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The blogpost Lessons From NASA Disasters: When Curiosity Deficits Kill is about the importance of freedom of curiosity for members of organizations. However it contains many Space Shuttle-related images.

The ones below show the Shuttle SRB's parachuting to Earth and floating end-up in the ocean.

  1. Why do these spent, open-ended (at one end) and possibly air-leaky hollow tubes still reliably float?
  2. Why do they appear to float stably in an upright position rather than on their side?

Space Shuttle SRB splashdown

STS-116_rocket_boosters_NASA_KSC-06PD-2794

2nd image's url includes "STS-116_rocket_boosters_NASA_KSC-06PD-2794" and the quoted source for these (and many other STS images) https://howlingpixel.com/i-en/Space_Shuttle_Solid_Rocket_Booster

For comparison, from Scott Manley's https://youtu.be/EH1nyPIvLjI (found in the currently-unanswered question Falcon 9 2nd stage pusher; how far does it continue to extend as it accelerates separation?)

floating Falcon 9 from Scott Manley's video

uhoh
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1 Answers1

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They floated upright because the hollow insides partially filled with water and the aft skirt of the booster was heavier than the front end (it had the hydraulic power units, the thrust vector control system, what is left of the nozzles, etc).

During recovery operations divers plugged the nozzle and air was blown into the booster to "dewater" it.

When sufficient water has been removed from the SRB, the booster will become unstable and float in a log mode.

An inflatable bag on the NP will be inflated, once the SRB assumes a horizontal mode and a de-watering hose will be deployed. Additional air is then forced into the SRB to achieve a pressure differential which will force the remaining water out of the SRB through the dewatering hose. The umbilical is then detached prior to towing operations. A towline is attached to a towing pendant on the nose of the SRB and transit to the refurbishment site is begun.

NP = Nozzle Plug

enter image description here

Image from the 1982 Press Manual

Information from Solid Rocket Booster Retrieval Operations.

Historical note: the dewatering operation was supposed to be done by an undersea robot, but this failed in development, so divers did it throughout the program.

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Organic Marble
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    Do you know if they had to continue to add air at some rate to compensate for air leaks? I know there were O-rings, but did they always remain air tight after all of the hot exhaust and vibrations? – uhoh Sep 07 '19 at 15:23
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    The document says the air hose was removed prior to towing ops, so if there was leakage, it must have been fairly minor. Also, if there was a significant leak the booster probably would have sunk before the recovery ship showed up. (A couple of SRBs did sink when they hit the water too hard because of parachute failures) – Organic Marble Sep 07 '19 at 15:25
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    google's creepy AI just suggested I watch Shuttle's Boosters Recovered in HD https://youtu.be/Gbtulv0mnlU – uhoh Sep 21 '19 at 01:00
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    @uhoh I've been experimenting with duckduckgo to avoid some of the creep! – Organic Marble Sep 21 '19 at 01:03
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    The boosters were built to withstand massive pressures from the combustion process. Any leaks would be catastrophic (Challenger). Seals that are capable of withstanding that environment won't suddenly develop leaks after burnout . – Hobbes Sep 21 '19 at 06:45
  • @Hobbes that's a good point, but at the bottom of the air space where it meets the liquid that's entered from the nozzle below, the external pressure of the water will be higher than the internal pressure of the air, since the air will be at a constant pressure and the water pressure will increase with depth. It won't be huge of course, but it will be in the opposite direction from the combustion pressure, and if it was designed wrong, (which it probably wasn't apparently, at least in this respect) it could possibly be less effective in this direction. – uhoh Sep 21 '19 at 07:11
  • No. The air has to counteract the water pressure, so the air pressure will be equal to the water pressure at the air/water interface. And since the water inside is connected to the water outside, the air pressure inside at all locations between the top and the air/water interface is higher than the water pressure outside. – Hobbes Sep 21 '19 at 08:39