Why Hephaesteus though?
I mean, yeah Hephaesteus Polymetis ("Hephaesteus of the many devices", an epithet praising the god's ingenuity in crafting almost all mythical weapons and armor in the greek myths), but Hephaesteus is also describes as "hobbled" (some text going so far as describing the god as differently abled) --- and there is the whole things with his marriage to Aphrodite, which is, well, a long line of adultery and abuse (which one to highlight in their relationship tends to be up to the author).
Esspecially the last two ones don't quite seem to fit with the "emancipation from planetary life"-ideology of the GEF.
There are a few other mythological personages that would fit to be the namesake with a better association:
Aegir from Norse mythology could be good fit as the (possibly) giant who personifies the sea and is a frequent host to feast in which the gods of Norse myth do their things -- which would speak to the communal use-aspect of the ship.
Another Norse mythology candidate would be Njord, for his association with fishing and seafearing, his role in many myths to give treasures and boons to those who petition him, as well as his status as one of the gods that would survive Ragnarök -- the last one speaking to the idea that the emancipation-ideology of the GEF views planetary living as unsustainable.
Hermes/Mecury (god of roads, travel and commerce) and Poseidon/Neptune (god ruling over the sea and all its aspects) are already taken in FS. But there is Nereus, aka Proteus, a wise, shapeshifting and primoridial being associated with the sea, often referred to as the "Old Man of the Sea", which is said to know of future events.
And of course if you are not shy of a little cultural appropriation, the cultures of the South Pacific Islands have an number of prominent deities and mythological figures associated with the sea and seafearing. One that comes to mind that would work with the aspect of the GEF and relationship with comets would be Paikea - the assumed name of the Maori ancestor Kahutia-te-rangi after he was rescued from drowning by a whale after invoking Tangaroa for help.