Re-entry trajectory of Flock 2b-2

From: Ted Molczan via Seesat-l <>
Date: Mon, 3 Oct 2016 23:16:11 -0400
When word arrived that the re-entry of Flock 2b-2 (98067HC / 40951) had been imaged from the U.K. on 2016 Oct 02 near
18:43 UTC, I quickly checked USSTRATCOM for a decay report. I saw that the final TIP message reported decay at 22:24:00
UTC, near 51.1 S, 97.8 E, with a time uncertainty of 46 minutes. I doubted that the TIP message could be off by nearly
four hours, but analysis of the observations reduced from the images confirms that that the re-entry occurred near 18:43
UTC. The mass of the object, 4.5 kg, is by far the lowest of the more than 250 historical re-entry sightings that I have
catalogued. The next closest objects were greater than 60 kg.

Richard Fleet recorded the fireball from Wilcot, Wiltshire, England, UK, using two meteor cameras. I relied on the
observations reduced from Richard's video by Cees Bassa:

I looked for a TLE that when propagated to decay using GMAT 2015a with a realistic area to mass ratio, would agree
closely in time and track with the observed trajectory.

I am not certain of the exact configuration and mass of Flock 2b-2. My guess is that it was similar to Flock 1C,
described in its orbital debris assessment report:

It was a 0.1 m X 0.1 m x 0.34 m rectangular prism, with a pair of 0.26 m x 0.3 m solar arrays. It's mass was 4.5 kg. 

Without the arrays, its mean area to mass ratio would have been about 0.01 m^2/kg. With the solar arrays facing into the
direction of motion, A/m was about 0.042 m^2/kg.

I found that propagating the penultimate TLE (epoch 16276.64232194) with A/m of 0.03481 m^2/kg, closely matched the
observations. Agreement in time was within about 1 s, and track within 1 deg.

The GMAT script used to generate the trajectory data is here:

To use the script, it may be necessary to edit the file paths at line 52 and 57. The latter points to a file of space
weather data, named sw19571001c.txt. It consists of data downloaded this morning from Dr. T.S. Kelso's CelesTrak site.
Use the contents of either of the two files on the following page.

For convenience, I have embedded the trajectory data into an ephemeris generating spreadsheet, which can be used to
evaluate suspected sighting reports:

The spreadsheet opens to an ephemeris for London, England at 5 s time intervals. The second sheet contains data at 1 s
intervals, which is helpful when evaluating numerical observations. Ephemerides for different locations can be computed
by editing the co-ordinates at col 15, rows 2-4.

Ted Molczan

Seesat-l mailing list
Received on Mon Oct 03 2016 - 22:16:51 UTC

This archive was generated by hypermail 2.3.0 : Tue Oct 04 2016 - 03:16:51 UTC