What are the names of the two drones that are not lost?
It is implied that, in the future, all plant life on Earth has become extinct. As many specimens as possible have been preserved in a series of  enormous, greenhouse-like geodesic domes, attached to a large spaceship named "Valley Forge", forming part of a fleet of American Airlines space freighters, currently just outside the orbit of Saturn. 
Freeman Lowell, one of four crewmen aboard, is the resident botanist and ecologist who carefully preserves a variety of plants for their eventual return to Earth and the reforestation of the planet. Lowell spends most of his time in the domes, both cultivating the crops and attending to the animal life.
The crew receives orders to jettison and destroy the domes (with nuclear charges) and return the freighters to commercial service. After four of the six domes are jettisoned and blown up Lowell rebels and opts instead to save the plants and animals on his ship. Lowell kills one of his crew-mates who arrives to plant explosives in his favorite dome, and his right leg is seriously injured in the process. He then jettisons and triggers the destruction of one of the remaining domes, trapping and killing the remaining two crewmen.
Enlisting the aid of the ship's three "drones" (service robots), Huey, Dewey and Louie (named after Donald Duck's nephews), Lowell stages a fake premature explosion as a ruse and sends the Valley Forge careening towards Saturn in an attempt to hijack the ship and flee with the last forest dome. He then reprograms the drones to perform surgery on his leg and sets the Valley Forge on a risky course through Saturn's rings. Later, as the ship endures the rough passage, Drone 3 (Louie) is lost, but the ship and its remaining dome emerge relatively undamaged on the other side of the rings.
Lowell and the surviving drones, Huey and Dewey, set out into deep space to maintain the forest. Lowell reprograms Huey and Dewey to plant trees and play poker. Lowell begins speaking to them constantly, as if they are children.
Huey Dewey