RE: LightSail-A: estimated post-sail deployment elements

From: Stephen Mackenzie via Seesat-l <seesat-l_at_satobs.org>
Date: Sun, 7 Jun 2015 13:30:37 -0400
What frequencies are being used by the beacons. Would be interesting to hear it on a visible pass. 



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On Saturday, June 6, 2015 Ted Molczan via Seesat-l <seesat-l_at_satobs.org> wrote:
Communication with LightSail-A (15025L / 40661) resumed Saturday, and its solar sail may be deployed on Sunday 2015 Jun 07, not long after 18:02 UTC: http://www.planetary.org/blogs/jason-davis/2015/20150506-lightsail-wakes-second-time-1.html "If battery levels continue to trend stably during Sunday's early morning ground station passes, sail deployment will be scheduled for 2:02 p.m. EDT (18:02 UTC)." The current orbital elements are: 1 90726U 15156.84281789 .00025322 00000-0 67301-3 0 253 2 90726 55.0121 269.9399 0247556 221.6417 288.5573 15.12666037 2455 Observers between about 20 N and 56 N will have morning visibility of the orbit. Those south of about 43 S will have evening visibility. I estimate that with its sail deployed, LightSail-A's standard visual magnitude will be about 4.4 (1000 km range, 90 deg phase angle), resulting in mag 2 to 3 on high-elevation, well illuminated passes. Judging by the much smaller NanoSail-D (10062L / 37361), LightSail-A's brightness may !
 vary considerably from one pass to another. It could be much fainter than expected, or flare to negative magnitudes. I suspect it will begin tumbling during its first pass through perigee. Marco Langbroek analyzed the flash period of NanoSail-D: http://sattrackcam.blogspot.ca/2011/06/nanosail-d-evolution-of-flash-pattern.html With its sail deployed, the rate of decay of LightSail-A will be enormous and difficult to predict with precision. I estimate final descent late on 2015 Jun 9 UTC. I have estimated the following TLEs to assist in visual, optical and radio tracking during the first 18 h post-sail deployment. 1 70001U 15158.79734543 .08393463 00000-0 21359 0 0 20 2 70001 55.0101 261.4702 0243810 226.4735 132.4935 15.13949689 03 1 70002U 15158.86337413 .08613548 00000-0 21534 0 0 62 2 70002 55.0093 261.1832 0240018 226.8670 132.2125 15.15058108 02 1 70003U 15158.92902983 .08770975 00000-0 21528 0 0 49 2 70003 55.0099 260.8978 0236172 227.2742 130.1542 15.16189165 06 1 700!
 04U 15158.99551514 .09386835 00000-0 22594 0 0 28 2 70004 55.0104 260.6091 0232270 227.6713 132.9136 15.17355447 03 1 70005U 15159.06032682 .09589525 00000-0 22592 0 0 27 2 70005 55.0116 260.3268 0228342 228.0528 126.8258 15.18572200 00 1 70006U 15159.12662708 .09808663 00000-0 22573 0 0 85 2 70006 55.0113 260.0374 0224364 228.4612 129.1443 15.19843776 03 1 70007U 15159.19203951 .10166942 00000-0 22884 0 0 77 2 70007 55.0090 259.7499 0220091 228.8694 126.9040 15.21126993 04 1 70008U 15159.25842929 .10793040 00000-0 23694 0 0 96 2 70008 55.0065 259.4571 0215818 229.2351 130.3703 15.22476955 03 1 70009U 15159.32430804 .11150602 00000-0 23840 0 0 39 2 70009 55.0067 259.1661 0211305 229.5642 131.3984 15.23899019 09 1 70010U 15159.38976868 .11468796 00000-0 23854 0 0 66 2 70010 55.0080 258.8773 0206687 229.9966 130.3720 15.25358870 00 1 70011U 15159.45515580 .11800000 00000-0 23862 0 0 51 2 70011 55.0090 258.5890 0201864 230.4677 129.2531 15.26858693 03 For planning observations based on the above TLEs, I recommend comparing predictions against the!
  pre-sail deployment TLE, and taking 50% of the difference in prediction time as the uncertainty, e.g. if a 700XX TLE predicts a pass 5 min., earlier than the 90726 TLE, then allow 2.5 min. prediction time uncertainty. I estimated the TLEs using the following procedure. I used SGP4 to propagate the 90726 TLE to the time of deployment, which I took to be Jun 07 at 18:10 UTC. TLE Analyzer 2.12 converted the result to a state vector type compatible with GMAT 2014a (General Mission Analysis Tool). I used GMAT to numerically propagate the orbit, based on the mass of the spacecraft (4.5 kg), the dimensions of its sail (~5.66 x 5.66 m^2), my guess that it will be tumbling, and the forecast space weather. GMAT produced Cartesian state vectors at close time intervals. I selected state vectors near successive ascending nodes and converted them to TLEs. I computed the mean ndot/2 and corresponding B* decay terms between successive TLEs, and inserted them into the TLEs. I intend to rev!
 ise these elements if the deployment occurs at a significantly different time, or subsequent radio tracking reveals a significantly different rate of decay. I also intend to produce TLEs past the period covered above, if I have sufficient data. Ted Molczan _______________________________________________ Seesat-l mailing list http://mailman.satobs.org/mailman/listinfo/seesat-l
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Received on Sun Jun 07 2015 - 12:31:59 UTC

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