SpaceX Falcon

Paul a écrit:En fait, SpaceX a déjà révolutionné l'industrie, avec des coût de lancement imbattable, le tout sans fonds gouvernementaux, ce qui est le réel exploit.

To complicate matters further, the landing site is limited in size and not entirely stationary. The autonomous spaceport drone ship is 300 by 100 feet, with wings that extend its width to 170 feet. While that may sound huge at first, to a Falcon 9 first stage coming from space, it seems very small. The legspan of the Falcon 9 first stage is about 70 feet and while the ship is equipped with powerful thrusters to help it stay in place, it is not actually anchored, so finding the bullseye becomes particularly tricky. During previous attempts, we could only expect a landing accuracy of within 10km. For this attempt, we’re targeting a landing accuracy of within 10 meters.

In a comment posted to his Twitter feed following the launch, Musk said the booster “made it to drone spaceport ship, but landed hard. Close, but no cigar this time. Bodes well for the future though.”
According to SpaceX, the booster was to conduct three separate engine burns to put it on course to re-enter the atmosphere and slow from 2,900 mph (4,600 km/h) to 4.5 mph at the point of touchdown on the barge, which measures 300 x 170 ft (91.5 x 52 m).
A boostback burn was to adjust the impact point of the vehicle, and supersonic retro-propulsion burn and deceleration fins were to slow its speed, followed by a single-engine landing burn.
Musk said the barge is “fine” and that some of the support equipment on its deck will need to be replaced. In addition, he said dark and foggy conditions thwarted the company’s attempt to record clear video footage of the landing attempt.
“Will piece it together from telemetry and … actual pieces,” he posted.

There's some discussion in the "Grid fins worked extremely well from hypersonic velocity to subsonic, but ran out of hydraulic fluid right before landing." thread.

The Falcon engines are known to be actuated by RP-1 hydraulic pressure. This is conveniently available from the fuel turbopump, and RP-1 is a fine hydraulic fluid. For terrestrial use, you want a heavier oil to provide a longer working life for the moving parts, to leak less, and to be more heat-resistant, none of which are issues for rocket engine use. The hydraulic outlet just vents back into the pump inlet, and it gets re-pressurized and burned.

However, there are two big problems with using this to power the grid fins:
1. As /u/gangli0n points out, the pressure is available at the bottom of the rocket, and would require a very very long pressure tube to get it to the grid fins at the top of the stage.

2.The pressure is available only when the engine is firing. The engine isn't running during much of the re-entry, when the fins are needed. (For flight, the guarantee that hydraulic pressure is available for thrust vectoring any time the engine is producing thrust to vector is very nice. But it bites us in this case.)

Therefore, it makes sense to have a separate pressurized reservoir of RP-1 to power the fins. This is why they can "run out" of hydraulic fluid. The reason for using RP-1 is because (as others pointed out) they're used to it, and second because they can dump the outflow into the main tank and use it a second time for rocket fuel.
Thus, the hydraulic fluid is "free" from a mass penalty point of view. The only cost is the high-pressure vessel to store the hydraulic RP-1 separately from the lower-pressure main tank.
The main thing I'm wondering about is what they use to pressurize the system. They're using nitrogen for the cold gas thrusters a popular choice. I'm not sure if they'd use the same nitrogen to pressurize the hydraulics, or something lighter like helium or hydrogen. (Yes, hydrogen is flammable. So is RP-1. I don't think hydrogen greatly increases the hazard.)

La direction des lanceurs du Cnes a démarré un réflexion sur une possible évolution de l'architecture d'Ariane 6 vers un concept semi-réutilisable à l'horizon 2025-2027 si ce type de solution devait s'avérer présenter un intérêt économique.