This Would Be A Perfect Add-On...

[zakueins]

Found this on Flickr...

http://www.flickr.com/photos/bricklovinfreakboy/2379990199/

A perfect little ship to dock at the ISS and fly around...

 

[Eagle]

Is that just a random lego model, or is it based on anything?

(Assuming we're making this ship up)How big do you want it?

EDIT: Also, how much delta v does it need?/How sci-fi or realistic should it be?

 

[zakueins]

Random LEGO model, assuming each stud is about 3m wide, the ship is about 48 meters (150 feet or so) long, and 18 meters in radius. Docking clamp in the bow (under a retractable plate perhaps).

The drive is a D/T fusion engine or a "superscience" fusion torch with gears. I'd say it's a "semi-hard" space opera-ish design. It has enough fuel to do a Earth/moon run and back (assuming a two-day trajectory) and have about five minutes of full thrust in combat. Say 3 Gs with full tanks top acceleration.

This guy has some other awesome ship desgins-

Microspace ships (small designs for inspiration!)
Ships And Station (perfect design for a Moon-orbiting station, I think...)
A Vaguely Soviet Warship (probably about 350m long or so, with gravity arms that are 40 m or so long...has the range to do Earth to Mars and back again, and still fight.)
A "FTL Test Ship" (it's probably a freighter in the whole 500-750 m length, with enough cargo clamps that you could probably mount twelve XR-5s on the external clamps and still have space to mount droppable cargo pods to a Mars or Titan colony).

Is that just a random lego model, or is it based on anything?

(Assuming we're making this ship up)How big do you want it?

EDIT: Also, how much delta v does it need?/How sci-fi or realistic should it be?