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Proof of the Prosaic Nature of the STS-48 Zig-Zag Video

The attached two charts provide convincing proof that the famous zig-zag dots of the STS-48 shuttle flight (September 1991) are exactly what space experts inside and outside NASA have always said they were: routine nearby small sunlit debris hit by the expanding exhaust of a shuttle steering rocket triggered randomly by the computer autopilot which was steering the spaceship. More elaborate and exotic "explanations" rely on misinterpretations of the images and on a deliberate omission of relevant data such as shown here (these two charts have never been published by proponents of extraordinary scenarios -- they apparently never asked NASA for them).



Chart 1 is a page from the mission's Flight Plan showing what was happening at the time of the zig-zag (approximately 20 hours 39 minutes 20 seconds GMT on Julian Date 258 -- or about 3:39 PM CDT on September 15, 1991. The crew was just waking up -- powerful prima facie evidence that they were not engaged in some intensive secret experiment. The shuttle was on "Orbit 44" and -- most significantly -- was flying southeastwards, just emerging from Earth's shadow (which it did in fifteen seconds centered at precisely 20:37:04 GMT). As it did, the space around it became bathed in sunlight that remained invisible to the TV view except when NEARBY objects drifted into them -- if the objects had NOT been nearby they would NOT have become illuminated at the same time the shuttle emerged into sunlight. Note also that the "beta angle" is 44 degrees, which means that as the shuttle and its aft pointed TV camera (viewing backwards along the flight path to observe lightning) rise into sunlight, the illumination is coming from 44 degrees off to the side of the direction of flight (north, as it turns out, or to the left, when facing into the direction of flight). Thus the shuttle's umbra -- the shadow it casts 'down sun' -- is tilted 44 degrees to the line of sight of the TV camera -- horizontally to the left, in the field of view as seen. This means that objects closest to the shuttle will be in its shadow and will only become visible when they drift out of the shadow into sunlight -- but it also means that objects along the same line-of-sight can be either IN shadow (if they are closer to the shuttle) or OUT of the shadow (if they are at a slightly greater range), a three dimensional concept that has escaped many of the theorists proposing extraordinary 'explanations'.



Chart 2 shows a plot of telemetry from the shuttle during a six minute interval around the time of the zig-zag. The displayed parameters are the roll-pitch-yaw angle rate errors of the shuttle (bottom), the angular rate the shuttle is drifting in all three axes (center), and the amount the angles differ from the desired direction loaded into the computer (upper section). The "digital autopilot" (or "DAP") is also told how much slack to allow the shuttle's drift before making a corrective rocket firing -- this is called a "deadband" and at the time of the zig-zag it was set at one degree. As can be read off the charts, the steering jet firing that was observed on the video as a flash occurred in response to a slow drift in 'pitch error' (see top section, dotted line labeled 'pitch'), which had gradually been approaching the 'deadband limit' of one degree over the previous three minutes. The timing of the firing is thus shown to be determined by a slow ordinary flight process, and any coincidences with other factors (such as sunrise) are only by random chance. Notice that the change in pitch rate caused by the rocket firing is about 0.010 degrees per second (as shown on the center section data), which over a period of one minute amounts to an angular distance of half a degree. Despite widespread assertions that the absence of a detectable change in background motion proves that the flash cannot be a steering rocket, this actual motion is far too small to be noticeable in the motion of background features, especially since at the shuttle's actual orientation (roughly wing down, nose to the side, belly "into the wind"), this half a degree per minute of different pitch motion (nose up or down relative to the shuttle body) merely moved the line-of-sight along the horizontal axis of the field of view.

Separate tables of telemetry from the steering jets (not shown here) indicate that jet R5D fired at 20:39:23.31 for precisely 1.68 seconds, and its symmetric twin L5D fired at 20:39:23.79 for precisely 1.2 seconds (it had not fired for the previous 13 minutes). They both stopped at the same time, 20:39:24.99. This is exactly the set of jets one would expect to fire to correct a small error in pitch, which persuasively connects the angle error telemetry chart with the jet firing history data. The reason the computer fired one jet slightly ahead of the other can be deduced from the angle chart (center section) which shows a slight rolling drift which was also corrected by the unbalanced firing of the pair. It should also be pointed out that as all experienced observers of shuttle TV images realize, the visible flare of these jet firings is only an occasional and sporadic feature of their actual firings, which at other times -- especially in periods of smooth, stable propellant flow -- can be invisible. Therefore the actual start, stop, and duration of the jet firing cannot be determined solely based on visual evidence on the TV image, a fact repeatedly but evidently fruitlessly made known to private researchers.

Note in passing that claims of major angular changes of the motion of some particles -- up to 135 degrees or more -- could be based on lack of appreciation of the three dimensional nature of the actual motion. Assuming a significant motion along the line-of-sight (which would be a characteristic of objects moving from inside the shuttle's shadow out into sunlight), even a relative small angular change in motion -- 10 or 20 degrees, for example -- would look much more significant when projected into a two-dimensional field- of-view plane normal to the line of sight. This can be easily demonstrated by drawing a line on a piece of paper, with a 20 degree course change at the midpoint, and then tilting the paper so that it is observed from near one end of the line -- the line can easily seem to 'reverse course' even though in 3D it only bent slightly. Since the shuttle and its cameras are near the points of origin of the shuttle-shed debris, this is an accurate model of expected visual effects.

One extraordinary (and hitherto unreported) coincidence about this incident also should be mentioned, because it demonstrates how easy it is to score a meaningless 'hit' if enough random variables are correlated in enough different ways. About five hours after the zig-zag, the shuttle had to make a small unplanned course change to avoid a "near miss" with a Russian satellite, Kosmos-955, two hours later. That spacecraft had been launched from Plesetsk on September 20, 1977, and had accidentally sparked the most spectacular "UFO panic" in Soviet history (the "jellyfish UFO" over Petrozavodsk and nearby cities was only the sunlit plumes of the booster rocket). The fact that the most famous "shuttle pseudo-UFO" and the most famous "Soviet pseudo-UFO" BOTH came within 15 kilometers of each other on the day of the shuttle zig-zag is an awesome coincidence which defies logical odds, except to say that in the end, "life's like that -- so what?" end



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