The Good News Continues to Roll In

Good space news, that is.  

The James Webb Space Telescope has fully deployed their solar shield, that tennis court-sized, kite-shaped sandwich of layers of Mylar that has been pictured here before.  NASA's Webb Telescope Twitter account noted:

This is it: we’ve just wrapped up one of the most challenging steps of our journey to #UnfoldTheUniverse.

With all five layers of sunshield tensioning complete, about 75% of our 344 single-point failures have been retired!

I have to admit this has given me heartburn since I first heard of it.  It's great to hear that Webb is now 75% of the way to working.  Only 86 possible single point failures left. 

You will notice that the temperature on the hot side of the sunshield peaks at 138 F while the coldest spot on the cold side is 456 degrees cooler at -318 F.  A pretty dramatic sun shielding. 

Today is Launch +10 days; according to that graphic, the next steps are to deploy the secondary mirror (after a day of preparation), and then start to deploy the main mirror.  Once that's done, the next eleven days will be getting the primary mirror segments in the right places.  To within a small fraction (1/10?) of the wavelength of the infrared light they're working with.

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Another piece of good news comes from SpaceX, where Elon Musk spent some time on Twitter and mentioned that the Raptor 2 engines are coming along well. 

Raptor 2 now operates routinely at 300 bar main chamber pressure. 

If you'll recall the story from early December when Musk floated the idea that bankruptcy could be a concern, the main issue was Raptor engines.  The backstory and details of the Raptor engine history that get the full picture across are over on Teslarati and are worth a look.  Just a month short of three years ago, February 10, 2019, in the first days that SpaceX started testing the first full-scale Raptor prototype (now called a Raptor 1), the engine briefly reached a main combustion chamber pressure just shy of 269 bar (3900 psi). That narrowly beat records set by Russia’s RD-270 and RD-180 engines.  The RD-270 never went into production, while the RD-180 is a well-established, good engine.  It's used on ULA’s Atlas V and the fact it's a Russian engine is the reason Atlas V flights are no longer being sold.  

18 months later, Musk revealed that one Raptor prototype was able to maintain that 300 bar pressure for over one solid minute.  The same engine briefly hit 330 bar (~4800 psi), producing 225 tons (~500,000 lb) of thrust at that point.  Over the last several months, their emphasis has moved onto the Raptor 2 engine which is reported to feature much a cleaner design; in both plumbing and wiring. 

On October 24th, Musk subtly live-tweeted one of the first Raptor 2 static fires, revealing that the engine reached a chamber pressure of 321 bar (~4650 psi) and briefly produced around 245 tons (~540,000 lbf) of thrust before destroying itself. Now, a little over two months later, Musk says that Raptor 2 prototypes are routinely operating at 300 bar without major issues, meaning that they can ignite and safely shut down after burning for several minutes at those pressures. In theory, given that 300 bar is Raptor 2’s targeted chamber pressure at max thrust, that means that the engine is now “routinely” operating at the level SpaceX wants and needs to take Starship to the next level.

The Texas Tank Watchers are debating whether Booster 4 and Starship 20 will ever launch or be scrapped to switch over to the Raptor 2 engines, since the Raptor 1 or 1.5 are dead end products.  I can see launching B4S20 or not launching.  Production quantity Raptor 2 engines don't exist right now so if they feel they need to launch, they have to use B4 or its kin.  The question is what they can learn by launching B4 that they can't learn another way.  Costs of the mission to get the benefits of what they learn.

Test firing of a Raptor 2 engine.  Elon Musk/Twitter.