I'm not sure, but I think some of the later ships have impossible dimensions for the amount of internals they're supposed to have.
Without knowing how big the internals are, it's very hard to say - and part of the problem is that the little information we have is extremely inconsistent - but no, not really. Elite Dangerous ships start off excessively large and get a lot bigger.
Cargo pods: cargo pods are roughly 2 cubic metres in size, so even a size 8 internal only takes up 512 cubic metres (let's double that if you want space between them for arbitrary retrieval and storage) which fits inside a Sidewinder, never mind a T-9 or Cutter. On the "cargo pod" metric every ship is massively larger than it needs to be for its optional internals (and core internals can be any size to make things work, other than the fuel tank which must be at
most as big as the optional internal of the same size)
Passenger cabins: at economy class you can store 1 passenger for every two cargo pods, and we've already been generous on the cargo pod space
SRVs: the size 2 SRV bay has the worst (implied) volume ratio, so a size 2 internal must be at least as big as a (folded) SRV. Fitting two of those inside an Eagle is a bit optimistic, especially if the Eagle's size 3 internal is twice as big again. This implies a size 2 internal is at least 48 cubic metres - around 8-16 times the size of the cargo pod estimate.
SLFs: the size 6 SLF bay packs in the most SLFs if you assume internals double in size each time at 16 SLFs. This is handwaved somewhat by SLFs being made of expanded polystyrene and therefore possible to store "as raw materials" in much less space, but it still needs room for the two active ones plus a bit more. This implies a size 5 internal is probably at least 400 cubic metres - around 5-10 times the estimate from the "cargo pod" measure. [2]
Based on that the minimum volume of each optional non-military internal would be:
1: 8 cubic metres (cargo rack)
2: 48 cubic metres (SRV bay)
3:
also 48 cubic metres (SRV bay)
4: 96 cubic metres (double SRV bay)
5: ~400 cubic metres (SLF bay) ... or 128 cubic metres (cargo rack) on a non-fighter-capable ship
6: ~800 cubic metres (double SLF bay)
7: maybe a little above 800 cubic metres (double SLF bay with more rebuild storage)
8: 1024 cubic metres (cargo rack)
(higher class internals aren't necessarily
bigger because the one thing that does double each time is cargo, and the SRV/SLF constraints often keep ahead of that anyway - they might just be better reinforced or have more power/data/fluid connections)
At the larger sizes, these are incredibly small and should fit with ease: the T-9's bounding box is 450,000 cubic metres and it fills most of it; the Asp's bounding box is around 55,000 cubic metres and it has plenty of room even taking up less than half of it.
The smaller ships start to have more problems but are still doing pretty well...
- the Keelback is the smallest where SLF sizes are a concern; it has a bounding box of around 30,000 cubic metres and fills most of it, so both its size 5 optionals can be big enough to be SLF-capable
- the Eagle and Sidewinder can both fit SRVs. The Sidewinder's bounding box is 1700 cubic metres and it occupies about half of that, the Eagle's is quite a bit bigger at 6500 cubic metres but it really doesn't take up very much of it. Either way, they can both spare 48 cubic metres per size 2+ internal though you might have to be a little careful with placing.
The main problem potentially comes with a lot of these spaces being implausibly
large in themselves for anything except their constraining fitting - the size 5 optional is 400 cubic metres, so in cargo rack configuration the cargo itself takes up just 64 cubic metres and surely
someone would have decided by now that putting each cargo pod on its own pedestal surrounded by fountains and statues and landscaped gardens was a little inefficient even if it does look nice in the brochures. In Economy Class passenger configuration this massive space - about the size of a terraced house! - holds just 16 people. And
even then, it's taking up so little of a Beluga's internal volume (approaching a million cubic metres! [3]) that the challenge for the passengers won't be getting comfortable once they're on board but
finding it in the first place.
The scales - as with
everything in ED smaller than a planet - are incredibly arbitrary and Frontier may well wish not to draw further attention to this with a detailed interiors representation, but physically fitting things into the available space won't be the problem.
[1] For comparison, a modern London Underground carriage has a bounding box of roughly 128 cubic metres and can carry 32 seated passengers and about 100 standing, so an Economy passenger cabin is basically one of those with only the seated passengers - quite a lot of spare space even for the cargo-constrained internals!
[2] Even if you throw out the "3-D printed" handwave and assume all SLFs are stored full-size but maybe slightly folded, by the time you get up to ships which can carry SLFs you're at ships big enough to hold them anyway. It just makes the 5+ optional internals even more ridiculously huge for anything not a SLF.
[3] Again for comparison, the largest 21st century ocean cruise ships might also have a volume approaching a million cubic metres. The ocean ship carries perhaps 5000 passengers in private 2-person rooms (plus all the other facilities outside their rooms), while the Beluga maxes out at 184 in Economy class (or just 40 in Luxury class).
