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takyon writes:

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.

Arthur T Knackerbracket has found the following story:

On Thursday night, SpaceX founder Elon Musk shared photos of Raptor rocket engines that recently left the company's factory in Hawthorne, Calif., headed out to be tested at its facility near McGregor, Texas. "Preparing to fire the Starship Raptor engine," he said by way of a caption on Twitter.

The photos were interesting, but Musk had additional comments about the engine that revealed much about how the company is proceeding with overall design of the vehicle it will power. SpaceX's approach seems focused on keeping costs down and moving as quickly as possible towards a launch of the Starship spacecraft and Super Heavy rocket in the early 2020s.

For example, Musk said, "Initially making one 200 metric ton thrust engine common across ship & booster to reach the Moon as fast as possible. Next versions will split to vacuum-optimized (380+ sec Isp) & sea-level thrust optimized (~250 ton)."

This comment is notable for a couple of reasons. First of all, the company appears to have decided to streamline the Raptor engine to a single design that will power both the rocket at liftoff, and the spaceship in the upper atmosphere and outer space. It will take less time to develop, test, and qualify a single engine. It will also cost less money.

Additionally, Musk notes that the goal is "to reach the Moon as fast as possible." The company still appears to be focused on lunar orbital flights, such as the #dearMoon project for Japanese businessman Yusaku Maezawa, as the first missions for Starship.

There is an added benefit to this approach: for the next two decades, NASA appears likely to be highly interested in developing infrastructure near and on the Moon. By flying Starship on early test flights to the same destination, SpaceX has a far greater chance to win government contracts for the delivery of cargo, and potentially astronauts, to the Moon. Heretofore, neither NASA nor the US military has shown much if any interest in SpaceX's ambitious rocket and spacecraft.

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Original Submission

takyon writes:

SpaceX Falcon 9 booster nails landing in lead-up to next NASA-sponsored reuse milestone

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.

SpaceX's Starhopper nails first untethered flight as CEO Elon Musk teases next test

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.