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Video: Falcon 9 rocket degassing over France

The second stage of SpaceX’s launch vehicle was filmed just after orbiting 51 Starlink satellites, also visible. Various plumes of gas indicate that the rocket is preparing to descend and burn up in the atmosphere.

It is 6:05 am in the south of France, Monday September 5, 2022, when Romain Lucchesi points his camera towards the northwest. Staying in the Vaucluse, the young astrophysicist is also a photographer by passion. “I had wanted to see the train of Starlink satellites close together for a while, before they scattered,” comments the postdoctoral fellow at the Florence observatory. He therefore planned his observation after having identified the takeoff of a Falcon 9 from Cape Canaveral, earlier in the night. SpaceX rocket carries 51 Starlinks making up 59e batch of communication satellites sent into space by Elon Musk’s company.

Two hours and an orbit and a half later, the Starlinks are deployed at an altitude of some 340 km (final destination: 540 km). Barely put into orbit, they are visible on the video in the form of a small luminous trail close to the rocket stage. On either side of this small luminous line, whose magnitude reaches 2.4 at its maximum brightness, a few points light up and go out. They are produced by rotating debris.

With plumes

“The gas plumes, on the other hand, were a surprise,” says Romain Lucchesi. By coincidence, the astrophotographer witnessed several maneuvers of the rocket. Visible from the start of the video, a cloud of gas in the shape of a bulb indicates that the second stage has just turned on its engine to brake, in order to deorbit and then return to burn in the atmosphere. Then, a butterfly-shaped plume emerges until minute 0:31. At this point, small helium tanks, called COPVs, are emptied symmetrically, whose role is to keep Falcon 9’s fuel under pressure. “We can clearly see the powerful impulse making a wave that quickly ends,” observes Gauthier Jourdain, consultant in complex systems architecture.

From minute 0:47, a new gas cloud appears. It corresponds to the purging of the two tanks (oxygen and kerosene) in space. A spiral is formed: the body of the rocket begins to turn on itself. “It is a collateral effect due to the fact that it is no longer under control,” adds the former aerospace engineer. This phase continues until the end of the video, while the rocket passes in front of the constellation of Orion, heading southeast (approx. at minute 2:50).

Seen from a distance of 16 km, the Falcon 9 takes off on September 5, 2022 at Cape Canaveral in Florida. On the left, the SLS of the Artemis 1 mission. © C&E/P. Henarejos

Degas before burning

By emptying it of any residual fluid, SpaceX reduces the risk of scattering the fragments produced during re-entry into the atmosphere. Heated, the gas can cause explosions, throwing this debris out of the fallout zone defined as safe.

As of September 8, 2022, 3259 Starlinks satellites have been sent in three years; 2991 are still in orbit and 2956 in working order. During July and August alone, ten new Starlinks clusters took off. Before SpaceX launched the first copy, there were less than 4,700 satellites, active or defunct, in orbit around the Earth.




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