Since it was first proposed [1], it was not a vacuum, and the original paper spends a lot of effort to distinguish a low-pressure tube from a vacuum. The design

Since it was first proposed [1], it was not a vacuum, and the original paper spends a lot of effort to distinguish a low-pressure tube from a vacuum. The design not only is not a vacuum, but relies on it not being a vacuum for propulsion. To be sure, it's extremely low pressure, with a pressure lower than Mars. But it is not a vacuum. [1] http://www.teslamotors.com/sites/default/files/blog_images/hyperloop-alpha.pdf http://www.teslamotors.com/sites/default/files/blog_images/h...