The dual space telescopes were headed toward a spot called L2 -- the second Lagrange point -- where they will operate in different orbits.
"L2 is a local gravitational point that is fixed in the Earth-sun system and is situated on Earth's night side," the ESA said. "It is an excellent location for both Herschel and Planck; it allows them to shield their sensitive instruments from solar radiation which may otherwise disturb observations and offers good sky visibility."
ESA officials said Herschel's orbit will be approximately 500,000 miles from L2. The final orbit for Planck will be an orbit about 250,000 miles from the same point.
Herschel, a far infrared telescope, is the first space observatory to cover the full far infrared and sub-millimeter wavebands, scientists said, and its mirror is the largest to be launched into space. The satellite is named for British astronomer Frederick William Herschel, who died in 1822. Among other things, Herschel discovered Uranus and infrared radiation.
Planck is named for German physicist and Nobel Prize winner Max Planck, who died in 1947 and who is considered the founder of quantum theory, Wikipedia said. The observatory is designed to make the most precise measurements yet of light at microwave wavelengths.