NASA is gearing up for the launch of its most ambitious space telescope or probe ever launched later this month. In that effort, it said engineers working on the launch of the James Webb Space Telescope have successfully completed the delicate operation to load the fuel it will use to propel itself while in space. The engineers are now preparing to place the folded instrument inside the top of a rocket, expected to blast off later this month to place the telescope into orbit.

The Webb telescope is a project undertaken jointly by NASA and the European Space Agency (ESA). It is designed to reveal the evolution of the universe from its early phases to the modern era. It will probe thoroughly the universe at infrared wavelengths and will become the primary workhorse, replacing the ageing Hubble Space Telescope that has been doing this work for 30 years.

Bigger than Hubble and wider than the Ariane 5 rocket taking it to space, the $10 billion project is the most complex attempt to launch an observatory in space yet. The James Webb Space Telescope is as big as a tennis court. It has a 6.5-meter-long panel of 18 gold-coated mirrors that sits over a large sun shield. The whole thing is to be neatly packed into the rocket before launch.

NASA said in a blog that Webb was moved to the fueling section at Europe’s Spaceport in French Guiana to safely handle the extremely toxic fuel. Sharing an image of the process, it added that specialists wore Self-Contained Atmospheric Protective Ensemble, or “SCAPE,” suits and the process continued for 10 days, starting on November 25.

The rocket thrusters on the James Webb Space Telescope use either hydrazine fuel or a special mixture of hydrazine fuel and dinitrogen tetroxide oxidizer. Webb’s spacecraft bus was filled with 159 litres of hydrazine fuel and 79.5 litres of dinitrogen tetroxide oxidizer. The fuel loading system was formally disconnected on December 3, followed by inspections and closeouts that concluded over the weekend, NASA said.

The James Webb Space Telescope launch is targeted for December 22.