SpaceX Starhopper Performs a Tethered Hop With a Raptor Engine Firing

The SpaceX Starhopper has performed a tethered hop with a Raptor engine firing.

SOURCES- Elon Twitte,

19 thoughts on “SpaceX Starhopper Performs a Tethered Hop With a Raptor Engine Firing”

  1. I hate digital cameras.

    Wasn’t there some special film used during Apollo that could deal with the harsh glare from exhaust–and the lunar surface?

  2. It’s not all that different from the sound a propane brush/grass burner makes on shutdown, for the same reasons apparently.

  3. Fair point.

    Bottom line: I’ve been trained since infancy to assume that something’s going to break when I hear a sound like that.

  4. All rocket engines are acoustically loud under normal operating conditions. That’s one reason they spray water around the base of the rocket – to absorb sound waves. The other is to prevent melting parts of the launch pad. I don’t think the post-fire toot is in the same noise class.

  5. Pretty much afraid it will take off.
    Raptor has an 200 ton trust and he hopper is lighter unless they add 160 something fuel and oxygen.

  6. So you’re basically saying that this is a resonance set up as the nozzle goes from choked to unchoked flow?

    That sounds… kinda bad. There’s a lot of energy being released in that vibration. I wouldn’t think it’d be great for the reusability of the combustion chamber.

  7. Every rocket they launch goes through a hold down hot fire. Better a new build fail while on the ground than a meter in the air.

  8. Testing is progressive. The last couple of weeks was things like tanking and de-tanking the propellants. Now they are going into actual engine firing. This exercises the software and electronics in addition to the engine. Once they are confident the parts are working together, they can remove the tethers and start flying. Then they can test the landing software, flight sensors, etc. You can’t check engine gimbaling (tilting), control thrusters, and propellant slosh when it’s tied to the ground.

    All of this is being done with a relatively cheap and disposable vehicle, which was made a lot heavier than the orbital Starship. Once they verify all the pieces work properly, all the knowledge and fixes will be translated to the second Starship prototype that will fly higher and faster. That one is being made more carefully, with thinner structure to be closer to final weight.

  9. The “toot” at the end is the engine acting like an organ pipe or horn, similar to the squeal of a balloon when you hold the neck nearly closed. Gas flow through a constriction (the throat between chamber and nozzle) sets up a vibration, which then reverberates at the natural frequency based on the size of the chamber and gas temperature.

    Why there is gas flow after the flame goes out is likely because they shut the oxygen just ahead of the methane, to prevent oxygen-rich combustion. After that, all the remaining gas from the turbopumps, down through the engine cooling channels and injector will blow out until their pressure is equal to air pressure.

    You don’t want oxygen-rich combustion because it tends to burn anything in its path.

  10. No, there’s absolutely about a six second lag between the video and audio. But at the end of the test (i.e., six seconds after the flames go out), there’s a huge groaning noise. It seems to be characteristic of all Raptor shutdowns.

  11. I think it’s just the sound of the static test itself due to the time it takes for the sound to reach the camera. Anyone can confirm ?

  12. I’m still dying to know what that horrid noise is at shutdown. It was present on the more recent horizontal static tests, too.

  13. It’s a new engine that is much more powerful than before. They need to make sure all systems work perfectly and that it holds together in a vehicle. They need to be able to throttle and gimbal with high precision to be able to do a controlled landing. This short test was probably not about throttling though.
    It’s standard engineering practice to do risk analysis and take steps from the results of that. Failures can be good but only if you learn more from them than you could have done with slow and careful testing. The Russians used to do it more like that and iterate often towards a working solution. The costs and delays due to a Starhopper failure at this point are simply too high to do rushed testing so they take smaller steps.
    They are still orders of magnitude quicker than their competitors.

  14. Won’t their flight data be compromised by the tethering, or are they afraid that the starhopped might take off like a bottle rocket? What do they tether it with?

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