What does "brainchild" in the paragrapth 4 mean

A．It is a 3-ft. metal pod.
B．It has eight 35-ft. metallic wings.
C．It can fly an altitude above 260 miles.
D．When it flies back to Earth, it will fall into pieces.

A．Most scientists are confident that the spacecraft will work well.
B．A more ambitious orbital flight will follow this mission.
C．The author is quite sure that this mission will make impossible technologies seem possible.
D．The key of the engineering of Cosmos I is building wings that can open and pivot.