MMS spacecraft have specular flashes

From: ronlee--- via Seesat-l <>
Date: Mon, 16 Mar 2015 22:05:44 -0600 (MDT)
I finally received day 15075 elsets today.  The Centaur is in
enough of a different orbit (mean motion) that it was never
seen in my previous sightings of these satellites.

I decided to observe the satellites a short arc further along
in their orbit to increase the observing time in an effort to
get a better magnitude.

Imagine my surprise when the first spacecraft (MMS 1) came into
view with a specular flash. Initially I thought that it was an
optical anomaly but that was discounted as the flashes repeated.

I simply counted the flash interval in my mind and it was
roughly 3.5 seconds.

I used the stopwatch for the next three spacecraft and the
flash interval is closer to actual as shown below:

MMS 1  ~3.5 seconds (least accurate)
MMS 2  2.5 seconds
MMS 3  2.5 seconds
MMS 4  3.0 seconds

There may have been secondary flashing at much lower intensity
but that is not confirmed.  Magnitude of the flashes is about
six but that has some uncertainty.

The center right ascension and declination of the observing
field is RA 11 hours, 16.3 minutes, Dec +12 deg, 43.5 min (J2000).

This is a few degrees below Theta Leonis.  The two brighter stars
in the field of view were HD97937 and HD97938 and close to M65
and M66.

Time of passing through the center of the field of view is
shown below and is within a few seconds.  All times are UTC on
17 March 2015

MMS 1    2:45:22 UTC
MMS 2    2:48:35 UTC
MMS 3    2:50:17 UTC
MMS 4    2:51:59 UTC

Observing location:  Falcon, CO USA
Lat=   38.9478  North
Long=  -104.5614  (104.5614 West)
Alt=   2073 meters

MMS magnitude when not flashing sometimes was 11 or less
but on average was closer to 10.  Based upon that, I will
lower my previous standard magnitude of 6 to 6.5.

I have no way to determine how to predict future flashing
other than to look in the same RA/Dec.  Perhaps someone
can use this information to predict future flashes
which may be observable in binoculars.

As for the timing, a MMS press kit states that they
rotate at three revolutions per minute.  That is one
revolution every 20 seconds.

There are eight solar panels (typically reflective)so
20 seconds divided by eight equals 2.5 seconds between
flashes. It looks like my times for MMS 2 and 3 are good.

MMS 1 flash timing was ballpark anyway.  I will have to
recheck the stopwatch on MMS 4 to see if I made a mistake
on it.

Observations made with an 8 inch Celestron telescope.

Press kit link below:

Ron Lee

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Received on Mon Mar 16 2015 - 23:06:23 UTC

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