Exciting progress in Boca! Hopper almost ready to hover. Based on tonight’s test, looks like 600 Hz Raptor vibration problem is fixed. pic.twitter.com/9bLWOHG0sV
— Elon Musk (@elonmusk) July 7, 2019
Great video. Couple notes: Raptor designed for subcooled CH4/O2, so propellant density & thrust increase up to ~8%, as needed for mission. 380 Isp & up to 50% thrust/weight improvement over time. Merlin thrust/weight doubled from V1, but Raptor is closer to optimum.
— Elon Musk (@elonmusk) May 25, 2019
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but, but….based on your ‘reporting’ , I thought we were already at a production rate of at least a thousand raptors per year
Ok great… I know the perfect alternate tuning for my electric guitar…
Judging by the frequency, the oscillation probably involved gaseous fuel/oxidizer, so likely after the first combustion. I’d expect vibration involving liquids to be higher frequency, since the speed of sound is much higher.
As linked above..
https://twitter.com/elonmusk/status/1143019549492744203
Previous tweet mentioned a stator being the issue.
https://twitter.com/elonmusk/status/1143019549492744203
Partway between D and E, an octave above middle C (which is 261.6 Hz)
I suspect it was acoustic vibrations in the combustion chamber. This has been a frequent problem with rocket engines. Essentially the throat makes them act like organ pipes, and it can be quite powerful enough to shake the engine apart.
At the temperatures in the combustion chamber, the speed of sound is higher, so it could be quite a bit smaller than 2 ft. Some dimension of the chamber resulted in a 600 Hz note.
what musical note is 600 hz?
It depends on what sort of harmonic mode it was, with liquid pumps longitudinal “pogo” vibrations are typically the hardest to engineer out of. If you can change the flow rates/thrust characteristics you can modify the plume acoustics. Sometimes requires nozzle redesign. Move things around, change components to change sympathetic frequencies, change mounts, re-do analyses, re-do quals. Vib 101.
I’m curious too. But certainly not entitled.
600 Hz indicates that the part that was excessively vibrating was big, a bit less than 2 ft in size. Maybe a pump housing that was a little too loose.
Fixed how? With what? By who? When?