The James Webb Space Telescope
The Baby Boom generation had the great fortune to grow up in what is often called “the golden age of space exploration”, a period of only 15 years that began with the launch of the first artificial satellite in 1957 and culminated with the final Apollo moon landing in 1972. That period was unique, with the backdrop of the Cold War and the bold objective set by President John F. Kennedy in his 1962 speech:
"I believe that this nation should commit itself to achieving the goal, before this decade is out, of landing a man on the moon and returning him safely to Earth."
After that goal was miraculously achieved, perhaps it was inevitable that the nation would lose much of its fascination with space. Nevertheless, NASA still forged ahead with both manned and unmanned missions, working on a reduced budget and with goals harder to appreciate for the average American. The Space Shuttle program never met its primary objective of dramatically reducing the cost of launching large payloads into orbit, and design flaws led to the tragic deaths of fourteen astronauts in the Challenger and Columbia disasters. There were also some costly mistakes involving engineering measurements that doomed one unmanned Mars vehicle and a nearly led to the failure of a highly touted Hubble Space Telescope mission. Thankfully, the latter was saved by a feat technological ingenuity that evoked memories of the ill-fated Apollo 13 mission and its fabled rescue.
Nevertheless, the last 50 years of NASA exploration since the final Apollo moon landing has brought some astounding achievements, particularly for the unmanned programs. Highlights have included:
- Five robotic rovers of increasing sophistication landed on Mars and have far exceeded their mission objectives over years of service.
- The Voyager I and II spacecraft sent back the first, spectacular, images of the far planets and their moons. Their beauty and variety astounded the scientific world and graced the pages of several popular magazines for years.
- The Magellan mission mapped the entire surface of Venus in great detail, using cloud-piercing radar, as well as recording the planet’s gravity field.
- The Cassini-Huygens mission to Saturn took unprecedented close-up images of the planet and its moons. Huygens landed on Titan, the largest moon in our solar system, and photographed its orange-tinted atmosphere and actual lakes of liquid methane!
- New Horizons travelled some three billion miles to the distant dwarf planet Pluto and took vivid pictures from as close as 7,750 miles above the surface.
- The Hubble Space Telescope was repaired by a dedicated Shuttle mission in 1993, some 3½ years after initial activation, and has since delivered about 120 gigabytes of image data every week, with subjects ranging from our outer planets to galaxies over 13 billion light years (76,422,000,000,000,000,000,000 miles) distant.
With Hubble only in service for some three years, NASA had already begun planning for a successor. The program was now a definite success and, with periodic maintenance, could last for decades. But complex spacecraft usually take over a decade to develop and modern technology advances quickly, so every mission’s obsolesce can be envisioned before it even launches. Hubble was no exception. The Next Generation Space Telescope, later renamed the James Webb Space Telescope (JWST), began anticipated several major enhancements:
- While Hubble imaged in the visible light spectrum, JWST would utilize infrared wavelengths, given several advantages:
- Distant regions of the universe are moving away from us at such high velocities that visible light originating from stars is shifted in wavelength to the infrared range.
- Infrared light is less obscured by gas and dust clouds than visible light.
- The relative temperatures of stars can be inferred from their specific infrared wavelengths.
- Instead of orbiting the earth, engineers would position the telescope at the Lagrange point, 1.5 million miles away from the earth. It would actually orbit the sun, in synchronization with the earth. There it would remain near enough for efficient radio communications but, given proper shielding from the sun, able to minimize random infrared radiation from unwanted sources.
- With advances in computer science and robotics, the telescope could be made much larger and more sensitive, unfolding in space from a compact package that would fit our current launch vehicle payload capabilities.
- A permanent external fairing, or housing, would not be required for Webb, so long as the radiation from one direction – the sun – could be blocked. This further enabled a much larger primary mirror diameter.
- While a Lagrange point orbit precluded the possibility of repairs after deployment, NASA deemed that current technology reduced the risk of catastrophic failure to an acceptable level when weighed against the clear advantage of the infrared imaging that is possible from that location.
The project took a full 25 years from inception to launch, with several major redesigns. It was a joint effort of NASA and the European and Canadian Space Agencies. The massive dimensions of the telescope can be seen in the full-scale mockup below. All components had to be designed to collapse to a small fraction of this size so it would fit within the payload fairing of the Ariane 5 launch vehicle. Achieving fully automated deployment from this configuration with 100% reliability presented a daunting engineering challenge.
Liftoff from the European Space Agency site in French Guiana took place on Christmas Day, 2021. JWST reached its final orbital position in about 30 days. Months of painstakingly careful deployment and calibration followed. There was considerable suspense as each of 344 potential single-point failures was successfully averted. Perhaps the most visible of these critical steps was the precision alignment process for the 18 individual hexagonal segments comprising the primary mirror. Over a three-month period, a series of photos was released to the public showing how the light of a single star converged from a random array of scattered images to a hexagonal pattern and, finally, into a single sharp spot of light. The zoomed-in final image at right shows the target star in detail but also reveals other objects not visible during the alignment process, some of which appear to be more distant spiral galaxies.
Another major step in deployment was the unfolding of the huge sun shield, consisting of 5 ultra-thin layers of custom reflective DuPont Kapton E film, each separated by several inches of the vacuum of space. The end configuration, which can be seen in the mockup photo, measures 69 by 46 feet. While the sun-facing side of the shield can reach +231 degrees Fahrenheit, its extreme insulation capability enables the telescope to maintain an operating temperature of no higher than -370 degrees Fahrenheit, a gradient of over 600 degrees. This minimizes any localized infrared radiation that would contaminate the desired images.
A press conference was held on July 12 at NASA's Goddard Space Flight Center in Greenbelt, Maryland, where the first full images from Webb were released, including the first two shown below. Note that since infrared light in not visible to us, all colors have been computer-adjusted.
The Deep Field image shows a plethora of galaxies up to 4.6 billion light years distant. The total field width of this image is like a grain of sand held at arm’s length, yet it includes hundreds of galaxies! The enhanced colors clearly show the huge variation in distance to each galaxy, and the effect of Red Shift. Analogous to points along a stretched rubber band, the farther away the light source, the greater the expansion of light waves and the redder the color appears. Also note the “lensing”, or curved distortion, of the most distant galaxies as their light has been bent by the gravitational force of galaxy clusters and their associated dark matter encountered during travel. Einstein’s Theory of General Relativity predicted this effect back in 1915.
The Cartwheel galaxy image was just released on August 2. The diameter of this galaxy is 144,300 light years, or 848,290,000,000,000,000 miles, quite similar to the Milky Way. The distance is 431 million light years, so we are seeing it as it looked during earth’s Silurian period, when the first land animals were emerging from the sea!
The last image shows the Webb’s capabilities at much nearer range, with magnificent detail. The planet Jupiter averages a “mere” 444 million miles, or about 45 light minutes, from earth. In this view, the famous “red spot”, which is a cyclonic storm, appears white. For perspective, the diameter of this feature is greater than that of the earth. The bright areas at the north and south poles are auroras, caused by the same effect as those seen on earth. Jupiter’s powerful magnetic field concentrates radiation from the sun at the poles. The resulting ionization of atmospheric gases emits light in the same manner as a neon sign.
These spectacular images are just a taste of what is to come. In fact, on September 1, NASA announced that Webb had captured the first actual image of a planet outside our Solar System! But is it worth the investment? The total cost to date of the project to date is about $10 billion which, after accounting for inflation, is about double its original budget. For comparison, NASA’s annual budget is about $22 billion. Each person will have an opinion on whether this kind of expenditure is justified, but one should consider the many thousands of scientists around the world who will consume this bounty of data for decades. We cannot begin to predict the discoveries about our universe that are likely to result. NASA will also provide educational resources for students and the public in general, as they have for so many of their programs. Many future astrophysicists are likely to come of age studying the wealth of data Webb will yield.