Monday, September 19, 2005, 23:24:36 LT
Just an hour ago, captured what now is becoming an
old friend: USA 129 (96-072A, #24680, a "Keyhole").
Image fogged by moonlight, but trail well discernable.
Two apparently good points, both about 0.1s late
relative to Ted's latest elset, with good crosstrack
values.
Spent a good part of the day searching for TNO's and
asteroids in NEAT data.
Both Ted and Pierre mailed me to point to the nice
residuals of yesterdays USA 129 observations.
Monday, September 19, 2005, 11:26:35 LT
Quick update to my last post:
* The context of other observations on USA 129
suggests that the delta T problem is gone.
This might indicate the change in used camera
settings indeed was the cause.
* Alas, I could not pry more than two nights of
data on the asteroid out of the NEAT archives.
This means it is no use submitting to the MPC.
Last night was an astrometry fiesta.
I captured Lacrosse 3 (97-064A, #25017) during its
19:40 UTC pass, crossing Delphinus. Following this
I captured USA 129 (96-072A, #24680) as it crossed
from Pegasus into Andromeda. The images were
heavily fogged by moonlight and the trails marginal,
but measurable.
In addition to this, I bumped into a potentially new
main belt asteroid while searching for TNO's in the
NEAT image archives. I am still in the process of
prying and measuring more images out of the archive
in order to get enough nights to submit it to the MPC.
I was quite tired last night, so I stopped early and
am in the process of continuing astrometry this morning.
It appears that my delta T values again come out
some ~0.3s "early" relative to other stations.
As this was not the case for my August data, I have
begun to suspect it is the result of my recent
change in camera settings (other setting for colour
and contrast, to bring out fainter trails better).
Apparently, this also changed the intitiation time
of the camera by an extra 0.3s.
As of now I will use the empirical 0.3s value to
adjust my timings accordingly.
Monday, September 12, 2005, 23:59:46 LT
An aurora warning was out, as the geomagnetic
activity was very high due to a series of X-class
flares on the sun today and yesterday.
Aurora was not seen, but Keyhole satellite USA 129
(96-072A, #24680) was captured by the camera at
20:43:10 UTC. A clear unambiguous trail is visible
on the image, yielding two points. I am very curious
as to how the delta T values will compare to those
of other stations this time. It will be running "early"
anyway because of the high geomagnetic activity (which
increases the drag, as the atmosphere expands due to
it).
An exposure was made one minute earlier too, but the
satellite is not visible on that image.
I posted a number of accuracy test lately. But now some
results have appeared that deviate. It concerns the data
on 96-072A (USA 129) of the 8th.
The problem is in the delta T values. They come out some
0.3-0.5s too early compared to other data gathered by
other stations around that time. It concerns data from
two separate images.
In below table, the asterisk-marked points are mine. The
other points are by David Brierley and Peter Wakelin.
The given delta T values are relative to Ted Molczan's
elset 05253.13803400.
deltaT
-0.10
-0.11
-0.37 *
-0.29 *
-0.48 *
0.04
0.06
0.07
0.07
0.08
0.11
0.05
0.10
-0.02
-0.11
-0.08
-0.03
-0.03
-0.03
-0.03
0.04
I am at a loss to explain this deviation.
Something in the timing is not right, but what?
The crosstrack value of the second point initially was
somewhat off (0.07 degree). This turned out to be because
I had switched the image reference time and object position
time in Astrorecord. When this was corrected, the crosstrack
value came out fine (but the delta T difference remained).
Yesterday evening I captured this image of the American Keyhole imaging satellite USA 129 (96-072A, #24680) starting to flare brightly near the zenith. A few seconds after the end of this exposure it reached magnitude -1.5. A second exposure starting 30 seconds later only shows a faint trail, estimated about magnitude +3.0.
2005-09-05, 23:40 LTLast night I could not get into sleep, even though I
tried hard. I hope this is not a return of the insomnia
that plagued me for months, untill a month ago I was
finally able to stop with sleeping medication.
As I was still awake at 4:30 am local time, I decided to
bring out the camera and target Lacrosse 4 (00-047A),
who made a pass around 5:08 am, the end of which was just
visible for me low in the east.
The winter constellations were rising this early in the
morning: the Pleiades and Mars shone brightly high in the
sky. Lacrosse 4 moved on the Auriga-Gemini border as it
cleared the edge of the house in the alley gap between my
house and the bank building opposite me. I captured a faint
but measurable trail.
A few minutes later I tried to target the Lacrosse 5rk
(the rocket that launched Lacrosse 5), but failed to
see it both visually and on the photograph.
I've been doing some accuracy tests lately to check
on the accuracy of my experimental photographic camera
setup, as I am always striving for improvement.
After comparing some of my datapoints with data by others
on the same satellites earlier (see earlier blog entries),
I took advantage of the current start of nice and favourable
ISS evening passes to use ISS as a test target and compare
obtained positions to an accurate ISS TLE.
I obtained 4 positions from 2 images for ISS during last
evenings 19:55 UTC pass: two (the first two) with ISS in
the zenith, two with ISS going into eclips low in the
southeast.
25544 98 067A 4352 F 20050904195525800 17 75 1900355+263390
25544 98 067A 4352 F 20050904195536500 17 75 1952060+282850
25544 98 067A 4352 F 20050904195635800 17 75 2321209+227230
25544 98 067A 4352 F 20050904195646500 17 75 2339494+210810
Using Scott Campbell's SatFit I compared them to an accurate
TLE for epoch 05247.96166413
The result is as follows:
AZ EL ASP XTRK deltaT Perr
( 1) 184.50 64.32 83.18 0.02 -0.02 0.028
( 2) 157.31 65.03 94.14 0.01 -0.02 0.027
( 3) 96.58 34.40 137.74 0.00 -0.06 0.032
( 4) 94.09 30.36 141.68 0.03 0.17 0.091
sum 0.05184
Of course I was very happy with this result. When I use
the TLE issued previous to the above one (05247.68884259),
I get:
AZ EL ASP XTRK deltaT Perr
( 1) 184.50 64.32 83.17 0.03 0.18 0.204
( 2) 157.31 65.03 94.12 0.03 0.18 0.205
( 3) 96.58 34.40 137.73 0.00 0.13 0.067
( 4) 94.09 30.36 141.66 0.03 0.37 0.171
sum 0.17140
...and the truth will be somewhere inbetween I guess.
The 4th point merits some comment, as it clearly deviates
in the series. The reason is that the 4th point was
obtained while ISS was going into eclips fast. Instead of
being the true end of the trail due to the end of the
exposure (the reference time for this point), it probably
is the point where ISS crossed the imaging threshold of the
camera while fading out. Hence it being "too late" compared
to the other points.
I've been thinking about the pittfals of my system, and
the obvious one is pointed out by point 4 in the above series.
A start- or endpoint of a trail is not reliable when it is
not marking the start or end of the exposure, but the point
where the brightness of the satellite crosses the imaging
threshold, the trail limiting magnitude of the camera. This can
happen when the sat fades in or fades out (or both) or is faint
and irregular in brightness. When that is the case, it should
translate in a first point that is apparently "too early",
and/or a second point that is apparently "too late". Whenever
such things are visible in my data compared to other datapoints,
this is probably the reason.
But for a bright sat not near eclips, this ISS test again
suggests the digital camera system performs quite well.
So far this little, encouraging test. Hereby, I also want to
thank Scott Campbell for making available his software.
Earlier today I wrote:
"Some 10-15 minutes before Lacrosse 4 I saw a nive bright
sat of about magnitude -1 to -2 low in the sky descending
to the southeast."
Of course, this was ISS.....
Targeted Lacrosse 4 (00-047A, #26473) again this evening.
Observing conditions were poor, the skies were hazy. Some
10-15 minutes before Lacrosse 4 I saw a nive bright sat
of about magnitude -1 to -2 low in the sky descending
to the southeast.
Lacrosse 4 made an Iridium-like flare, something which I
have not seen a Lacrosse do before. Starting at about
magnitude +2.5 when I started the exposure, it brightened
and gave a brief flare of about magnitude +0.5 some 10
seconds after the end of the exposure. The onset of this
was just captured on the image, the end tip of the trail
on the exposure is suddenly bright and fat.
This last point is some 0.2 seconds late relative to elset
05245.92208782
Thursday, September 01, 2005, 17:09:02 LT
Worked last night (31 Aug) with the camera in the new
colour/contrast setting. Images come out more dull now,
but I do have the distinct impression that faint trails
do show up better.
Catched USA 129 (96-072A, #24680), a Keyhole optical
imaging satellite with a decimeter resolution capability.
Faint trail but the measured positions come out fine.
Also catched a sat I initially could not identify. IDSat
gave no clear match. Ted Molczan then identified it as
ENVISAT. It puzzled me that IDSat did not gave me that
match, untill the solution jumped to me this morning
while I was commuting in the bus: a sign error in my
location's longitude? Indeed, a check when back home showed
this to be the case...
Spacewatch resumed operation again a few days ago, so the
mornings that I am at home are filled with hunting NEA's
again...
And after a series of clear nights, it is raining again...
