How were the twin STEREO observatories placed into their respective orbits?
The twin STEREO observatories were launched together aboard a Delta II rocket. To place them into orbit in the most efficient and cost-effective manner possible, STEREO mission designers used lunar gravity to redirect the observatories to their appropriate orbits — something the launch vehicle alone cannot do. For the first three months after launch, the observatories flew an orbit from a point close to Earth to one that extends just beyond the moon. Mission Operations personnel at The Johns Hopkins University Applied Physics Laboratory, in Laurel, Md., synchronized observatory orbits so they encountered the moon about two months after launch, at which time one of them was close enough to use the moon’s gravity to redirect it to an orbit lagging behind Earth. Approximately one month later, the second observatory encountered the moon again and was redirected to its orbit ahead of Earth.
