[meteorite-list] Chelyabinsk trajectory modeling -- how well did we do? Part 1 of 2

From: Michael Farmer <mike_at_meteoritecentral.com>
Date: Wed, 16 Oct 2013 11:57:46 -0700
Message-ID: <0AA7555B-CD30-48AB-9DBE-3138ADF15A3C_at_meteoriteguy.com>

Amazing work Rob, was every helpful while hunting in Chelyabinsk. Your work is much appreciated.
Did you ever get a piece?
Michael Farmer


Sent from my iPhone

> On Oct 16, 2013, at 11:10 AM, "Matson, Robert D." <ROBERT.D.MATSON at leidos.com> wrote:
>
> Hi Jim,
>
>> What I would like to know, after they can confirm the weight of this
> last
>> recovery, is if path calculations proved accurate by those that were
> doing
>> the calculations????? Was anyone able to actually calculate the
> trajectory
>> accurately (different mass calculations) with the information that was
> able
>> to be gathered over the first month or so after the fall. Has anyone
>> calculated any dark flight data based on any of the finds that have
> been
>> recovered?
>
> The answers are yes, yes and yes. :-)
>
> Esko Lyytinen was one of the first to generate a preliminary orbit and
> track on
> February 15th -- less than 24 hours after the event. Esko and I worked
> with Bill
> Gray to generate an ephemeris (just on the off-chance that the asteroid
> had any
> chance of having been serendipitously imaged in the days/hours prior to
> impact),
> which Bill posted at the following link:
>
> http://projectpluto.com/temp/chelyab.htm
>
> Unfortunately, the approach direction had a solar elongation of less
> than
> 20 degrees, so ground-based telescopic observation was not possible.
>
> One week later, I triangulated two space-based images of the meteor,
> yielding
> an estimate of the following terminal burst time/location:
>
> ECF position (in km) at 15 Feb 2013 03:20:33 UT: 1787.29, 3237.68,
> 5207.62
> ECF velocity vector (in km/sec) at same time: +12.8, -13.3, -2.4.
>
> This vector's bearing is 279.8 degrees -- within only a few degrees of
> what Esko
> had computed a week earlier from ground-based videos.
>
> With the vector in hand, the next task was to locate upper atmospheric
> wind data
> so that I could run my dark flight model, and I quickly found radiosonde
> data
> for the two nearest stations: Orenburg and Kurgan. Since Kurgan was
> about half
> the distance from the meteor as Orenburg, I weighted the Kurgan data
> correspondingly higher to come up with my profile. I ran my
> ablation/dark-flight
> model assuming a typical chondritic density, generating preliminary
> impact
> points for masses of various sizes from 10 grams to 100 kg. Here's the
> message
> I sent to Bill, Esko and Marco Langbroek on 22 February (and a similar
> message
> to Peter Brown):
>
>> Hi Esko/Bill/Marco,
>>
>> Using radiosonde upper atmospheric wind data from Kurgan launched a
>> little over 3 hours prior to the fall, my dark flight code computes
>> the following impact coordinates for a variety of post-ablation masses
>
>> (assuming bulk density of 3.3 g/cm^3):
>>
>> 100 kg: 54.850 N, 60.448 E
>> 10 kg: 54.821 N, 60.665 E
>> 1 kg: 54.794 N, 60.844 E
>> 100 g: 54.765 N, 60.983 E
>> 30 g: 54.749 N, 61.041 E
>> 10 g: 54.728 N, 61.122 E
>>
>> My heaviest mass does not quite reach Chebarkul Lake, but it is within
>
>> the uncertainty of the terminal burst coordinates that I was provided.
>> Overall, I think my impact coordinates may be a little south of the
>> actual impact track, suggesting my wind speed estimate is a little on
>> the high side.
>>
>> --Rob
>
> Interestingly (in light of the mass just recovered from Lake Chebarkul),
> Esko suggested I extend the mass range to cover 1000 kg, which I did.
>
> The very next morning (Saturday, Feb. 23rd) a Central Bureau Electronic
> Telegram was released for the trajectory and orbit of the Chelyabinsk
> superbolide:
>
> - - - - - -
> Electronic Telegram No.
> 3423
> Central Bureau for Astronomical Telegrams
> INTERNATIONAL ASTRONOMICAL UNION
> CBAT Director: Daniel W. E. Green; Hoffman Lab 209; Harvard University;
> 20 Oxford St.; Cambridge, MA 02138; U.S.A.
> e-mail: cbatiau at eps.harvard.edu (alternate cbat at iau.org)
> URL http://www.cbat.eps.harvard.edu/index.html
> Prepared using the Tamkin Foundation Computer Network
>
>
> TRAJECTORY AND ORBIT OF THE CHELYABINSK SUPERBOLIDE
> Jiri Borovicka, Pavel Spurny, and Lukas Shrbeny, Astronomical
> Institute
> of the Academy of Sciences, Ondrejov, Czech Republic, report that they
> have
> computed the atmospheric trajectory and velocity of the superbolide of
> 2013
> Feb. 15.139 UT (3h20m UT), which caused some damage in the city of
> Chelyabinsk, Russia. They used seven casual video records provisionally
> calibrated with Google Maps tools. The trajectory was assumed to be
> linear.
> The geographical coordinates of selected points along the trajectory are
> as
> tabulated below:
>
> Relative Longitude Latitude Height Velocity Notes
> Time (s) (deg E) (deg N) (km) (km/s)
>
> 0.00 64.266 54.508 91.83 17.5 beginning
> of
>
> registration
> 9.18 61.913 54.788 41.02 17.5 minor
> flare
> 11.20 61.455 54.836 31.73 17.5 major
> flare
> 12.36 61.159 54.867 25.81 17.5 flare
> 13.20 60.920 54.891 21.05 12.5 minor
> flare
> 16.20 60.606 54.922 14.94 4.3 end of
>
> registration
>
> The observed trajectory was 254 km long. The azimuth of the trajectory
> was
> 279.5 degrees, and the slope was 16.5 degrees to the horizontal (for the
> end
> point). The uncertainty of the radiant is about one degree. The
> uncertainty
> of the position of the trajectory is about 1 km (at the beginning, up to
> 4
> km).
> The pre-entry object that caused the superbolide was relatively
> fragile.
> Severe fragmentation started at a height of 32 km under dynamic pressure
> of 4
> MPa. The mass of the largest fragment, which landed in the lake
> Chebarkul,
> was estimated to be 200-500 kg. One or two meteorites of the mass of
> several
> tens of kg can be expected not far from the village Travniki. One piece
> of
> mass approximately 1 kg may have landed to the northwest of Shchapino.
> Numerous small fragments can be expected in the wide band located about
> 5 km
> south of the trajectory, mostly between longitudes 60.9 and 61.35
> degrees.
> The blast wave, which strongly affected Chelyabinsk, was generated
> between heights of 25 and 30 km. The radiant and heliocentric orbit
> were
> calculated to be as follows:
>
> Apparent radiant: Right ascension 328.6 +/- 1.0 deg
> (equinox 2000.0) Declination +8.0 +/- 1.0 deg
> Velocity 17.5 +/- 0.5 km/s
>
> Geocentric radiant: Right ascension 334.7 +/- 1.2 deg
> Declination -1.0 +/- 1.4 deg
> Velocity 13.2 +/- 0.7 km/s
>
> Orbit: a = 1.55 +/- 0.07 AU e = 0.50 +/- 0.02
> q = 0.768 +/- 0.011 AU Q = 2.33 +/- 0.14
> AU
> (equinox 2000.0) Peri. = 109.7 +/- 1.8 deg Node = 326.41 deg
> i = 3.6 +/- 0.7 deg
>
> The data do not allow determination of the initial mass of the object
> prior
> to entering the atmosphere. The trajectory will be further refined in
> the
> future, provided that proper in situ calibrations of the videos are
> made.
>
>
> NOTE: These 'Central Bureau Electronic Telegrams' are sometimes
> superseded by text appearing later in the printed IAU Circulars.
>
> (C) Copyright 2013 CBAT
> 2013 February 23 (CBET 3423) Daniel W. E.
> Green
>
> - - - - - -
>
> This trajectory confirmed my suspicion that the true track was slightly
> north of my Friday estimate, so I reran the dark flight model using the
> new
> CBAT-based trajectory. Midday Saturday, I sent this to Esko, Marco and
> Marc
> Fries (and a similar message to Peter Brown):
>
>> Hi Esko/Marco,
>
>> Here are the predicted wind-drifted impact coordinates using the
> trajectory
>> from the CBAT:
>
>> Mass Lat Long
>> ------- ------- -------
>> 1000 kg 54.9559 60.1786
>> 100 kg 54.9268 60.4247
>> 10 kg 54.8975 60.6452
>> 1 kg 54.8676 60.8369
>> 100 g 54.8359 60.9954
>> 30 g 54.8186 61.0637
>> 10 g 54.8013 61.1201
>
>> The heaviest masses look like a very nice match to Lake Chebarkul. ...
>
> - - - - -
>
> A line connecting the 100-kg and 1000-kg coordinates above intersects
> the
> southern half of Lake Chebarkul -- meaning that a multi-hundred kilo
> mass
> would be required to "hit the bull's eye". Esko addressed this point
> specifically:
>
> "Ok Rob, this would mean a hit to the lake with a weight of about 300 kg
> quite well consistent with the CBAT value - range. This is also quite
> well
> consistent to our value of around 400 to 800 kg."
>
> To be continued in part 2, hopefully later today... --Rob
>
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Received on Wed 16 Oct 2013 02:57:46 PM PDT