New work in progress, a Dornier design for a space tug, with the option of 2, 4, or 6 aqdditional fuel tanks.
This one is coming together fast!
I found my references on the always excellent ATOMIC ROCKETS web site:
http://www.projectrho.com/public_html/rocket/realdesigns2.php#spacetugdornier
As run by Winchell Chung:
https://twitter.com/nyrath
Nick