Grail consists of two identical spacecraft that were launched side by side on a rocket on Sept. 10.

Twenty-five years ago, in the late summer of 1977, two identical spacecraft took off on missions of exploration deep into the outer solar system.

The two identical spacecraft are in polar orbits about 130 miles apart.

Mariner 3 and Mariner 4 were identical spacecraft designed to carry out the first flybys of Mars.

An almost identical spacecraft with different instruments might be launched in l996 for a four-year stay around Saturn and its moons.

The probes were identical spacecraft, each consisting of an orbiter and an attached lander.

Of course, the two identical spacecraft could choose different trajectories and targets.

The mission is composed of four identical spacecraft flying in a tetrahedral formation.

Two identical spacecraft were launched into orbits that cause them to (respectively) pull further ahead of and fall gradually behind the Earth.

It is trailed by Voyager 2, an identical spacecraft launched on a different path in the same year, 1977.