Managers of the James Webb Space Telescope are relying on innovation in a dozen key materials and assemblies—and the magic of red-shifted light—to bring scientists closer to the Big Bang than they have ever been.
Assurances that their mission plan for the giant infrared telescope will meet the program’s science objectives is allowing the construction of flight hardware in parallel with the drive toward a critical design review next year.
Its 6.5-meter (21-ft.) -dia. primary mirror will distinguish the JWST as the world’s largest orbiting observatory in any wavelength when it begins operations. It also will be the largest infrared (IR) telescope in existence. Launch is penciled in for June 2014, but pressure for more assurance-testing may delay that.
If the launch schedule holds, the telescope’s operations should overlap the final days of NASA’s most famous observatory, the Hubble Space Telescope. “The prospect of Hubble and Webb operating at the same time is very exciting,” says the JWST’s deputy senior project scientist, Jon Gardner, chief of the Goddard Space Flight Center’s Observational Cosmology Laboratory. “Their capabilities are in many ways complementary.”
So are their science teams. More than 7,000 astronomers who have been involved with Hubble over its two decades of service are expected to use Webb, says Gardner. Hubble observes in visible, ultraviolet and near-IR wavelengths (0.1 to 2.5 microns); Webb does so in near- and mid-IR (0.6 to 28 microns). Webb’s resolving power of 0.1 arc-sec. will allow it to see an object the size of a soccer ball 340 mi. away, performance similar to that of Hubble’s 2.4-meter mirror. The difference is that Webb’s IR range will allow it to see objects 10-100 times more faint than Hubble can, opening the door to the Universe’s earliest days.
The Hubble was given an important boost last year when its Widefield Camera 3’s (WFC 3) near-IR instrument was enhanced in its last space shuttle servicing visit. As a result, it has breached the 1-billion-year threshold near the Big Bang that began the Universe 13.7 billion years ago. It is now seeing objects 600-800 million years after that event. The Webb’s greater resolving power in infrared, and that wavelength’s ability to see past dust that obscures light from the Universe’s earliest days, should give astronomers images of events just 250 million years after the Universe was born.
Seeing that far back will reveal clusters of the Universe’s earliest objects as they were being formed, says JWST Senior Project Scientist John Mather, a Nobel Laureate at Goddard. Astronomer Marcia Rieke of the University of Arizona expects to see disks of matter becoming planets around stars.
Observing the physical and chemical properties of planetary systems and their potential for supporting life are among Webb’s major goals. The telescope should be able to see relatively small planets—a few times the size of Earth—that Hubble cannot, says Gardner. But it also will have greater sensitivity to the atmospheres of stars closer to Earth. It even can provide close-ups of planets within the Solar System, so long as they are the duller ones like Mars, not bright Venus or Mercury, which would overpower its optics at so close a range.
The spacecraft will carry four science payloads. A Mid-IR Instrument (MIRI), from a consortium of European countries, the European Space Agency (ESA) and the NASA Jet Propulsion Laboratory, uses three detector arrays that will operate as low as 4K (-452F). They are the only ones employing an active refrigerated system, but it does not rely on a liquid helium bath that would limit its longevity.
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