GODDARD SPACE FLIGHT CENTER, MD — The James Webb Space Telescope (JWST) is NASA’s top priority science mission launching in this decade and will have the capability to “look back towards the very first objects that formed after the Big Bang,” said Dr. John Mather, NASA’s Nobel Prize Winning scientist, in an exclusive interview with AmericaSpace at NASA Goddard.
The mammoth JWST is currently under construction in the world’s largest clean room at NASA’s Goddard Space Flight Center in Greenbelt, Md., where AmericaSpace spoke with Dr. John Mather, who serves as the telescopes Senior Project Scientist for NASA, and other top managers during an onsite visit to key Goddard facilities overseeing the assembly and testing of Webb’s telescope components.
Mather received the Nobel Prize in Physics in 2006 for his work on NASA’s Cosmic Background Explorer Satellite (COBE) along with George Smoot, “for their discovery of the blackbody form and anisotropy of the cosmic microwave background radiation,” according to the Nobel citation. COBE was launched in 1989.
NASA has overall responsibility for JWST, which is a joint international collaborative project between NASA, ESA (European Space Agency), and CSA (Canadian Space Agency), comprising more than 17 countries.
NASA Goddard Space Flight Center provides overall management, systems engineering, and the ISIM science module. Northrop Grumman is the prime contractor.
After many delays and cost overruns, the huge telescope is on track to launch in October 2018 atop an ESA Ariane V ECA rocket from the Guiana Space Center in Kourou, French Guiana.
The JWST is the successor telescope to the hugely successful NASA/ESA Hubble Space Telescope (HST) launched aboard NASA’s Space Shuttle Discovery over 24 years ago in 1990 and the Spitzer Space Telescope launched by a Delta II in 2003.
Webb is designed to look at the first light of the Universe and will be able to peer back in time to when the first stars and first galaxies were forming. It will also study the formation and evolution of planetary systems and investigate their potential for supporting life.
To accomplish its objectives, Webb is focused on different wavelengths compared to Hubble.
Whereas Hubble was optimized for visible light, Webb is optimized for infrared light covering wavelengths from 0.6 to 28.5 microns.
What can the James Webb Space Telescope (JWST) do that Hubble and Spitzer cannot do? What’s the advantage? I asked Mather.
“First, James Webb can see farther in space and time. So it can look back towards the very first objects that formed after the Big Bang,” Mather told me.
“Second, it can see inside dust clouds where stars and planets are being born today.”
“Third, it can see things that are cold—like room temperature compared to stars. So it can pick up all kinds of things that are invisible to the Hubble telescope. And also that cannot be observed from the ground because the atmosphere of the Earth blocks the signals or it radiates infrared itself.”
“So all that plus JWST also being much bigger. The bigger part means that we’ll get a much sharper image. So it can see a lot farther.”
Spitzer can also see into the dust clouds. So what’s the difference, is it resolution? I asked.
“Yes, the resolution is much better and matters a lot there,” Mather replied.
“Spitzers pictures are blurry by comparison with what Hubble can get or what JWST can get.”
“So there is a whole lot more detail available with the bigger Webb telescope.”
Is it an order of magnitude different? I inquired.
“Yes, at least an order of magnitude better. There is far more spatial resolution [with Webb],” Mather said
Here’s some background comparing JWST and HST to explain Webb’s vastly improved capabilities.
Webb is outfitted with a segmented 6.5-meter (21 ft 4 in) diameter aperture primary mirror. It’s the largest mirror ever placed in space and weighs 705 kg.
Hubble’s single mirror measures only 2.4 m (7.9 ft) and was limited in size to fit inside the space shuttle cargo bay. The world famous telescope was deployed in 1990 by a crew that included current NASA Administrator Charles Bolden and designed to be serviced by shuttle astronauts.
Altogether there were five follow on shuttle servicing missions that swapped out science instruments, solar panels, gyroscopes, the computer, and more. The last flight was STS-125, which took place in 2009 and included John Grunsfeld as lead spacewalker. Grunsfeld is now NASA Associate Administrator for the Science Mission Directorate.
These servicing missions significantly upgraded Hubble’s capabilities and have kept it alive and producing cutting edge research far beyond its original design lifetime.
However, Webb can’t be upgraded by astronaut crews.
“JWST is not designed to be serviced,” Mather stated. “Our job is to make sure it works. We have two of everything. So it’s practice, practice, practice.”
So, Webb’s mirror is 6.25 times larger than Hubble’s and collects about six times more light than HST.
Despite Webb’s larger mirror, its mass of 6,500 kg (14,300 lb) is just over half that of HST because of advances in lightweight technology.
But the 6.5-meter-wide mirror had to be built from segments because it must be folded into a stacked configuration for launch in order to fit inside a small Ariane V rocket sporting a payload fairing only five meters in diameter.
“It’s a bit like designing a ship in a bottle,” JWST scientists have said about the requirement to fold and pack the mirrors and the even larger tennis court-sized sun-shield inside the rocket’s much narrower fairing.
Indeed Webb’s primary mirror is comprised of 18 individual hexagonal segments and configured into a nearly circular arrangement.
The hexagonal shaped mirrors are all made of beryllium and are gold coated. Each one is 1.3 meters (4.3 feet) in diameter and weighs about 20 kg (46 pounds). Hubble’s mirror is aluminum coated.
“They will be assembled here at Goddard [onto the backplane structure], then shipped to Johnson Space Center,” Mather explained. Optical testing will be conducted at JSC.
Each mirror is equipped with seven computer controlled actuators to allow the individual mirror segments to work together in unison. The actuators were designed to move the mirrors by only a tiny amount of 5-6 nanometers. A human hair is 100,000 nanometers thick by comparison.
Once in space , Webb’s solar array will be deployed immediately followed by the high gain antenna two hours later. Thrusters will fire to start the journey to place it into orbit around the Sun almost a million miles (1.5 million Km) from Earth at a position called L2—the second Sun-Earth Lagrange point.
By contrast, Hubble is in low-Earth orbit soaring at an altitude of just 350 miles (570 km) above Earth, making it easily accessible to shuttle astronaut repair crews.
During the journey to L2, the mirrors, sunshield, and everything else about JWST will then be unfolded in a carefully choreographed and highly complex sequence lasting about six months, including science instrument calibration.
After mirror deployment, engineers will spend about two months to align the 18 segments of the primary mirror to the proper curvature.
The tennis court-sized sunshade will unfurl in steps and passively cool the telescope and its instruments via permanent shade to approximately 45 kelvins, -380 degrees F, -233 C. The extreme cold is required for the telescope to function in the infrared (IR) wavelengths and detect distant objects. Hubble is not cooled.
IR is needed to detect starlight emanating from newly forming stars and planets in our galaxy that are hidden behind dense dust clouds and obscured from view in visible light.
Routine JWST science operations are scheduled to begin about six months after launch.
One of Webb’s primary goals now relates to its abilities regarding planetary detection. Initially, when JWST was conceived, it was thought that it would not be possible to detect planets, is that right? I asked.
“Well we didn’t plan for Webb to look for planets,” Mather told me.
“We didn’t design it for that. But now we can use it for that [looking for planets]. We had to learn how to run it.”
In part two of our discussion with Dr. John Mather we’ll focus more on JWST’s mission to detect planets and investigate their atmospheres.
And we’ll detail how the combined science suite of JWST’s four state-of-the-art instruments is currently undergoing critical testing at Goddard.
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