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michal

Wow - 10G's during re-entry?

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As i understand it, the human body can stand up to 8G without passing out.Sustaining 8G leads to disorientation. Levels of 10G cause instant blackout.I believe this is the level suffered by every launch, by the occupants.

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>I believe this is the level suffered by every launch, by the>occupants.Not so. Neither the Space Shuttle nor the old Saturn V booster during the Apollo era subjected astronauts to loads even approaching 10 G. In case of the Space Shuttle the maximum load is around 3 G.Michael J.http://img142.imageshack.us/img142/9320/apollo17vf7.jpg

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The human body can, with a little training and some equipment, withstand 10 Gs for a short period of time.Just going off the top of my head here with these numbers: Most people will lose consciousness somewhere between 3 and 4.5 Gs sustained. You can pull around 5 if you use an "AGSM" (Anti-G Straining Maneuver) or something like that. A "G-suit" will buy you another 1 or 2 Gs by squeezing the blood out of your legs.Tactical and aerobatic aircraft routinely experience 6-8 Gs, with about 9 being the max.Personally, I grayed out at the bottom of a loop once, pulling about 3-4 Gs, because I didn't do a proper AGSM. Last time I made that mistake! I didn't pass out, but I remember suddenly not being able to see anything below the glareshield.Dave

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>The human body can, with a little training and some>equipment, withstand 10 Gs for a short period of time.Actually human body can take a lot of g-forces before there is an actual harm to a body. It all depends on the direction of the force, its duration and the posture of the body.If the force is perpendicular to the spine (which is the case of a landing space capsule) the tolerance is much higher.In 1954 NASA conducted some tests on some volunteers and someone in a rocket sled was able to withstand 46 g.Michael J.http://img142.imageshack.us/img142/9320/apollo17vf7.jpg

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"In 1954 NASA conducted some tests on some volunteers and someone in a rocket sled was able to withstand 46 g."I'd hate to have been the person in that sled when Nasa went for 47 g's ;)

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I would imagine they conducted the tests with cadavers and analyzed the results before using live volunteers.Remember that like the Mercury, Gemini and Apollo spacecraft, Soyuz capsules reenter with their crews lying on their backs. Crews on the American shuttle reenter sitting upright, only lying on their backs during the launch. The Orion Crew Exploration Vehicle (CEV) will return to the reclining reentry orientation. Reclining reduces problems with multiple Gs, especially the blackout issues people experience sitting upright when blood is pulled towards the feet.Imagine riding a looping roller coaster in a guest restraint that has a "seat" resembling the one on a bicycle. If you don't know the trick, it takes much of the fun out of it!:-ukliam

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Now the press is reporting that the high G steep reentry was the result of the service/propulsion module remaining attached after the explosive bolts that were supposed to jettison it were supposed to fire. The resulting drag made the spacecraft start reentry in a face forward orientation instead of the normal back first orientation. The reentry module was able to rotate into the proper orientation after the propulsion module burned away. One report indicated that not only the immediately preceding Soyuz had that problem, but that one in early 1969 had a delayed jettisoning too. Yes, spacecraft of that general design have been flying for FORTY YEARS!For those that haven't seen the diagrams, the Soyuz reentry module (also the one occupied during launch) is the center of three modules. The pressurized orbital module at the top/front (domed on both ends) includes the docking port, while the service/propulsion module has retro rockets, solar panels and probably expendables tanks (oxygen, maneuvering propellant, water etc). The orbital and propulsion modules are jettisoned before reentry.I saw one animation on a TV network that incorrectly showed the orbital module reentering. The reentry module is the one shaped like a hollow point bullet (flat end is the heat shield). I suspect the brush fire reported at the landing site was started by the braking rockets that fire a VERY short time before touchdown.

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>Do astronauts train for this? Has anyone in the forums>experienced such G-Forces in any type of aircraft?http://en.wikipedia.org/wiki/High-G_trainingYes, I know wikipedia is a questionable source for many things - but this looks like a pretty good summary.As far as aircraft - I don't think any aircraft with wings can sustain 10G without becoming a loosly associated collection of parts.Also humans survive much higher G forces for very short periods of time without blackout or loss of consciousness.Some of the crash black boxes in all late model automobiles show very short duration G loads of 20G or higher in highway crashes.Race car drivers frequently sustain extremely short G loads over 40G.But it depends upon the individual human. Jovy Marcelo died at the Indianapolis Motor Speedway on May 15, 1992 from a relatively low speed crash - for that type car - estimated at 172mph. He suffered a fracture at the base of his skull from the sudden deceleration.Less than 10 years later Dale Earnhardt hit the turn four wall at Daytona in the last lap of the Daytona 500 at a lower speed - estimated as near 150 mph - and died from a similar G force induced fracture.

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> As far as aircraft - I don't think any aircraft with wings can sustain 10G without becoming a loosly associated collection of parts.The Extra 300 can go to +/- 10G with a single occupant (+/- 8G with two occupants), see this page and many others on the web:http://www.air-races.com/aircraft/Extra%20300L.htmCheers,Martin

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>I suspect the brush fire reported at the landing site>was started by the braking rockets that fire a VERY short time>before touchdown.We now know that the brush fire had nothing to do with the landing - local farmers were burning crop stubble near the spot where Soyuz touched down - the fire actually consumed the parachutes. The crew briefly opened the hatch after the landing but quickly closed it after seeing the ground fire and smoke.Michael J.http://img142.imageshack.us/img142/9320/apollo17vf7.jpg

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