Not very. Just enough for a dozen-ish people in close quarters, their research equipment, powerful engines (by civilian standards), sensors, and other essentials. At a guess, maybe 3-4 times the size of a runabout.
If I had the time this would make a nice project, would it be able to land?
I don't know. I depicted it as remaining in orbit. It probably could land if it needed to, but generally wouldn't.
Relevant passages from The Buried Age
While Langford worked to recruit the personnel, Picard saw about hiring a suitable ship. With university backing, he arranged with Centauri III’s leading civilian spacecraft firm to provide a custom vessel, high-powered for maximum warp speed (considerably less than Starfleet’s fastest, but excellent for a civilian ship). Since the crew would be only a dozen or so, life-support needs were reduced, increasing the power available for velocity. The ship would also be sleek and narrow, like the rocketships of old, presenting a minimal cross section to oncoming space debris and radiation and reducing the power requirements for navigational deflection. For a Starfleet vessel, designed with the possibility of combat in mind, such a design was impractical since enemies could approach from any direction. But this craft was built purely for moving forward as fast as possible.
The ship has a "compact bridge -- little more than a cockpit, really." The bridge has a door that can be locked from the inside. There is a "compact science lab" and a "compact lounge" (I sense a theme). I refer to a transporter stage but not a transporter room; given that the transporter gets a good deal of use as an archaeological tool, the transporter stage might be part of the lab facilities. The ceilings aren't especially high, adequate for humans but too low for the taller Caldonian member of the crew.
How big was Cousteau's Calypso
? That might be a good analogy. Hmm, Wikipedia puts it at 42 meters long, 3 decks, with a crew capacity of 27. I don't think Cleo's Needle
needs to be that large, since the crew is half that.
Hmm, thinking it over, I'd guess the Needle
might have two decks -- assuming something roughly cylindrical with room for chambers on either side of a narrow central corridor, two decks seems right for giving it a height comparable to its width. Since it's pretty narrow, a length around 40-45 meters might be about right -- that's a little over twice the length of a runabout, but a runabout's only got one deck (plus the warp core on top).