Astronomers dealt with a major several problems since the inception of astronomy. First, objects give off electromagnetic radiation. The human eye’s ability to detect the visible spectrum restricts us from seeing other electromagnetic radiation. Second, distant objects wavelengths become difficult to detect. Third, the Earth’s environment (Atmosphere, vibrations from wind and heat variations) distorts the data collected.
Ground-based telescopes successfully aided in lessening the first two issues. The Atmosphere remained a challenge for ground-based astronomy. The emissions by distant stars get perturbed by the different layers in the atmosphere. Portions of the emissions of those distant objects get absorbed.
Hubble Space Telescope
NASA gives credit to theoretical physicist and astronomer Lyman Spitzer for first proposing a large space telescope in 1946. Spitzer affirmed that such a space-based observatory would take clearer images with a wider wavelength band than any ground-based telescope.
Space-based telescopes provided a solution for all the major issues. These telescopes when equipped with innovative instruments can detect a wide variety of electromagnetic spectrum, unperturbed by the environment of Earth. The relative minor pull of gravity in space allows for large telescopes not feasible to build on the Earth. Space-based telescopes provide clearer, more precise observations than ground-based telescopes. The Hubble Space Telescope positioned in a 350-mile high orbit above the blurring effects of the atmosphere allows it to capture images with 10 times the typical clarity of any ground-based telescope.
How big is Hubble?
Hubble’s size closely resembles the size of a large school bus. The spacecraft is 43.5 feet (13.3 meters) long and 14 feet (4.3 meters) in diameter at its widest point. Hubble weighs about 25,000 pounds (11,340 kilograms) on the ground. The microgravity in orbit renders it essentially weightless in orbit. During the launch, Hubble filled the payload bay of the Space Shuttle Discovery in April 1990.
The cost of space-based telescopes quickly increases with size and mass. Hubble’s one part mirror pushed the limits of modern technology to build such a large abature telescope main mirror. The telescope’s original total cost estimate of about US$400 million didn’t happen as expected. The telescope cost about US$4.7 billion by the time of its launch aboard the space shuttle. https://www.nasa.gov/sites/default/files/atoms/files/hstoverview2019.pdf
Even Hubble isn’t powerful enough to peer into the distant universe to unveil many secrets. For that, NASA needs a bigger, more advanced telescope.
JWST
NASA recently announced that the James Webb Space Telescope (JWST) launch date pushed back again. Building such a large and complex space telescope with exacting specifications costs a lot of money. How much money? Like the Hubble space telescope, the JWST budget the initial estimates for JWST don’t compare to reality. Over 8 billion dollars and the costs keep spiraling out of control.
The technical details out of the way, the space telescope offers breakthrough science that is otherwise impossible to do on Earth. Remember one key advantage of space telescopes includes their unhindered view of the heavens away from the distortion caused by the Earth’s Atmosphere.
Segmentation.
JWST also measures bigger than Hubble. A lot bigger. The telescope comes in at 21 feet (6.4 m) in diameter. To make JWST this big, NASA took an alternative design and manufacturing approach. The telescope uses 18 hexagonal segments made from gold-plated beryllium.
NASA went with this novel approach for space telescopes, but not new to astronomy. In the 1970s the idea to build a telescope 10-meter diameter primary mirror kicked off. To achieve this size, scientists proposed building with a segmented primary mirror made of 36 hexagonal segments. The Keck telescope project officially started in 1984 and entered service in 1993. Several other telescopes, including JWST, follow in the success of the Keck telescope.
How does a segmented telescope work?
Segmented telescopes work similarly to Light reflects from the hexagonal segments into a secondary mirror to redirect into the science instruments. On Earth, the segmented mirrors require substantial stiffening. to meet the stiffness requirements, the Keck telescope needs about 270 tons of steel for the large telescope to remain resistant to the deforming forces of gravity as it tracks objects across the night sky.
The segmented mirror approach provided JWST with another benefit, reduced mass. By placing JWST in space, the forces of gravity acting on it are reduced greatly so the required mass to stiffen it to resist it drastically drops. Ten JWST weight the same as the Hubble Space Telescope. The 18 beryllium mirror segments each weighs 46 pounds (20 kilograms).
Lagrange point placement
JWST also orbits much further away from Earth at a unique orbit called a Lagrange point. Specifically, JWST will orbit about 930,000 miles (1.5 million kilometers) away from Earth at the Lagrange 2 (L2) point. JWST will keep its mirror at a temperature of minus 388 degrees Fahrenheit (minus 233 degrees Celsius). The cold and the telescope’s distance from the Earth will give JWST the precision to observe red-shifted light from the early universe.
“A huge advantage of deep space (like L2), when compared to Earth orbit, is that we can radiate the heat away,” said Jonathan P. Gardner, the Deputy Senior Project Scientist on the Webb Telescope mission and Chief of the Observational Cosmology Laboratory at NASA’s Goddard Space Flight Center in Greenbelt, Md. “Webb works in the infrared, which is heat radiation. To see the infrared light from distant stars and galaxies, the telescope has to be cold. Webb’s large sunshield will protect it from both Sunlight and Earthlight, allowing it to cool to 225 degrees below zero Celsius (minus 370 Fahrenheit).” For the sun shield to be effective, JWST needs to be in an orbit where the sun and Earth are in about the same direction, allowing it an unfettered view into deep space and time.
About The Author
Bill D’Zio
Co-Founder at WestEastSpace.com
Bill founded WestEastSpace.com after returning to China in 2019 to be supportive of his wife’s career. Moving to China meant leaving the US rocket/launch industry behind, as the USA and China don’t see eye to eye on cooperation in space. Bill has an engineering degree and is an experienced leader of international cross-functional teams with experience in evaluating, optimizing and awarding sub-contracts for complex systems. Bill has worked with ASME Components, Instrumentation and Controls (I&C) for use in launch vehicles, satellites, aerospace nuclear, and industrial applications.
Bill provides consulting services for engineering, supply chain, and project management.
