SpaceX's "bleeding" steel vessel can suffer from clogged pores


SpaceX, the aerospace company founded by Elon Musk, is working diligently on an extremely ambitious project: permanently installing people on Mars.

To help realize this vision, Musk is developing a massive, fully reusable launch system called Starship.

The spacecraft is designed as a 180-foot-tall spacecraft that will launch into orbit over Super Heavy, a rocket booster of about 220 feet, according to the latest Musk descriptions. The spacecraft is designed to be refueled into low Earth orbit to propel 100 passengers and more than 100 tons of cargo at a time to Mars.

But the success or failure of the launching system – and by extension of Musk's plan to safeguard mankind – may result from the viability of two major and recent design changes, which Musk described as "radical" and "deliciously counterintuitive".

A change involves the construction of the spaceship of stainless steel alloys instead of carbon fiber composites. However, according to experts from the aerospace industry, the most surprising change is the way Starship will try not to burn themselves in the atmospheres of Mars and the Earth.

Instead of relying on thousands of heavy ceramic tiles to shield Starship from the heat, as NASA did with its space shuttle, Musk says the spacecraft will "bleed" the fuel from the rocket through tiny pores to cool. In theory, placing a liquid between Starship steel skin and the hot plasma generated while it was crisscrossing the atmospheric gases would prevent the destruction of the ship.

Read more: Astronaut Chris Hadfield says we could have visited Mars decades ago – here's why we do not have one

But it remains to be seen whether SpaceX will be able to have a launch system of unprecedented size and design, says Walt Engelund, aerospace engineer and director of the Space Technology and Exploration Directorate. NASA Langley.

"NASA has been fighting large-scale entries, descents and landings for decades, and we spent a lot of time thinking about how we could proceed on Mars," Engelund told Business Insider. "We landed on the Curiosity rover of a metric ton – that's the most important thing we've ever deposited on the surface of Mars."

To move from the Martian landing of a robot the size of a car to a ship the size of a building filled with humans, said Engelund, it's "a few "orders of magnitude," about 100 times, harder than the Curiosity landing, which is "probably one of the most difficult things we've ever done at NASA."

"It will not be easy for us or SpaceX," said Engelund.

Why Starship has turned into a heavy metal rocket

Musk thinks he can build an autonomous city on the red planet in 2050. He wants individual tickets for March to be as cheap as a house on Earth and return trips are free.

The Starship-Super Heavy launch system is the way Musk plans to achieve this goal, and he said the move to stainless steel alloys is a way to reduce costs and build the system faster.

"The ship will look like cash," Musk said about the change in December, adding that the ship would have a polished mirror finish to help reflect the heat – a real cold factor case.

Illustration of the next SpaceX spacecraft and Super Heavy propeller (center), next to NASA's Saturn V lunar rocket (left) and SpaceX's Falcon 9 rocket (right).
© Kimi Talvitie

In an interview with Popular Mechanics, Musk explained that steel is about 67 times more economical in weight than lightweight but very robust carbon fiber composites, which SpaceX had planned to use up to 60 times as much. ;in September. Steel is also easier to work than carbon fiber, allows faster prototyping and is more resistant to intense heat.

Mr Musk added that the strength of steel is "50% enhanced" when it touches ultra-cold liquids, including cryogenic oxygen and methane that Starship could use to get rid of it. propel in space.

Read more: SpaceX has tested a Raptor rocket engine with "crazy power" for lunar and martian missions. The future of Musk will depend on its unmatched performance.

The problem with steel, however, is that the material is dense and heavy. At least one of the first versions of the General Dynamics Atlas missile, made from metal, crumpled under its own weight on a launch pad.

However, Musk suggested that the use of steel by SpaceX was very different and would make the spaceship redesigned stronger, more durable and lighter. In the end, he said, the hardware change will improve the performance of the rocket ship compared to the old model.

"I am convinced that a stainless steel vessel will be lighter than advanced aluminum or carbon fiber, because of its resistance to weight relative to temperature and the reduced need for thermal protection. "said Musk tweeted in January.

But as hard as steel is, it is not invincible, especially when it forms the skin of a spaceship that screams through atmospheric gases.

Sweating and bleeding to survive

An illustration of the next SpaceX spacecraft and the SpaceX Super Heavy propeller. Musk says the launch system will be made from polished stainless steel alloys to a mirror-like finish.
© Kimi Talvitie

Starship could enter through the atmospheres of Mars and Earth to 19,000 mph. At such speeds, Musc m saidparts of the ship's belly, like its nose, could be exposed to temperatures of about 2700 degrees Fahrenheit.

It's enough heat to destroy the steel alloy that Musk said that SpaceX could use for Starship's outer skin. Called 310S, the material is often presented as a heat resistant metal because it contains a lot of chromium and nickel. (This is not very different from the steel used in pots and pans.) But the 310S steel nevertheless begins to react with oxygen and corrode itself to about 2,000 degrees and thoroughly to about 2,400.

The rocket needs protection against the intense heat, that's why Musk's plans call for Starship's body cool down using liquid fuel during landing.

Musk told Popular Mechanics that he had decided to give up on space shuttle-like thermal tiles to save weight and avoid the risk of a damaged or lost tile compromising a heat shield.

Read more: This veteran NASA astronaut has tried the new space ships SpaceX and Boeing – here's what she thinks

Instead, he explained, Starship would "bleed" or sweat fuel for rocket through tiny holes in its steel skin, and this liquid layer would take away the overwhelming heat from the entrance to it. ;atmosphere.

"On the wind side, what I want is to have the very first regenerative heat shield – a double-walled stainless steel shell – like a stainless steel sandwich," said Musk. "You run fuel or water between the sandwich layer, then you have micro-perforations on the outside – very small perforations – and you basically bleed water, or you can purge fuel, through the micro-perforations on the outside, you would not see them unless you get close to it. "

He added that the heat shield would duplicate by reinforcing Starship's steel body.

"To my knowledge, this has never been proposed before," said Musk.

Experts told Business Insider that Musk is right to say that no spacecraft ever went into orbit and returned to Earth with such a heat shield. But the concept of sweating or "sweat" thermal protection is not new, and it has always been a delicate technical challenge.

Sweat cooling for lunar men and ICBM

Musk says the Starship launch system will be polished to give a mirror finish.
© Kimi Talvitie

Sweating or "active cooling" has existed for millions of years in the form of mammalian skin. When the temperature of the human body is too high, for example, microscopic pores evacuate sweat. This liquid then evaporates to evacuate excess heat and prevent overheating.

With regard to sweaty spacecraft, NASA began playing with the nature-inspired cooling system before landing astronauts on the moon.

"The idea of ​​transpiratory cooling is not new – it has been around for decades," Engelund said.

A patent filed by NASA in 1965 suggested using astronaut urine to cool a heat shield at the bottom of a space capsule. Also in 2006, the space agency had spent at least $ 70,000 looking for an inflatable, sweat-cooled thermal shield that could help land a spacecraft on Mars.

"Sweating" has also played a role in the Cold War arms race. In March 1976, the US Department of Defense tested a sweat-cooled nose for reentry vehicles. These reentry vehicles are designed to fly in space over intercontinental ballistic missiles, to re-enter the Earth's atmosphere at thousands of kilometers per hour, and to strike distant targets with nuclear warheads.

But according to historical records of the US Air Force, the project was canceled later in the 1970s because of limited funding and "design problems that had hindered the effort of development". Engineers have instead opted for simpler "ablative" heat shields that insulate a vehicle while burning during the school year.

Information about problems with defense-related sweat-related heat shields is generally ranked. But George Herbert, an aerospace engineer who studied the military uses of space launchers, told Business Insider in an e-mail that "reported and known problems include blocked perspiration holes".

In other words, a problem common to teenage skin: clogged pores.

& # 39; And if a bird poop on your rocket? & # 39;

NASA's Space Shuttle Challenger kicks off in Cape Canaveral, Florida, on January 28, 1986, disturbing nearby bird swarms.

Several experts told Business Insider that they were concerned about the blocking issue of Starship's heat shield design.

"You can imagine that it would not take much to plug something like that, it was microscopic pores," Engelund said.

Dwayne Day, who helped investigate the loss of NASA's Columbia Space Shuttle Columbia and its crew, envisioned a vexing scenario that the ship would face on any launch site on Earth.

"What if a bird pooped on your rocket and it clogged a few holes, then when the thing comes back, no coolant comes out of those holes and this part of the vehicle overheats?" Day wrote in an email to Business Insider.

Engelund stated that it had witnessed problems with dirty cooling systems during tests at NASA's hypersonic wind tunnels. During such experiments, vehicle models are placed in the tunnel – which can blow air at thousands of kilometers per hour – to study their performance. Some tests included thermal shields that pumped liquids into channels just under the skin of the model to cool, but not all models survived.

"I have seen cases where you will get a clogged channel (…) and it will immediately result in perforation problems," Engelund said. "A model will disappear in a hypersonic wind tunnel, it almost vaporizes, there is so much energy and heat."

Musk said that the use of methane as a coolant could be better than water.

"Rapid water spraying can counter-intuitively cause freezing and blockage of cooling channels," he said. said in a tweet last month.

But Engelund also sees challenges with the methane option. When exposed to high temperatures, carbon atoms in hydrocarbons (such as methane) can "coke" or agglutinate and become solid. Such debris can then block fine structures such as pores.

"I would be very worried about this," Engelund said, adding that impurities in fuel were another major problem, which could also lead to hooves.

According to Engelund, one possible way to solve these problems is to simply add more pores than it seems necessary, "just in case a small percentage of the perforations get clogged or if the channels supplying coolant lead to these perforations ".

In addition to the problems associated with bird droppings and clogging, there is fine dust blowing on Mars. This could be lodged in Starship's saturated fuel pores, and it might be difficult to find and remove these blockages on the red planet.

"Inspection and certification, in general, would pose a problem for a large-scale active system like this – especially in Mars, where you do not have access to a large portico or to large ones. towers to climb and inspect, "Engelund said. "I guess you could use drones, maybe that's one thing he thinks about."

Can Starship weather the heat?

Musk only shared fragments of Starship's latest design and did not present a complete picture to the public, as he did in the past. (The renderings in this story are courtesy of Kimi Talvitie, a 3D artist.)

But musk m said in December, it "would provide a detailed explanation in March / April", pending the successful launch of a prototype "test hopper" built by the company in Texas.

Read more: SpaceX's giant rocket was damaged by high winds in Texas – the cheekbone tipped, and Elon Musk says repairs will take weeks

In the meantime, Musk shared a video (above) that seems to show the testing of a metal heat shield for Starship. It is still unclear how much SpaceX research has focused on the concept of transpiration cooling.

"It's a huge risk if they do not work to qualify and validate what they want to do," Herbert said. "But if they did, it could be a real winner for their new design."

If that does not work, said Engelund, it's not necessarily a stalemate for Musk's Starship.

"He might find that it's unbearable or too expensive to certify or test, and he might find a better idea," Engelund said. "He's been really good at this during his career."

SpaceX also expects constant changes and adjustments as engineers work to make Starship a reality.

"We use the same iterative approach in the design that led to the success of the Falcon 1, Falcon 9, Falcon Heavy and Dragon programs," a company representative told Business Insider in an email, referring to the latest rocket and spaceship of the company drawings.

But SpaceX rejects any comparison between Starship and the NASA Curiosity robot.

"Curiosity pushed the limits of Mars in the 1970s [entry, descent, and landing] Technology, including a specific parachute-based EDL architecture, "said SpaceX," we take a totally different approach, taking advantage of what we've done with Falcon 9, and we have ample opportunity for the demonstrate on Earth before flying to Mars. "

Despite the significant hurdles SpaceX seems to encounter in its quest to launch and land a spacecraft on Mars, no expert we talked to said that the SpaceX system was improbable.

"They surprised a lot of people and have a lot of smart people working for them, and Elon seems to be really committed and dedicated to that," said Engelund. "Maybe we could do some things with them, I guess there will be some."

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