Ok, let's assume (that means making an ass of u and me)
The Galaxy is as big as the free trader, 85m.
Based on that I measured the pixel sizes and came to the following values:
Length: 85m
Width: 61m
Height: 30m
Based on that the big cargo door in the back is 5 meters high and 4 meters wide. Interesting fact: That numbers are not much rounded. Which is quite nice.
****************************************
I also assumed based on what we see in the picture I posted earlier that the Galaxy is roughly double the length of the Centurion, that makes the Centurion 40 m long. That's longer than a Raptor or a Broadsword but still somewhere in the heavy fighter category. The rest of the values is based on that:
Length: 40m
Width: 31m
Height: 12m
So the cockpit glass we see is 2.8 meters long. That still sounds plausible I think, although this fighter is now almost as big as a Broadsword.
*****************************************
The Tarsus: It looks smaller as the Centurion at first glance but I assumed it is as long. So 40 meters.
Based on that here are the sizes:
Length: 40m
Width: 12,5m
Height: 12m (14 with radar dish)
So the main cockpit window is 1.2 meters high and 4.2 meters wide. Doesn't sound that bad IMHO
********************************************
The Orion:
The windowed part of its cockpit is roughly as wide as that of the Galaxy in the ship trader picture posted earlier. The one of the Galaxy is 12 meters wide. Now I transferred that to the Orion and got the follwing values:
Length: 63m
Width: 57m
Height: 33m (38m with radar dish)
So the cargo door is 9.55 meters wide and 8.3 meters high.
*******************************************
Now let's look at the cargo capacity:
Because of its shape and huge reactors for weapons the Centurion carries only 50 units of Cargo although it is as long and as high as the Tarsus. But look at it: The Tarsus is blockier and the height and length of the Centurion originate in the engines and the long front fuselage which isn't very wide. Also the Centurion's long front part contains the radar so no cargo space there. After all I don't wonder why the Tarsus can carry much more cargo.
The Orion is another thing though. It looks quite big. But much of its size is actually the really big engines and that strange part between the cockpit and the rest of the ship. I can't imagine that a lot of cargo can be stored there. Still I wonder why it doesn't have gretar capacity than the Tarsus since it is a bit bigger.
EDIT: And while it is smaller than the Galaxy it has a bigger cargo door. So pilots flying the orion might specialize on bigger single parts that can't be unassembled. while the Galaxy can store much more overall, but not in such large containers
The Galaxy is big. It also has big engines but you can see at first glance that the area to store the cargo is much better shaped. I think it is clear why it has so much capacity.
If I ever get my lazy *** into my chair and start modeling with Blender again I will use those values I think. They don't seem completely out of place (a few meters give or take) and the Centurion would still be able to land on a carrier. So everything I would like to have is there.