Tom Godwin 
The Barbarians [PDF ebook] 

In three bloody years, Ragnarok survivors ended the Gern Empire and freed Earth and the Athena colony. But Earthers fear and hate the great strength and speed bred over generations under heavy gravity that won the victory. Now a new threat strikes Ragnarok and the rest of mankind refuses to help.
A nice sequel to the first Ragnarok book, but the characters seem a little dense considering it is obvious who the bad guys are and it takes them half the book to figure it out. It was a quick read though and nice to return to some unique sci-fi perspectives on mankind's future and survival as a species.