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[i]Until recently (last 10 years) it was thought humans could not survive impacts of 100g's or more. There was all kinds of misinformation about safety in automotive wrecks, much of it "intuitive" or shade-tree in nature, and therefore incorrect or at best unreliable. Progressive motor racing sanctioning bodies, and the inventors of the HANS Device, starting investigating vehicle crashes in a scientific manner using laboratory sled tests to help understand the situation. Impacts are over in under 100 milliseconds (often half that) and are very complex events. Dr. Hubbard (HANS inventor) was instrumental in developing the crash dummy used to simulate these impacts. Even today it is not possible to perfectly duplicate a human in an auto crash. The current dummy, for instance, although very advanced has a solid spine and an aluminum chest - both very different from real people. Research, mainly by HANS and others, showed drivers could survive much higher wrecks if they were packaged correctly. Put simply, you have to limit the things the driver can interact with. In 1999, Ritchie Hearn survived a 140g impact with a concrete wall - he suffered a broken foot, and was wearing a HANS Device. In 2001, there were four high profile deaths in NASCAR auto racing - one which was Dale Earnhardt. Earnhardt died at an impact speed of 43mph. He would absolutely have been saved by a HANS Device, this was not a big impact. This fatality pushed NASCAR into the front lines of safety research. Previously a bit behind in this area, they now lead the world. They have a database of over 4,000 crashes that attempts to correlate accident severity (both in delta V or change in velocity and peak g - there is some discussion over which is more valuable) with injury. The military has similar databases, and there is some kind of accident severity index that allows data to be used back and forth between the databases. However, the seat and harness systems used in these safety systems are very confining. They are not practical for a space vehicle. One critical value is the tension put on the straps. Often a crew member reaches in and helps the driver strap down. That isn't possible in a returning space vehicle, and the astronauts might be tired or otherwise busy and not give this enough attention. But it is super critical to the performance of the restraint system, and NASA found this out in early testing. They would make a tiny change in the tightness of the straps and get a huge change in the test result and got confused, not understanding the importance of this value. So the challenge is to give NASA astronauts the level of safety a modern race car offers. NASA thinks it must limit the impacts to 20g's and this brought some discussion. Some engineers believe the capsule can be designed to safely see the crew through a 100g impact. NASA counters that kind of impact would destroy the vehicle so it wouldn't matter. NASA misses the point that drivers often walk away from destroyed vehicles, and the race boys miss the point that a NASCAR does not contain pressurized hydrazine or ammonia etc. NASA wants to use the ideas of smart safety experts including their own, and the NASCAR injury prediction database, to try and establish safety levels for Orion.[/i]
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