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Aviation History
1963
1963 - 2176.PDF
FLIGHT International, 12 December 1963 977 COSMOS CALCULATIONS By J. A. Pilkington BSc THE launch of the first Cosmos satellite on March 16,1962, marked a major change in Soviet official information policy. Previously the Russians had announced the weight of all space payloads which they had launched into Earth orbit or beyond, although certain other details—such as spacecraft dimensions and the size and weight of final-stage rocket bodies—were kept secret. For the Cosmos scries, however, in spite of the fact that these satellites are described as "scientific," not even the payload weights have been divulged. This article, based on direct observations of certain Cosmos satellites, deduces the probable size and weight of the 49° Cosmos craft. THE Cosmos satellites are of two types. One group is launched north-eastwards into a 65° orbit from a site near Baikonur— either Karsakpay (latitude 47.7°N, longitude about 66.5°E) about 260 miles north-east of the Aral Sea, or Tyuratam (45.6°N, 63.4°E) about 100 miles east of the Aral Sea. According to orbital elements published by the USA, the first orbit of each of these satellites has covered virtually the same path as those of all previous 65° Soviet satellites, and the 65° Cosmos craft could have originated from either of these sites. In size and weight they are probably somewhere between Sputnik 4 and a Vostok; ten have been launched, all of which have been commanded out of their 90min orbits from three to ten days later. Satellites of the second Cosmos type, those in 49° orbits, are the main subject of this article. The launch site used is probably near Kapustin Yar (48.6°N, 45.8°E), about 220 miles northwest of the Caspian Sea. By comparison with the 65° satellites, the 49° Cosmos craft have initial orbital periods which have been much higher— ranging from 91min to almost 103min—and they have remained aloft until their natural re-entry between two and 16 months later. The USA, from its routine tracking under the NORAD system, acquires "radar signatures" of these and all other satellites, and these signatures can be analysed to give the approximate size of objects which would return the observed reflected signal strength. Such an analysis, however, would be kept highly secret. But amateur observing stations in Britain can supply similar data, by noting the apparent stellar magnitude of the satellite as it crosses the sky. In this article we shall use this information to deduce the shape and size of the Cosmos satellites, and from an estimated density calculate their probable weight. Shape of the satellites The shape of a satellite •« very important in determining the appearance of it in the sky. A cylindrical rocket body generally flashes smoothly as it turns end aver end, an Altair taking about four seconds and a low Agena per haps ten. A satellite carrying solar paddles or other extensions, e.g., Ariel 1 and Alouette 1, may flash quite brightly although irregularly. TABLE I Satellite Transit 2A Tiros 3 Anna IB Greatest range of magnitude +4 to +10 +4 to +10 +5 to +9 Mean max and mean min magni tude +7.66 & +7.93 +7.78 & +8.23 +7.55 & +7.94 No of esti mates 72 40 31 Mean height (km) 840 780 1,130 Mean magni tude M +7.80 +8.00 +7.75 Polygonal spacecraft encrusted with solar cells, such as Tiros, will flash rapidly or "twinkle," while a smooth sphere will stay steady in magnitude, only fading as it changes its phase with respect to the Sun. The Cosmos satellites listed in Table 2 have been observed to be fairly steady (see the mean variation column), occasionally showing slightly irregular fluctuations every few seconds, and so we will assume them to be roughly spherical. Size of the satellites To discover their size, we must first find out the stellar magnitude of a one-metre diameter sphere at a slant range of 1,000km. The American spacecraft Transit 2A, Tiros 3, and Anna IB all have stable circular orbits, stay steady in magnitude and have known sizes. Their magnitudes are given in Table 1. To the observed magnitude we apply two corrections, the first (mj) being equal to 5 log10 (Si/S2) where SJS,; is the ratio of the satellite slant range to 1,000km (the slant range is found graphically using an assumed ground range of 3C0km and the mean height tabulated). The second correction (m2) equals 2.5 logi0 (ajaj) where ai/a2 is the ratio of the satellite surface area to that of a Satellite Vanguard 2 Courier IB Transit 2A Tiros 3 Sputnik 1 Sputnik 3 Lunik 1 Lunik 2 Lunik 3 Venus probe Mars 1 probe Lunik 1 rocket Vostok i Shape sphere sphere sphere cylinder sphere cone sphere sphere ellipsoid cylinder cylinder cylinder cone- cylinder TABLE Size (metres) 0.51 dia 1.30 dia 0.91 dia 0.48 long 1.07 dia 0.58 dia 3.76 long 1.73 dia 0.9 dia 0.9 dia 1.31 long 1.19 dia 2.30 long 1.05 dia 3.3 long I.I dia 3.7 long 3.0 dia 9.0 long? 3.0 dia 3 Weight (kg) 9.8 230 101 129 83.6 1327 362 390 278.5 643.5 893.5 1100 4730 Density (kg/cm») 141 200 256 299 1030 451 949 1022 273 360 285 42 74! Length/ width ratio 1.0 1.0 1.0 2.23 1.0 2.17 1.0 1.0 1.10 1.93 3.0 1.23 3.0f M„ + 0 + 0. TABLE 2 Cosmos Satellite I 2 3 5 6 8 II Greatest range of magnitude + 3 to +9 +4 to +8 +4 to +8 + 3 to +9 +3 to +9 +3 to +8 Mean max and mean min magni tude +5.43 & +6.01 +5.39 & +6.13 + 5.16 & +6.07 +5.56 & +6.37 estimate • +5.02 & +5.04 +5.36 & +5.63 No of esti mates 12 47 7 20 31 24 Mean height (km) 450 630 400 720 280 370 465 m, + 1.34 +0.77 + I.SI +0.54 + 1.94 + 1.62 + 1.26 one-metre sphere (assuming that the brightness of a spherical satellite is proportional to its surface area). The final column shows a one-metre sphere at l.OCOkm range to be magnitude +7.84, which may now be compared with the observed Cosmos magnitudes given in the second table. The Cosmos spacecraft are unlike the three US ones above in that their orbits are quite eccentric, the extreme case being Cosmos 5, whose height varied between 190km and 1,590km. The air drag at perigee height also caused their orbits to shrink in size and, because of these two factors, it is difficult to choose an average height at which most magnitude estimates were made. More observers would see the satellite when it was at perigee and therefore brighter, and yet the satellite would be visible more often at apogee, where it exceeds the height of the Earth's shadow. The height we have chosen, therefore, is a medium one—in fact the average height of the satellite half way through its lifetime (Table 2). Applying the correction m1( we find the absolute magnitudes of the satellites M at a —0.21 —0.37 +0.14 +7.87 +8.03 +7.63 Absolute magni tude +7.06 +6.53 +7.13 + 6.51 +6765 + 6.76 Mean variation ±0.29 ±0.37 ±0.45 ±0.40 ±0.01 ±0.14
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