Toro Rosso owner Red Bull has signed the New Zealander and Le Mans winner to replace Pierre Gasly this weekend, as the Frenchman is racing in Japan.
Hartley, a former Red Bull reserve driver who has never raced in F1, admits he is studying hard.
“I was given instructions for the car which is 50 pages,” he told Newstalk ZB radio.
“I will have four hours of practice before qualifying and I’d like to think it’s enough to get the speed I need,” Hartley, 27, added.
Hartley thinks he was selected by Red Bull because of his success in the top Le Mans category LMP1, where he is a top driver for Porsche.
“If we talk about laptime, the difference is not so great — around 7 to 8 seconds,” he said.
“That is not so much, especially in the race.
“I drive very fast cars, so I think Red Bull invited me partly for this reason but also because WEC cars are very technically complex. We use hybrid technologies, so in this regard it is similar to formula one.
“But it’s a big step for me, because six or seven years have passed since I drove open wheel cars. But I try to look at things simply as well,” Hartley said.
“It’s a racing car, it has four wheels, and for a driver to go fast you have all the same physical laws. So in principle it’s similar,” he added.
There is speculation Hartley’s appearance in Austin will not actually be a one off, as he could be asked to return for the final three races of 2017 in the place of Russian Daniil Kvyat.
“It’s only by seeing him over the course of two to three weekends at least that they will build up a real picture of what a talent Brendon Hartley really is,” former F1 figure Mark Gallagher told Newshub.