For an example of effective Internet access for the very patient, google the term "pskmail".  With bandwidths that are exponents of 31.25, (31.25,62.5,125,250,500 and 1000 Htz) and practial after-error-correction data rates that are very close to those numbers; the spectral efficiency of PSK on shortwave is very close to 1:1.  Which is excellent for anything that bounces off a kilometers thick refractor, normally called the ionosphere.  The range using relatively affordable equipment is uncontested at normal power levels.  Could this be used to datacast the blockchain? No.  Could this be used to broadcast locally generated transactions?  Yes.  Could this be used to broadcast requests for missed blocks?  Yes.