The James Webb Space Telescope Has Its Launch Date Set

In the world of delayed big NASA projects, it's somewhat of a competition to decide which is the worst.  However you choose, the James Web Space Telescope has to be up for consideration.  Originally conceived of as an improved upgrade for the Hubble Space Telescope (HST), development began in 1996, 25 years ago.  The planned launch date was 2007, 14 year ago.  Since then, its record has looked like this:

In an at least partial defense of the contractors and centers causing those delays, this is a complex project and the program has changed over the years.  If there's any justification for what I call the "old space" practice of cost-plus development, a program like this is it.  Cost-plus is a guaranteed profit paid over the costs of the programs for when they contract to develop something that no one has ever done before.  Since no one has ever designed and built a multiple mirror telescope to be deployed in orbit and sent to a place where no one can get to it to service it, there figure to be things that get discovered along the way and increase the cost to the builders.

The JWST or just Webb is designed to be an infrared observatory, observing in wavelength bands that don't penetrate Earth's atmosphere.  The HST was designed to be a monolithic mirror, and since it had to fit in the Space Shuttle's cargo bay, it's not a particularly large instrument.  The primary mirror aperture is about 94 inches which isn't big for world class observatory - Earthbound observatories have had bigger primaries than that for over a hundred years.  The Webb's primary is a multiple piece mirror that totals 256 inches aperture. 

When comparing two telescopes on Earth, aperture (mirror size in this case) is certainly the first figure of merit to look at and the bigger the better.  The advantage of space telescopes is the ability to see in parts of the spectrum that don't get through the atmosphere, and see it without atmospheric turbulence.  The HST was built able to see part of the infrared and into the visible light spectrum.  Webb is built for infrared only.

The orbit for the Webb is also unusual.  Hubble is in Earth orbit.  Webb will actually be in solar orbit at the L2 LaGrange Point (graphic of the LaGrange points) over 932,000 miles from Earth, almost four times the Earth-Moon distance.  The L2 point is along a radius from the sun, through the Earth and out the other side, making the JWST 932,000 miles farther from the sun than the Earth in solar orbit.

NASA announced in August that the James Webb Space Telescope had passed its final ground-based tests and was being prepared for shipment to its launch site in Kourou, French Guiana. Now, the oft-delayed $10 billion telescope has an official launch date: December 18, 2021.

To get there, the Webb will launch on an Ariane 5 rocket from the European Space Agency.  

Why is NASA's most expensive scientific instrument ever launching on a European rocket? Because the European Space Agency is conducting the launch for NASA in return for a share of observation time using the infrared telescope. Webb will observe wavelengths of light longer than those of the Hubble Space telescope, and this should allow the new instrument to see the earliest galaxies of the Universe.

The Ariane 5 is among the last delays to the JWST launch.  

This summer, as NASA has worked to address the final issues with Webb, the European Space Agency and Arianespace have had problems of their own with the Ariane 5 rocket. A venerable rocket in service for more than 25 years, the Ariane 5 was grounded from August 2020 to July 2021 due to a payload fairing issue. However, officials with Arianespace say the fairing issue has been diagnosed and addressed with a redesign, and the rocket launched successfully on July 30, 2021.

There is one other launch of an Ariane 5 scheduled before December's JWST launch.  If the modified payload fairing works out properly, that could be the final hurdle in the way.  

NASA’s James Webb Space Telescope was placed in Johnson Space Center’s historic Chamber A for vacuum testing on June 20, 2017.  NASA Photo.  

The folded telescope is on a sun shield base roughly the length and width of a tennis court - 69.5ft long by 46.5 feet long.  That will need to unfold for the telescope to be shielded from the sun.

Unfurling the 21-meter-long telescope in deep space requires 50 major deployments and 178 major release mechanisms. All of these systems must work or the instrument will fail. There is no easy means of servicing the telescope at its location near a Sun-Earth LaGrange point 1.5 million km from Earth, or four times the distance to the Moon. 

This is a high stakes gamble - of your money, if you're an American taxpayer.  Most of you will remember that the Hubble Telescope had a poorly made primary mirror that had to be fixed with corrective optics before it could focus properly.  That kind of error would end this mission.  That quoted paragraph lists another 228 things that could end the mission.