Ao contrário do Hubble, o JWST não obterá imagens nos comprimentos de onda visíveis, mas apenas em infra-vermelhos.
Também ao contrário do Hubble, não será lançado do Space Shuttle - que em 2013 já deverá estar desactivado - mas da ogiva de um foguetão - o que lhe permitirá também atingir uma órbita (muito) mais elevada.
Teóricamente será capaz de obter imagens de quando o Universo apenas tinha 400 milhões de anos de idade - o que corresponde à sua infância muito precoce, em termos humanos! Com sorte obterá imagens dos primeiros objectos luminosos do Universo!
1 - Espelhos
O JWST é equipado com 18 espelhos hexagonais, de berílio, cada um com 1,29 m de diâmetro. O berílio é mais leve, forte e estável que o vidro. O espelho composto deverá ter metade do peso do espelho do Hubble, mas é 2,5 vezes maior. Cada segmento pode ser orientado em 6 direcções diferentes.
2 - Micro-obturadores
O colector de imagem do JWST tem 62.415 aberturas, cada uma com cerca de 100 x 200 microns de dimensão. Estes poderão captar espetrogramas de 100 galáxias de cada vez. Os obturadores poderão ser abertos independentemente, conforme as galáxias que estejam no campo de visão do JWST.
3 - Dispositivos infra-vermelhos
Existem 4 dispositivos de captação de imagem de muito alta resolução instalados no JWST - semelhantes aos chips das máquinas fotográficas digitais normais. Existe uma camera fotográfica sensível ao espectro próximo do infra-vermelho, um espectrógrafo sensível à mesma gama de comprimentos de onda, uma camera sensível ao meio do espectro infravermelho, e um sensor para orientação de precisão.4 - Pára-Sol
Destina-se a proteger o JWST da luz e radiação infra-vermelha (calor) do Sol, que invalidaria o trabalho deste telescópio. É composto por 5 camadas de alumínio e silício do tamanho de um court de ténis! São necessárias 5 camadas para proteger o JWST de impactos por micro-meteoritos.
O JWST ficará localizado num ponto do espaço designado L2 - o ponto Lagrange 2 - onde a gravidade da Terra e do Sol têm a mesma força. Este ponto é a cerca de 1.500.000 kms de distância da Terra. Qualquer missão de serviço, à semelhança das que ocorreram para o Hubble, será impossível com as tecnologias actuais. O JWST estará 5 vezes mais distante da Terra do que a Lua! Qualquer avaria não será reparável. (Ver actualização abaixo).
Actualização em 3 de Agosto de 2007: A NASA vai adicionar um anel de acoplagem ao JWST, para permitir uma possível missão futura de serviço pelas naves Orion!!!
NASA to add docking ring to Hubble heir
James Webb Space Telescope could accommodate astronauts’ service call
By Brian Berger
Updated: 7:28 p.m. ET May 23, 2007
NASA is adding a docking ring to the James Webb Space Telescope (JWST) just in case a visit by astronauts aboard a future Orion Crew Exploration Vehicle is needed to complete deployment of the multibillion-dollar orbiting observatory. The U.S. space agency made the announcement May 10 during the unveiling of a full-scale model of the JWST on the National Mall here.
Billed as the successor to the Hubble Space Telescope, the JWST is slated to launch in mid-2013. By the time it is fully expanded as it is deployed at a gravitationally stable spot some 1.5 million kilometers from Earth, the spacecraft will be about the length of a tennis court. Building, launching and operating the infrared telescope for 10 years is expected to cost $4.5 billion, making it the most expensive science mission NASA has in development.
"We cannot make the James Webb Space Telescope fully serviceable like the Hubble because that would cost so much money that I don't think this country could afford it," said Edward Weiler, director of NASA Goddard Space Flight Center, the Greenbelt, Md., facility in charge of the Webb telescope. "However, what if you have a bad day when you put this thing a million miles out and everything folds out except for an antenna ... it gets stuck? Or a solar panel doesn't fold out completely, and you say, 'gee, I wish we could send an astronaut just to give it a kick'?"
Weiler said NASA Administrator Mike Griffin asked the James Webb team two years ago to examine whether it was worthwhile to design the telescope to accommodate a visit from Orion.
According to Weiler, it is.
"We are going to design for the James Webb Space Telescope a little ring that the Crew Exploration Vehicle could dock with so if we had a bad day the astronauts could go out to James Webb and do minimal, gross things," he said. "They couldn't replace instruments, they couldn't change out things, but they could fix things that were obviously wrong."
Weiler said it is his hope and expectation that an astronaut service call never proves necessary. That point was seconded by Martin Mohan, the JWST program manager at Redondo Beach, Calif.-based Northrop Grumman Space Technology.
"We are spending a great deal of time in testing to make sure that JWST deploys reliably on orbit," Mohan said. "That is one of the core competencies of Northrop Grumman Space Technology. That was, we believe, one of the factors in our selection. That doesn't mean we take it lightly in any stretch of the imagination."
The decision to add a docking ring to the Webb telescope was news to Griffin. Asked about it May 16, he said: "A year or two ago I asked people if it wouldn't be smart to at least have some capability to dock Orion with James Webb such that if people wanted to service it, they could do so. It only seems to me to make sense to not preclude that. I didn't tell them to do it. So if they are doing it, they must have studied it and come to the conclusion that it is a worthwhile thing to do."
Meanwhile, a NASA review board recently determined that all 10 new technologies key to the success of the JWST are mature enough to move into the detailed engineering phase of the program. Among those new technologies are near-infrared detectors, sunshield materials and lightweight cryogenic mirrors.
"The invention is done more than six years ahead of launch," Mohan said. "That's an unprecedented achievement."
Weiler agreed, saying that Hubble's launch was delayed several years because its enabling technologies were not ready, adding hundreds of millions of dollars to the cost of the project.
Mohan said that thanks to the new technologies, Webb's 6.5-meter mirror will weigh only half of what Hubble's mirror weighs yet will provide nine times as much light-collecting power.
The Ball Aerospace-designed mirror, which is already in fabrication, consists of 18 separate segments that will be unfolded during deployment and held in place by composite structures developed by Minneapolis-based Alliant Techsystems.
Weiler said the JWST has met every budget and technical milestone in the 20 months since NASA restructured the project, delaying its launch two years and adding $1 billion to the life-cycle cost estimate. The project's next major review is slated for March 2008.
As expensive as JWST might seem, Weiler said, when all is said and done it will cost roughly half of what NASA has spent on Hubble — about $7 billion to $8 billion adjusted for inflation and measured according to the same accounting methods that govern Webb.