Musk’s comments came on Wednesday during an appearance at the International Space Station Research and Development Conference. Musk said there will be a “lot of risk associated with Falcon Heavy,” the launch vehicle planned to eventually spearhead SpaceX’s colonization of Mars. While he said the rocket would ultimately “be a great vehicle,” getting there will likely be rocky.

The Falcon Heavy requires the simultaneous ignition of 27 engines, three times as many as the Falcon 9 rocket. Musk said the project has turned out to be more challenging than expected, and that “there’s a lot that could go wrong there.” At least in early test flights, he continued: There is a “real good chance that that vehicle does not make it to orbit. I want to make sure to set expectations accordingly. I hope it makes it far enough away from the pad that it does not cause pad damage – I would consider even that a win, to be honest.”

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Failure, though, is a necessary hurdle in developing the huge vehicle. “This is one of those things that’s really difficult to test on the ground,” said Musk, looking much more energetic than he did at a National Governor’s Association meeting last Saturday. He invited anyone interested to visit Cape Canaveral for the Falcon Heavy’s initial test launch, though there’s currently no date set for that.

“It’s guaranteed to be exciting.”