Condign volumes 1 to 3

Read from the scan by GLM-OCR; expect the odd misread word.

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the remaining four minutes 'catching up' on the small angle needed to bring it to the same direction relative to the sun. The same satellite will also have a time-shift in arrival at the observer's latitude, by several minutes. Clearly this varies with orbit type. The daily shift to the West is shown at Figure 6 for near circular orbits. Hence, from the UAP aspect reports could be received, shifted in time and elevation angle on successive days/nights with an observer in the same position or by an observer in a different position.

13. Figure 7 shows two successive ground tracks of a 90 minute period satellite at an inclination of $ 6 5^{\circ} $ . This shows that the $ 2 2. 5^{\circ} $ shift in track longitude is such that it is unlikely that the same observer will see two successive transits. The spell of visibility of a particular satellite varies as the orbital plane swings westward. For example, a 500Km altitude satellite will reach a point where the shadow height is less than 500Km. The satellite will be visible in the evening for some weeks, but as it swings further west will be invisible because of the glare of the setting sun. Next, it will pass over in daylight for many weeks, then into morning twilight and after a spell of potential morning visibility will once again enter eclipse before repeating the cycle.

14. Spells of Visibility Satellites (in circular orbit) can pass over on either a north or southbound track. It is important to note the concept of 'spells of visibility' because these are likely to generate successive spurious UAP reports. It can be shown that evening visibility lasts for $ \mathrm{v} / 4(1-\times) $ days, where v is the length of one evening's visibility time and the value $ \times $ (the daily westward shift) is given from Figure 6. For example, for a satellite at 400km altitude, visibility is $ \sim 2 $ hours per evening/night, the value of $ \times $ is zero (polar orbit), the visibility is 30 days. With an inclination of $ 70^{\circ} $ , period 92 minutes, then $ \times $ is 2.8 (Figure 6), hence the spell of visibility is reduced to $ 30 / 3.8\approx 8 $ days. If satellite height is increased the spell of visibility increases. This rule of thumb becomes inaccurate after $ \sim 1 $ month - but is of no concern for UAP elimination purposes. The important fact is that a given satellite is observable (given atmospheric clarity) for a number of successive days and this can result in mistaken reporting as a UAP on one or more of these days.

15. After a spell of visibility a circular orbit satellite becomes visible again (from the same location) after 1440/4 (1+x) days or 12/(1+x) months. Slightly different rules apply to eccentric orbits.

16. Angle of Elevation This is one parameter which often occurs in UAP reports. Figure 8(a) and 8(b) show the angle/range/altitude relationship.

17. Flash Periods It is possible to time the satellite flash period. This feature may appear in UAP reports. Flashes (seen with the naked eye) from MOLNIYA satellites have been reported at once per minute (even from 40,000km range). These flashes tend to come from flat panels and have magnitudes which can exceed those of VENUS at its brightest.

18. Sightline Rates UAP reports occasionally include times and angles. Some examples are:

(a) Satellite at 200km altitude. The minimum orbital speed is $ 7 9 0 0 \mathrm{m}. \mathrm{s}^{-1} $ (e.g. SKYLAB altitude 235km).

(b) Satellite at moon distance travels at $ 9 7 5 \mathrm{m}. \mathrm{s}^{-1}. $

(c) An equatorial orbit (circular) at 10,200km passes once every eight hours.

(d) A 100-300 nautical mile high orbit passes typically, once every 90 minutes.