Hubble: ๐Hello, my instrument is broken and I am calling for an on-site repair.
๐ฉโ๐ป: Are you still under warranty?
Hubble: Although I'm already 31, your company offered a "lifetime warranty" to me.
๐ฉโ๐ป: Got it. Let me check the address with you first.
Hubble: I'm in low-Earth orbit, at an altitude of approximately 547 km.
๐ฉโ๐ป: No problem, please expect a repairer ๐จ๐ปโ๐ right at your place tomorrow.
Webb: ๐Hello, do you offer door-to-door repair service?
Webb: Of course. I was in position on 24 Jan, it's less than a month ago.
๐ฉโ๐ป: I see. Let me check the address with you first.
Webb: I'm living at the 2nd Lagrangian point that is located 1.5 million km from the Earth.
๐ฉโ๐ป: eh...I'm sorry, your residence is out of our service areaโฆ
Webb: oh, it's not that far actually, let me tell you the way to get hereโฆ
The "Lagrangian point", named after the mathematician Joseph-Louis Lagrange, is a special location where the gravitational forces of the celestial bodies cancel each other out. Taking the Sun-Earth system as an example, there are five Lagrangian points. Satellites or space telescopes could orbit around the Lagrangian points and they only need a small amount of fuel to stay in their oribits for long-term missions. Observatories currently operating at the Lagrangian points include the Solar Heliospheric Observatory (SOHO), the Gaia probe and the Solar TErrestrial RElations Observatory A (STEREO A), etc.
The Webb Space Telescope (Webb) is currently orbiting the second Lagrangian point (L2) while following the Earth to revolve around the Sun at the same time. L2 is on the same side of the Sun as the Earth and the Moon. Therefore, by placing the Webb at L2, its sunshields just need to remain facing the Sun at all times to protect it from sunlight and infrared from the Earth and the Moon. (as shown in the video; video credit: NASA's Goddard Space Flight Center)
๐ฉโ๐ป: Hmm...I understand that L2 is an ideal location to stay. But we cannot provide you with an onsite maintenance service technically.
Webb: What! I worth tens of billions of US dollars!?
Although we cannot provide "door-to-door repair service" for Webb, there is no need to worry as Webb has successfully accomplished a series of intricate deployment steps since its launch. Also, it recently has sent us the first sets of photos captured by its infrared camera recently, showing us starlight collected by its 18 mirror segments.
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