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SpaceX schedules first Super Heavy static fire after installing three Raptors

After an apparent false start on Wednesday morning, SpaceX has distributed a second safety alert among Boca Chica residents in anticipation of the first static fire of a Super Heavy booster as early as July 15th.

Delineated by highway and beach closures filed in advance with Cameron County, Thursday’s window stretches from 12pm to 8pm or 10pm CDT (UTC-5), giving SpaceX 8-10 hours to put the first functional Super Heavy booster prototype through its most challenging tests yet.

Known as a static fire, what is a mostly routine test for operational rockets is a bit more of a challenge for a first-of-its-kind prototype. Notably, on July 12th, Super Heavy Booster 3 survived its first ‘cryogenic proof’ pressure test, withstanding the thermal and mechanical stresses created when the rocket was filled with a few hundreds tons of liquid nitrogen and the expanding gases created as that cryogenic fluid then warmed and boiled. However, Booster 3 has yet to perform any kind of test involving the combustible, explosive liquid oxygen and methane propellant needed to fuel Raptor engines.

By all appearances, SpaceX aims to roll Super Heavy’s first wet dress rehearsal (WDR; like a ‘cryo proof’ with real propellant) and static fire into one busy day of testing. That combined WDR and static fire will likely be the first time ever that a launch vehicle as large as Super Heavy has attempted to pressurize its tanks autogenously, referring to the process of using a rocket’s own fuel and oxidizer to generate ullage gas. Starship prototypes notoriously struggled with their smaller autogenous pressurization systems – and jerry-rigged alternatives – on several occasions.

Super Heavy booster prototype B3 survived its first major test on Monday, paving the way for a possible static fire later this week. (NASASpaceflight.com)
SpaceX has installed three Raptors on Super Heavy Booster 3 in the days shortly before and after its cryo proof. (NASASpaceflight – bocachicagal)

In other words, even an ignition-free wet dress rehearsal test completed with autogenous pressurization would be a major success and hurdle surmounted for Super Heavy. If SpaceX manages to perform the first booster WDR and static fire on the same day, it would indicate that the company has extreme confidence in Super Heavy.

Despite an aborted attempt on July 11th, SpaceX outfitted the rocket with one Raptor on Saturday, July 10th and installed another two engines in quick succession on Tuesday, July 13th – likely in an odd triangular configuration on the booster’s central nine-engine ‘thrust puck.’ Why that particular configuration was chosen instead of something more symmetric is unclear but it does decrease the odds of a multi-engine test on Super Heavy’s first static fire without a clear reason to assume that testing such an odd engine placement would provide some valuable insight.

In comparison, two engines on opposite sides of Super Heavy’s inner ‘ring’ or three engines forming a line across that ring are two configurations that boosters are very likely to use during landing burns. Regardless, according to Next Spaceflight’s Michael Baylor, SpaceX may start Super Heavy B3’s static fire test campaign with just one engine, so it’s not impossible that the current configuration is just a part of the incomplete process of installing five or more engines.

As with all Starship development, it’s equally likely that Super Heavy’s first wet dress rehearsal and static fire test attempts will slip late into the window, to Friday, or even to the week of July 19th. Stay tuned for updates!

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SpaceX to build world’s most advanced rocket engine factory in Central Texas

CEO Elon Musk says that SpaceX has plans to build the “most advanced rocket engine factory in the world” in Central Texas to support the growing needs of Starship and Super Heavy.

If all goes according to plan, that facility could also become the highest-output rocket factory ever built, churning out hundreds of Raptor engines each year to outfit a vast interplanetary fleet of Starships and the earthbound Super Heavy boosters that will send them on their way to Earth orbit, the Moon, Mars, and beyond.

Musk revealed plans for a dedicated Raptor engine factory on July 10th – shortly after showing off an impressive group of at least ten qualified Raptor engines staged inside a production tent at SpaceX’s Boca Chica Starship factory. In just the three days since that photo, SpaceX has installed three Raptor engines – possibly all of which were visible in the July 10th family photo – on the first functional Super Heavy booster prototype.

A day later, Musk revealed that SpaceX had finally settled on a crucial aspect of Super Heavy’s design, determining that operational Starship boosters will ultimately be outfitted with 33 more or less identical Raptor engines. Following another surprise Musk reveal earlier this month, that means that every two-stage Starship vehicle will require 39 to 42 Raptor engines – 36-39 sea level variants and three vacuum-optimized engines with larger nozzles.

While Raptor’s current design isn’t quite there, Musk says that SpaceX will debut an upgraded “Raptor 2” engine in the not too distant future, raising maximum thrust to 230 tons (~510,000 lbf). Aside from the removal of a few structural components required for engine gimballing on 20 booster Raptors, every engine on Starship – save for 3-6 vacuum variants – will thus be identical.

According to Musk, a new cutting-edge SpaceX factory located at the company’s expansive McGregor, Texas rocket development and testing facilities factory will ultimately mass-produce between 800 and 1000 Raptor 2 engines per year. Raptor Vacuum production will remain at SpaceX’s Hawthorne, California headquarters alongside work on mysterious “new, experimental designs.” Under the new paradigm sketched out by Musk, Raptor would mirror SpaceX’s Merlin engine family – comprised of two commonized sea level and vacuum variants (Merlin 1 and Merlin Vacuum) for more than a decade.

A visual comparison of Merlin 1D (optimized for sea level) and Merlin Vacuum. (SpaceX)
Raptor and Raptor Vacuum, September 2020. (SpaceX)

With just a single high-volume variant required, Raptor 2 production could be extraordinarily efficient and would easily outpace any other large liquid engine production in history at 800-1000 engines completed each year. Technically, at its peak in the 1970s and 1980s, the Soviet Union was producing hundreds of R7 (Soyuz) booster engines annually and upwards of 1000+ per year if one counts the several different kinds of engines on each R7/Soyuz booster. However, the annual production of a single variant of any other large liquid rocket engine in history has never come close to the targets set out by Musk for SpaceX’s Raptor 2 factory.

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SpaceX begins installing Raptor engines on first Super Heavy booster

SpaceX has installed a Raptor engine on a Super Heavy booster prototype for the first time, defying expectations and setting the rocket up for two major tests as early as this week.

On Thursday, July 8th, SpaceX briefly filled Super Heavy Booster 3’s (B3) propellant tanks with benign nitrogen gas. The vehicle seemingly came to life for the first time that morning when it was spotted using its tank vents – a generally incontrovertible sign that the complex mechanical system that is a rocket is functional. Later that day, the public highway and beach adjacent to SpaceX’s launch site were briefly closed for what was expected to be an ambient pressure and/or cryogenic proof test.

Booster 3 never got to the cryogenic proof test – easily confirmed thanks to the frost that forms on most rockets’ exteriors as main tanks are filled with extremely cold liquid nitrogen. No such frost formed, no major venting occurred, and the road was only closed for the first two hours of a six-hour test window.

According to Next Spaceflight’s Michael Baylor, SpaceX did complete a “brief ambient proof” during that relatively short closure, though very little activity was visible during the test. Friday’s 14-hour test window was canceled the next morning, leaving SpaceX the rest of the weekend to prepare the first functional Super Heavy booster for its first truly challenging test – cryo proof.

Instead, late on Saturday, July 10th, SpaceX rolled Raptor 57 (R57) from build site to launch pad and began installing the engine on Booster 3 just a few hours later. Prior to Raptor 57’s installation, most prominent (albeit unofficial) voices in the SpaceX fan community anticipated no more than cryogenic proof testing for Booster 3 – no static fires, in other words.

However, it was fairly apparent that Super Heavy Booster 3 and the modified suborbital launch mount it was installed on were both outfitted for testing more complex than a cryo proof alone. Notably, B3 rolled to the pad with multiple labeled methane pressure vessels (COPVs), extensive plumbing, and autogenous pressurization control panels installed – all of which continued to be actively worked on after the booster was installed at the launch site.

B3 features a myriad of plumbing, virtually none of which would be useful for cryo proof testing with liquid nitrogen. (NASASpaceflight – bocachicagal)

While it’s technically not impossible to build a ground testing Starship prototype that’s capable of a wide variety of tests but never actually used to its full extent, doing so would be well out of character for SpaceX and make little sense in general. As such, it’s not a major surprise that SpaceX has now begun to install Raptor engines on Super Heavy Booster 3. What is surprising is that SpaceX is installing Raptor engines on a first-of-its-kind Super Heavy prototype before any fully integrated booster has completed cryogenic testing.

Based on Starship’s ~18-month test history, there is a real possibility Super Heavy B3 will fail during cryogenic proof testing. Even accepting that SpaceX’s testing processes and expertise have matured dramatically after dozens of Starship tests on the ground and in flight, the chance remains. In other words, SpaceX’s decision to begin installing Raptors on Super Heavy before ensuring structural and mechanical integrity implies some combination of unusual confidence in a prototype as unproven as Booster 3 and a distinct lack of concern at the prospect of losing at least two Raptor engines in a hypothetical test failure.

Knowing SpaceX and CEO Elon Musk’s goals for Raptor, the latter implication isn’t much of a surprise but it’s always interesting to have direct visual evidence that Raptor is, in fact, so cheap to build and easy to install that the minor effort and few days of possible delays required to reduce the risk of losing multiple engines just aren’t worth it.

As of July 11th, a second Raptor engine is staged and waiting for installation beside Booster 3. (NASASpaceflight – bocachicagal)

As such, it’s now clear that Super Heavy Booster 3 will have at least one or two Raptor engines installed during its very first cryogenic proof test – currently no earlier than 12pm to 8pm CDT (UTC-5) on Monday, July 12th. Assuming SpaceX’s confidence is well-placed and Booster 3 passes its first cryogenic tests without issue, the real question now is how many Raptors will be installed and ignited during Super Heavy’s first static fire test?

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SpaceX sends Starship’s first vacuum Raptor engine to Boca Chica

For the first time, SpaceX has shipped a vacuum-optimized Raptor engine to its Boca Chica, Texas Starship factory days after the company’s present reiterated plans for an inaugural orbital launch attempt as early as July.

Back in March 2021, CEO Elon Musk confirmed that he’d set SpaceX a goal of attempting Starship’s first orbital launch no later than the end of July – around four and a half months distant at the time. Fifteen weeks later, though the prospects of an orbital launch attempt happening in July have practically shrunk to zero, SpaceX COO and President Gwynne Shotwell – best known for acting as a more grounded foil to Musk’s often impractical schedule estimates – reiterated that the company is still “shooting for July” for Starship’s first orbital launch attempt.

As of late June, hitting that target would require SpaceX to string together numerous extraordinary feats of engineering and rocketry in record time or attempt some extremely unorthodox corner-cutting.

The launch pad and launch vehicle hardware needed for Starship’s first space shot are currently far from ready for flight. On June 24th, Musk unexpectedly revealed that the Super Heavy booster prototype SpaceX is now in the late stages of assembly isn’t actually the booster that will carry Starship on its first space launch attempt. In other words, though dozens of rings in various states of work are strewn about SpaceX’s Boca Chica factory, the company has yet to begin assembling the massive 65m (~215 ft) tall booster required for the first orbital launch attempt.

Using Super Heavy Booster 3 (B3) as a ruler, assembly could easily take 9-10 weeks – starting whenever the process actually begins. If SpaceX started stacking Booster 4 today, in other words, it’s unlikely that the rocket would even be complete by the end of August. Barring SpaceX taking unprecedented shortcuts, completing the booster is just part of the process of preparing for flight and B4 would still need to be qualified for flight, likely involving at least one cryogenic proof and static fire test.

In a best-case scenario where SpaceX begins assembly today, manages to halve Booster 4 assembly time in one fell swoop, the sneaks the second Super Heavy ever completed through qualification testing in a single week, the orbital flight test booster still wouldn’t be ready for Starship installation (likely another unprecedented first) before mid-August.

That would then leave SpaceX five or six weeks to fully assemble Starship S20, a process that has yet to begin. Like Starship SN15, which Musk said sported “hundreds of improvements”, Musk has also stated that Ship 20 and all after it will feature another batch of upgrades needed to take Starship orbital. Starship SN15 was very gradually stacked and assembled over the course of almost four months, though that slow assembly can likely be blamed on the fact that SpaceX is busy testing Starships SN8 through SN11 and was effectively waiting to see if any other major changes might be required.

Starship SN20’s (now S20) thrust dome is the first non-pathfinder hardware to feature Raptor Vacuum mounts. (NASASpaceflight – bocachicagal)

While most of S20’s upgrades are a mystery, the ship’s thrust dome – spotted in work at Boca Chica earlier this month – has already confirmed that the prototype will be the first with the necessary hardware for Raptor Vacuum engine installation. That likely means that S20 will also be the first Starship to attempt to static fire six Raptor engines*, potentially producing more thrust than a Falcon 9 booster. On June 27th, one such vacuum-optimized Raptor (RVac) arrived in Boca Chica for the first time ever, making it clear that the comparatively brand new engine may already be ready to start integrated Starship testing.

*Update: SpaceX CEO Elon Musk says that the Raptor Vacuum delivered to Boca Chica on June 27th is, in fact, meant for Starship S20, seemingly confirming that the prototype will fly with a full six Raptor engines.

Of course, beyond Starship and Super Heavy, SpaceX also has a great deal of work left to get the rocket’s first orbital-class launch facilities partially operational. SpaceX will need to complete and activate at least one or two more custom-built propellant storage tanks, sleeve those three or four tanks with three or four massive thermos-like ‘shells,’ complete thousands of feet of insulated plumbing and wiring, finish a massive ‘launch table,’ install that table on a six-legged ‘launch mount;’ outfit that table and mount with an array of power, avionics, hydraulics, and fueling equipment and plumbing; complete a ~145m (~475 ft) ‘integration tower,’ and perform the first fit checks and shakedown tests with a real booster or Starship.

Only then will SpaceX be able to attempt Starship’s first space launch. All told, it might not be literally impossible for SpaceX to complete all the above work in less than five weeks, but it’s safe to say that the odds of that happening could probably make a lottery ticket blush. Regardless, if Starship reaches orbit at any point before the end of 2021, it would beat out simpler “next-generation” rockets like Ariane 6, ULA’s Vulcan, and Blue Origin’s New Glenn despite beginning concerted development years later and with a far less certain funding situation.

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SpaceX inaugurates two new Starship engine test stands with a static fire

Barely four months after breaking ground, SpaceX has completed a dual-bay Starship engine test stand and inaugurated the new facility with a Raptor static fire.

That means that SpaceX’s McGregor, Texas test and development center now has more capacity to test individual Starship engines than the Merlin 1D and Merlin Vacuum engines that power the company’s workhorse Falcon 9 and Falcon Heavy rockets – and less than two and a half years after full-scale Raptor testing first began. SpaceX needs that capacity more than ever before as it shifts its focus from medium-altitude, three-engine Starship production and launches to true orbital test flights with six-engine ships and 29-engine Super Heavy boosters.

Every one of those 35 engines – all of which are expected to be expended after a single orbital test flight – will first need to be qualified for flight via static fire tests in McGregor. As of last month, SpaceX had four separate Raptor test facilities – two horizontal bays, one vertical stand, and a separate bay used for some kind of subcomponent testing. That left Starship in a similar boat as Falcon, which has relied on three vertical Merlin test bays for more than a decade.

As SpaceX found out, Falcon Heavy production – requiring 27 M1Ds and one MVAC – can almost completely swamp those three Merlin test stands for the better part of a month or two. Given that signs are pointing to every orbital Starship test flight requiring almost three-dozen new Raptors, the qualification testing situation will be even more challenging if SpaceX wants to continue the program’s rapid pace of development and more or less monthly launches.

Based on aerial photos taken by a NASASpaceflight L2 forum contributor and later published in a February 2021 article, groundbreaking began in the last week of January. Within two months, the bulk of the dual-bay stand’s structure and plumbing appeared to be in place. Within three months, everything appeared to be ready to go and a Raptor was present for apparent fit checks. Finally, on June 4th, the stand came to life for the first time with a brief 15-second Raptor static fire – likely more to verify the brand new facility’s readiness than to test Raptor itself.

SpaceX thus built two brand new test stands from a dirt lot to completion in ~18 weeks, expanding McGregor’s full-scale Raptor test capabilities by at least ~67% in one fell swoop. That means that if qualifying 35 Raptors might have previously taken 5-8 weeks, McGregor can now feasibly complete the same work in 3-5 weeks and probably continue some level of experimental testing at the same time. Now, SpaceX just has to mass-produce and qualify dozens of Raptor engines at a pace likely unprecedented even in its exceptionally productive engine production and testing history.

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SpaceX Texas test HQ fires up a dozen Falcon, Starship rocket engines in six hours

Though it often falls under the radar relative to SpaceX’s high-profile Boca Chica Starship hub, another even more important Texas outpost appears to be busier than ever testing the rocket engines and boosters instrumental to all SpaceX operations.

Famous for occasionally supporting half a dozen or more rocket tests on busy days, SpaceX’s McGregor, Texas facilities showed off exactly that kind of rapid-fire activity on Friday, March 19th, flexing the sheer variety and volume of rocket hardware liable to pass through its gates.

A 2017 overview provides the best recent view behind the scenes of SpaceX’s McGregor, TX rocket development and testing facilities.

Located on the grounds of a former US military explosives factory, SpaceX’s McGregor, Texas rocket development and test facilities have been testing Falcon, Dragon, and Starship parts and supporting each program’s development for a decade and a half. After being fabricated and assembled in Hawthorne, California virtually every single active propulsive component SpaceX has flown spent some amount of time in McGregor.

For boosters, every cold gas maneuvering thruster is qualified in Texas before being sent back to Hawthorne for final installation. Each stage’s nine Merlin 1D engines are individually tested in McGregor, shipped back to Hawthorne, installed on a booster, shipped back to McGregor, and static fired as an integrated first stage before SpaceX deems a Falcon 9 or Falcon Heavy core ready for flight. The exact same process (individual engines followed by integrated vehicles) is performed with Falcon upper stages and their Merlin Vacuum engines, as well as all Dragon spacecraft and their Draco (and SuperDraco) thrusters. The same is true for the Raptor engines and cold-gas thrusters that power Starship.

On March 19th, nearly all of those different engines and vehicles – and the separate stands used to test each of them – came together for an exceptionally busy day at McGregor. According to local resident Reagan (@bluemoondance74), who lives within earshot of SpaceX’s extraordinarily busy rocket testing HQ, at least five unique tests were performed in just six hours – all but one of which was squeezed into the last ~125 minutes.

Around 2:40 pm, an unknown test – possibly a Merlin Vacuum (MVac) or Merlin 1D (M1D) engine – kicked off the salvo. Four hours later, SpaceX completed arguably the most significant test of the day, firing up the first Falcon Heavy center core to head to McGregor in almost 24 months. Assuming that static fire was a success, the booster will be inspected, have its tanks cleaned, and be shipped to Florida to complete the first stage of SpaceX’s fourth Falcon Heavy rocket for a launch as early as July.

An hour and a half after the Falcon Heavy center core’s static fire, SpaceX fired up a Raptor engine (either a sea level or vacuum variant), followed by another likely M1D or MVac test just minutes later. Finally, at 8:52 pm, SpaceX ignited a second Raptor engine at an entirely separate vertical test stand (known as the tripod stand) recently modified to support testing Starship engines in a more flight-like configuration. Altogether, assuming no repeated tests, SpaceX effectively tested a booster and 13 (9+4) rocket engines in a little over six hours.

Both Merlin 1D test bays are usually occupied. (SpaceX)
Sans nozzle, a Merlin Vacuum engine is static fired on a stand adjacent to those M1D bays. (SpaceX)
A sea-level Raptor operates at one of McGregor’s two horizontal test bays. (SpaceX)
SpaceX tests Raptor Vacuum prototypes on the same horizontal bays. (SpaceX)
A vertical test stand also helps SpaceX test Raptors in more flight-like conditions.

More likely than not, one or both of those Raptors will soon find themselves on a Starship or Super Heavy prototype in Boca Chica. The M1D and/or MVac engines will assuredly find a place on a future Falcon booster or upper stage. The Falcon Heavy center core (B1065 or B1066) is scheduled to launch as early as July 2021 and – if SpaceX can end its center core curse and recover it in one piece – will hopefully support many more launches after that.

All told, SpaceX’s McGregor rocket testing HQ is about as busy as – if not busier than – it’s ever been as the company works towards an unprecedentedly ambitious 48-launch 2021 manifest, builds and flies at least four Dragon spacecraft, and pursues an even more ambitious effort to begin orbital Starship launches this summer. Quieted away in rural Texas, McGregor may largely go unnoticed but its infrastructure remains as integral as ever for virtually every single SpaceX project – past, present, and future.

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SpaceX’s next three-Raptor Starship static fire delayed by winds, says Elon Musk

CEO Elon Musk says that SpaceX’s second three-Raptor Starship static fire test has been delayed several days by bad weather at the company’s South Texas launch facilities.

Prior to Musk’s tweet, all signs pointed to a second static fire test as early as 5am to 11am CDT on Friday, October 30th – made official by a paper safety notice SpaceX distributes to remaining Boca Chica Village residents around 12-24 hours prior. Unfortunately, however, Musk says that SpaceX ran into “some challenges with high winds” – seemingly canceling today’s static fire attempt.

SpaceX has successfully installed three Raptors on Starship SN8 and is scheduled to attempt the first triple-engine static fire as early as October 14th. (Elon Musk)

On the other hand, there’s a chance that SpaceX’s October 30th safety warning and 5am-11am window could be for Starship SN8’s first wet dress rehearsal (WDR) with a nosecone (and thus a liquid oxygen header tank) installed. A wet dress rehearsal refers to the process of putting a rocket through a flow identical to what is done on launch day – albeit short of actually igniting or launching the rocket. In that sense, it’s essentially one step shorter than a static fire.

Road closure filings prior to November 1st are ambiguous, however, with no specific purpose disclosed. Technically, as long as SpaceX doesn’t perform a static fire or flight test without giving residents significant prior notice and necessary FAA/FCC approvals, road closures can more or less be used to whatever end the company deems necessary.

As far as triple-Raptor static fire testing goes, it’s unclear how anything less than mechanically dangerous wind conditions could interfere with Starship. Given that winds of 20-30 mph (and gusts even higher) are far from uncommon on the South Texas coast, Starship will need to be able to tolerate – and launch in – even worse weather.

Starship SN8 is no longer attached to a crane at its nose, leaving the task of withstanding wind sway entirely up to the launch mount and the rocket’s rigidity. (NASASpaceflight – bocachicagal)

Prototype testing is substantially different than operational flight procedures, though, and well-characterized test conditions and repeatability are essential for a company like SpaceX where the ‘build-test-fly-fail’ philosophy is the foundation of R&D. The process of functionally and permanently mating Starship SN8’s tank/engine and nose sections – a first for the Starship program – began less than ten days ago, so Musk is most likely referring to wind disrupting SN8’s on-pad integration.

SpaceX’s extensive reliance upon wheeled boom lifts to ferry workers around and inside Starship SN8 and the sheer scale and surface area of the rocket likely translate to an unsteady and relatively unsafe work environment in high winds.

Regardless of whether SpaceX actually puts Starship SN8 through any kind of tests on October 30th, the company has four more road closures (i.e. test windows) scheduled from Sunday to Wednesday. Aside from a 7pm to 1am CST (UTC-6) window on November 1st, SpaceX’s Mon-Wed testing will occur between 9am and 11pm. In Cameron County, Texas regulatory documents, SpaceX says it will use those windows for “SN8 Nose Cone Cryoproof” testing, referring to the process of filling the rocket’s tanks with supercool liquid nitrogen to verify their behavior at extreme temperatures.

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SpaceX swaps Starship Raptor engine for one last pre-flight test

On the same day SpaceX stacked a flightworthy Starship prototype to its full height for the first time, the company decided to swap one of the rocket’s three Raptor engines ahead of one last major pre-flight test.

Curiously, at the same time as SpaceX engineers and technicians were removing Raptor serial number 39 (SN39) from Starship SN8, a second Raptor – SN36 – was briefly removed from a specialized transport truck. Once SN39 was removed, both it and SN36 were loaded onto a separate flatbed and carefully driven back to SpaceX’s Boca Chica Starship factory.

It’s unclear why SpaceX seemingly aborted October 22nd’s in situ Raptor replacement but Raptor SN36 (presumed) was ultimately installed in SN39’s place on Starship around midnight on October 23rd. Regardless of why, SpaceX did what it always does and reacted almost immediately, quickly replacing a Raptor engine to keep Starship SN8 on schedule for what could be its last test before an ambitious 15 km (50,000 ft) launch debut.

SpaceX began installing Starship SN8’s nose section on October 22nd. (NASASpaceflight – bocachicagal)
By October 26th, the newly assembled Starship was standing under its own weight. (NASASpaceflight – bocachicagal)

According to SpaceX CEO Elon Musk, Starship SN8 is expected to complete two separate triple-Raptor static fire tests before the company is ready to commit the rocket to such an ambitious flight test. SN8 completed what was the Starship and Raptor programs’ first multi-engine static fire test ever a mere two days before SpaceX began installing the rocket’s nosecone – a milestone curiously absent from Musk’s tweet.

It’s possible that Musk was speaking under the assumption that SN8 would be fully assembled before it began static fire operations, with “checkouts” referring to touch-free inspections between two back-to-back Raptor tests to simulate the in-flight reignition Starship SN8 will need to perform during its flight debut. If that’s the case, SN8 may need to pass two more static fires before being cleared for flight.

Raptor SN36 was first delivered to the launch site by semi truck on October 22nd.(NASASpaceflight – bocachicagal)
Raptor SN39 was soon removed from Starship but both engines were eventually taken back to the build site. (NASASpaceflight – bocachicagal)

Either way, SpaceX has already scheduled unlabeled Boca Chica road closures from 8am to 11pm CDT (UTC-5) on October 28th and 29th and 5am to 11am CDT on October 30th. Given the length of those closures, their purpose is almost certainly to support Starship SN8’s next static fire test campaign. With SN8’s nose now fully installed, SpaceX will likely focus on testing the liquid oxygen header tank located in the tip to ensure that the smaller sub-tanks meant to hold Starship’s landing propellant are working as expected and capable of supplying three thirsty Raptor engines.

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SpaceX Starship prototype gearing up for first static fire with three Raptor engines

Two days after Elon Musk announced that Starship SN8 “passed cryo proof” testing, SpaceX has begun installing three Raptor engines on the rocket for the first multi-Raptor static fire ever attempted.

On October 9th, the CEO revealed that the first SpaceX Starship prototype bound for a crucial high-altitude test flight had successfully completed cryogenic proof testing after four full nights of work. Curiously, Musk didn’t say much else but past comments indicated that SpaceX would follow up a successful Starship SN8 cryo proof test by installing three Raptors for the first attempt at a historic engine testing milestone: the multi-engine static fire.

Two Raptors head to the launch pad. (LabPadre)

Recently discussed on Teslarati, Starship SN8 was the first flightworthy prototype to have functional aerodynamic control surfaces (flaps) installed, a milestone SpaceX passed on September 23rd. The rocket was rolled to the launch pad three days later but forced to sit at the pad for four days until high winds died down, at which point SpaceX was able to install SN8 on the launch mount.

“If SN8 reaches the necessary pressure and survives the stress of its cryo proof(s), it will likely become the first Starship to attempt a triple-Raptor static fire – a first for the engine, too. Starship SN8’s first cryo proof attempt is scheduled no earlier than 9pm-6am CDT (UTC-5) on Sunday, October 4th with backup windows on the 5th and 6th. The first static fire attempt – possibly beginning with one Raptor or jumping straight to three – could happen several days after a successful cryo proof.

According to Elon Musk, SpaceX will static fire SN8 twice before attempting its 15 km (~50,000 ft) launch debut. More likely than not, SpaceX will attempt a triple-engine static fire with the Starship as-is, install SN8’s nosecone and forward flaps, and attempt a second static fire while only drawing propellant from the rocket’s smaller header tanks (one of which is located in the tip of its nose). Only time (or Elon tweets) will tell.”


Teslarati.com — October 1st, 2020

As speculated on October 1st, it appears that SpaceX will indeed proceed with Raptor static fire testing before installing Starship SN8’s nose section, reducing the schedule impact and cost of a hypothetical failure. Although modern computer simulations are far better than they used to be, there is still always some inherent risk present during the first multi-engine static fire of a rocket, as operating multiple rocket engines in close proximity can produce complex interactions that are hard to predict.

Based on the fact that SpaceX has already shipped two Raptors to the launch pad, it looks like Starship SN8 will begin static fire testing with three engines installed, although there’s still a chance SpaceX will sequentially proceed through one, two, and three-Raptor tests.

Regardless, SpaceX has yet to file for road closures for Starship SN8’s first static fire test campaign. Based on past tests with Starships SN4, SN5, and SN6, the first static fire attempt could happen just a few days to a week after engine installation and will be preceded by at least one or two wet dress rehearsals (WDRs) and Raptor ‘spin prime’ and/or preburner tests. Per Musk, after the first successful static fire, SpaceX will inspect the rocket (and likely install its nose section) before performing another static fire to clear Starship SN8 for flight. Stay tuned for updates!

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SpaceX’s first orbital Starship engine just breathed fire

Less than three weeks after shipping to Texas, SpaceX says that Starship’s first Raptor Vacuum engine has completed a “full duration test fire” on the march towards orbital test flights.

Known as Raptor Vacuum or RVac, the engine is almost entirely based off of its sea level-optimized cousin, taking all of the complex turbomachinery and combustion chambers that represent the bulk of a rocket engine. Things start to diverge below the throat of the combustion chamber (the narrow part of the central hourglass-like curve), where SpaceX has expanded Raptor’s existing bell nozzle by a factor of five or more.

SpaceX’s reusable Starship spacecraft will use a mix of three sea level Raptors and three Raptor Vacuum engines to give it the thrust it needs to reach orbit and ensure efficient operations both in atmosphere and vacuum.

Raptor Vacuum (roughly) to scale alongside Raptor Sea Level, a Space Shuttle Main Engine (SSME), and a Saturn V F-1. (Teslarati)

In simple terms, a rocket engine can benefit from a vacuum-optimized nozzle because the added surface area (more or less) gives the extremely high-pressure gases exiting its combustion chamber even more footholds to push against. Rocket nozzles are at their most efficient when the engine’s exhaust gas finishes expanding to match ambient pressure at the exact moment it exits the bell. Logically, at sea level on Earth, the ambient air pressure is quite high, meaning that rocket exhaust doesn’t have to expand as much to equalize.

In the vacuum of space, however, exhaust gases must expand far more to reach the same pressure as its surroundings. For rocket propulsion, that extra expansion can be exploited to make a more efficient engine, squeezing extra energy out of the same propellant and in a perfect vacuum, the most efficient nozzle would technically be infinite. Engineering and physical infinities don’t exactly get along, unfortunately, so vacuum rocket engineers are forced to settle on a nozzle size at a scale that humans can feasibly manufacture.

In theory, Starship doesn’t need Raptor Vacuum engines to be a functioning orbital spacecraft and CEO Elon Musk himself floated a design with seven sea-level engines just two years ago. Since then, the SpaceX CEO revealed that Raptor was making such good progress that the company undid the removal of vacuum-optimized engines from Starship’s baseline design.

Look, Ma, no vacuum engines! (SpaceX)

It’s unclear exactly what SpaceX means when it says that Raptor Vacuum SN1 completed a “full duration test fire.” For Starship, a full-duration orbital insertion burn – beginning immediately after Super Heavy booster separate – would likely be no shorter than five or six minutes. Even for SpaceX, going from shipping the very first engine (Raptor Vacuum) produced to a successful several-minute static fire in less than three weeks’ time would be an almost inconceivable feat of engineering. The feat would imply that SpaceX is already extremely comfortable with several-minute Raptor burns – perhaps the single biggest hurdle standing between Starship and orbit.

More likely, “full duration test fire” simply refers to the fact that the pathfinder Raptor Vacuum engine managed to ignite, burn, and shut down on schedule – avoiding a premature shutdown, in other words. For an engine as large and complex as Raptor, even that downgraded interpretation would represent an impressive achievement.

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