Re: [meteorite-list] Speed that meteors enter dark flight?
There are a number of papers out there which address modeling meteor flight, both during ablation and dark phases. In fact, you can produce a reasonably good estimate with nothing more than some basic physics and an Excel spreadsheet. For more accurate analysis, you need to implement a good numerical integrator and incorporate an ablation/fragmentation model. Dark flight modeling is fairly straightforward, but depends on accurate high altitude wind data, which may or may not be available, depending on the time and location of the event you are studying. Chris *** Chris L Peterson Cloudbait Observatory http://www.cloudbait.com On 3/7/2012 11:55 AM, Graham Ensor wrote: Thanks Chris...that gives me something to work with...It's one of those questions I've wanted answering for a while now. Will be interesting to see any advice on calculating the trajectory curve from this? Cheers, Graham __ Visit the Archives at http://www.meteoritecentral.com/mailing-list-archives.html Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list
Re: [meteorite-list] Speed that meteors enter dark flight?
The simple answer is it depends on a lot of changing factors and broadly ranging bounded assumptions. I can only share some of those here to show why it is not a an easy answer. http://en.wikipedia.org/wiki/Drag_coefficient For one of those assumptions, you have to select amongst some drag coefficients/cross-sections. Typically: sphere, half sphere, cone and streamlined. One might assume that anything tumbling with sharp edges is really facing high sheer forces and more likely to shear apart. The drag cross section governs the air dampening of the gravity acceleration which typically lies between 120-400 miles per hour terminal velocity. This in itself requires choosing an assumption. The formulas in the link require an air density (aka fluid density) average value as it isn't set up for a changing density which can be considerable in a steep trajectory. There is a general acceptance that the air is too thick below 5 miles/8 km above sea level for a meteor below 1 meter to maintain incandescence velocities. ( 88% of the atmosphere lies at or below 7 miles) Air density is increasing at a dramatically increasing rate. In some respect so long as it is a deep penetration to say under 12miles there should be ample distance to travel to a point of all cosmic velocity being bled off and fall from gravity acceleration alone. We'll assume a range of 4000-4500 kph for retardation. One has to estimate a mass where total cosmic velocity can be expended: which can be up to 10 tons/9000kg according to the AMS faq page. I've also heard up to one meter but if you want to choose a typical value pick 1kg. One has to also integrate an acceleration factor as gravity is at work even during retardation to extinction( note: retardation point is used in our science but may be a misnomer but I won't get into a crust argument). So there is quiet a bit in the way of assumptions and perhaps a lot more inaccuracy of accepted values. Since we are in the I wonder mode-- lets choose a surrogate meteorite/oid which has more data: http://hypertextbook.com/facts/JianHuang.shtml Freefall parachutist records. Captain Joseph Kittinger entered the record books when he stepped from the gondola of a helium balloon floating at an altitude of 31,330 m (102,800 feet) and took the longest skydive in history He fell for four minutes and 36 seconds, reaching a maximum speed of 614 miles per hour (988 km/h before opening his parachute at 18,000 feet (5,500 m). It takes an average sky diver 14±1 to fall one mile. according to a graphic (pdf) on this page: http://www.greenharbor.com/fffolder/math.html and a skydiver will fall about 10,000ft. in one minute including the 12 seconds to reach terminal velocity of 120mph. All that said it Chris's answer is pretty much within a 3-10 second limit and impact in under 2 minutes max 95% of the time. Elton Sorry for all the co-mingling of metric and SAE values. On Wed, Mar 7, 2012 at 1:58 PM, Chris Peterson c...@alumni.caltech.edu wrote: It depends on the mass of the body. But realistically, under typical conditions that might lead to meteorite production, I think it's safe to say that this happens almost instantly. For example, a 100 kg stone that survives to 20 km height will be experiencing a deceleration of ~1500 m/s^2. A 10 kg stone will experience ~4000 m/s^2. Of course, no stone is likely to survive the forces that would result without breaking up. You need to play all sorts of games with different parameters for mass, speed, and height to find survivable scenarios. They all produce a very short period of dark flight before terminal velocity. This is why the retardation point is typically overhead any strewn field, and you don't usually have meteorites significantly down field from the retardation point. In fact, wind during dark flight may move meteorites farther than their last bit of momentum did- and that can be in any direction. Chris *** Chris L Peterson Cloudbait Observatory http://www.cloudbait.com On 3/7/2012 11:45 AM, Mike Hankey wrote: the follow up to this question/answer I still wonder about is: after dark flight begins, how many seconds will it take to completely decelerate so that all forward momentum is lost after dark flight starts. for example: if the meteor goes dark at 4km/s how many seconds before it will be at 0km/s and/or what does that deceleration curve look like? __ Visit the Archives at http://www.meteoritecentral.com/mailing-list-archives.html Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list
Re: [meteorite-list] Speed that meteors enter dark flight?
Ablation and incandescent flight typically end at about 3-4 km/s. Chris *** Chris L Peterson Cloudbait Observatory http://www.cloudbait.com On 3/7/2012 10:43 AM, Graham Ensor wrote: Hi All, I have been wondering lately if there have been calculations done on the speeds that meteors stop their hot flight and enter dark flight. What speed does a body have to reach before it generates a hot plasma ball that shows as a fireball...or in other words how fast could a body travel without becoming incandescent. I know this is going to vary depending on altitude or thickness of atmosphere and possibly size. Has anyone seen data that shows this? Cheers, Graham __ Visit the Archives at http://www.meteoritecentral.com/mailing-list-archives.html Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list
Re: [meteorite-list] Speed that meteors enter dark flight?
the follow up to this question/answer I still wonder about is: after dark flight begins, how many seconds will it take to completely decelerate so that all forward momentum is lost after dark flight starts. for example: if the meteor goes dark at 4km/s how many seconds before it will be at 0km/s and/or what does that deceleration curve look like? On Wed, Mar 7, 2012 at 1:14 PM, Chris Peterson c...@alumni.caltech.edu wrote: Ablation and incandescent flight typically end at about 3-4 km/s. Chris *** Chris L Peterson Cloudbait Observatory http://www.cloudbait.com On 3/7/2012 10:43 AM, Graham Ensor wrote: Hi All, I have been wondering lately if there have been calculations done on the speeds that meteors stop their hot flight and enter dark flight. What speed does a body have to reach before it generates a hot plasma ball that shows as a fireball...or in other words how fast could a body travel without becoming incandescent. I know this is going to vary depending on altitude or thickness of atmosphere and possibly size. Has anyone seen data that shows this? Cheers, Graham __ Visit the Archives at http://www.meteoritecentral.com/mailing-list-archives.html Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list __ Visit the Archives at http://www.meteoritecentral.com/mailing-list-archives.html Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list
Re: [meteorite-list] Speed that meteors enter dark flight?
Thanks Chris...that gives me something to work with...It's one of those questions I've wanted answering for a while now. Will be interesting to see any advice on calculating the trajectory curve from this? Cheers, Graham On Wed, Mar 7, 2012 at 6:14 PM, Chris Peterson c...@alumni.caltech.edu wrote: Ablation and incandescent flight typically end at about 3-4 km/s. Chris *** Chris L Peterson Cloudbait Observatory http://www.cloudbait.com On 3/7/2012 10:43 AM, Graham Ensor wrote: Hi All, I have been wondering lately if there have been calculations done on the speeds that meteors stop their hot flight and enter dark flight. What speed does a body have to reach before it generates a hot plasma ball that shows as a fireball...or in other words how fast could a body travel without becoming incandescent. I know this is going to vary depending on altitude or thickness of atmosphere and possibly size. Has anyone seen data that shows this? Cheers, Graham __ Visit the Archives at http://www.meteoritecentral.com/mailing-list-archives.html Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list __ Visit the Archives at http://www.meteoritecentral.com/mailing-list-archives.html Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list
