NROL-76 elements from observations

From: Ted Molczan via Seesat-l <seesat-l_at_satobs.org>
Date: Sun, 4 Jun 2017 09:49:56 -0400
The following elements have been derived from observations by Leo Barhorst, Russell Eberst, Kevin Fetter, David Hopkins,
Marco Langbroek, Alberto Rango and Mike Waterman:

USA 276                                                  389 X 409 km
1 42689U 17022A   17155.10977510  .00003750  00000-0  51941-4 0    02
2 42689  50.0034 107.5651 0014909 116.4838 243.7661 15.56244436    01
Arc 20170530.95-0604.13 WRMS resid 0.045 totl 0.015 xtrk

Below are updated conjunction estimates for the closest approaches on 2017 Jun 03 with range <= ~100 km. For USA 276, I
used the above TLE. For ISS, I used USSTRATCOM's epoch 17154.48611204 TLE.

                   ISS sub-satellite point     USA 276 sub-sat point
                  -------------------------  ------------------------- 
  TCA      Range    Lat      Lon      Alt      Lat      Lon      Alt
  UTC       km      deg      deg      km       deg      deg      km     Illum.
11:43:12   88.31  43.26 N 170.90 E   410.24  43.67 N 170.07 E   392.49  shadow
12:29:12   66.16  43.87 S  22.16 W   418.71  44.12 S  22.84 W   423.17  sunlight
13:15:35   27.66  43.71 N 146.41 E   410.40  43.81 N 146.21 E   392.51  shadow
14:01:48    4.39  43.87 S  45.71 W   418.70  43.87 S  45.72 W   423.06  sunlight
14:47:58   47.84  44.15 N 121.91 E   410.55  43.95 N 122.35 E   392.54  shadow
15:34:25   65.23  43.85 S  69.20 W   418.68  43.59 S  68.53 W   422.94  sunlight
16:20:19  111.23  44.64 N  97.24 E   410.73  44.14 N  98.33 E   392.58  shadow

Although the conjunctions are now history, the above are not necessarily the final results. Tracking of USA 276 over the
next several nights could yield elements that lead to different results.

The final column denotes the state of illumination of both spacecraft. Both were either in Earth's shadow or in
sunlight. The conjunctions in shadow occurred roughly one minute after entry into eclipse.

At the TCA of 14:01:48 UTC, USA 276 passed 4.4 km directly above ISS. The relative angular velocity of one spacecraft
seen from the other was about 6.3 deg/s (at 10 km range, approaching and departing, the angular velocity was a more
sedate approx. 1.2 deg/s). 

The phase angle changed considerably during the period within 10 km range. At TCA, from the vantage of USA 276, the
solar phase angle of ISS was 69 deg, and it was about magnitude -14; from the vantage of ISS, the phase angle of USA 276
was 111 deg, and it was about magnitude -5. 

The planar separation of USA 267 and ISS will remain close for some time, so a rendezvous remains technically feasible.
If delta-V is a significant constraint, then the minimum energy manoeuvre would occur on Jun 24, when USA 276 and ISS
would have the same RAAN, leaving only a 1.6 deg change of inclination.

Ted Molczan


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Received on Sun Jun 04 2017 - 08:51:01 UTC

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