Author Astronaut Scott Kelly is back on Earth..  (Read 3829 times)

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Astronaut Scott Kelly is back on Earth..
« Reply #30 on: March 07, 2016, 07:33:30 PM »
Spaceflight osteopenia (bone loss during spaceflight) is less than 1%/month on ISS.  Normal bone loss for the aged is 1.5-2% per year and 2-3% per year is normal for post menopausal men.

New drugs are shown to almost stop this process of spaceflight osteopenia. Combined with exercise bone and muscle wasting can be virtually arrested.

Space medicine is very important because even now the accurate study sample size is very small.  Much early Mir and older science is inaccurate.

The extra height comes from the decompression on the spinal vertebrae causing the disc to swell. The height is lost quickly when gravity is restored.


A lot of the highest G loads are felt when the capsules are decelerating from orbital velocity as the vehicle is re entering the atmosphere.  Esp. during off nominal entry profiles.  We are talkking about decelerating from 17,500 mph to a terminal velocity speed.  The parachute speed to the retro rocket firing is jolting, but the sustained G loads are much less.

2 football players tackling each other reach accelerations of 70 g's, but only for a few milliseconds.

peace
Hog

You bring up some really good points Hog.  For example, the magnitude of deceleration loads on crew during reentry never occured to me.  Any data showing crew injuries from those loads?  Still, and as I'm sure you understand, the sheer magnitude of g loads is not the only important factor when looking at injury potential.  On-set rate, duration (as you alluded), direction (X,Y,Z axes) etc of the loads are as important as magnitude.  Much of the data/understanding we have on such loadings, exspecially in the Gx axis, came from Col Stapp's rocket sled rides at Holloman.

Using chemical rockets (six per capsule) to decelerate the Soyuz on landing introduces a number of variables produced by the performance tolerances of such rockets.  Both ignition time and burn rate of such rockets is generally +/- 10%, thrust output maybe a little tighter.  A build-up of these, and possible other, tolerances relative to rocket performance parameters could cause signficant asymmetric loading at impact.  In other words, all of the rockets could perform within performance specifications, yet cause the capsule to hit the ground at angles producing injurious loading.  Since a large number of Soyuz landings occured under extreme secrecy during Soviet rule, it's possible there were injuries sustained for these and other reasons of which we have no knowledge.