Okay, so, I'm possibly insane, but I designed a dog breed for space. This is a draft and incomplete.
[]'s are "margin notes", stuff that doesn't fit in a document's regular flow but should be stated nonetheless.
Size: 20-25 lbs max.
Colors: Varies between white to dark brown.
Age: Typically lives between 13-15 standard years. Maturation rate is similar to other small breeds.
Description: This dog breed, a multi-generational mix of a golden retreiver and a poodle, has been genetically engineered and bred for life aboard orbital habitats, starships, and starbases. Recognized by the Terran Kennel Club as the "Orbital Goldendoodle", or "Orbie", it's been marketed mainly towards Starfleet and Federation Merchant Marine personnel, but has also proven popular among dwellers in orbital habitats and other cramped spaces.
[Yes, yes, the name isn't the most creative, but I tried.

]
Breed traits:
The Orbital Goldendoodle won't eat *anything*, but it can sometimes come close - it's been bred and genetically engineered to accept more than the usual spectrum of dog food, just in case there isn't a replicator handy with which to replicate your dog's favorite brand of kibble.
[Whether it be a dog who only eats premium kibble or who, worse, insists on canned dog food, this eliminates a major issue with keeping pets aboard an orbital habitat or starship - sometimes there just aren't replicators available for human food, let alone dog food, and so food might vary significantly from day to day.]
Unfortunately, this increased acceptance also means that the breed just *loves* to beg for table scraps - a habit most breeders train their dogs out of, but still something to note.
[If it can eat more than just dog food...Well, it'll try to eat more than just dog food.]
Personality-wise, these are easy-going, independent dogs, unflappable and well-suited to being left alone with little more than a warm bed and a chew toy for up to 12 hours at a time. It helps that the Orbital Goldendoodle was bred specifically to be highly trainable - while Starfleet and the Federation Customs Service have not yet been convinced of the need for working dogs, that is a stated goal of the breed designers. Until then, Orbital Goldendoodles are most often pets and therapy dogs aboard orbital habitats, starbases, and starships.
[The way I see it, Starfleet believes, sometimes too much, in its technology. They haven't used working dogs for centuries, despite the fact that you can often train dogs to do initial scans where tech could be foiled. The exceptions would be therapy dogs - I could see that being a big market for dogs, assisting counselors in their therapeutic protocols - and perhaps for police work on planetside installations.]
The Orbie is genetically engineered to be hypoallergenic.
Issues:
While the Orbital Goldendoodle is excellent around people (especially children) of all species, and other pets, it can sometimes be too obedient. Put simply, this dog breed can in rare cases be attacked and just sit there, not reacting, despite being wounded. Most Orbies, though, are instinctively protective if provoked - it just takes a lot to provoke them, one reason they're so beloved by parents of small children.
About 1 percent of Orbies suffers from hip dysplasia - it is uncommon, but closely watched for by breeders and vets.
[Not something they can edit out with genetic engineering, unfortunately; it comes with the Golden Retriever background.]
While the Orbie does well in confined spaces and smaller living environments like starships and apartments, this comes at a cost: Outside of its quarters, it *needs* to be on a leash for all but short periods. Going off-leash is not advised outside of the "den" - Orbies tend to take that as a cue for playtime, and act accordingly, especially as puppies.
A purebred Orbie is rarer, and more expensive, than a cross-breed - the breed has only been recognized since the 2370s, and so many breeders keep their purebreds for breeding stock. Purebred puppies are available on the open market, but almost never un-neutered.