1.   Because it will be out of radio contact with Earth throughout the descent, the spacecraft will operate on pre-programmed instructions during the final minutes before landing.

2.   The spacecraft operates mainly on solar-generated electricity.

3.   The spacecraft is operating by commands that were stored in its computer a month ago.

4.   With one remotely controlled spacecraft operating just inches from another at times, the sortie was unprecedented in the annals of human spaceflight.