"Pseudo-MPEC" for SOLRAD 11A = 1976-023C = NORAD 08748 = WB31C9F = XC83E0D = 6N070E7 = 6N070E8
Created 2016 Dec 29 15:10:46 UT using Find_Orb
Some interesting links about this satellite:
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General information on SOLRAD 11 A and B
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NSSDC information about SOLRAD 11A
• Updated pseudo-MPEC based on subsequent observations
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Description of experiments on the SOLRAD 11 satellites
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TLEs (Two-Line Elements) for this object (and other artsats on these pages)
You can click here to get customized ephemerides for this object from the Minor Planet Center's DASO Page.
Discovery story: On 2016 February 8, the Mt. Lemmon Survey (MLS) found a new, fast-moving object, which they designated XC83E0D, and tracked it for 104 minutes. Data was, as usual, posted on NEOCP. There was enough data to see that it was definitely an artificial satellite, in a near-circular orbit with a period of about five days. (As you'll see, I wasn't optimistic about tracking it further.)
Once we realized it was an artsat, the object was dropped from the NEOCP and listed as "XC83E0D was not a minor planet". But we still had the question of what it actually was. The orbit didn't resemble any of the assorted artificial satellites tracked by minor planet observers. The orbit looked as if it might be one of the SOLRAD 11A or 11B spacecraft, or possibly the kick motor used to put them in that unusual orbit. But we didn't really have all that much data. The object was faint, and I assumed we would lose it and have to hope that somebody spotted it again by pure luck. I did make a post on MPML to see if anybody had observations that might not have made it on to NEOCP, but it was a real long shot and I didn't get any takers. Dave Tholen kindly offered to give it a try from Mauna Kea, but it would have been down around magnitude 24 with large ephemeris uncertainty; we agreed it would be a waste of good telescope time.
I ran all this past Peter Birtwhistle and Jonathan McDowell, with whom I've often discussed artsat-related questions. Peter suggested a possible link to WB31C9F, an object observed briefly at the Catalina Sky Survey (CSS) more than a year earlier.
At first, I had doubts about being able to get an orbit linking the two arcs. Running the "new" arc back a year, the uncertainty amounted to three full revolutions. The best-fit orbit missed the WB31C9F observations by more than 50 degrees. This turned out to present less of a problem than I expected, though. I tried constraining the orbit (based still only on the 2016 data) to have a slightly smaller semimajor axis, which caused that "miss distance" to decrease. Eventually, it was only about a degree. I removed the constraint, turned on all observations, and attempted to fit the result. It worked, but with mean residuals of 22 arcseconds.
So I tried again, this time increasing the semimajor axis and going around 310 degrees; in other words, I assumed there had been one fewer orbit over the intervening thirteen months. Again, I got close to the 2015 observations, turned them on, removed the constraint, and did some "full step"s. This time, the mean residual was about 11 arcseconds.
This suggested I was headed in the correct direction, and indeed, when I dropped yet another revolution, I got an orbit with mean residuals of slightly over an arcsecond. (They're only that large because the object is fast-moving. The errors are almost entirely along the direction of motion.)
Jonathan was able to find orbital elements for both SOLRAD 11A and 11B, from 1977 July 1. The satellites were deliberately kept at opposite ends of the earth. Projecting our orbit back, we ended up within four degrees of SOLRAD 11A. (With more data, this later improved to within 1.5 degrees. It actually ought to be even better than that; I suspect non-gravitational forces have confused things a little over the intervening 38 years.)
By this point, I was about 90% confident that WB31C9F and XC83E0D were the same object, and that they were SOLRAD 11A. But on 2016 February 11, Peter got some more observations (shown below) within about ten arcseconds of prediction, dispelling all doubts. Armed with this, I went through the MPC's "one-night stand" file, looking for objects with suitable motion close to the predicted location. It turned out that the object had been observed in 2006, again by CSS, designated 6N070E7 and 6N070E8, about 40' from prediction (but with exactly the correct motion). You can click here for a pseudo-MPEC with all observations included.
As you'll see, the fit is a little rough. There are some non-gravitational forces at work here that are not correctly modelled. (The usual "simple" solar radiation pressure model doesn't help, nor does adding in a tangential term. It looks more as if the object is accelerating or decelerating relative to its orbit around the earth, which would be a little weird.)
Astrometry: 6N070E7 C2006 07 09.45497 23 20 27.70 -06 54 09.5 x16.6 Vr 703 6N070E7 C2006 07 09.45528 23 20 31.77 -06 53 55.0 x16.5 Vr 703 6N070E7 C2006 07 09.45552 23 20 34.94 -06 53 43.5 x16.4 Vr 703 6N070E7 C2006 07 09.45576 23 20 38.29 -06 53 32.2 x16.5 Vr 703 6N070E8 C2006 07 09.45629 23 20 45.42 -06 53 06.2 x16.5 Vr 703 6N070E8 C2006 07 09.45653 23 20 48.62 -06 52 54.9 x16.5 Vr 703 6N070E8 C2006 07 09.45676 23 20 51.79 -06 52 43.5 x16.4 Vr 703 6N070E8 C2006 07 09.45700 23 20 54.92 -06 52 32.1 x16.4 Vr 703 1976-023C C2015 01 17.44953 09 44 01.41 +24 19 10.1 15.1 V D0541703 1976-023C C2015 01 17.44980 09 44 05.04 +24 18 37.9 15.1 V D0541703 1976-023C C2015 01 17.45007 09 44 08.79 +24 18 04.6 15.1 V D0541703 1976-023C C2015 01 17.45034 09 44 12.39 +24 17 32.6 15.1 V D0541703 1976-023C C2015 01 17.46751 09 48 08.67 +23 42 04.7 15.2 V D0541703 1976-023C C2015 01 17.46778 09 48 12.57 +23 41 29.0 15.7 V D0541703 1976-023C C2015 01 17.46805 09 48 16.06 +23 40 57.3 15.2 V D0541703 1976-023C C2015 01 17.46832 09 48 19.76 +23 40 23.6 15.2 V D0541703 1976-023C C2015 01 17.48899 09 53 04.78 +22 56 27.6 15.3 V D0541703 1976-023C C2015 01 17.48926 09 53 08.50 +22 55 52.7 15.2 V D0541703 1976-023C C2015 01 17.48953 09 53 11.78 +22 55 21.6 16.1 V D0541703 1976-023C C2015 01 17.48980 09 53 15.91 +22 54 43.3 15.3 V D0541703 1976-023C C2016 02 08.46940 12 02 46.88 -01 16 52.6 21.0 V D0541G96 1976-023C C2016 02 08.47597 12 03 56.88 -01 33 39.5 D0541G96 1976-023C C2016 02 08.48911 12 06 17.76 -02 07 07.8 D0541G96 1976-023C C2016 02 08.51641 12 11 14.59 -03 16 18.8 D0541G96 1976-023C C2016 02 08.51677 12 11 18.47 -03 17 12.7 19.6 V D0541G96 1976-023C C2016 02 08.51713 12 11 22.32 -03 18 05.4 D0541G96 1976-023C C2016 02 08.51749 12 11 26.38 -03 19 01.4 D0541G96 1976-023C C2016 02 08.54055 12 15 42.88 -04 16 51.9 21.3 V D0541G96 1976-023C C2016 02 08.54088 12 15 46.47 -04 17 39.5 D0541G96 1976-023C C2016 02 08.54153 12 15 53.67 -04 19 15.3 D0541G96 1976-023C KC2016 02 11.75968403 12 55.10 +26 07 22.5 17.8 R D0541J95 1976-023C KC2016 02 11.76275503 13 41.06 +26 12 43.9 17.9 R D0541J95 1976-023C KC2016 02 11.77222903 16 03.40 +26 29 03.0 18.1 R D0541J95 1976-023C KC2016 02 11.78175503 18 27.54 +26 45 06.3 17.4 R D0541J95 1976-023C KC2016 02 11.78463503 19 11.30 +26 49 53.6 17.6 R D0541J95 1976-023C tC2016 12 29.27187 09 26 26.23 +23 41 10.5 15.7 R Y00 1976-023C tC2016 12 29.27351 09 26 46.43 +23 37 39.8 15.9 R Y00 1976-023C tC2016 12 29.27520 09 27 07.27 +23 34 01.5 16.0 R Y00 Station data: (703) Catalina Sky Survey (N32.417003 W110.732640) US/Arizona. Observers E. J. Christensen, A. R. Gibbs, A. D. Grauer, R. E. Hill, J. A. Johnson, R. A. Kowalski, S. M. Larson, F. C. Shelly. 0.68 m Schmidt + CCD. (G96) Mt. Lemmon Survey (N32.442751 W110.788720) US/Arizona. Observers E. J. Christensen, A. R. Gibbs, A. D. Grauer, R. E. Hill, J. A. Johnson, R. A. Kowalski, S. M. Larson, F. C. Shelly. 1.5-m reflector + CCD. (J95) Great Shefford (N51.474967 W1.447000) UK. Observer P. Birtwhistle. 0.40-m f/6.0 Schmidt-Cassegrain + CCD. (Y00) SONEAR Observatory, Oliveira (S20.715080 W44.784960) Brazil. Observers C. Jacques, E. Pimentel, J. Barros. Measurer C. Jacques. 0.28-m f/2.2 astrograph + CCD. Orbital elements: SOLRAD 11A = 1976-023C = NORAD 08748 = WB31C9F = XC83E0D Perigee 2015 Jul 1.995224 +/- 0.00794 TT = 23:53:07 (JD 2457205.495224) Epoch 2015 Jul 1.0 TT = JDT 2457204.5 Gray M 289.6398750 +/- 0.56 (J2000 equatorial) n 70.6977712758 +/- 3.87e-6 Peri. 335.3020040 +/- 0.56 a125025.81401 +/- 0.00456 Node 5.7155447 +/- 0.00037 e 0.000618539 +/- 7e-6 Incl. 35.1891558 +/- 0.00008 P7332.48m/5.092d H 30.6 G 0.15 U 4.4 q 124948.48059 +/- 0.872 Q 125103.14744 +/- 0.879 30 of 38 observations 2015 Jan. 17-2016 Dec. 29; mean residual 3".870
Residuals in arcseconds: 060709 703( 887+ 169+) 150117 703 2.31+ 1.38- 160208 G96 2.12- 2.72+ 060709 703( 885+ 168+) 150117 703 .826- .842+ 160208 G96 5.33- 5.56+ 060709 703( 884+ 168+) 150117 703 1.08- 1.08+ 160208 G96 7.22- 7.40+ 060709 703( 886+ 168+) 150117 703 2.80- 1.78+ 160208 G96 9.08- 8.95+ 060709 703( 886+ 168+) 150117 703 2.97- 1.81+ 160211 J95 2.43- .887- 060709 703( 886+ 168+) 150117 703 9.22- 5.65+ 160211 J95 1.92- .752- 060709 703( 887+ 168+) 150117 703 3.74- 2.30+ 160211 J95 .349- .734+ 060709 703( 885+ 168+) 160208 G96 9.01+ 6.21- 160211 J95 2.90+ 1.85+ 150117 703 2.81+ 1.24- 160208 G96 6.52+ 5.00- 160211 J95 3.82+ 2.40+ 150117 703 1.64+ .461- 160208 G96 3.73+ 1.61- 161229 Y00 1.67+ 3.90- 150117 703 2.11+ .772- 160208 G96 .658- 1.81+ 161229 Y00 2.82+ 3.80- 150117 703 .534+ .233+ 160208 G96 1.88- 2.42+ 161229 Y00 4.42+ 4.31- 150117 703 .178- .405+ 160208 G96 3.56- 4.22+ Ephemerides (geocentric): Date (UTC) HH RA Dec delta r elong mag " sig PA ---- -- -- -- ------------ ------------ ------ ------ ----- --- ---- --- 2016 12 29 15 10 56 13.260 +08 36 05.54 125283 .98375 116.1 17.4 0.2 125 2016 12 29 16 11 05 59.272 +06 56 50.02 125284 .98372 113.3 17.5 0.1 124 2016 12 29 17 11 15 41.138 +05 16 49.95 125283 .98368 110.4 17.6 0.0 158 2016 12 29 18 11 25 19.868 +03 36 16.18 125281 .98364 107.6 17.7 0.1 128 2016 12 29 19 11 34 56.472 +01 55 19.42 125277 .98360 104.8 17.8 0.3 128 2016 12 29 20 11 44 31.959 +00 14 10.20 125272 .98355 102.0 17.9 0.4 127 2016 12 29 21 11 54 07.342 -01 27 00.96 125266 .98351 99.1 18.0 0.6 127 2016 12 29 22 12 03 43.634 -03 08 03.57 125258 .98347 96.3 18.1 0.7 127 2016 12 29 23 12 13 21.845 -04 48 47.10 125248 .98343 93.5 18.2 0.9 127 2016 12 30 00 12 23 02.992 -06 29 00.89 125238 .98339 90.6 18.3 1.0 126 2016 12 30 01 12 32 48.086 -08 08 34.12 125225 .98334 87.8 18.4 1.2 126 2016 12 30 02 12 42 38.142 -09 47 15.74 125212 .98330 85.0 18.6 1.4 125 2016 12 30 03 12 52 34.170 -11 24 54.42 125197 .98326 82.1 18.7 1.5 125 2016 12 30 04 13 02 37.178 -13 01 18.51 125180 .98322 79.3 18.8 1.7 124 2016 12 30 05 13 12 48.164 -14 36 15.94 125163 .98318 76.5 19.0 1.9 124 2016 12 30 06 13 23 08.114 -16 09 34.24 125144 .98314 73.6 19.1 2.1 123 2016 12 30 07 13 33 37.994 -17 41 00.45 125123 .98309 70.8 19.3 2.2 122 2016 12 30 08 13 44 18.742 -19 10 21.10 125102 .98306 68.0 19.5 2.4 121 2016 12 30 09 13 55 11.260 -20 37 22.20 125079 .98302 65.1 19.6 2.6 120 2016 12 30 10 14 06 16.398 -22 01 49.19 125056 .98298 62.3 19.8 2.8 119 2016 12 30 11 14 17 34.940 -23 23 26.98 125031 .98294 59.5 20?? 3.0 118 2016 12 30 12 14 29 07.588 -24 41 59.95 125006 .98291 56.6 20?? 3.2 117 2016 12 30 13 14 40 54.943 -25 57 12.00 124980 .98287 53.8 20?? 3.3 116 2016 12 30 14 14 52 57.478 -27 08 46.59 124953 .98284 51.0 20?? 3.5 114 2016 12 30 15 15 05 15.520 -28 16 26.87 124926 .98281 48.2 21?? 3.7 113 2016 12 30 16 15 17 49.222 -29 19 55.80 124898 .98278 45.4 21?? 3.9 111 2016 12 30 17 15 30 38.540 -30 18 56.27 124870 .98275 42.6 21?? 4.0 110 2016 12 30 18 15 43 43.208 -31 13 11.35 124841 .98272 39.8 22?? 4.2 108 2016 12 30 19 15 57 02.720 -32 02 24.47 124813 .98269 37.1 22?? 4.4 106 2016 12 30 20 16 10 36.310 -32 46 19.71 124784 .98267 34.3 22?? 4.5 104 2016 12 30 21 16 24 22.949 -33 24 42.07 124756 .98265 31.6 23?? 4.7 102 2016 12 30 22 16 38 21.341 -33 57 17.77 124728 .98263 28.9 23?? 4.8 100 2016 12 30 23 16 52 29.933 -34 23 54.53 124700 .98261 26.3 24?? 5.0 98 2016 12 31 00 17 06 46.935 -34 44 21.89 124673 .98259 23.7 25?? 5.1 96 2016 12 31 01 17 21 10.358 -34 58 31.47 124647 .98258 21.1 25?? 5.2 94 2016 12 31 02 17 35 38.047 -35 06 17.18 124622 .98256 18.7 26?? 5.3 92 2016 12 31 03 17 50 07.741 -35 07 35.39 124597 .98255 16.5 27?? 5.5 90 2016 12 31 04 18 04 37.128 -35 02 25.05 124574 .98255 14.5 28?? 5.6 88 2016 12 31 05 18 19 03.906 -34 50 47.72 124552 .98254 12.8 29?? 5.7 86 2016 12 31 06 18 33 25.840 -34 32 47.51 124531 .98254 11.6 30?? 5.8 84 2016 12 31 07 18 47 40.826 -34 08 30.98 124512 .98253 11.1 31?? 5.8 82 2016 12 31 08 19 01 46.933 -33 38 06.96 124494 .98253 11.4 30?? 5.9 80 2016 12 31 09 19 15 42.444 -33 01 46.33 124478 .98254 12.3 30?? 6.0 78 2016 12 31 10 19 29 25.888 -32 19 41.71 124464 .98254 13.8 29?? 6.0 76 2016 12 31 11 19 42 56.054 -31 32 07.24 124451 .98255 15.7 27?? 6.1 74 2016 12 31 12 19 56 11.999 -30 39 18.22 124441 .98255 17.9 26?? 6.1 72 2016 12 31 13 20 09 13.044 -29 41 30.85 124433 .98256 20.2 26?? 6.1 71 2016 12 31 14 20 21 58.765 -28 39 01.95 124426 .98258 22.7 25?? 6.2 69 2016 12 31 15 20 34 28.972 -27 32 08.71 124422 .98259 25.3 24?? 6.2 68 2016 12 31 16 20 46 43.690 -26 21 08.47 124420 .98261 27.9 24?? 6.2 66