Key Facts

This image is from Webb’s NIRCam instrument, which saw this nebula in the near-infrared.

extending the tantalizing discoveries of the Hubble Space Telescope.

Engineers Prep James Webb Telescope for Integration

So big it has to fold origami-style to fit in the rocket and will unfold like a “Transformer” in space.

Webb Lagrange Points

Webb orbits the Sun 1.5 million kilometers from the Earth. (Hubble orbits 560 kilometers above the Earth.)

NASA’s Webb Sunshield Successfully Unfolds and Tensions in Final Tests

Webb has a 5-layer sunshield that protects the telescope from the infrared radiation of the Sun, Earth, and Moon; like having sun protection of SPF 1 million.

The image shows the galaxy cluster SMACS 0723 as it appeared 4.6 billion years ago

iIt will peer back in time over 13.5 billion years to see the first galaxies born after the Big the ISS.

Key Facts

Launch Date
December 25, 2021 07:20am EST (2021-12-25 12:20 GMT/UTC)
Launch Vehicle
Mission Duration
5 - 10 years
Total Payload Mass
Approx 6200 kg, including observatory, on-orbit consumables and launch vehicle adaptor.
Diameter of Primary Mirror
6.5 m (21.3 ft) approximately
Clear Aperture of Primary Mirror
25 m2
Primary Mirror Material
beryllium coated with gold
Mass of Primary Mirror
705 kg
Mass of a Single Primary Mirror Segment
20.1 kg for a single beryllium mirror, 39.48 kg for one entire primary mirror segment assembly (PMSA).
Focal Length
131.4 meters
Number of Primary Mirror Segments
Optical Resolution
~0.1 arc-seconds
Wavelength Coverage
0.6 - 28.5 microns
Size of Sun Shield
21.197 m x 14.162 m (69.5 ft x 46.5 ft)
Temperature of Sun Shield Layers
Layer 1:
Max temperature 383K = approx 231F

Layer 5:
Max temperature 221K = approx -80F
Min temperature 36K = approx -394F
1.5 million km from Earth orbiting the L2 Point
Operating Temperature
under 50 K (-370 °F)
Gold Coating
Thickness of gold coating = 100 x 10-9 meters (1000 angstroms). Surface area = 25 m2. Using these numbers plus the density of gold at room temperature (19.3 g/cm3), the coating is calculated to use 48.25g of gold, about equal to the mass of a golf ball. (A golf ball has a mass of 45.9 grams. Note mass does not equal size!)

Mission Goals


Major Innovations

  • MIRRORS - Folding segmented mirror : The Webb Telescope team also decided to build the mirror in segments on a structure which folds up, like the leaves of a drop-leaf table, so that it can fit into a rocket. 
  • MIRRORS - Lightweight optics : NASA set out to research new ways to build mirrors for telescopes. The Advanced Mirror System Demonstrator (AMSD) program was a four-year partnership between NASA, the National Reconnaissance Office and the US Air Force to study ways to build lightweight mirrors. 
  • MIRRORS - Cryogenic actuators & mirror control : Lee Feinberg, Webb Optical Telescope Element Manager at NASA Goddard explains, "Aligning the primary mirror segments as though they are a single large mirror means each mirror is aligned to 1/10,000th the thickness of a human hair. What's even more amazing is that the engineers and scientists working on the Webb telescope literally had to invent how to do this."
  • MIRRORS - Wave Front Sensing: Wavefront sensing and control was developed to sense and correct any errors in the telescope's optics. This is essential to making the 18 mirror segments work together as a single giant mirror.
  • Webb's Sunshield : The sunshield reduces the temperature between the hot and cold side of the spacecraft by almost 600 degrees Fahrenheit in the span of its 5 layer, 4.8m height - from approximately 185F (85C) on the hot side to approximately -388F (-233C) on the cold side.
  • Sunshield coatings: Webb deployed a tennis-court sized Sunshield made of five thin layers of Kapton E with aluminum and doped-silicon coatings to reflect the sun's heat back into space.
  • Improved Detectors: Webb has extended the state of the art for infrared detectors by producing arrays that are lower noise, larger format, and longer lasting than their predecessors.
  • Micro-shutters : Microshutters are tiny windows with shutters that each measure 100 by 200 microns, or about the size of a bundle of only a few human hairs. The microshutter device can select many objects in one viewing for simultaneous high-resolution observation which means much more scientific investigation can get done in less time.
  • Cryocooler: Webb's MIRI instrument carries detectors that need to be at a temperature of less than 7 kelvin to operate properly. This temperature is not possible on Webb by passive means alone, so Webb carries an innovative "cryocooler" that is dedicated to cooling MIRI's detectors
  • Backplane : The backplane must carry more than 2400kg (2 1/2 tons) of hardware. It is required to be essentially motionless so the mirrors can see far into deep space. To meet this requirement, the backplane was engineered to be steady down to 32 nanometers, which is 1/10,000 the diameter of a human hair.
  • Cryogenic Data Acquisition ASIC : "A-to-D" conversion is nothing new, but the technical challenge that Webb faced was doing it at the observatory's super-cold cryogenic operating temperatures in an Application-Specific Integrated Circuit (ASIC).