RE: Confusing satellites
Ted Molczan (molczan@neocom.ca)
Thu, 9 Nov 1995 14:17:55 -0500
Walter Nissen quoted the following from Russell Eberst:
> It is very easy to confuse satellites what with the multitude
> of objects in orbit. I try to fit in observations of as many
> satellites as possible, as consistent with being accurate. This
> of course involves a compromise and often completing obs on one
> satellite, with only a minute or so before the next is due.
> So I get the predicted R.A. and Dec and check if the azimuth and
> elevations are increasing or decreasing i.e. if it's going
> left to right or right-to-left and if its going up or down.
> Grabbing the binoculars, I point them where the predicts
> indicate, and look for something going up (or down) and l>r or
> r>l. If an object is seen that doesn't fit the expectation then
> it is ignored, and I wait for one that does fit.
Russell describes a challenge faced by all intensive observers.
In the late 80's, I did some fairly intensive observing, that is
to say, I tried to obtain at least two accurate time/position
measurements per object, tracking objects as little as 5 minutes
apart in time. That kind of activity puts a real premium on
such skills as organization, map reading, "star hopping",
perception and memory. Even with well developed skills, it is
always a challenge to keep up with the parade of satellites.
Often I found my self fighting the clock, trying to adequately
document my last obs (sufficient for later detailed reduction
of position and time) while leaving sufficient time to acquire
the next target.
Russell's comments about checking whether or not the expected
object will be moving up or down or left to right describe exactly
the process I followed. The only problem, is that it takes precious
time, so I found a way to automate the process, as the following
sample ephemeris shows. In particular, I draw your attention to
the column labeled "FE":
9/11/95 18:05 - 23:05 ST J2000.0 EL > 15 40 Pleasant Blvd.
Radarsat 95059A 23710 Bull = 17 Ted Molczan
SGP4 Age = 2.1 d Unc = 0 s ( 25%) 416-921-1564 (h/w)
TIME %I Mv AZ EL R.A. DEC FE VANG RANGE ALT
-------- -- ---- --- -- ----- ----- -- ---- ----- -----
17:58:17 42 6.6 178 15 21:01 -31.5 7 0.11 2016 787
17:59:24 41 6.2 182 23 20:45 -22.9 7 0.16 1603 788
18:00:11 40 5.8 187 31 20:30 -14.6 7 0.22 1337 788
18:00:45 39 5.5 193 39 20:16 -6.6 7 0.28 1165 788
18:01:12 38 5.3 200 45 20:02 1.3 7 0.34 1048 789
18:01:34 37 5.2 209 52 19:48 8.9 7 0.40 970 789
18:01:53 37 5.1 220 57 19:34 16.2 8 0.44 919 789
18:02:10 36 5.0 233 61 19:19 23.2 8 0.47 888 789
18:02:26 36 5.0 249 63 19:02 30.0 9 0.49 874 790
18:02:41 36 4.9 266 63 18:43 36.3 9 0.49 873 790
18:02:56 37 5.0 281 61 18:22 42.3 10 0.48 886 790
18:03:12 37 5.0 294 57 17:55 48.1 10 0.45 913 790
18:03:29 38 5.1 305 53 17:21 53.3 10 0.42 956 790
18:03:47 39 5.2 313 48 16:41 57.6 11 0.37 1015 791
18:04:07 40 5.3 319 42 15:53 60.7 11 0.33 1094 791
18:04:30 40 5.5 324 37 14:57 62.5 11 0.28 1200 791
18:04:57 41 5.7 328 31 13:59 62.7 11 0.23 1338 791
18:05:30 42 6.0 332 25 13:03 61.3 11 0.18 1523 792
18:06:11 43 6.3 335 19 12:16 58.6 11 0.14 1767 792
18:07:03 44 6.6 338 13 11:37 54.8 11 0.11 2093 793
To understand FE, picture the field of view you see through your
binoculars as the face of a clock. The FE is the closest hour of the
clock face at which the object will enter your field of view, assuming
you are centred on the RA and DEC of the ephemeris point. So an FE of
6 means the object will move from bottom to top; an FE of 9, means it
will move from left to right. I simply note the FE beside each point
I plot in my star atlas when I prepare for an observing session. No muss,
no fuss.
In addition to reducing the risk of tracking the wrong object, the FE
is helpful when looking for very faint objects, because it helps one to
focus his/her gaze at the points where the object is most likely to
pass.
Computing the FE is not particularly difficult, as long as you are
good at vector algebra. I have long ago forgotten most of the vector
algebra I learned in school, but I have been able to count on some of my
younger friends to help me out. If anyone wants the formulas in the
form of BASIC statements, compatible with SGP/SGP4, I will be pleased
to dig them up and post them.
bye for now