Justin Ray quoted me in his recent Spaceflight Now article on the next generation of NRO electro-optical satellites, which I refer to here generically as KH-11, after the first in this line of spacecraft: http://spaceflightnow.com/2015/05/01/next-round-of-u-s-optical-spy-satellites-to-start-launching-in-2018/ This message expands on my speculative comments to SFN regarding the possible orbit of the next generation KH-11. Do these orbits look familiar? 257 X 480 km 1 09627U 76125A 77302.90734402 .00119502 00000-0 56198-3 0 1940 2 09627 96.9731 4.6079 0165221 69.1494 293.5049 15.65601255 48883 266 X 469 km 1 10947U 78060A 78247.71082122 .00074707 00000-0 39215-3 0 587 2 10947 96.8081 313.1420 0151023 211.8432 147.3767 15.65930608 12801 271 X 497 km 1 12799U 81085A 81309.26749698 .00134649 00000-0 82252-3 0 868 2 12799 96.9644 16.8713 0166620 290.9083 67.6810 15.60160104 9748 261 X 534 km 1 13659U 82111A 83131.25417423 .00076757 24516-5 41956-3 0 2032 2 13659 96.9789 243.8482 0201137 214.2647 144.6906 15.55435485 27223 They bear a strong family resemblance to the present orbit of USA 186, now on its extended mission: USA 186 265 X 454 km 1 28888U 05042A 15128.78609485 .00050000 00000-0 25019-3 0 07 2 28888 96.8751 166.9978 0139599 169.0805 190.9193 15.68713458 03 The old TLEs are of deceased members of the family line - four of the first five KH-11 spacecraft. It is interesting to see the resurrection of the old orbit for USA 186's extended mission. During its primary mission (2005-2013), it occupied the standard western KH orbital plane, where it operated in the ~250 X 1000 km orbit introduced in 1985. Its replacement, USA 245 (13043A / 39232), continues to use the higher orbit. During USA 161's ~9 years as the standard eastern plane KH-11, its perigee ranged between ~310 km and 400 km; typical apogee was between ~900 km and 1000 km. After it was replaced by USA 224 (11002A / 37348), it adopted its present nearly circular 390 km orbit for its extended mission. Our latest elements are based on observations at the end of the summer 2014 northern hemisphere visibility window: USA 161 383 X 388 km 1 26934U 01044A 14270.56049043 .00016000 00000-0 20177-3 0 08 2 26934 96.9959 41.0452 0003500 14.9902 345.0096 15.59586592 04 Could the present low orbits of USA 161 and USA 186 be clues of what to expect from the next generation KH (first launch expected in 2018 on a Delta 4-Heavy)? Looking farther back in time, the previous generation of high-res s/c was the KH-8 (Gambit 3) film-return type, first launched in 1966. It's standard perigee height was about half that of the lowest KH-11 perigee. Here is an example: KH 8-22 131 X 430 km 1 03984U 69050A 69154.67924923 .00200000 00000-0 97482-5 0 01 2 03984 110.0179 190.1720 0224999 128.0998 233.9501 15.97027143 09 The perigee height was dictated by the required best resolution and the size of its primary mirror, which was ~1.2 m in diameter. The drag experienced by KH-8 was severe, which limited its orbital life; however, film-capacity was the main determinant of its useful life. The useful life of the electro-optical KH-11 is limited only by the quantity of fuel it carries and the durability of its hardware. For a given quantity of fuel, the greater the perigee height, the greater the useful life. The diameter of KH-11's primary mirror is double that of KH-8, 2.4 m, enabling it to achieve approximately the same resolution from double the perigee height. Therefore, we can conclude that the doubling of mirror diameter was to maintain, not improve resolution. In comments on a draft of this post, Allen Thomson informed me that, "the diffraction-limited ~7 cm resolution that the KH-11 gets from 250 km and the KH-8 got from half that, is in the range of the 5 - 10 cm resolution limit imposed by atmospheric turbulence as worked out by David Fried and, independently, by John C. Evvard in the mid-1960s. So I don't think dropping the perigee (or going to a bigger aperture) would achieve better resolution -- they're already maxed out." Allen cited the following papers: http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19690003603.pdf https://www.osapublishing.org/abstract.cfm?id=53168 It is known that the primary mirror of the next generation KH is the same diameter as that of the present generation, 2.4 m. Amazingly, this was openly announced: http://spacenews.com/us-intelligence-official-drops-hint-about-next-gen-spy-sat-capability/ Given the significantly greater payload of Delta 4-Heavy over Titan-4B, I could imagine the next generation KH carrying a much greater fuel load, that would permit it to operate for a long time in orbits like those currently inhabited by USA 161 and USA 186. Given that the mirror diameter will remain 2.4 m, and the resolution limit imposed by atmospheric turbulence, it is reasonable to assume that the perigee will be about the same as the present ~250 km. The advantage of the reduced apogee is more nearly constant resolution during each revolution about the Earth. A likely advantage of the ~250 X 1000 km orbit (besides reduced drag), was wide-area coverage from near apogee. I suspect that need can now be met by the small commercial imagers that sell data to the gov't, which would facilitate using lower apogee orbits. Ted Molczan _______________________________________________ Seesat-l mailing list http://mailman.satobs.org/mailman/listinfo/seesat-lReceived on Tue May 12 2015 - 13:53:34 UTC
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