Enormous and powerful, Asgard motherships were more formidable than Goa'uld ha'tak vessels and were legendary among the Jaffa. They were powered by four neutrino ion generators and were equipped with powerful defensive shields, transport beam technology, sensors, communication systems which included holographic projection, medical systems including stasis pods, as well as a sophisticated cloaking device that enabled them to avoid detection from satellites and telescopes when in orbit around Earth. Most of the ship's systems were controlled by a series of small rounded stones which activated systems as they are moved into position on a control panel. Because the controls were so intuitive, it was possible to pilot a ship almost single-handedly, and often Asgard motherships did not require a large crew for operation.
The Biliskner was Thor's Asgard mothership which SG-1 first witnessed when it appeared above Cimmeria, an Asgard protected world. When the Biliskner became infested by Replicators and sent on a course toward Earth, SG-1 assisted Thor by destroying the deceleration drive, deliberately causing the ship to accelerate out of control and burn up in Earth's atmosphere. The Biliskner crashed into the Pacific Ocean about 400 miles off the coast of California.
The "O'Neill," named for Colonel Jack O'Neill, was the first Asgard ship designed solely to fight the war with the Replicators. Its hull, made of a new naquadah, trinium, and carbon alloy, made it the most advanced technological creation of the Asgard. It was deliberately destroyed in a deception to lure the Replicators away from Thor's homeworld, thus scoring a small victory and giving temporary hope to the Asgard.
Later Asgard motherships were built using a similar but slightly modified design. These motherships were enormously powerful with hyperdrive engines capable of traveling the distance between galaxies in a matter of hours. One such ship was the "Daniel Jackson," named for Dr. Daniel Jackson. Thor piloted this ship to Hala where his mission was to determine that the Replicators had been drawn into a black hole, and his ship was among the fleet of approximately six motherships that engaged in the battle to defend Orilla from the Replicators. Many of the Asgard ships had carried in their computers the stored minds of the Asgard race when they fled their homeworld on Hala and attempted to rebuild their civilization on Orilla.
Often Asgard ships had remained undetected in orbit above Earth, monitoring all hyperspace activity in the vicinity of the planet, and Loki had conducted his unsanctioned experiments on human abductees from his ship in Earth's orbit. The Asgard had also joined Earth as an ally and participated in the battle against the Ori invasion at the supergate. However, as the Asgard race faced extinction due to physiological degeneration, they chose to destroy their homeworld of Orilla, and their massive motherships are presumed to have been annihilated with their world. Their legacy, however, lives on in the technology installed aboard the Odyssey.
Episode Reference: Thor's Chariot, Fair Game, Shades of Grey, Nemesis, Small Victories, Revelations, Prometheus, Unnatural Selection, Fragile Balance, New Order, Reckoning, Camelot, Flesh and Blood, Unending