There seems to be a technical ambiguity in the original, which is going to confuse your translation. In lower frequency radio transmission (such as the HF part of the spectrum), part of the radio wave transmitted hugs the ground and travels close to it, while the other part of it goes off into the atmosphere. These are two components of the wave, and are called the "ground wave" and the "sky wave". The ground wave, in turn, consists of two components: The "surface wave", and the "space wave".

However, from your original it seems that there is some ambiguity as to weather they mean "sky wave" or "space wave" when they say "onda espacial". From the context, it looks like they are talking about "sky wave" yet they said "espacial". Tough call.

See here for a better description:

http://www.tpub.com/content/neets/14182/css/14182_75.htm

and

http://www.tpub.com/content/neets/14182/css/14182_76.htm

Maybe you should go with "space wave", just to be safe, in which case to be technically correct, you would have to translate "onda terrestre" as "surface wave" rather than as "ground wave", since the "space wave" is actually part of the ground wave, and not separate from it.

Do you have more context on the usage of these terms?