from the SHINY! dept.
Popular Mechanics has interviewed SpaceX CEO Elon Musk about his decision to move to a stainless steel design for Starship Super Heavy (formerly BFR). The interview reveals new details about the design, including micro-perforations on the outside of the windward side of the rocket that can bleed water or fuel for cooling:
Ryan D'Agostino: How does stainless steel compare [to carbon fiber]?
Elon Musk: The thing that's counterintuitive about the stainless steel is, it's obviously cheap, it's obviously fast—but it's not obviously the lightest. But it is actually the lightest. If you look at the properties of a high-quality stainless steel, the thing that isn't obvious is that at cryogenic temperatures, the strength is boosted by 50 percent.
Most steels, as you get to cryogenic temperatures, they become very brittle. You've seen the trick with liquid nitrogen on typical carbon steel: You spray liquid nitrogen, you can hit it with a hammer, it shatters like glass. That's true of most steels, but not of stainless steel that has a high chrome-nickel content. That actually increases in strength, and ductility is still very high. So you have, like, 12 to 18 percent ductility at, say, minus 330 degrees Fahrenheit. Very ductile, very tough. No fracture issues.
[...] [Here's] the other benefit of steel: It has a high melting point. Much higher than aluminum, and although carbon fiber doesn't melt, the resin gets destroyed at a certain temperature. So typically aluminum or carbon fiber, for a steady-state operating temperature, you're really limited to about 300 degrees Fahrenheit. It's not that high. You can take little brief excursions above that, maybe 350. Four hundred, you're really pushing it. It weakens. And there are some carbon fibers that can take 400 degrees Fahrenheit, but then you have strength knockdowns. But steel, you can do 1500, 1600 degrees Fahrenheit.
[...] On the windward side, what I want to do is have the first-ever regenerative heat shield. A double-walled stainless shell—like a stainless-steel sandwich, essentially, with two layers. You just need, essentially, two layers that are joined with stringers. You flow either fuel or water in between the sandwich layer, and then you have micro-perforations on the outside—very tiny perforations—and you essentially bleed water, or you could bleed fuel, through the micro-perforations on the outside. You wouldn't see them unless you got up close. But you use transpiration cooling to cool the windward side of the rocket. So the whole thing will still look fully chrome, like this cocktail shaker in front of us. But one side will be double-walled and that serves a double purpose, which is to stiffen the structure of the vehicle so it does not suffer from the fate of the Atlas. You have a heat shield that serves double duty as structure.
The steel used will be about $3/kg vs. $135/kg ($200/kg assuming a 35% scrap rate) for carbon fiber.
Also at Futurism.
Nikkei Asian Review reports that SpaceX is establishing a business relationship with Japanese material manufacturer Toray Industries. They're supposedly working on a $1.99 billion to $2.98 billion USD deal in which Toray will supply SpaceX with sheets of carbon fiber.
The two sides are aiming to finalize the agreement this fall after hammering out prices, time frames and other terms.
The likely plan is to supply carbon fiber sheets from a Toray production center in Alabama, with SpaceX to further process the material into end products. Adding dedicated production lines at a South Carolina plant will be considered if SpaceX's demand for carbon fiber grows as expected.
In Ars Technica's regurgitation of this story, one delicious chunk of information is brought to the surface (albeit coated in the putrid vile of a misused "irony"):
In a bit of irony, Toray is likely to produce carbon fibers for SpaceX at its Decatur, Alabama-based factory, which is located in the same city where SpaceX competitor United Launch Alliance manufactures its rockets.
One angle the Nekkei Asian Review article touches on is that per-rocket cost should matter less now that SpaceX is successfully landing rockets.
SpaceX aims to hold down expenses by re-using rockets and spacecraft. Originally, the company made rockets mostly out of aluminum to keep costs low, using carbon fiber only for a few parts, such as connecting joints.
Another angle mentioned is SpaceX's ambitions for Mars.
SpaceX is switching to carbon fibers from aluminum as it develops heavy rockets for carrying people and large quantities of material. A lighter body would allow more cargo to be loaded, which would cut transport costs.
The Falcon Heavy rocket, currently under development, would carry more than three times the payload that the Falcon 9, the current model in service, is capable of handling. The rocket is slated for a test launch as early as the end of the year. SpaceX will start launching satellites next year and carry out a joint unmanned mission to Mars with NASA in May 2018.
Do Soylentils think that this move towards carbon fiber has more to do with reusable rocket advances, or the requirements of Mars missions? Are those issues even separable? What other angles should we be discussing?
During a press conference at his company's Hawthorne, CA headquarters, SpaceX CEO Elon Musk announced the first planned private passenger to travel into deep space and around the Moon. Yusaku Maezawa, a billionaire fashion entrepreneur and art collector, paid an undisclosed amount to become one of the first people to fly on a SpaceX Big Falcon Rocket (BFR), with a target date of 2023. If the launch happens, he won't be going alone. Maezawa (aka "MZ") plans to invite at least six to eight artists to accompany him on a journey around the Moon. The passengers chosen may be painters, sculptors, musicians, fashion designers, dancers, film directors, architects, etc. and are intended to represent the Earth and participate in an art exhibition after returning to Earth. Musk himself has also been invited. The project is called #dearMoon.
Yusaku Maezawa approached SpaceX and made a contribution that will pay for a "non-trivial" amount of the BFR's development costs. During the Q&A, Musk estimated that the entire development of BFR would cost around $5 billion, or no less than $2 billion and no more than $10 billion. Other potential sources of funding for BFR development include SpaceX's top priority, Crew Dragon flights to the International Space Station (ISS), as well as satellite launches and Starlink satellite broadband service.
Maezawa (along with a guest) was a previously announced anonymous customer for a Falcon Heavy ride around the Moon. SpaceX currently has no plans to human-rate the Falcon Heavy. The switch from Falcon Heavy to BFR will substantially increase the maximum number of passengers and comfort level attainable on a nearly week-long mission, since the Crew Dragon 2 has a pressurized volume of just 10 m3, about 1% of the volume of the BFS.
SpaceX's Starship and Super Heavy (formerly Big Falcon Spaceship and Big Falcon Booster, or Big Falcon Rocket) have undergone further changes following a "final" iteration of the design in September. Elon Musk also said that a downscaled Starship hopper (for vertical takeoffs and landings) will "hopefully" be tested starting in March or April 2019, which is months sooner than a "late 2019" estimate made by SpaceX CEO Gwynne Shotwell in September.
Recent photos taken of SpaceX's operation in Boca Chica, Texas have shown a stainless steel nose cone being built. The new stainless steel design was confirmed by Elon Musk, along with numerous other details. Musk said that stainless steel can beat carbon fiber composites due to its superior strength-to-mass ratio and "mirror-like" thermal reflectivity. SpaceX is using an on-site foundry to create its own steel "superalloy", although some steel parts will be made by a supplier. Finally, the test hopper will feature three "radically redesigned" Raptor engines while being slightly shorter than the full-scale Starship, although it will share the same 9-meter diameter:
While the suggestion that Raptor's turbopumps (basically fuel pumps) would need at least 100,000 HP per engine seems to indicate that the flight design's thrust has been appreciably uprated, a past figure of ~2000 kN (450,000 lbf) per engine suggests that Starship V0.1 could weigh as much as an entire Falcon 9 Block 5 rocket (~1.2 million pounds, 550,000 kg) and still having a solid 80-100% of Falcon 9's liftoff thrust. Put simply, the rocket that appears to be coming together in the boonies of South Texas could rival almost any other liquid fuel rocket booster in service, while still being the testbed for BFR's upper stage alone.
While it's ambiguous if several additional comments applied to the Starship prototype, the final product, or both, Musk also indicated that some of the biggest benefits of a shift away from carbon composites to stainless steel would be relative ease with which the material handles extreme heating. Thanks to the fact that stainless steel can ultimately be polished to mirror-like levels of reflectivity and that mirrors are some of the most efficient reflectors of thermal energy (heat), shiny and unpainted steel would ultimately perform far better than carbon composites and could end up requiring "much less" heat shielding for the same performance.
Perhaps most unintuitive is the fact that steel can apparently beat carbon composites when it comes to usable strength-to-weight ratios at supercool temperatures. According to Musk, steel also performs "vastly better" at high temperatures and appreciably better at room temperatures. A comment made on Saturday may lend additional credence to what seems at face value to contradict basic material intuition – at least some of the stainless steel SpaceX is examing would be a special (presumably SpaceX-engineered) alloy that has undergone what is known as cryogenic treatment, in which metals are subjected to extremely cold conditions to create some seriously unintuitive properties. Ultimately, cold-formed/worked or cryo-treated steel can be dramatically lighter and more wear-resistant than traditional hot-rolled steel.
Elon Musk hinted at a "delightfully counter-intuitive" redesign in November, which was almost certainly a reference to the use of stainless steel instead of carbon fiber composites. Here's a video (10m14s) which offers some speculation about how a steel Starship could effectively conduct and radiate away heat.
Also at Business Insider.
Elon Musk has been at SpaceX's test site for its rocket engines in central Texas this weekend. The facility near McGregor is where the company both tests Merlin engines for Falcon 9 flights, and also performs some experimental firings.
Due to a variety of reasons including financial pressures, SpaceX is pushing hard on the development of its next-generation Super Heavy rocket and Starship spacecraft. This was evidenced this weekend when, at 1:15am Central Time on Sunday morning, Musk shared a nighttime picture of himself on the test stand at McGregor, saying "with engineering team getting ready to fire new Raptor rocket engine." It was the dead of night on Super Bowl weekend, and they were working on an engine that won't go into space for a few years. But that didn't matter.
The test itself appears to have taken place later on Sunday. Eyewitness reports in Central Texas noted a large pop on Sunday evening, and more later Sunday night. Musk himself tweeted a photo shortly before 10pm local time, and thereafter a video. The test firing itself lasts for a few seconds, and was evidently successful. "First firing of Starship Raptor flight engine! So proud of great work by @SpaceX team!!" Musk wrote.
Also at Fox News.
Previously, the EU-propped Ariane Group's CEO scoffed at the idea of pursuing reusable rockets (the upcoming Ariane 6 is fully expendable) due to Europe having a small market of 5-10 launches per year, as well as the potential effects on rocket-building jobs:
[Chief executive of Ariane Group, Alain] Charmeau said the Ariane rocket does not launch often enough to justify the investment into reusability. (It would need about 30 launches a year to justify these costs, he said). And then Charmeau said something telling about why reusability doesn't make sense to a government-backed rocket company—jobs.
"Let us say we had ten guaranteed launches per year in Europe and we had a rocket which we can use ten times—we would build exactly one rocket per year," he said. "That makes no sense. I cannot tell my teams: 'Goodbye, see you next year!'"
This seems a moment of real irony. Whereas earlier in the interview Charmeau accuses the US government of subsidizing SpaceX, a few minutes later he says the Ariane Group can't make a reusable rocket because it would be too efficient. For Europe, a difficult decision now looms. It can either keep subsidizing its own launch business in order to maintain an independent capability, or it can give in to Elon Musk and SpaceX, and Jeff Bezos and Blue Origin. Charmeau seems to have a clear view of where he thinks the continent should go.
Now, the attitude has changed:
This month, the European Commission revealed a new three-year project to develop technologies needed for two proposed reusable launch vehicles. The commission provided €3 million to the German space agency, DLR, and five companies to, in the words of a news release about the project, "tackle the shortcoming of know-how in reusable rockets in Europe."
This new RETALT project's goals are pretty explicit about copying the retro-propulsive engine firing technique used by SpaceX to land its Falcon 9 rocket first stages back on land and on autonomous drone ships. The Falcon 9 rocket's ability to land and fly again is "currently dominating the global market," the European project states. "We are convinced that it is absolutely necessary to investigate Retro Propulsion Assisted Landing Technologies to make re-usability state-of-the-art in Europe."
Ariane Group isn't one of the five companies, but then again, €3 million isn't a lot of money.
Even a fully reusable rocket is on the table:
[...] attitude of the new RETALT project appears to have indicated European acceptance of the inevitability of reusable launch vehicles. Engineers will work toward two different concepts. The first will be a Falcon-9-like rocket that will make use of seven modified Vulcain 2 rocket engines and have the capacity to lift up to 30 tons to low-Earth orbit. The second will be a more revolutionary single-stage-to-orbit vehicle that looks like the Roton rocket developed by Rotary Rocket about two decades ago.
They should mine Elon Musk's Twitter for clues. Try making the rocket out of stainless steel.
SpaceX has nailed its 24th Falcon booster reuse and 44th Falcon booster landing with Falcon 9 B1056's flawless Landing Zone-1 recovery, setting the booster up to become the first SpaceX rocket NASA has flown on three times.
According to NASASpaceflight.com, NASA had already moved from a conservative "maybe" to a much firmer "yes, but..." on the second-reuse question, pending – of course – the successful completion of B1056's second launch and landing. As of now, the Block 5 booster has indeed successfully completed its second orbital-class mission, setting itself up for a milestone NASA reuse that could happen as early as December 2019 on CRS-19, Dragon 1's second-to-last planned International Space Station (ISS) resupply mission.
Starhopper has completed its first untethered flight ever, simultaneously a small step for the awkward prototype and a giant leap for SpaceX's Starship/Super Heavy program as the next-gen launch vehicle is carried into a new phase: flight testing.
Despite the spectacular and reportedly successful hover and divert test, Starhopper's powerful Raptor engine appears to have started a significant fire, placing SpaceX's Starhopper pad in a precarious position per the fire's apparent adjacency to full liquid oxygen tanks. Ironically, despite Starhopper's seeming predilection as of late towards catching itself on fire, the large rocket testbed appears to be entirely unscorched as a brush fire burns around a few hundred feet distant.
[...] According to Elon Musk, the SpaceX CEO will present an update on the company's progress designing, building, and testing Starship and Super Heavy soon after Starhopper's first successful flight, meaning it could potentially happen within the next week or two. Additionally, Musk deemed Starhopper's July 25th flight a success and indicated that SpaceX would attempt to put Starhopper through a more ambitious 200m (650 ft) hop in a week or two, continuing what is expected to be an increasingly arduous serious of tests for the prototype.