vast supply of liquid methane and oxygen propellant it will already be carrying to the Moon or Mars. Ultimately, though, Musk says that those hot gas attitude control thrusters will debut on the Super Heavy booster assigned to Starship’s first orbital test flight. While SpaceX’s initial July target now appears to be out of the question, all flight and pad hardware could still be ready to launch as early as August or September.
Update: One month after Elon Musk stated that SpaceX was “aiming” to have hot gas thrusters on the first flightworthy Super Heavy booster, the CEO says those thrusters would be “an unnecessary complication for now” and “are being removed to speed up time to” Starship’s first orbital launch.
Elon Musk
SpaceX’s Starship program is already bouncing back from Booster 18 fiasco
Just over a week since Booster 18 met its untimely end, SpaceX is now busy stacking Booster 19, and at a very rapid pace, too.
SpaceX is already bouncing back from the fiasco that it experienced during Starship Booster 18’s initial tests earlier this month.
Just over a week since Booster 18 met its untimely end, SpaceX is now busy stacking Booster 19, and at a very rapid pace, too.
Starship V3 Booster 19 is rising
As per Starbase watchers on X, SpaceX rolled out the fourth aft section of Booster 19 to Starbase’s MegaBay this weekend, stacking it to reach 15 rings tall with just a few sections remaining. This marks the fastest booster assembly to date at four sections in five days. This is quite impressive, and it bodes well for SpaceX’s Starship V3 program, which is expected to be a notable step up from the V2 program, which was retired after a flawless Flight 11.
Starship watcher TankWatchers noted the tempo on X, stating, “During the night the A4 section of Booster 19 rolled out to the MegaBay. With 4 sections in just 5 days, this is shaping up to be the fastest booster stack ever.” Fellow Starbase watcher TestFlight echoed the same sentiments. “Booster 19 is now 15 rings tall, with 3 aft sections remaining!” the space enthusiast wrote.
Aggressive targets despite Booster 18 fiasco
SpaceX’s V3 program encountered a speed bump earlier this month when Booster 18, just one day after rolling out into the factory, experienced a major anomaly during gas system pressure testing at SpaceX’s Massey facility in Starbase, Texas. While no propellant was loaded, no engines were installed, and no one was injured in the incident, the unexpected end of Booster 18 sparked speculation that the Starship V3 program could face delays.
-->Despite the Booster 18 fiasco, however, SpaceX announced that “Starship’s twelfth flight test remains targeted for the first quarter of 2026.” Elon Musk shared a similar timeline on X earlier this year, with the CEO stating that “ V3 is a massive upgrade from the current V2 and should be through production and testing by end of year, with heavy flight activity next year.”
Considering that Booster 19 seems to be moving through its production phases quickly, perhaps SpaceX’s Q1 2026 target for Flight 12 might indeed be more than feasible.
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Elon Musk makes a key Tesla Optimus detail official
“Since we are naming the singular, we will also name the plural, so Optimi it is,” Musk wrote on X.
Tesla CEO Elon Musk just made a key detail about Optimus official. In a post on X, the CEO clarified some key wording about Optimus, which should help the media and the public become more familiar with the humanoid robot.
Elon Musk makes Optimus’ plural term official
Elon Musk posted a number of Optimus-related posts on X this weekend. On Saturday, he stated that Optimus would be the Von Neumann probe, a machine that could eventually be capable of replicating itself. This capability, it seems, would be the key to Tesla achieving Elon Musk’s ambitious Optimus production targets.
Amidst the conversations about Optimus on X, a user of the social media platform asked the CEO what the plural term for the humanoid robot will be. As per Musk, Tesla will be setting the plural term for Optimus since the company also decided on the robot’s singular term. “Since we are naming the singular, we will also name the plural, so Optimi it is,” Musk wrote in his reply on X.
This makes it official. For media outlets such as Teslarati, numerous Optimus bots are now called Optimi. It rolls off the tongue pretty well, too.
Optimi will be a common sight worldwide
While Musk’s comment may seem pretty mundane to some, it is actually very important. Optimus is intended to be Tesla’s highest volume product, with the CEO estimating that the humanoid robot could eventually see annual production rates in the hundreds of millions, perhaps even more. Since Optimi will be a very common sight worldwide, it is good that people can now get used to terms describing the humanoid robot.
-->During the Tesla 2025 Annual Shareholder Meeting, Musk stated that the humanoid robot will see “the fastest production ramp of any product of any large complex manufactured product ever,” starting with a one-million-Optimi-per-year production line at the Fremont Factory. Giga Texas would get an even bigger Optimus production line, which should be capable of producing tens of millions of Optimi per year.
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Tesla is improving Giga Berlin’s free “Giga Train” service for employees
With this initiative, Tesla aims to boost the number of Gigafactory Berlin employees commuting by rail while keeping the shuttle free for all riders.
Tesla will expand its factory shuttle service in Germany beginning January 4, adding direct rail trips from Berlin Ostbahnhof to Giga Berlin-Brandenburg in Grünheide.
With this initiative, Tesla aims to boost the number of Gigafactory Berlin employees commuting by rail while keeping the shuttle free for all riders.
New shuttle route
As noted in a report from rbb24, the updated service, which will start January 4, will run between the Berlin Ostbahnhof East Station and the Erkner Station at the Gigafactory Berlin complex. Tesla stated that the timetable mirrors shift changes for the facility’s employees, and similar to before, the service will be completely free. The train will offer six direct trips per day as well.
“The service includes six daily trips, which also cover our shift times. The trains will run between Berlin Ostbahnhof (with a stop at Ostkreuz) and Erkner station to the Gigafactory,” Tesla Germany stated.
Even with construction continuing at Fangschleuse and Köpenick stations, the company said the route has been optimized to maintain a predictable 35-minute travel time. The update follows earlier phases of Tesla’s “Giga Train” program, which initially connected Erkner to the factory grounds before expanding to Berlin-Lichtenberg.
-->Tesla pushes for majority rail commuting
Tesla began production at Grünheide in March 2022, and the factory’s workforce has since grown to around 11,500 employees, with an estimated 60% commuting from Berlin. The facility produces the Model Y, Tesla’s best-selling vehicle, for both Germany and other territories.
The company has repeatedly emphasized its goal of having more than half its staff use public transportation rather than cars, positioning the shuttle as a key part of that initiative. In keeping with the factory’s sustainability focus, Tesla continues to allow even non-employees to ride the shuttle free of charge, making it a broader mobility option for the area.
SpaceX’s Starship program is already bouncing back from Booster 18 fiasco
Elon Musk makes a key Tesla Optimus detail official
