I believe our debt is backed by real estate and our 401Ks.
It wouldn't surprise me if someday the US does grant China or some other major debtor drilling rights in Alaska, maybe even in the ANWR which Dims have prevented us from exploring and drilling for years. Or other mineral rights in some area of the US.
There won't be any other way to pay the debt unless the gov't stops continually growing it and begins reducing it.