Are you aware of the use of Lagrange points for the James Web Space Telescope

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Offline Alan McDougall

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As an amateur astronomer I of course knew about the five Lagrange points of stability that exist between the earth and moon , but never though I would see the day when these were to be used as a practical solution such as for the James Web telescope to by launched into orbit in a few years if all things go smoothly

(My Comment Alan McDougall)

The James Webb Space Telescope is an infrared-detecting observatory that will soar through space at the Second Sun-Earth Lagrange Point, an orbit far beyond Earth's Moon. Webb's giant sunshield will protect it from stray heat and light, while its large mirror enables it to effectively capture infrared light, bringing us the clearest picture ever of objects that emit this invisible radiation early galaxies, just-forming stars, clouds of gas and dust, and much more.

Webb has an ambitious design that tackles the two main challenges for an infrared telescope: it has to have a large mirror, in order to best capture the long infrared wavelength; and it has to be kept cold, in order to keep unwanted sources of infrared from interfering with the emissions it attempts to detect.


Lagrange points, named after their discoverer, Joseph Louis Lagrange, are five special points around two orbiting bodies where gravity allows a third, smaller body to orbit at a fixed distance from the larger bodies. In our case, these two bodies are the Sun and the Earth. The Webb telescope is being sent to one of these stable orbital points via rocket.

Webb's planners have several good reasons for this choice. At the Second Lagrange Point L2), 940,000 miles (1.5 million km) from Earth, the telescope will be able to keep its tennis court-sized sunshield between its sensitive equipment and the Earth, Sun and Moon, yet remain in an orbit that makes operations and communications easy. Just as important, Earth won't obstruct the telescope's view.

Although an L2 orbit offers several advantages, the most important is its location out beyond Earth. Warm objects emit infrared light in great amounts. That means the infrared detectors in Webb's instruments must operate at very cold temperatures (about -375 degrees Fahrenheit, or 40 Kelvin or -233.3 degrees Celsius). Without cooling, these instruments wouldn't be able to see beyond the radiation they generate on their own. Webb would be unable to carry enough of its own coolant and fit inside its rocket, so a cold orbit around the Sun offers an ideal solution.


At this distant orbit, the Webb telescope is too far from Earth to have the protection of our planet's magnetic field, which blocks high-energy cosmic rays. Cosmic rays can interfere with the telescope's signals or even build up electrical charges that can create the equivalent of small lightning strikes on the telescope. Such sparks can hurt sensitive equipment or damage the telescope's materials. Webb has been engineered to take this into account, with extra shielding for detectors and conduction areas in the sunshield to prevent voltages from accumulating.

Webb doesn't look like your typical telescope. This is because it's not enclosed in a tube or dome. Telescopes that see primarily visible light, like Hubble, use tubes to keep stray light from entering their instruments. But Webb's infrared detectors have to be protected primarily from heat sources, so it uses an open design that allows heat to dissipate easily into space. Webb's sunshield, which unfurls after Webb is released from its rocket, consists of five layers of a heat-resistant material called silicon-coated Kapton. Each layer further deflects any heat or light that penetrates the previous layers.

« Last Edit: 14/07/2016 04:29:03 by evan_au »
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Offline evan_au

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Quote from: Alan McDougal
Are you aware of the use of Lagrange points for the James Web Space Telescope?
It won't be the first space probe to utilize the Lagrange points.

The Lagrange point between the Earth and Sun is very useful for studying the Sun and solar winds (eg the SOHO probe).

In this case, they don't position the space probe exactly at the Lagrangian point, since the Sun's powerful microwave emissions would drown out the signals from the space probe. Instead they place the probe in an orbit around the Lagrangian point, so that a large satellite dish can separate the space probe signals from the wideband noise produced by the disk of the Sun.

See the list at: