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Sian Proctor made history in September, when she became the first Black female pilot of a spacecraft during a SpaceX mission — but she won't be flying around on Earth in one of Elon Musk's Teslas.

Sian Proctor

Sian Proctor was ferried to the launch pad in a Tesla Model X. (Joe Raedle/Getty Images)

The geoscientist, who was a member of the all-civilian Inspiration4 crew, revealed on Twitter this week that she'd purchased a Ford Mustang Mach-E, causing many commenters to scratch their heads at the decision.

She explained the choice wasn't meant as a slight at the owner of SpaceX, but mostly due to practical concerns.

"Tesla is a great company & I LOVE SpaceX. But there were many factors to my decision. A year ago I was divorced, broke, & living w/my brother. What a difference a year can make! I’m full of #gratitude for my 1st EV & I believe we are stronger working together toward a better," Proctor wrote.

She added that the lower base price and $7,500 tax credit the Mustang Mach-E qualifies for, along with its availability, sealed the deal.

Sian Proctor

Sian Proctor was a candidate to become a NASA astronaut in 2009. (Eugene Gologursky/Getty Images for TIME Studios and Known)

"The overall feel and ergonomics is important and I loved my test drive but availability, tax credit, and overall final price where the three biggest factors," Proctor tweeted.

"You can only order a new Tesla. There aren’t any in stock."

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Due to its massive sales over the past decade, Tesla has exhausted its allotment of federal tax credits, while Ford has yet to reach the 200,000-vehicle limit that triggers the phase-out of the incentive.

The Tesla Model Y currently starts at $60,190 while the base Ford Mustang Mach-E is $37,495 after the credit is deducted.

Proctor also made it clear that Ford did not give her the car as a promotional stunt.

"I fully purchased it. I’m flattered that everyone thinks someone, Tesla or Ford, would give me a car. Of course I’d totally take it if they did!"

Musk has not yet commented on Proctor's car, but Ford CEO Jim Farley did congratulate her, posting, "Congrats on your new ride, @DrSianProctor! The Space White was a great choice."

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