The Staff Report by Songbird is a bit misleading because it implies that the original Bowie song was an album track. The song, which was always called “Space Oddity,” was a huge hit single in the U.K. in 1969. (My memory says it got to number 1; Wiki says it got to number 5 in the U.K. charts, but as several different charts were in use in the U.K. at that time, we might both be right. In any case, it was a big hit in an era when singles chart hits mattered.)
Although it was on his album, I do not think the album itself sold well at the time (none of the other songs sounded anything like “Space Oddity,” or, indeed, like his later work). In fact, Bowie basically sank back into obscurity for about the next 3 years. Then, in 1972 he made a major comeback and established himself as a big star, and his new fans started buying up his older, previously obscure, records. At that time the original album with “Space Oddity” on it (initially called David Bowie in the U.K. and Man of Words/Man of Music in the U.S., where not even the single had been a real hit) was reissued under the title Space Oddity, presumably because many people still would have remembered the 1969 hit single.
I have always assumed that “Major Tom” was just intended as a generic astronaut name.
I never quite got why the press were so interested in his shirts.