The long awaited launch of the James Webb Space Telescope has slipped another day to Christmas morning. The launch window opens at 7:20 AM EST, 12:20PM UTC. There are no kids around the house to be anxiously awake on the big day, so I guess I'll have to set an alarm.
As we are all eagerly anticipating launch, you might be wondering how to watch the launch and what to expect. Good news! NASA and its partners are planning a launch broadcast celebration that will be viewable in several different ways. Live countdown commentary and launch broadcast will begin at 6 a.m. EST (11:00 UTC) on Dec. 25 and air on NASA Television and the agency’s website, as well as YouTube, Twitter, Facebook, LinkedIn, Twitch, Daily Motion, Theta.TV, and NASA’s App. You can also join the Facebook event to watch the launch live and interact with others watching the launch. The launch broadcast will continue until approximately one hour past launch, to follow the first several critical milestones post-launch. The actual launch window opens at 7:20 a.m. EST (12:20 UTC) and lasts for 31 minutes – we can launch at any point during that window.
—Amber Straughn, Webb deputy project scientist for communications, NASA’s Goddard Space Flight Center.
As a reminder, this launch is by the European Space Agency and is taking place in Kouro, French Guyana, which is important to me because I can't go outside to watch it. This is a scary-complex mission and I did more of an overview of the program in early September, but once launched there's on the order of 300 steps that have to operate as intended if the telescope is to be successful.
The telescope primary mirror is made of hexagonal mirror tiles and is hinged
to be made small enough to fit into the Ariane 5 launch vehicle. Those
need to be unfolded and locked into final position to fractions of a
wavelength of light in order for the telescope to work. It's an
exceptionally sensitive infrared telescope that will be in orbit around the
sun, not the Earth, at the
L2 LaGrange Point
(graphic of the LaGrange points) over 932,000 miles from Earth. That
means there's nothing to shade that exceptionally sensitive heat detector
from the sun - unless they build it onto the telescope. 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. To borrow from my September post.
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.
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.
On December 17th, SpaceX subjected Super Heavy B4 to a cryogenic proof test about twice as ambitious as B3’s, filling the booster maybe a sixth of the way with a few hundred tons of liquid nitrogen (LN2). What isn’t clear is if that test also raised the booster’s propellant tanks to flight pressures (6-8 bar or 90-115 psi). If Booster 4 did reach those pressures, the test is even more significant – partially proving that the rocket is ready for flight. On December 21st, SpaceX performed a similar series of cryogenic tests, again partially filling Booster 4 with about the same amount of liquid nitrogen but doing so two or three times in a row. Again, the Super Heavy survived the several-hour ordeal without any obvious issues. Still, a number of additional tests – some even more important – are still in front of SpaceX and Super Heavy B4.
The obvious tests are to fuel B4 completely. It's possible they'd use liquid nitrogen
(LN2) instead of the actual liquid oxygen (LOx) and methane (LCH4) Super Heavy is designed to fly with for an early test. LN2 is denser than both LOx and LCH4, so partial tank loads of LN2 could get B4 up to full lift off weight, if that's a valuable test.
There are many steps to go before the first launch of a Starship and Super Heavy mission. They have yet to do a static firing of 29 engines and my guess is they'll probably start with a small number and add more engines gradually until the full 29 get tested. I can see a lot of WDRs (Wet Dress Rehearsals) happening in the next several weeks. It would be crazy to try to peg a date for the first flight, but I think the chances of a launch in the first week of January are about zero. Perhaps by the end of the month.