CNSP

Now that the James Webb Space Telescope (JWSP) has deployed its 21-foot, gold-coated primary mirror, it is in good shape as it heads for the Sun-Earth’s second Lagrange point, known as L2, which is nearly 1 million miles from Earth. However, it will not be the first spacecraft to park in this spot to conduct a scientific mission.

I looked around to get a good inventory of what was operating, and will be operating, at L2 when JWST arrives and found the best listing on Wikipedia. Here is the inventory:

Past missions at L2:

• From 2001 to 2010: NASA’s Wilkinson Microwave Anisotropy Probe (WMAP) observed the cosmic microwave background.
• From 2003 to 2004: NASA’s WIND studied radio waves and plasma that occur in the solar wind and in the Earth’s magnetosphere (now in L1).
• From 2009 to 2013: The European Space Agency’s (ESA) Herschel Space Observatory sifted through star-forming clouds to trace the path by which potentially life-forming molecules, such as water, form.
• From 2009 to 2013: The ESA’s Planck spacecraft observatory mapped the anisotropies of the cosmic microwave background at microwave and infrared frequencies, with high sensitivity and small angular resolution. 
• From 2011 to 2012: Chinese National Space Programs’s Chang’e 2 tested the Chinese tracking and control network (after first serving as a lunar probe).

Current missions at L2:

• Since 2014: The ESA Gaia probe has been measuring the positions, distances and motions of stars, with a mission to construct a 3D space catalog containing approximately 1 billion astronomical objects (stars, planets, comets, asteroids, quasars, and more).
• Since 2019: The joint Russian-German high-energy astrophysics observatory Spektr-RG has been conducting a seven-year X-ray survey, the first in the medium X-ray band less than 10 keV energies, and the first to map an estimated 100,000 galaxy clusters.

Of course, there are future missions planned for L2, and plenty of craft operating in L1, L4, and L5. That will be a story or two for another time.