Space Cryogenics

摘要

The European Space Agency has launched an ambi tious effort to explore the infrared universe, in particular the cosmic microwave background. It will launch two spacecraft, Planck and Herschel, on a single Ariane 5 launch vehicle in July 2008. Planck will conduct an all-sky survey, but will not point to a specific object, Herschel will be a true observatory, able to look at any specific target. Each will be sent to a looping orbit around the Lagrangian point L2 which is about 150 million kilometers outside Earth's orbit on the earth-sun line. At L2, the inward pull of the earth and sun just balance the centripetal force of the motion around the sun.