James Webb telescope a successor to Hubble

March 17th, 2016, Published in Articles: EE Publishers, Articles: EngineerIT


2018 will see another giant telescope venture into Space to study the solar system, enabling scientists understand more about its formation and how Earth became capable of supporting life. Named the James Webb Space Telescope, it will look across vast distances to find the earliest stars and galaxies and study the atmospheres of mysterious worlds orbiting the stars. The observatory will also investigate objects in Earth’s own neighbourhood – planets, moons, comets and asteroids in our solar system.

James Webb

James Webb




The man whose name NASA has chosen to bestow upon the successor to the Hubble Space Telescope is most commonly linked to the Apollo moon programme, not to science. Yet many believe that James E. Webb, who ran the fledgling space agency from February 1961 to October 1968, did more for science than perhaps any other government official and that it is only fitting that the next generation space telescope would be named after him.




Scheduled for launch in 2018, the  James Webb telescope (JWT) will carry four scienctific instruments to take images of and collect information about the physical characteristics and compositions of astronomical objects. Together, these instruments will cover the near- and mid-infrared parts of the spectrum, including wavelengths that are important when looking for water and other clues about the evolution and potential habitability of a planetary system.

The JWT often gets called the replacement for Hubble, but NASA prefers to call it a successor. JWT is the scientific successor to Hubble; its scientific goals were motivated by results from Hubble. Hubble’s science pushed scientists to look to longer wavelengths to “go beyond” what Hubble has already done. In particular, more distant objects are more highly redshifted, and their light is pushed from the UV and optical into the near-infrared. Thus observations of these distant objects (like the first galaxies formed in the universe, for example) requires an infrared telescope.

The other reason that JWT is not a replacement for Hubble is that its capabilities are not identical. It will primarily look at the universe in the infrared, while Hubble studies it primarily at optical and ultraviolet wavelengths (though it has some infrared capability). JWT also has a much bigger mirror than Hubble. This larger light collecting area means that JWT can peer further back into time than Hubble is capable of doing. Hubble is in a very close orbit around the earth, while JWT will be 1,5-million km away at the second Lagrange (L2) point.

From its vantage point of 1,5-million km beyond Earth, the JWT will have a spectacular view of objects in the solar system. It will orbit the sun at a position called the Lagrange point 2, or L2, which will help to keep the telescope’s temperature stable – instability distorts its view – and allows the large sun shield to protect the observatory from the light and heat of the sun and Earth.

Scientists envision using the observatory to monitor the water cycle on Mars, look at weather patterns on Saturn’s moon Titan, and hunt for new rings around the giant planets. Comets could be tracked, and the water and gases they release during their journeys could be mapped. Ices and minerals could be identified on the surfaces of moons, asteroids and distant minor planets, helping researchers better understand the evolution of our solar system.

To observe planets and other bright bodies, scientists will be able to reduce the amount of light by reading out smaller portions of the detectors very rapidly or by filtering out all but a few wavelengths of light. For moving targets, the entire telescope will move, using non-linear tracking to follow objects along curved paths – a more realistic motion that yields better accuracy.

It is estimated that from its orbital position, the JWT telescope could have access to observe nearly three-fourths of the near-Earth object population each year. Nearly all asteroids and comets beyond Mars could be observed, as well as all but the three innermost planets – Mercury, Venus and Earth. The observatory also will be able to see minor planets and other objects beyond Neptune – and even watch them cross in front of nearby stars.

Global studies will be possible, because the JWT will be able to image the entire disk (or face) of many planets, moons and small objects with high resolution. This will help scientists map water, carbon dioxide, methane and other gases, to see how the atmospheres of planets (or moons) change from season to season or when night falls – and to detect sudden plumes of gases that might warrant further investigation. Some investigations could even be detailed enough to look at emissions from individual volcanoes on Jupiter’s moon Io.

Studies like these will help scientists refine their models of how our solar system formed and evolved to support life.

Engineers are seen installing the secondary mirror onto the telescope. Credits: NASA/Chris Gunn

Engineers are seen installing the secondary mirror onto the telescope. Credits: NASA/Chris Gunn

The instruments that will fly aboard NASA’s JWT not only have to be tough enough to survive in the cold of space, but they also have to work properly in the electromagnetic environment on the spacecraft, so they’re tested for both. Recently, they passed a test for the latter in a very unique room.

Stepping inside NASA’s electromagnetic interference or EMI laboratory at NASA’s Goddard Space Flight Centre in Greenbelt, Maryland feels like stepping inside a Lady Gaga music video. Inside this white room where conical structures jut out from the walls, a team of engineers clad in “bunny suits” recently and successfully completed one of the key environmental tests for the integrated science instrument module (ISIM), the science payload of the JWT.

The ISIM can be considered the eyes and ears of the JWT and the purpose of the test was to verify that these eyes and ears will be compatible with the electromagnetic environment on the spacecraft.

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