Webster spells it "o-r-b-i-t-e-r" and does not even offer "o-r-b-i-t-o-r" as an alternate spelling.
Thinking the Disney app image you posted may have had "o-r" as a typo, I went to the Disneyland website, and sure enough, they spell it "o-r" on the website attraction description as well (and presumably in DLR as well).
But as Westerner points out, as it's a proper noun they can spell it however they like.
It is a curious thing. Thanks for pointing it out.
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