[Neocp_artsats] hb0009 = ZTF0IiT = ETBO, I think

Bill Gray pluto at projectpluto.com
Fri Mar 19 22:58:10 EDT 2021


    At the very least,  hb0009 is geocentric junk :

Orbital elements:  hb0009
    Perigee 2021 Mar 19.960667 +/- 0.00179 TT = 23:03:21.6 (JD 2459293.460667)
Epoch 2021 Mar 20.0 TT = JDT 2459293.5                        Gray
M  15.134154860 +/- 0.7             (J2000 equator)
n 384.767160832 +/- 1.69            Peri.   14.817302 +/- 0.044
a 40408.38627 +/- 118               Node     5.077057 +/- 0.0026
e   0.69818938 +/- 0.00158          Incl.   40.588751 +/- 0.024
P1347.28m/0.936d           H 32.8   G  0.15   U 13.1
q 12195.67981 +/- 99.5    Q 68621.09273 +/- 136
 From 6 observations 2021 Mar. 19 (3.2 hr); mean residual 0".897

    By default,  Find_Orb latches onto a higher geocentric orbit and
fits four observations badly.  Set a distance of 70000 km,  do a few
Herget steps and a few full steps,  and it converges to this much
more reasonable orbit.  The residuals look bad,  especially since
ATLAS tends to get tiny residuals for bright objects :

Residuals in arcseconds:
210319 T08 1.07- 1.75+    210319 T08 .384- .501+    210319 T08 .331+ .304-
210319 T08 1.14+ 1.86-    210319 T08 .131+ .226-    210319 T08 .157- .138+

    But the large residuals are entirely because this is a fast-mover.
Put the resids into along-track in seconds/cross-track in arcseconds
form,  and suddenly,  the observations seem quite reasonable :

Residuals in seconds along-track and arcseconds cross-track :
210319 T08 -.59s .117-    210319 T08 -.19s .020+    210319 T08 +.13s .080-
210319 T08 +.63s .115+    210319 T08 +78ms .026+    210319 T08 -60ms .035+

    The orbit looks like a passable match to an object found by
ZTF three months ago.  The orbit was so miserably determined that
I wasn't even sure it was geocentric,  but I added it to my list
of "betcha somebody's going to find this again someday" objects.
Not much is in orbits at this inclination with this eccentricity,
so a chance match is unlikely.

Orbital elements:  ZTF0IiT
    Perigee 2020 Dec 21.587250 +/- 0.809 TT = 14:05:38.4 (JD 2459205.087250)
Epoch 2020 Dec 22.0 TT = JDT 2459205.5                        Gray
M 127.254601146 +/- 120             (J2000 equator)
n 308.309464151 +/- 380             Peri.  248.312695 +/- 35
a 46839.50195 +/- 38469             Node     3.334993 +/- 14
e   0.62942143 +/- 0.513            Incl.   40.190057 +/- 1.6
P1681.40m/1.168d           H 32.7   G  0.15   U 16.7
q 17357.71545 +/- 38259    Q 76321.28845 +/- 38753
 From 4 observations 2020 Dec. 22 (44.5 min); mean residual 0".387

    Unless more data comes in,  I don't expect to actually find an orbit
linking ZTF0IiT = hb0009,  especially since the object is probably an
ETBO.  (Which means I could probably fit a bunch of orbits to the
current data,  and would believe none of them very much.)

-- Bill



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