It's still a few days until Metop will be launched but after just a few orbits some observers in Greece, Spain and North America might be able to see Iridium-like flares from Metop - at least if my theory is correct. So I better post this right away. Once in orbit, Metop will deploy three double sets of radar antennae (ASCAT - Advanced Scatterometer; actually one set is fixed mounted and doesn't need deployment). The antennae surfaces look smooth and reflecting on pictures and one would expect them ideal for causing flares. They point 45, 90 and 135 degrees to the left and to the right of the flight direction. Only the three surfaces which point to the left can produces flares. The deployable antennae (45 and 135 deg) are pitched down 47 degrees and are dimensioned 3.00 m x 0.40 m, the fixed mounted antenna (90 deg) is pitched down 56.5 deg with dimension 2.20 m x 0.55 m. So each surface is 1.2 square meters - thus smaller than the Iridium MMA but I guess it might still be good for mag -5 or even mag -6. If you do have a program for calculating Iridium flares it is not enough, however, to substitute the (yaw, pitch) angles of (-45, -47), (-90, -56.5), (-135, -47) for the Iridium MMA angles of (-120, -40), (0, -40), (+120, -40) to properly predict Metop flares because most of the time Metop will operate with a modified local attitude called Yaw Steering Mode. In this mode the satellite will yaw to allign one axis with the ground trace velocity vector (rather than with the inertial velocity vector as do most other satellites). (Also the nadir pointing direction is with regard to the local normal of the Earth reference ellipsoid rather than the center of the Earth.) The difference amounts to 4.6 deg at the equator to 0 deg at the apex near the poles. On the first day or so Metop probably operates in a normal local mode. With that I would get flares in Central Greece at 19:54/19:55 UTC (17-JUL-06) and in South-East Spain at 21:35 - 21:37 UTC (17-JUL-06). For the first two nighttime passes of Metop over the U.S. there might be flares along the Florida peninsula and the Carolinas and beyond as well as the South-West and into Colorado on the evening of 17-JUL-06 local time. My prediction for that would be (18-JUL-06 UTC): 2:34 24.59N, 81.74W 2:35 27.38N, 81.85W 2:36 30.10N, 81.88W 2:37 32.72N, 81.76W 2:38 35.20N, 81.43W 2:39 37.43N, 80.80W 2:40 39.20N, 79.68W 2:41 39.70N, 77.55W 4:18 31.80N, 107.17W 4:19 34.33N, 106.93W 4:20 36.67N, 106.42W 4:21 38.66N 105.51W 4:22 39.84N, 103.87W Should Yaw Steering Mode already be active the positions will shift toward the South-East. Those flares would be from the fixed mounted antenna. The other antennae are scheduled for deployment around 29 hour after launch. To find out where to look for Metop you can use the following TLEs until Spacetrack comes up with some: Metop Sep 1 99999U 06099A 06198.73395324 .00000028 00000-0 26562-4 0 1 2 99999 98.7337 257.5914 0024535 156.6977 131.5842 14.21428546 1 If you are unable to do your own calculations but want to try looking for these first Metop passes just let me know (don't forget your coordinates!). Of course all this is nothing but a theory. First and foremost Metop must be launched successfully on 17-JUL-06 at 16:28:10 UTC. And then observations will show whether or not I've made a fool out of myself! Gerhard HOLTKAMP Darmstadt, Germany ------------------------------------------------------------------------- Subscribe/Unsubscribe info, Frequently Asked Questions, SeeSat-L archive: http://www.satobs.org/seesat/seesatindex.html
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