Engineers conduct an “acceptance” of the James Webb Space Telescope’s mid-infrared instrument at NASA’s Goddard Space Flight Center after departing from the UK.
JPL flight technicians Johnny Melendez (right) and Joe Mora inspect the MIRI cryocooler before shipping it to Northrop Grumman in Redondo Beach, California.There, the cooler is attached to the body of the Webb telescope.
This part of the MIRI instrument, seen at Appleton Laboratory in Rutherford, UK, contains infrared detectors.The cryocooler is located away from the detector because it operates at a higher temperature.A tube carrying cold helium connects the two sections.
MIRI (left) sits on a balance beam at Northrop Grumman in Redondo Beach as engineers prepare to use an overhead crane to attach it to the Integrated Scientific Instrument Module (ISIM).The ISIM is Webb’s core, the four science instruments that house the telescope.
Before the MIRI instrument — one of the four science instruments on the observatory — can operate, it must be cooled to nearly the coldest temperature that matter can reach.
NASA’s James Webb Space Telescope, scheduled to launch on December 24, is the largest space observatory in history, and it has an equally daunting task: collecting infrared light from far-flung corners of the universe, allowing scientists to probe the structure and origins of the universe .Our universe and our place in it.
Many cosmic objects — including stars and planets, and the gas and dust from which they form — emit infrared light, sometimes called thermal radiation.But so are most other warm objects, like toasters, humans, and electronics.That means Webb’s four infrared instruments can detect their own infrared light.To reduce these emissions, the instrument must be very cold—about 40 Kelvin, or minus 388 degrees Fahrenheit (minus 233 degrees Celsius).But to function properly, the detectors inside the mid-infrared instrument, or MIRI, must get colder: below 7 Kelvin (minus 448 degrees Fahrenheit, or minus 266 degrees Celsius).
That’s just a few degrees above absolute zero (0 Kelvin) – the coldest temperature theoretically possible, although it’s never physically reachable because it represents the complete absence of any heat.(However, MIRI is not the coldest imaging instrument operating in space.)
Temperature is essentially a measure of how fast atoms are moving, and in addition to detecting their own infrared light, Webb detectors can be triggered by their own thermal vibrations.MIRI detects light in a lower energy range than the other three instruments.As a result, its detectors are more sensitive to thermal vibrations.These unwanted signals are what astronomers call “noise,” and they can overwhelm the faint signals Webb is trying to detect.
After launch, Webb will deploy a tennis-court-sized visor that shields MIRI and other instruments from the sun’s heat, allowing them to cool passively.Starting about 77 days after launch, MIRI’s cryocooler will take 19 days to reduce the temperature of the instrument’s detectors to below 7 Kelvin.
“It’s relatively easy to cool things down to that temperature on Earth, often for scientific or industrial applications,” said Konstantin Penanen, a cryocooler expert at NASA’s Jet Propulsion Laboratory in Southern California. , which manages the MIRI instrument for NASA.”But those Earth-based systems are very bulky and energy inefficient. For a space observatory, we need a cooler that is physically compact, energy efficient, and it has to be highly reliable because we can’t go out and fix it. So these are the challenges we face. , in that regard, I would say MIRI cryocoolers are definitely at the forefront.”
One of Webb’s scientific goals is to study the properties of the first stars that formed in the universe.Webb’s near-infrared camera or NIRCam instrument will be able to detect these extremely distant objects, and MIRI will help scientists confirm that these faint sources of light are clusters of first-generation stars, rather than second-generation stars that formed later in a galaxy evolution.
By looking at dust clouds that are thicker than near-infrared instruments, MIRI will reveal the birthplaces of stars.It will also detect molecules commonly found on Earth — such as water, carbon dioxide and methane, as well as molecules of rocky minerals such as silicates — in the cool environments around nearby stars, where planets may form.Near-infrared instruments are better at detecting these molecules as vapors in hotter environments, while MIRI can see them as ice.
“By combining U.S. and European expertise, we have developed MIRI as the power of Webb, which will enable astronomers from around the world to answer big questions about how stars, planets and galaxies form and evolve,” said Gillian Wright, Co-lead of the MIRI science team and European Principal Investigator for the instrument at the UK Astronomical Technology Centre (UK ATC).
The MIRI cryocooler uses helium gas—enough to fill about nine party balloons—to carry heat away from the instrument’s detectors.Two electric compressors pump helium through a tube that extends to where the detector is located.The tube runs through a block of metal that is also attached to the detector; the cooled helium absorbs excess heat from the block, keeping the detector’s operating temperature below 7 Kelvin.The heated (but still cold) gas then returns to the compressor, where it expels the excess heat, and the cycle begins again.Fundamentally, the system is similar to that used in household refrigerators and air conditioners.
The pipes that carry helium are made of gold-plated stainless steel and are less than one-tenth of an inch (2.5 mm) in diameter.It extends about 30 feet (10 meters) from the compressor located in the spacecraft bus area to the MIRI detector in the optical telescope element located behind the observatory’s honeycomb primary mirror.Hardware called a deployable tower assembly, or DTA, connects the two areas.When packed for launch, the DTA is compressed, a bit like a piston, to help install the stowed observatory into the protection on top of the rocket.Once in space, the tower will extend to separate the room-temperature spacecraft bus from the cooler optical telescope instruments and allow the sunshade and telescope to fully deploy.
This animation shows the ideal execution of the James Webb Space Telescope deployment hours and days after launch.The expansion of the central deployable tower assembly will increase the distance between the two parts of the MIRI.They are connected by helical tubes with cooled helium.
But the elongation process requires the helium tube to be extended with the expandable tower assembly.So the tube coils like a spring, which is why MIRI engineers nicknamed this part of the tube “Slinky”.
“There are some challenges in working on a system that spans multiple regions of the observatory,” said Analyn Schneider, JPL MIRI program manager. “These different regions are led by different organizations or centers, including Northrop Grumman and the U.S. NASA’s Goddard Space Flight Center, we have to talk to everyone. There’s no other hardware on the telescope that needs to do that, so it’s a challenge unique to MIRI. It’s definitely been a long line for MIRI cryocoolers road, and we’re ready to see it in space.”
The James Webb Space Telescope will launch in 2021 as the world’s premier space science observatory.Webb will unravel the mysteries of our solar system, look to distant worlds around other stars, and explore the mysterious structures and origins of our universe and our place.Webb is an international initiative led by NASA and its partners ESA (European Space Agency) and the Canadian Space Agency.
MIRI was developed through a 50-50 partnership between NASA and ESA (European Space Agency).JPL leads the US effort for MIRI, and a multinational consortium of European astronomical institutes contributes to ESA.George Rieke of the University of Arizona is MIRI’s US science team leader.Gillian Wright is the head of MIRI’s European scientific team.
Alistair Glasse of ATC, UK is MIRI Instrument Scientist and Michael Ressler is US Project Scientist at JPL.Laszlo Tamas of the UK ATC runs the European Union.The development of the MIRI cryocooler was led and managed by JPL in collaboration with NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and Northrop Grumman in Redondo Beach, California.