On Oct. 12th, 2021, after years of waiting and cost overruns, the James Webb Space TelescopeJWST) finally arrived safely at Europe’s Spaceport in Kourou, French Guiana. The crews began unboxing the next-generation observatory and getting it ready for integration with the Ariane 5 rocket that will take it to space. Then, an “incident” occurred where a clamp band suddenly released, sending vibrations throughout the facility. Once again, the JWST’s launch date was pushed back while crews investigated the source of the problem.

But lo and behold, the due diligence is now done, and the James Webb is back on track! According to the latest news from the ESA, crews have finished fueling the JWST’s thrusters in preparation for its launch, which is scheduled for Dec. 22nd. The Webb will use these thrusters to make course corrections after separating from the Ariane 5 rocket in orbit, maintaining its prescribed orbit, and repointing the observatory during operations.

The process took place in a dedicated fuelling hall at the Centre Spatial Guyanais (CSG) and took ten days to complete (from Nov. 23rd to Dec. 3rd). The reason it takes so long is that fuelling a satellite requires extensive setup and preparation. Equipment and connections need to be set up in advance, safety protocols must be followed to the letter, and the fuel tanks must be pressurized.

With integration and testing formally concluded for the James Webb Space Telescope, NASA’s next giant leap into the cosmic unknown will soon be underway. Credits: NASA/Chris Gunn

The JWST’s propellant tanks were filled with 168 kg (370 lbs) hydrazine fuel and 133 kg (293 lbs) of dinitrogen tetroxide oxidizer. Since these propellants are extremely toxic, each had to be filled separately by specialists wearing Self-Contained Atmospheric Protective Ensemble (SCAPE) suits. With fueling complete, the crews have since moved into the next phase of preparations, known as “combined operations.”

This step is where the specialists who have been working separately to prepare the JWST and the Ariane 5 rocket will come together as one team. Once the Webb is hoisted into place, the combined team will then load the capsule atop the Ariane 5 launch vehicle and place it inside the Ariane 5’s specially adapted fairing. In preparation, the JWST and the Ariane 5 launch vehicle were both brought together in the Final Assembly building on Dec. 7th for the last phase of preparations before launch.

The transfer took place during the early morning hours and required a special 23 metric ton (25.35 US ton) transport container to ensure the JWST made it to the Final Assembly building safely. The JWST had previously been in this building in November alongside the Ariane 5, shortly before the incident with the clamp occurred. The observatory had been fueled and crews were preparing to attach it to the Launch Vehicle Adapter (LVA), which is used to integrate the observatory with the Ariane 5’s upper stage.

It was on this occasion that a clamp band suddenly released on the LVA, and the integration process had to be scrubbed. But with Webb now refueled and ready to be stacked with the Ariane 5, the crews at CSG can once again attempt to hoist Webb to the upper platform and integrate it with the Ariane 5’s upper stage, then encapsulate it inside its special payload fairing. This will be the final preparation before launch, which is still scheduled for Dec. 22nd.

With its complex design, advanced mirrors, and advanced suite of scientific instruments, Webb will be the largest, most powerful telescope ever launched into space. As part of an international collaboration between NASA, the ESA, and the Canadian Space Agency (CSA), Webb will use its advanced infrared imaging capability, spectrographs, and a coronagraph to observe unseen and poorly-understood aspects of the Universe.

These include conducting a census of cooler objects in the Universe like red dwarfs, brown dwarfs, nebulae, and circumstellar disks (which give rise to planets). It will also observe smaller, rocky planets that orbit closer to their stars, helping to complete the census of exoplanets and the characterization of potentially habitable worlds. And perhaps most
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