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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 lands new partnership with Uber as Semi takes center stage

Tesla and Uber will work together, using the company’s all-electric Semi, to make sustainable Class 8 electric trucks more affordable with three main strategies: Subsidized Pricing, Predictable Growth, and Optimization of Utilization.

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Credit: Uber

The Tesla Semi has led to a new partnership between the company and Uber, as the two are launching a program that aims to revolutionize logistics by making sustainable commercial vehicles more accessible.

Uber announced on Tuesday that it was planning to launch the Dedicated EV Fleet Accelerator Program in a new partnership with Tesla. Uber’s Freight division is mainly responsible for the new program, which it calls a “first-of-its-kind buyer’s program designed to make electric freight more affordable and accessible by addressing key adoption barriers.”

Tesla and Uber will work together, using the company’s all-electric Semi, to make sustainable Class 8 electric trucks more affordable with three main strategies: Subsidized Pricing, Predictable Growth, and Optimization of Utilization.

  • Subsidized Price: Fleets purchasing Tesla Semis through this program will receive a subsidy on the purchase price.   
  • Predictable Growth: Fleets will integrate their Tesla Semis into Uber Freight’s dedicated solutions for shippers for a pre-determined period. This creates an opportunity for carriers to forecast revenue with confidence, while shippers gain consistent access to reliable, zero-emission capacity. 
  • Optimize Utilization: Uber Freight taps into its extensive freight network to match carriers with consistent, high-quality freight from our strong shipper base—helping ensure the addition of these Tesla Semis stay fully utilized and carriers see dedicated, real, measurable returns from the start

Tesla will work directly with interested companies to iron out technical details about the Semi, as well as its cost of ownership based on the tailored needs of their business. Fleets can expect savings on the first day, Uber says, as they will avoid diesel fuel costs and reduced maintenance, a widely known advantage of EVs.

Uber announced that it had partnered with select carriers to pilot the Dedicated EV Fleet Accelerator Program prior to its launch:

“During the 2-month pilot program, the Tesla Semis showcased both reliability and efficiency for Uber Freight’s shipper network. Over 394 hours of drive time, carriers covered 12,377 miles. With an average net energy consumption of just 1.72 kWh per mile and only 60 hours of total charge time, these results highlight the operational viability of Tesla Semis on demanding freight lanes. “

In its press release launching the program, Uber effectively highlights how the use of the Semi can impact a company’s margins and profitability through fuel savings, reduced maintenance costs, and lower total cost of ownership.

This is something that turns so many people away from gas cars and toward EVs, so it’s no surprise that Uber wanted to emphasize this point on a larger scale with a company that utilizes a fleet of vehicles.

Tesla Semi shows strong results in ArcBest’s real-world freight trial

Tesla has been experimenting with a select group of companies, as well. It partnered with PepsiCo. several years ago, in an effort to launch a pilot program for the Semi. It had excellent results, showing higher efficiency, lower costs, and an exceptional ability to handle long runs.

Drivers have had a lot of positive things to say:

Tesla Semi earns strong reviews from veteran truckers

The Semi will enter mass production next year, but we anticipate that some companies will commit to Uber’s new platform well before then.

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Energy

Tesla recalls Powerwall 2 units in Australia

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(Credit: nathanwoodgc /Instagram)

Tesla will recall Powerwall 2 units in Australia after a handful of property owners reported fires that caused “minor property damage.” The fires were attributed to cells used by Tesla in the Powerwall 2.

Tesla Powerwall is a battery storage unit that retains energy from solar panels and is used by homeowners and businesses to maintain power in the event of an outage. It also helps alleviate the need to rely on the grid, which can help stabilize power locally.

Powerwall owners can also enroll in the Virtual Power Plant (VPP) program, which allows them to sell energy back to the grid, helping to reduce energy bills. Tesla revealed last year that over 100,000 Powerwalls were participating in the program.

Tesla announces 100k Powerwalls are participating in Virtual Power Plants

The Australia Competition and Consumer Commission said in a filing that it received several reports from owners of fires that led to minor damage. The Australian government agency did not disclose the number of units impacted by the recall.

The issue is related to the cells, which Tesla sources from a third-party company.

Anyone whose Powerwall 2 unit is impacted by the recall will be notified through the Tesla app, the company said.

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Cybertruck

Tesla launches Cybertruck orders in a new market with a catch

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Credit: Tesla

Tesla is launching Cybertruck orders in a new market, but there’s a bit of a catch.

The Cybertruck was launched in the Middle East earlier this year, as Tesla launched the ability to place a reservation for the all-electric pickup in the United Arab Emirates. It would be the first market outside of North America that would have the ability to place an order for the Cybertruck.

Tesla confirms Cybertruck will make its way out of North America this year

Other markets where the vehicle has been widely requested, like Europe and Asia, have still not approved the vehicle to be sold to the public, mostly because of size and design restrictions.

However, in the UAE, Tesla is opening up the ability for those who placed reservations for the vehicle to finally put in their order. The Order Configurator is only available to those who have already placed a reservation; it is not yet available to the public.

Tesla said it would open up the public online configurator across the Middle East in the coming weeks:

The UAE is not the only country that will have access to the Cybertruck, as fans in other Middle Eastern countries will also be able to place orders soon. Tesla announced back in April that Saudi Arabia and Qatar would also have Cybertruck deliveries.

These vehicles will be built at Tesla’s Gigafactory Texas plant just outside of Austin, as Gigafactory Berlin and Gigafactory Shanghai, two factories located in the same hemisphere as the Middle East, do not have established lines for Cybertruck production.

As for the other markets, Tesla CEO Elon Musk has hinted that the company could develop a smaller Cybertruck for those markets, as he admitted that in the long term, it likely made sense to build a more compact version for regions where roads are traditionally tighter.

Elon Musk hints at smaller Tesla Cybertruck version down the road

There has been no evidence of Tesla developing this more compact version, but it could eventually happen.

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