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SpaceX’s Starship Raptor Vacuum engine plans laid out by CEO Elon Musk
Elon Musk says that SpaceX Starship engine upgrades are on track to begin static fire tests of a Raptor Vacuum variant as few as a “couple months” from now.
Designed to enable more efficient performance in thin atmosphere or vacuum, Musk admitted that the first version(s) of Raptor Vacuum (RVac) will likely be a compromise between efficiency and speed of development. Nevertheless, the faster SpaceX can prepare Raptor Vacuum for flight, the easier it will be for Starship to begin serious (sub)orbital flight tests.
As it turns out, SpaceX’s first and only official render of Raptor – published in September 2016 – showed the engine’s vacuum-optimized variant. In the years since, CEO Elon Musk has vacillated between keeping the vacuum engines as a central Starship feature and simply replacing them with regular sea level Raptors to expedite the spacecraft’s debut. The 2016 and 2017 vehicles featured a mixture of vacuum and sea-level engines, whereas Musk revealed a vehicle with sea-level engines only in 2018.
Perhaps less than a month after Musk’s September 2018 presentation, the SpaceX CEO made the decision to radically redesign the vehicle – newly christened Starship and Super Heavy – by moving from a carbon composite aerostructure to stainless steel. At first, the seven SL Raptors remained a part of the design, but Musk took to Twitter in 2019 to indicate that SpaceX had changed gears again and had reprioritized Raptor Vacuum development.
This came as a bit of surprise and it should go without saying that there’s a significant chance that Musk/SpaceX will oscillate in the opposite direction once again before Raptor Vacuum is actually ready for flight. This time, though, Musk has sketched out a development schedule and strategy that suggests SpaceX is much more serious this time.
Most notably, Musk claims that the first Raptor Vacuum prototype could be ready for static fire testing just a “couple months” from now, an immensely ambitious schedule for any large liquid rocket engine development program. Nevertheless, Musk did indicate that the “V1.0” Raptor Vacuum design would be significantly compromised and “suboptimal”, an intentional decision to prioritize the engine’s “speed of development”.
Even then, Musk believes that the first variant – featuring a shortened bell nozzle – could still be up to 12% more efficient than sea level Raptors and thus already 70-80% of the way to the physical limit of methane-oxygen rocket efficiency.
On a positive note, shrinking V1.0 Raptor Vacuum’s nozzle a bit from its nominal length will likely mean that SpaceX can static fire fully-integrated engines at its McGregor, TX test facilities, critical for speedy development. If not, the company has experience with alternatives through Merlin Vacuum, which can only be tested on the ground with its lengthy nozzle detached. This method just makes it dramatically harder to optimize a vacuum nozzle design, as full-scale, flight-like testing is nearly impossible if a given vacuum engine can’t be tested on the ground with said nozzle installed.
Vacuum engines need such large and unwieldy nozzles in order to make them as efficient as possible. In a very simplistic sense, a rocket engine nozzle directs the flow of superheated, ultrafast gases in order to squeeze as much momentum transfer as possible out of available propellant. The lower the pressure of the surrounding atmosphere is, the more those gases will expand immediately after leaving the nozzle – giant vacuum nozzles simply try to harness the additional momentum available from that extra expansion. This is why rocket exhausts appear to spread and thin out as launch vehicles reach higher and higher altitudes.
In this sense, the perfect theoretical vacuum nozzle is quite literally infinitely long. The job of vacuum rocket engineers is to find the perfect balance between that impractical theoretical perfection and the limits of real-world materials and dynamics. In theory, SpaceX’s sea-level Raptor engines have already been designed to operate in vacuum conditions, while the engine’s closed-cycle design and regeneratively (i.e. propellant) cooled nozzle should apply well to a vacuum design.
If SpaceX is lucky, there will be few roadblocks in the way of simply lengthening a SL Raptor-style nozzle and calling it a day, in which case it would be impressive but not all that surprising if SpaceX is actually able to begin RVac testing before the end of 2019. Once a rough V1.0 engine is in place, the process of optimizing efficiency can be done slowly and methodically, all while exploiting an unprecedented wealth of data from flight and orbit-tested Raptor Vacuum engines.
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Investor's Corner
NASA taps SpaceX to launch the telescope that could unlock new worlds
NASA’s Roman Space Telescope heads to orbit this August aboard SpaceX’s Falcon Heavy with massive scientific ambitions.
SpaceX is set to play a central role in one of NASA’s most anticipated science missions in years. The company’s Falcon Heavy rocket, currently the most powerful operational launch vehicle in the world, will carry the Nancy Grace Roman Space Telescope into orbit on August 30 from Kennedy Space Center in Florida. Roman is now in final preparations inside the Payload Hazardous Servicing Facility, where on June 26 technicians used a crane to lift the observatory into a specialized stand for fueling and pre-launch testing.
Roman is named after Nancy Grace Roman, NASA’s first chief of astronomy, whose career helped shape how the agency approaches space science.
NASA chose SpaceX Falcon Heavy because of Roman’s needs to reach a specific orbit far from Earth, well beyond where a standard Falcon 9 can deliver it. The Falcon Heavy, which first flew in 2018, has since become NASA’s go-to option for missions that need serious muscle without the cost and complexity of older launch systems.
Celebrating SpaceX’s Falcon Heavy Tesla Roadster launch, seven years later (Op-Ed)
Roman will carry a field of view at least 100 times wider than the Hubble Space Telescope, meaning it can photograph enormous swaths of the universe in a single shot rather than the narrow slices Hubble captures. That difference in scale is significant. While Hubble reshaped our understanding of the cosmos over 30 years, Roman is built to work faster and wider, surveying hundreds of millions of galaxies at once.
One of Roman’s most compelling capabilities is its potential to discover and photograph planets orbiting stars outside our solar system, and with enough precision to directly image planets that would otherwise be lost. That means scientists could study the atmosphere and surface characteristics of distant worlds rather than simply confirming they exist. Combined with Roman’s sweeping field of view, the telescope could detect thousands of exoplanets, and some of those planets may be in habitable zones where liquid water could exist. No telescope currently in operation has this level of power and capability. That capability alone could change what we know about other worlds, and perhaps finally answer the question: are we the only intelligent lifeforms in existence?
What Roman actually finds once it reaches orbit is an open question, and that is exactly what makes this launch worth watching.
Tesla has confirmed a crucial detail of its Miami Robotaxi launch, stating that the fleet is operating on an Unsupervised basis, joining a few other cities where company employees do not watch over the vehicles from inside.
Tesla’s Head of AI, Ashok Elluswamy, confirmed the detail on X, answering a highly speculated question about the Robotaxi Service in Miami, which was launched on June 3:
Unsupervised
— Ashok Elluswamy (@aelluswamy) July 3, 2026
The first launch of Robotaxi in Florida, Miami presents a unique opportunity for Tesla as it is operating the Unsupervised Robotaxi ride-hailing service in a major tourist hotspot in the Sunshine State. It also signals the suite will expand to other cities soon; many have requested Orlando, a heavy tourist spot with Disney and other resorts nearby, get access to the program soon as well.
Miami is getting a conservative rollout as well, just as Tesla has done with other cities. The initial geofence covers a compact 10–14 square mile zone in western Miami-Dade County, primarily West Miami extending toward Doral and Sweetwater. It is bounded roughly by SR-826 (Palmetto Expressway) to the north and US-41 (Tamiami Trail) to the south, excluding downtown Miami, Miami Beach, the airport, and most of Coral Gables.
Tesla has also been pretty slim on other details. For example, Tesla has not disclosed the exact fleet size, but field reports and license plate tracking indicate just two unsupervised Model Y vehicles were active on launch day, increasing to three within 48 hours.
According to The Road to Autonomy, a nearby staging lot near Miami International Airport holds dozens of Cybercabs alongside additional Model Y units, suggesting capacity for rapid scaling as demand and data collection grow.
The confirmation of Robotaxi being Unsupervised carries immense weight. It establishes that Tesla’s Miami Robotaxi operations run without human safety drivers or remote supervision, relying entirely on the company’s Full Self-Driving technology. Miami becomes the second major U.S. city after Austin to offer unsupervised Robotaxi rides from day one.
The move reflects rapid progress in Tesla’s AI efforts. Neural networks trained on vast real-world data now handle complex urban environments, including South Florida’s heavy traffic, pedestrians, and rainy conditions. Industry observers see it as validation of Tesla’s vision-centric, data-driven approach versus traditional rule-based systems; a truly unorthodox approach in this day and age.
Challenges remain, including regulatory oversight, public trust, and scaling the fleet to match geofence ambitions. Miami’s small initial footprint and limited vehicles highlight a deliberate, measured expansion strategy focused on safety and data gathering.
Nevertheless, the unsupervised confirmation marks a pivotal milestone. It showcases technical readiness and advances Tesla’s vision of transforming vehicles into autonomous revenue generators while reshaping urban mobility. For Miami users, driverless transportation has moved from concept to reality.
A California radiologist who drove his Tesla Model Y off a 250-foot cliff in an attempt to kill his family has had his charges dismissed after doctors say he is “doing well” in a mental health program.
Dharmesh Patel was charged with three counts of attempted murder in connection with a January 2023 crash where he drove his Tesla off a cliff, injuring his wife and two children, aged 7 and 4 at the time.
Patel drove the Tesla off Devil’s Slide in California, an area that is extremely rough to the point that investigators and rescuers expected the worst when arriving at the scene for the first time. Patel supposedly had schizoaffective disorder, according to Deputy District Attorney Dominique Davis.
Shockingly, Patel’s wife, who was in the vehicle, testified that she did not want her husband to be prosecuted, noting that their children missed their father and they wanted him to come back home. Patel’s attorney argued, “not everyone who commits a crime is a criminal.”
Doctor who took Tesla off cliff gets support from unlikely person
A three-day trial in Mental Health Diversion Court ruled in Patel’s favor, which kept him out of jail and instead on house arrest. He was admitted to a Mental Health Diversion Program, which he successfully completed, the Associated Press reported. San Mateo County District Attorney Steve Wagstaffe said the judge was “required by law” to dismiss the charges:
“If the person who’s given mental health diversion follows the treatment plan, there’s nothing that can be done, and at the end of the two years he gets it wiped out of his record.”
Wagstaffe said he has argued, along with other DAs in California, to have attempted murder removed from the list of charges eligible to be dismissed due to mental health diversion programs.
Patel had the charges officially dismissed on Monday; his wife waited for him as he left court and they departed the building together, according to Mercury News. Patel surrendered his California medical license in December.
The crash has been one of the best examples of Tesla’s incredible engineering, which has saved four lives in this particular instance. The car was totalled but kept the four human beings alive and safe, which is something that many referred to as “an absolute miracle.”
NASA taps SpaceX to launch the telescope that could unlock new worlds
Tesla confirms crucial detail of Miami Robotaxi launch
