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SpaceX says Crew Dragon capsule exploded due to exotic titanium fire

Crew Dragon tests its SuperDraco-powered launch abort system in 2015. (SpaceX)

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SpaceX has announced via an official update and conference call the preliminary results of a failure investigation convened immediately after Crew Dragon capsule C201 exploded in the midst of an April 20th static fire test.

Hosted by SpaceX Vice President of Mission Assurance Hans Koenigsmann and NASA Commercial Crew Program manager Kathy Lueders, the call provided some minor additional insight beyond a fairly extensive press release issued just prior. According to the preliminary results from SpaceX’s failure investigation, Crew Dragon’s explosion was unrelated to the spacecraft’s propellant tanks, Draco maneuvering thrusters, or SuperDraco abort engines. Rather, the cause lies in a more exotic and unanticipated chemical/material interaction between a plumbing valve, liquid oxidizer, and a helium-based pressurization system.

When metal burns

According to Hans Koenigsmann, SpaceX is approximately 80% of the way through what is known as the fault tree, essentially meaning that the failure investigation is 80% complete. That additional 20% could certainly throw some curveballs but the SpaceX executive was fairly confident that the results presented on July 15th would be representative of the final conclusion.

The ultimate (likely) cause of Crew Dragon’s extremely energetic and destructive explosion centers around the spacecraft’s extensive SuperDraco/Draco plumbing and its associated pressurization system, which uses helium to keep the pressure-fed engines, propellant tanks, and feed lines around 2400 psi (16.5 megapascals). Necessarily, this method of pressurization means that there is direct contact between the pressurant (helium) and the oxidizer/fuel, thus requiring some sort of valve preventing the pressurized fluid from flowing into the pressurization system.

A detailed view of some of the Draco and SuperDraco-related plumbing used on Crew Dragon – in this case, the capsule that will now fly SpaceX’s In-Flight Abort test. (Pauline Acalin, August 2018)

During flight-proven Crew Dragon capsule C201’s April 20th static fire testing, that is reportedly exactly what happened. Over the course of ground testing, a “check valve” separating the pressurization system and oxidizer leaked what SpaceX described as a “slug” of nitrogen tetroxide oxidizer (NTO) into the helium pressurization lines. Around T-100 milliseconds to a planned ignition of the vehicle’s 8 SuperDraco abort engines, the pressurization system rapidly “initialized” (i.e. quickly pressurized the oxidizer and fuel to operational pressures, ~2400 psi).

To do this, helium is rapidly pushed through a check valve – designed with low-molecular-mass helium in mind – to physically pressurize the propellant systems. Unintentionally, the NTO that leaked ‘upstream’ through that valve effectively was taken along for the ride with the high-pressure burst of helium. In essence, picture that you crash your car, only to discover that your nice, fluffy airbag has accidentally been replaced with a bag of sand, and you might be able to visualize the unintended forces Dragon’s check valve (the metaphorical airbag) was subjected to when a “slug” of dense oxidizer was rammed into it at high speed.

Crew Dragon C201 displays its heat shield after the spacecraft’s first orbital-velocity Earth reentry, March 8th. (NASA/Cory Huston)

In itself, this sort of failure mode is not hugely surprising and SpaceX may have even been aware of some sort of check valve leak(s) and accepted what it believed to be a minor risk in order to continue the test and perhaps examine Dragon’s performance under suboptimal conditions. What SpaceX says it did not realize was just how energetic the reaction between the NTO and the check valve could be. SpaceX’s understanding is that the high-speed slug of dense NTO was traveling so fast and at such a high pressure that, by impacting the titanium check valve, it quite literally broke the valve and may have chemically ignited the metal, thus introducing a slug of burning NTO into the liberated NTO system itself – effectively a match tossed into a powder keg.

It’s unclear if the ignition came from a chemical reaction between titanium (a technically flammable metal similar to magnesium) and NTO, or if the source came from the titanium valve being smashed apart, perhaps quite literally creating a spark as metal debris violently interacted. Either way, the solution – as SpaceX perceives it – is the same: instead of a mechanical check valve (simple but still not 100% passive), the barrier between pressurant and oxidizer (as well as fuel, most likely) will be replaced with something known as a burst disk. According to Koenigsmann, only a handful (~4) of those valves exist and thus need to be replaced by burst disks, a relatively fast and easy fix.

Burst disks are single-use and inherently unreusable, but they are also completely passive and simply do not leak until subjected to a specific amount of pressure. Because they are single-use, they can’t be directly tested prior to flight, limiting some of the in-principle reliability for the sake of an extremely leak-proof barrier.

A test of one of Crew Dragon’s four ‘powerpacks’, featuring two SuperDracos and three Dracos. (SpaceX)

Ultimately, both Koenigsmann and Lueders went out of their way to avoid answering any questions about SpaceX’s Crew Dragon upcoming test and launch schedule and what sort of delays the explosion will ultimately incur. Both individuals were nevertheless upbeat and by the sound of it, delays to Crew Dragon will be far less severe relative to delays caused by a pressure vessel or engine failure. For the time being, NASA has published a tentative target of mid-November 2019 for Crew Dragon’s first crewed launch to the International Space Station, while Lueders and Koenigsmann expressed hope in a 2019 launch but refused to give a specific estimate of the odds of that occurring.

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Eric Ralph is Teslarati's senior spaceflight reporter and has been covering the industry in some capacity for almost half a decade, largely spurred in 2016 by a trip to Mexico to watch Elon Musk reveal SpaceX's plans for Mars in person. Aside from spreading interest and excitement about spaceflight far and wide, his primary goal is to cover humanity's ongoing efforts to expand beyond Earth to the Moon, Mars, and elsewhere.

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Tesla teases new market entrance with confusing and cryptic message

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(Credit: Tesla)

Tesla teased its entrance into a new market with a confusing and what appeared to be cryptic message on the social media platform X.

The company has been teasing its entrance into several markets, including Africa, which would be a first, and South America, where it only operates in Chile.

In September, Tesla started creating active job postings for the Colombian market, hinting it would expand its presence in South America and launch in a new country for the first time in two years.

Tesla job postings seem to show next surprise market entry

The jobs were related to various roles, including Associate Sales Manager, Advisors in Sales and Delivery, and Service Technicians. These are all roles that would indicate Tesla is planning to launch a wide-scale effort to sell, manage, and repair vehicles in the market.

Last night, Tesla posted its latest hint, a cryptic video that seems to show the outline of Colombia, teasing its closer than ever to market entry:

This would be the next expansion into a continent where it does not have much of a presence for Tesla. Currently, there are only two Supercharger locations on the entire continent, and they’re both in Chile.

Tesla will obviously need to expand upon this crucial part of the ownership experience to enable a more confident consumer base in South America as a whole. However, it is not impossible, as many other EV charging infrastructures are available, and home charging is always a suitable option for those who have access to it.

Surprisingly, Tesla seems to be more concerned about these middle-market countries as opposed to the larger markets in South America, but that could be by design.

If Tesla were to launch in Brazil initially, it may not be able to handle the uptick in demand, and infrastructure expansion could be more difficult. Brazil may be on its list in the upcoming years, but not as of right now.

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Tesla expands crucial Supercharging feature for easier access

It is a useful tool, especially during hours of congestion. However, it has not been super effective for those who drive non-Tesla EVs, as other OEMs use UI platforms like Google’s Android Auto or Apple’s iOS.

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Credit: Tesla

Tesla has expanded a crucial Supercharging feature that helps owners identify stall availability at nearby locations.

Tesla said on Tuesday night that its “Live Availability” feature, which shows EV owners how many stalls are available at a Supercharger station, to Google Maps, a third-party app:

Already offering it in its own vehicles, the Live Availability feature that Teslas have is a helpful feature that helps you choose an appropriate station with plugs that are immediately available.

A number on an icon where the Supercharger is located lets EV drivers know how many stalls are available.

It is a useful tool, especially during hours of congestion. However, it has not been super effective for those who drive non-Tesla EVs, as other OEMs use UI platforms like Google’s Android Auto or Apple’s iOS.

Essentially, when those drivers needed to charge at a Supercharger that enables non-Tesla EVs to plug in, there was a bit more of a gamble. There was no guarantee that a plug would be available, and with no way to see how many are open, it was a risk.

Tesla adding this feature allows people to have a more convenient and easier-to-use experience if they are in a non-Tesla EV. With the already expansive Supercharger Network being available to so many EV owners, there is more congestion than ever.

This new feature makes the entire experience better for all owners, especially as there is more transparency regarding the availability of plugs at Supercharger stalls.

It will be interesting to see if Tesla is able to expand on this new move, as Apple Maps compatibility is an obvious goal of the company’s in the future, we could imagine. In fact, this is one of the first times an Android Auto feature is available to those owners before it became an option for iOS users.

Apple owners tend to get priority with new features within the Tesla App itself.

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Elon Musk’s Boring Co goes extra hard in Nashville with first rock-crushing TBM

The Boring Company’s machine for the project is now in final testing.

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Credit: The Boring Company/X

The Boring Company is gearing up to tackle one of its toughest projects yet, a new tunnel system beneath Nashville’s notoriously tough limestone terrain. Unlike the soft-soil conditions of Las Vegas and Austin, the Music City Loop will require a “hard-rock” boring machine capable of drilling through dense, erosion-resistant bedrock. 

The Boring Company’s machine for the project is now in final testing.

A boring hard-rock tunneling machine

The Boring Company revealed on X that its new hard-rock TBM can generate up to 4 million pounds of grip force and 1.5 million pounds of maximum thrust load. It also features a 15-filter dust removal system designed to keep operations clean and efficient during excavation even in places where hard rock is present.

Previous Boring Co. projects, including its Loop tunnels in Las Vegas, Austin, and Bastrop, were dug primarily through soft soils. Nashville’s geology, however, poses a different challenge. Boring Company CEO and President Steve Davis mentioned this challenge during the project’s announcement in late July.

“It’s a tough place to tunnel, Nashville. If we were optimizing for the easiest places to tunnel, it would not be here. You have extremely hard rock, like way harder than it should be. It’s an engineering problem that’s fairly easy and straightforward to solve,” Davis said.

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Nashville’s limestone terrain

Experts have stated that the city’s subsurface conditions make it one of the more complex tunneling environments in the U.S. The Outer Nashville Basin is composed of cherty Mississippian-age limestone, a strong yet soluble rock that can dissolve over time, creating underground voids and caves, as noted in a report from The Tennessean.

Jakob Walter, the founder and principal engineer of Haushepherd, shared his thoughts on these challenges. “Limestone is generally a stable sedimentary bedrock material with strength parameters that are favorable for tunneling. Limestone is however fairly soluble when compared to other rack materials, and can dissolve over long periods of time when exposed to water. 

“Unexpected encounters with these features while tunneling can result in significant construction delays and potential instability of the excavation. In urban locations, structures at the ground surface should also be constantly monitored with robotic total stations or similar surveying equipment to identify any early signs of movement or distress,” he said.

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