by Bruce Maccabee and Brad Sparks SKYLAB 3 FIGURE 1 THE FOURTH PHOTO

The sighting by Alan Bean, Owen Garriott and Jack Lousma, of a red "satellite" occurred on September 20, 1973 (day 263, revolution 1863 of their spaceflight) at approximately 1635 to 1645 GMT. (Brad Sparks was alerted to this sighting by a brief mention of it in an Associated Press report. It was also mentioned in Robert Emenegger's 1974 book "UFOs, Past Present and Future.") OWEN GARRIOTT JACK LOUSMA SKYLAB 3 ASTRONAUTS AT A PRESS CONFERENCE .........................................................................

The sighting was logged in Alan Bean's personal diary of the flight, written within a few hours of the event. He wrote, "Out the wardroom window we saw a bright red light with a bright/dim period of 10 sec. It got brighter and drifted along with us for 20 minutes or also was moving relative to the stars. It may have been very near. It was the brightest object we've seen" The next mention of the sighting was in a radio conversation with ground control. This is reported in the following document compiled by James Oberg in 1977: The second manned Skylab visit was within five days of returning to earth after a record-breaking 59 day expedition. The crew had awakened at 0700 GMT and would go to sleep at 2300 GMT. They had eaten lunch in the wardroom and were doing a 'procedures review' in the wardroom prior to beginning a new series of experiments in the afternoon. During the sighting the crew was out of contact with the ground control. The on-board tape recorder was not turned on and the first recorded mention of the incident was on a ground link some 4.5 hours after the event. Garriott had taken four photographs. During the taped discussion the conversation went as follows: LOUSMA: "Did you tell him about that satellite we saw? BEAN: Yes, we saw a great satellite. We didn't know if we told you about it. LOUSMA: The closest and brightest one we've seen. BEAN: Huge one. LOUSMA: We've seen several. It was a red one. CAPCOM: No, you may have told somebody, but it wasn't this team. I don't remember hearing about it. LOUSMA: I guess we didn't report it. It was reflecting in red light and oscillating at, oh, counting it's period of brightest to dimmest, about ten seconds. It led us into sunset. That was about three revs ago, I think. Something like that, wasn't it Owen? (no answer by Owen; topics changed.) Note: "Three revolutions ago," at about 1.5 hours per revolution is 4.5 hours before. Garriott said later that the object did not lead the Skylab into sunset, but rather followed the Skylab into sunset. (see below) Below is the original Oberg document. Note that the above document indicates that the location was over the southwestern Indian Ocean during revolution # 1863 (see map below). ........................................................................... Further information is available in the transcript of the debriefing that took place on or about October 4. Transcriptions are given below the documents.


During the debriefing there were two sections in which the "red satellite" was discussed. The first discussion is presented starting on page 7-4: LOUSMA: Things we saw out the window. GARRIOTT: For example we saw that satellite about a week before splashdown. That was one of the most unusual things that we saw and I guess Jack noticed it looking out the window. This bright reddish object was was out there and we tracked it for about 5 or 10 minutes. It was obviously a satellite in a very similar orbit to our own. It was rotating and had a period of almost exactly 10 seconds because you could see the brightness vary with that period. We followed it until sunset and it went out of sunlight just 5 to 7 seconds after we did. It held its position nearly the same in the wardroom window for that 10 minute interval. It was reddish in color even when we were well above the horizon. As we approached sunset it turned more reddish, presumably because of the sunlight change. What satellite it was and how it happened to end up in such a similar orbit no one ever explained to us. And I would like to hear a few words from someone about that satellite. BEAN: You bet. We never saw it again. You'd think we would have seen it the next night or it would cycle by another time. Maybe it did and we weren't looking out the window. LOUSMA: You might point out that it never did take the shape of an object but it was always brighter than any other star or planet in the night sky. It was much brighter. BEAN: We tried monitors and everything on it but we could never make it into anything other than a bright light. LOUSMA: In doing T002 I had on other occasions, at least once or twice, seen other satellites although they appeared as star points of light. The debriefing then switched to other topics. On page 20-1, during the debriefing on visual sightings the red satellite was discussed again: "GARRIOTT: Do you want to talk about that satellite? LOUSMA: I saw a couple of satellites that appeared like a satellite would on earth. I saw one that was not like one you would see on earth, so why don't you mention it? GARRIOTT: OK. About a week or 10 days before recovery and we were still waiting for information to be supplied to us about the identification. Jack first notices this rather large red star out the wardroom window. Upon close examination, it was much brighter than Jupiter or any of the other planets. It had a reddish hue to it, even though it was well above the horizon. The light from the Sun was not passing close to the Earth's limb at the time. We observed it for about 10 minutes prior to sunset. It was slowly rotating because it had a variation in brightness with a 10-seconds period. As I was saying, we observed it for about 10 minutes, until we went into darkness, and it also followed us into darkness about 5-seconds later. From the 5 to 10 second delay in it's disappearance we surmised that it was not more than 30 to 50 nautical miles [35 to 58 statute miles or 56 to 93 km] from our location. From its original position in the wardroom window, it did not move more than 10 or 20 degrees over the 10 minutes or so that we watched it. Its orbit was very close to that of our own. We never saw it on any earlier or succeeding orbits and we'd be quite interested in having its identification established. It's all debriefed in terms of time on channel A, so the precise timing and location can be picked up from there." NOTE: according to Oberg the Channel A tape recorder was not on, so the exact time cannot be determined. NOTE: Soon after this debriefing Garriott told one of us (Sparks) during an interview that his best estimate of the time interval between the Skylab going into sunset and the red light's disppearance was about 5-6 seconds. Garriott explained exactly how he counted out the seconds "one thousand one, one thousand two, etc." NOTE: Alan Bean wrote in his flight diary that the red satellite "drifted along with us for 20 minutes or more." Hence the object may have been seen for considerably longer than the 10 minutes stated by Garriott during the debriefing several weeks later. One of us (Sparks) asked an expert in satellite observation to take the NORAD tracking data and use his satellite observation program SkyMapPro, to determine Skylab 3's latitude-longitude-time coordinates and shadow entry, which turned out to be between 1645 and 1646 GMT (Greenwich Mean Time) or UTC (Universal Time Coordinated)(it was sunlit at 1645 and in the shadow at 1646). This fits the above reported 1645 GMT time and places 10-minute duration sighting at about 1635-1645. At 1645-1646 GMT Skylab was over Madagascar Channel at the extreme western edge of the Indian Ocean. Ground track of Skylab Orbital Workshop Time Time Latitude Longitude Altitude Speed Lighting hr:min km(nm) km/sec(nm/sec) ---- ------ --------- -------- ----- ----- ------- 20 Sep 1973 16:40 0446'15"S 02606'28"E 434.6 (234.7) 7.651(4.13) SUN 20 Sep 1973 16:41 0744'11"S 02821'55"E 435.7 7.650 " 20 Sep 1973 16:42 1041'08"S 03039'27"E 436.8 7.649 " 20 Sep 1973 16:43 1336'44"S 03259'52"E 438.1 7.648 " 20 Sep 1973 16:44 1630'35"S 03524'06"E 439.3 7.647 " 20 Sep 1973 16:45 1922'15"S 03753'03"E 440.6 7.646 " 20 Sep 1973 16:46 2211'17"S 04027'43"E 442.0 7.645 SHADOW 20 Sep 1973 16:47 2457'09"S 04309'10"E 443.4 7.643 " 20 Sep 1973 16:48 2739'17"S 04558'31"E 444.7 7.642 " 20 Sep 1973 16:49 3017'01"S 04856'57"E 446.1 7.641 " 20 Sep 1973 16:50 3249'38"S 05205'44"E 447.4 (241.6) 7.640(4.12) " (270-278 statute (4.75 statute miles/sec) miles/second) Latitute-Longitude values are to nearest 1 arcminute and altitudes to nearest kilometer. A map has been constructed from the above data, showing the shadow boundary on the earth and the track of the Skylab (white line):


The first and last photos presented here are pictures of the earth taken, with the same camera, before and after the sighting. These photos are mentioned in the NASA publication, "Photographic Index and Scene Identification," NASA-TM-X-69780, that was tabulated by Richard Underwood and co-workers in November, 1973. (See click here). In that document the photos are listed twice. Page 41 lists the photos that were contained in film magazine #CX-35. These photos were taken with a 35 mm Nikon camera with a lens of either 55 or 300 mm focal length using a film called SO-368 which is comparable to a type of Ektachrome (MS2448). According to the tabulation the photos labelled SL3-118-2132 through 2135 (frames 1- 4) were associated with the "S-230 experiment." Then photos SL3-118-2136 and 2137 (frames 5,6)were taken during the Goddard laser beacon experiment. These photos are described as "underexposed" and "blurred." According to the report on the laser beacon experiment ("Evaluation of Skylab Earth Laser Beacon Imagery," March, 1975; see Click Here), these beacon photos were taken on September 4 with a hand-held Nikon camera set at f/4.5 to f8 and with a shutter time of 1/500 to 1/250 of a second. It is important to know this because these may have been the settings and focal length when the four photos of interest here were taken, photos SL3 - 118 - 2138, 2139,2140 and 2141. The "Photographic Index...." lists these four as "Satellite, unmanned" on page 41 and as "blank" on page 245. The two different descriptions may have resulted as follows (speculation): when the photo index team first went through the photos they did not know that Garriott had photographed a "red satellite," so, looking quickly at the photos they saw nothing obvious and listed them as blank; later they learned that he photographed (what he thought was) a satellite and they changed the description, placing the new description in the front section of the report but leaving the original description at the "far end" (appendix) of the report. The next photo, SL3 - 118 - 2142 is identified as "Lake Erie, Ohio, Ontario, clouds." Photos 2137,38,39,40,41 and 42 are shown below. HERE IS THE SECOND PHOTO OF THE LASER BEACON EXPERIMENT. Although Garriott, who took the picture, said he could see the beacon it is not evident in this photo (nor is it evident in the preceding photo). HERE IS THE FIRST PHOTO OF THE OBJECT. The first photo of the object shows a featureless red "dot". HERE IS THE SECOND PHOTO OF THE OBJECT. The second photo shows a slightly larger image, slightly off round and yellowish in the center. The yellowish color at the center is typical of an overexposed color photo of a distant, bright red object or light. (There are also two other faint red dot images. They don't seem to be internal camera reflections. They seem to be too bright to be reflections in the window glass. Perhaps they were two more "red satellites.") HERE IS A BLOWUP OF THE ABOVE IMAGE THE RED "DOT" IS BARELY VISIBLE IN THE FOLLOWING PHOTO SO I HAVE DRAWN A CIRCLE AROUND IT. PHOTO 2141 CONTAINS THE MOST INTERESTING IMAGE BECAUSE IT ALLOWS FOR AN ESTIMATE OF SIZE AS REPRESENTED BY THE SPACINGS BETWEEN THE RED "BLOB" IMAGES The photo shown at the beginning of this article is a blowup of the fourth photo to show the odd shape of the red glowing object (or objects?). HERE IS PHOTO 2142, MORE OF THE EARTH AND HERE IS ANOTHER OF THE SKYLAB ..................................................................................


THE IMPORTANCE OF BEING ABLE TO CALCULATE THE SIZE OF THE OBJECT There is no doubt that there was some thing "out there" for the astronauts to see and photograph. Furthermore, it appeared "big," bright and red. The question then is, what was it? The available information does not allow for a specific identification of the object but if it were possible to estimate the size we could decide whether or not this could have been a man-made earth satellite. Manmade satellites at the time of this sighting, except for the Skylab itself, were on the order of 10 m in maximum dimension or less. Thus if the size estimated from the available data is noticeably larger than 10 m, the object was not a manmade satellite. NOT ALL THE IMAGES ARE USEFUL FOR SIZE CALCULATION The images in the first three photos show only "dot" images with no structure. These are not useful for estimating the size of the object because the size of a "dot" image made by a distant bright light is generally larger than the image would be if the optical system could provide a perfect "geometrically accurate" image. The extra image size is a result of diffraction, lens aberration and sideways diffusion of the light within the film. Thus, in the case of a "dot" image the most one can say is that the object which made the image was no larger than the geometric size that corresponds to the size of the outer boundary of the dot image. (How to calculate the geometric size is described below.) (NOTE: The image sizes of extremely distant lights that make only "dot" images, like images of stars, depend in mostly upon the brightness, with the brighter stars making bigger images. Astronomers have made use of this phenomenon to determine relative star brightnesses from photographs of stars.) POTENTIAL EXPLANATIONS FOR THE IMAGE SHAPE IN THE FOURTH PHOTO Whereas the calculation of geometric size of a single dot is not a useful estimate of size, when there are two or more dots, separated by even a short distance, there is the possibility to calculate the distance between the dots (as projected onto a plane perpendicular to the line of sight; see below) and use this as a measure of size of the object. Evidently only the fourth photo could provide information that would allow a calculation of size. The question, then, is this: is the shape of the image be a representation of the actual shape of the object or is there another explanation for the image shape? THE FOURTH PHOTO IS NOT A CAMERA ARTIFACT OR FILM FLAW If the the brightness structure of the image is not truly representative of the shape of the object then is it an artifact of (a) rapid motion of a single light (red object) carrying out a complex "maneuver" during the film exposure time (shutter time), (b) a rapid motion of the camera during the shutter time, (c) extreme aberration of the optical system or (d)a film flaw? It is my considered opinion, having looked at hundreds (or more) of photos of lights at night taken under widely varying circumstances that it is neither (b) nor (c) nor (d) for reasons explained below. If (a) is considered to be the cause of the fourth image shape then "manmade satellite" is automatically ruled out since no manmade satellite could move fast enough to carry out such a maneuver within the shutter time, believed to have been 1/250 sec. In other words if (a) is the answer the object must be considered unidentified and highly anomalous, whatever that might mean (end of story!). I consider (c) to be an invalid explanation for the image shape. Aberration can be operationally defined as the characteristic of a lens that causes the size of a "dot" image to be larger than the size determined by diffraction alone (which is determined by the diameter of the lens opening or aperture). Aberration may also distort an image shape such as converting a round image into an ellipse or even a complicated shape. As an example of the effect of extreme optical aberration imagine imaging through a thick glass bottle. However, in good quality lenses aberration is very small and certainly wouldn't be so bad as to convert a dot image into a complex structure. If the lens system did have that much aberration it would have affected the first three images the same way. Furthermore, all images, including the other photos the astronauts took would show evidence of this extreme aberration. Therefore (c) can not be an explanation for the shape of the fourth image. I also consider (d) to be an invalid explanation. To create an image like that would require that the film itself be scratched in two perpendiclar directions and partway through the various color layers of the film. But this film was handled with care and was not likely to be scratched. Furthermore this image does not look like a typical scratch with slightly jagged or very sharp edges and bright white places where the film emulsion was completely removed. The only remaining explanation to be considered is (b), camera motion. The smearing or the "elongation" of an image by camera motion is well known to photographers, especially those who use telephoto lenses mounted on hand held cameras. (NOTE: the type of vibration or camera motion that changes the pointing direction of the camera is rotation of the camera body and lens. Rotation about the horizontal axis creates an up-down image smear, rotation about the vertical axis creates a left-right image smear and, of course, complex combinations of these axial rotations create complex smears.) Relatively long time exposures (longer than 1/30 sec) of distant lights will generally show sllightly elongated or short arc-shaped images. Longer exposures such as 1/2 second or longer will show long, wavy arcs, arcs of short radius of curvature, loops and such. These "elongations" or smears of an image of a point of light can result from hand vibrations which cause the pointing direction of the camera lens to move about in random directions centered on some average pointing direction. Such vibrations probably would have occurred in this case but may have been smaller than on earth because in the zero-g environment the cameraman did not have to "struggle" with the weight of the camera and lens. There are two standard solutions to the vibration problem: a tripod or solid frame which supports the camera or a "fast" shutter. In this case there was no tripod but there was a fast shutter, presumed to have been 1/250 of a second. The fact that the first three images are dots indicate that the shutter time was short (otherwise they, too, would be smeared or elongated images). The slight elongation or ellipticity of the second image might be evidence of slight camera vibration rather than being a characteristic of the object itself. If so, then this is an indication of the small amount of vibration during the shutter time. That would, by itself, rule out explanation (b). But there is another aspect of the image that rules out camera motion even if the shutter time were not short. The image shape consists of a slightly curved (nearly vertical) right side and a leftward protrusion that is at about a 45 deg angle to the right side. If this shape were created by camera motion alone, it would require that the camera rotation make a very fast change from rotation about a horizontal axis (that creates the nearly vertical line) to rotation about a tilted axis (that creates the leftward protrusion). Furthermore, each bright spot would correspond to a momentary pause in the rotation or a rotation reversal. Camera rotations such as these, because of the inertia of the camera and lens, do not occur without the formation of loops in the image. But there are no loops. Hence, for the above reasons, in my opinion, the shape of the image is not a result of camera vibration. CALCULATION OF OBJECT SIZE The previous analysis indicates that the image shape is most likely a representation of the actual brightness structure of the object. For objects which are close enough or large enough to show definite structure such as distinctly separated image dots or shapes there is a way to estimate the object size from the image size. For such an image the size is geometrically related to the actual object size by a ratio equation that can be stated as follows: the image size(width, length, spacing of "blobs" as measured in the focal plane), herein called I, divided by the focal length, F, is equal to the size (width or length, as measured in a plane that is perpendicular to the line of sight) to the object, O, divided by the distance to the object, D. In equation form this is: I/F = O/D, which is based on the law of similar triangles with a common vertex at the center of the lens. (Usually the resolution capability of the camera is determined by whether or not this relation holds for a particular image of a particular object at a particular distance.) What can and what can't be resolved depends upon the optical quality of the camera lens and other factors related to the camera and film. If an object or light makes a "dot" image on the film, then the calculated size of the object is (probably) much larger than the actual size of the object, as described above. However, when there are distinguishable features of the image that are clearly separated by distance on the film it is possible to estimate the spacing between the features which made the images. The first three Skylab 3 photos are of little value in trying to estimate the size of the red object by measuring the size of individual "dot" images and multiplying by D/F. But in the fourth photo there is a considerable spacing between images of "dots". This means that the distance between dots has been resolved by the camera even though the dots themselves have not been resolved. [There "dots" are somewhat elongated so, strictly speaking, they are not exactly "dots."] On a direct copy (1:1) of the original film the maximum spacing between "dots," specifically the spacings between the centers of the upper and lower dots, is about 0.87 mm. The focal length of the camera was (probably) 300 mm (it might have been 55 mm; see below). Thus the ratio I/F equals about 0.87/300 = 0.0029 (in radian measure) (or, if the focal length was 55 mm, the ratio is .87/55 = 0.0158). As pointed out above, this ratio is proportional to the object size, as measured perpendicular the line of sight (i.e., as "projected" onto a plane surface that is perpendicular to the line of sight), divided by the distance. If the distance from the Skylab to the object could be determined it would be possible to determine the "projected" size of the object by using the equation O = D (I/F). There was no radar and no other distance measuring equipment on the Skylab so there was no way of making a direct measurement of distance. However, a fortuitous event occurred which gave Garriott an idea of how to estimate the distance, assuming the object was a manmade satellite: the Skylab went into the earth's shadow. Garriott, who was the first scientist at the Skylab, had the presence of mind to count the seconds between when the Skylab went into the earth's shadow and when the object, which appeared to be following the Skylab, disappeared. He assumed the object was visible only by reflected sunlight, an assumption which is reasonable if the object were another orbiting satellite. (If the object had been a bright source of red light [there were no satellites with bright red lights attached] then his assumption would not necessarily apply.) He also assumed that the red object was behind the Skylab and traveling at the same speed which, according to the table above, was about 7.64 km/sec. Based on these assumptions, and his estimated time until it disappeared, 5 - 10 seconds, the calculated distance between the Skylab and the object was (5 to 10 seconds) times 7.64 km/sec = 38 to 76 km. Assuming that the fourth photo was taken just before Skylab went into the shadow (an "unfounded" assumption since we don't know at what times, during the sighting, any of the photos were taken) and using the shorter distance estimate along with the ratio I/F = 0.0029 we find O = D(I/F) = D(0.0029) = 38 km x 0.0029 = 0.11 km = 110 m or about 336 ft as projected onto a plane perpendicular to the line of sight. If D were 76 km the calculated size would be twice as large. (Sparks spoke to Garriott in October, 1973, soon after the mission had been completed. Sparks asked how Garriott estimated the time until the "satellite" went into the shadow. Garriott said he counted off the seconds as "one thousand one, one thousand two", etc. and estimated 5 to 6 seconds this way. Hence these authors believe that the lower time estimate is probably more likely to be correct.) The width of the image, measured from the middle "dot" to the end of the "extension" at the left side of the middle dot, is about 1/3 of the spacing between the upper and lower dots. Thus the width would be about 37 m or 112 ft if 38 km away and 74 m or 224 ft if 76 km away. Now let's assume that the various dots that form the fourth image are reflections from points or small reflective areas of a "typical" earth satellite (manmade!). Then this calculation indicates that the spacing between two reflective portions of the satellite was 336 or more feet. However, in 1973 there was no satellite remotely approaching that size (and only the space station is comparable now, over 30 years later). (NOTE: The Skylab-3 itself with docked Apollo module was the largest satellite object in orbit at the time, about 150 feet long.) The calculation just done is a lower bound on the spacing between the outermost bright spots for the assumed distance. The calculation assumes that an imaginary straight line connecting the upper and lower red lights (or red reflective areas) on the object was perpendicular to the line of sight from the camera to the object. If a line drawn between the red lights was not perpendicular to the line of sight, then the spacing between them was greater than estimated above (by the factor 1/sinA where A is the acute angle between the sighting line and the line between points on the object; there is no way of knowing what A was so 90 degrees is assumed here, resulting an an estimate of the minimum spacing between lights or reflective areas). (NOTE: when this discussion was first published there was a question as to whether the focal length was 300 or 55 mm. One of us (Maccabee) had made a notation (in 1977 when copies of these photos were first obtained) that the focal length was 300 mm, but we recently learned that there were 5 Nikon cameras and each had either a 55 or 300 mm lens. This raised the question of whether or not the focal length could have been 55 mm. The question has now been resolved by the combination of the photo index and the report on the beacon experiment, as described above. Although it was 16 days between the laser beacon experiment and the date of these four photos, we believe it highly unlikely that they would have changed the lens on this camera if they wanted to take wide angle (55 mm) photos since they had four other Nikon cameras available, several of which had 55 mm lenses. We assume that Garriott simply grabbed a Nikon with the 300 mm lens, namely, the one used many days before during the beacon experiment.) COULD IT HAVE BEEN A MANMADE SATELLITE? The possible identifications divide into two general classes: (a) conventional explanations that assume a manmade/earth-launched satellite and (b) unconventional explanations that assume it was not an earth- launched satellite. Explanations of type (b) allow for the object to do "anything" because the object is assumed not to be limited by earth's gravity. In particular, (b)-type explanations allow for the object to make non-orbital motions, such as travel at velocities greater or less than the orbital velocity that is appropriate for its altitude. (For an object that is "trapped" by earth's gravity the orbital velocity depends upon the radial distance from the center of the earth). For example, one might imagine that the reason the object appeared as a dot in three photos and then as a structured object in the fourth is that the object was at a large distance from the Skylab during the (unknown) time duration of the first three photos and then, between the third and fourth photos, it suddenly moved much closer to the Skylab, at which time its structure could be resolved by the camera. If this happened, then the object made motions that are not consistent with being a satellite subject to orbital motion around the earth. There are many other non-orbital motions which one could imagine if the object was not a satellite and one could spend a long time trying to study all of these. However, the main point is that if the object was not confined to an orbit, since there were no manmade objects capable of such motions in the vicinity of the Skylab, the object would have to be considered truly anomalous, an Unidentified Space Object (USO, not to be confused with "USO: Unidentified Submerged Object"). Explanations of type (a) are the only ones that can be tested against known physics of satellites so the question arises, does the conventional hypothesis, that it was a satellite, fit the data? This hypothesis runs into trouble immediately when compared with the photographic and visual data. Both visually and photographically the object appeared bright red in color. Noting this color but assuming it was a satellite or some object that could have been reflecting sunlight, Garriott pointed out that when it was first seen and for about 10 minutes afterward the object and Skylab were not in a region of the orbit where the sunlight would have passed through the earth's atmosphere and therefore would have been reddened by scattering from particulate matter in the atmosphere (as in a red sunset). Hence the red color could not have been a result of the reflection of reddened sunlight from a typical satellite. To explain the red color Garriott may have assumed (although he never mentioned this assumption) that the satellite was painted red. He awaited an identification by NASA, but there was none because there were no satellites with red surfaces. The surfaces are typically painted black or white or are unpainted bare metal. RED LIGHTS ON A SATELLITE? An alternative hypothesis is that it was a satellite emitting intense red light. Garriott probably didn't consider this to be a possible explanation since there were no known satellites with bright red lights. The assumption that the astronauts were watching the red lights on an object and not reddened solar reflections leads to the conclusion that Garriott's method of estimating the distance could have been wrong. If the object had red lights then the fact that these lights disappeared shortly after Skylab went into the earth's shadow would not necessarily mean that it had also traveled into the earth's shadow. It could have been at any distance and simply turned off its lights 5 - 10 sec after the Skylab "disappeared" into darkness. But if this were true then Garriott's estimate of distance as described above could be a happy coincidence or it could have been a mistake. One interesting consequence of the red light hypothesis, which includes the assumption that the lights were turned off 5 - 10 seconds after Skylab went into darkness, is that the object could have been a lot closer to Skylab than Garriott estimated. Assume, for example, that the spacing between the lights on the assumed "satellite" was 10 m (33 ft), the maximum size of manmade satellites (including booster rockets) in 1973. Then the formula used above can be rewritten to give the distance that an object would have to be away from the camera in order to produce an image of the measured size. With O = 10 m, D = O(F/I) = O(1/0.0029) = 10/0.0029 = 3.4 km (2.1 mi). If the spacings of lights were less than 10 m then the distance would also be proportionally smaller. (Note: the result of this calculation, that a manmade satellite would be less than 3.5 km away when the fourth photo was taken, is referenced in the discussion below.) DISCUSSION OF POTENTIAL EXPLANATIONS FOR THE GROWTH IN IMAGE SIZE ASSUMING IT WAS A SATELLITE Since the focal length of the camera was constant, if the distance is also assumed to have been constant (at about 3.5 km) then the radical change in image size could result from reorientation/rotation of the satellite such that what initially appeared as a single small reflector of sunlight (during the first three photos) became a multiple reflector of sunlight (four main reflector points with connecting "structure") during the fourth photo. The shape of a satellite that would be consistent with this hypothesis is left to the imagination of the reader. Another hypothesis has been considered in order to explain the difference in image size between the first three photos and the fourth. This hypothesis is based on the assumption that the failure of the camera and film to resolve the structure during the first three photos is not an artifact of satellite orientation but rather a consequence of a much greater distance to the supposed satellite during the time that the first three photos were obtained. It is further assumed that the supposed satellite was in an elliptical orbit and was approaching the Skylab from the rear. Although Alan Bean wrote that the supposed satellite was seen for "20 minutes or more," for the purposes of this calculation we will use Garriott's estimate of about 10 minutes. Therefore the large difference in image sizes can be explained if one assumes that the first three photos were taken during the first minute while the satellite was still very far away and that the fourth was taken roughly 9 - 10 minutes later when the assumed satellite was much closer. Further to this hypothesis, one can carry out a "model calculation" using possible numerical values of the pertinent quantities in order to determine whether or not this hypothesis makes sense. The model makes the following assumptions: the object was an orbiting satellite; the first three photos were taken while it was distant and traveling toward the Skylab at a reasonable speed for an orbiting satellite; ten minutes later the object was close enough to the Skylab so that the camera could resolve bright spots on the satellite and create the image in the fourth photo. The key paramaters in this model are the initial distance, assumed to be 63 km, the satellite size, assumed to be 10 m, and the closing velocity, assumed to be 0.1 km/sec. At this approach velocity during the first minute the distance would have decreased by 6 km, hardly noticeable at a 63 km distance. Then, about 10 minutes = 600 seconds later, at the assumed time of the fourth photo, the separation would have been only about 63 km - (600 sec)(.1 km/sec) = 3 km and the angular size of the object, (O/D), would have been 60/3 = 20 times greater than at 63 km and more of the structure would be resolved by the camera. (Note: this hypothesis differs from the similar one described previously in the following way: whereas previously it was assumed that the object maintained a roughly fixed, large distance during the time of the first three photos and then it suddenly made an "un-satellite-like" rapid motion toward the Skylab, in this hypothesis the object/satellite is assumed to have approached in a steady manner consistent with an elliptical orbit as described below.) The preceding model can be further tested for consistency. Comparing the size of the image in the fourth photo with the sizes of the "dot" images in the preceding photos it would appear that the object would have had to be 20 or more times farther from the Skylab during the first three photos than at the time of the last photo in order to be far enough away to prevent the camera from resolving the image. Calculations presented above show that a man-made satellite (ca. 10 m in length) would have to be about 3 km away in order to make an image the size of the one in the fourth photo, assuming the 300 mm focal length lens was used. Twenty or more times farther away would place the initial distance at 60 km or more. The above model calculation assumed that the object crossed this 60 km distance in about 10 minutes or 600 seconds meaning that it would have been traveling faster than the Skylab, specifically, 60 km /600 sec = 0.100 km/s (about 200 mph) faster The Skylab was traveling at about 7,640 m/s, so the object, under these assumptions, would have traveled at about 7,740 m/s. The Skylab was in a nearly perfectly circular orbit (eccentricity esentially zero). The object is assumed to have been traveling in the same orbital plane and at the altitude of the Skylab, about 442 km. It was traveling faster, under these assumptions, and so its orbital eccentricity was larger than zero. The equation for eccentricity, e, based on the radial distance from the center of the earth at perigee, Rp, and the velocity at perigee, Vp, is e = (RpVp^2/GM) - 1 where GM = 4 x 10^14 m^3/sec^2. Using Rp = A + Re = (altitude + radius of earth) = 442 km + 6378 km = 6820 km and Vp = 7,740 m/s yields e = .0214. The semimajor axis of this ellipse is a = Rp/(1-e) = 6,969 km and the apogee height that corresponds to these values of Rp and e is Ra - Re = 2a - Rp -Re = 13,940 km - 6,820 km - 6378 km = 740 km. The period of the satellite in the elliptical orbit would have been P = 2 (pi)(a^1.5)/(GM)^.5 = 5,779 s or 96.3 minutes which is only about 3 minutes longer than the Skylab orbit time (93.4 min). The result of this calculation is that the object would have been very close to the Skylab for many minutes. The results would be similar for an object in a slightly different orbital plane, a plane close to the 50 degree inclination of the Skylab orbit in order to be within viewing range for up to 10 minutes. The previous model shows that the image size growth could result from the approach from behind of a (red) satellite. The approach speed is reasonable but it means that the hypothetical (red) satellite would be in a more elliptical orbit. However, this is not the problem with this hypothesis. The real problem is in the timing. Assume, as above, that the fourth photo was taken just before the Skylab went into the shadow. Then, at that time the assumed (red) satellite was about 3 km away from the Skylab. It was approaching the shadow boundary at a speed of about 7.7 km/sec. If it had been directly behind the Skylab it would have crossed the shadow boundary about (3 km/7.7 km/sec =) 0.39 sec after the Skylab, clearly much less time than estimated by Garriott. Suppose, instead, that the satellite had been 3 km higher and "above" (rather than directly behind) the Skylab when the Skylab went into the shadow. Then the distance (along its orbit) of the object from the shadow boundary would have been about 3 km/tan 21 = 7.8 km at the time the Skylab went into the shadow. (In this equation 21 degrees is the vertical angle-the angle measured in the vertical plane-that the orbit makes with the shadow boundary at the point where the orbit crosses the boundary.) The satellite would travel this distance in about 1 second, again much less than the time difference estimated by Garriott. The preceding calculations illustrate the problem with assuming that the object was the size of a large manmade satellite and therefore about 3 km away when the fourth photo which was taken. The problem is that, regardless of the direction assumed from the Skylab to the supposed satellite, the satellite would pass into the shadow no longer than about 1 second after the Skylab. If the assumed satellite were smaller than 10 m in size, say a meter or so, such as something ejected from the Skylab then it would have been even closer than 3 km and the time lag would have been even less. Assume, again, that the satellite or object was directly behind the Skylab. For it to pass into the shadow 5 seconds after the Skylab, the distance of the satellite from the shadow boundary, as measured along its orbit, would have had to have been at least (5 sec x 7.7 km/sec =) 38.5 km at the time when the Skylab crossed the shadow boundary. Thus at the time of the fourth photo (assumed to have been taken just before the Skylab went into the shadow) the distance would have been 38 km or greater. If the supposed satellite had been at a higher altitude and "above" the Skylab when Skylab crossed the shadow boundary it could have been closer to the Skylab than 38 km and still take 5 seconds to reach the shadow boundary. For this to occur the distance above the Skylab would have been (38.5 tan 21 =) 14.8 km which means that at the time of the fourth photo the distance would have been around 15 km. Using this distance to calculate size yields (0.0029 x 15,000 m =) 43 m, which is still four times the size of the largest satellite (other than the Skylab itself). Thus we see that it is "difficult" (impossible?) for the satellite (or ejected debris) hypothesis to satisfy two sighting requirements at the same time: 1) the size of the object, as determined by the distance and angular size (from the fourth photo) must be comparable to or smaller than that of a large satellite and 2) the time difference between when the Skylab crossed the shadow boundary and when the object/satellite crossed the boundary must be 5 seconds or more. Unfortunately there is no information on the actual direction from the Skylab to the object. Garriott said the direction to the object moved no more than 10 - 20 degrees, but he didn't provide the actual sighting direction. His assumption that the object followed Skylab into darkness suggests that the object was "behind" the Skylab, but in what direction behind we do not know. We can, therefore, drop the tacit assumption used above that the red object was directly behind the Skylab and allow it to approach from some other direction. The simplest alternative assumption is that the red object was in an orbit at the same altitude as the Skylab and traveling at the same orbital speed but that it was in a different orbital plane. Assume that the object and Skylab were approaching the location where the orbital planes cross. Then the distance between them was decreasing, finally reaching "zero" where the planes cross. (In 3 - D space the intersection of two different orbital planes forms a line that passes through the center of the earth. Imagine that the orbital planes are viewed from "above" - a point far from the earth - and seen edge on. Then the crossing of the planes (the intersection line) will appear to be a point. The tracks of two satellites in different orbital planes, in the vicinity of the orbital plane intersection, appear to be (nearly) straight lines that cross at the intersection point. This crossing point is above the earth at the altitude of the satellites. This corresponds to a "sideswipe" scenario where the approach velocity is completely due to a difference in orbital inclination angle from that of the Skylab's 50-degree inclination. This scenario is illustrated in the track map, below, where the red object is shown approaching the Skylab at this 45-degree angle from the west rather than on the other (east) side. In this illustration the angle between the two orbits is greatly exaggerated. It is possible to describe a specific model that will allow for an estimate of the difference in orbital plane inclinations. Built into this model are the following assumptions: (a) the object must have been about 20 times farther from the Skylab when the first photos were taken than it was when the last photo was taken, (b) the first photos were taken during the first minute of observation (c) they were separated by 3 km when the fourth photo was taken, and (d) the last photo was taken about 9.5 minutes after the initial photos. The latter assumption means that the Skylab traveled about 9.5 min x 60 sec/min x 7.645 km/sec = 4588 km during the assumed time between photos. Twenty times 3 km is 60 km, so assume that the object was 60 km away from Skylab when it was first observed. Now imagine drawing two converging straight lines, each almost horizontal, on a paper. The point where they cross represents the orbital plane crossover line as seen "end-on." Place the Skylab at some distance to the left of the crossover point on the upper of the two lines and place the object at the same distance on the lower of the two lines. Draw a line between the points. This line is the separation, S1 and the triangle just created is isosceles: it has two equal sides. The Skylab and the object are imagined to be moving at the same speed along these lines toward the right, toward the intersection point. Now move to the right toward the intersection point and at some position, still to the left of the intersection point, draw another line that is parallel to S1. This line, called S2, forms a much shorter isosceles triangle. The distance along each orbit line from S1 to S2 is called A. By the above assumptions A = 4588 km, S1 = 60 km and S2 = 3 km. Now it is necessary to calculate the vertex angle, a, from these data. The calculation is straightforward because of the simplified geometry. Using the law of similar triangles and trigonometric relations one can show that a = 2 arcsin{[(S1/2)-(S2/2)]/A} = 2 arcsin{[30 - 1.5]/4588} = 0.71 degrees. Other reasonable assumptions about the initial and final separations will lead to similarly small angles. (By these assumptions, when the Skylab and object were 3 km apart and Skylab was going into darkness, they were still at some considerable distance from the orbit plane crossover point. That distance, from the 3 km separation to the crossover, would be B = (3/2)/sin(.71) = 121 km.) Although the scenario just discussed must be immediately discarded since the unknown would pass into the shadow at at the same time as Skylab (because the orbits are at the same altitude), it does illustrate the following point: if the red object is assumed to have been a manmade satellite, then, because of the long time it was visible, its orbital inclination must have been very close to that of Skylab, probably within a degree or so, i.e., say, 49 - 51 degrees. [Another scenario that has been considered is based on three assumptions that are the "opposite" of what has been assumed above: 1) all the photos were taken at the beginning of the sighting, say, within the first minute, 2) the object was closest at the beginning of the sighting and 3) the object was traveling more slowly than the Skylab. It is also assumed that the object was a man-made satellite 10 m (or less) in size so that the initial distance at the time of the fourth photo was about 3 km. [It is further assumed that the three "dot" images that precede the fourth photo were a result of some rotation of the object such that only single red reflections or single red lights were visible to the astronauts, an assumption that already rules out this explanation.] Garriott's estimate of about 5 sec time lag indicates that the assumed satellite would have moved away to about 38 km behind the Skylab when it passed into the shadow. This scenario raises the following questions: 1) why didn't the astronauts continue to take photos since they clearly watched the object for, maybe, 9 minutes after taking 4 photos during the first minute (as assumed), 2) why didn't they indicate in their report that it was getting dimmer and smaller and clearly moving away from them as it dropped back? Of course, as shown above, its orbit would have been very close to that of the Skylab.] A 51-52-degree inclination is in fact one of the most common inclinations in space history for satellite objects, as it is the prime launch heading for many Russian launches from its original Tyuratam (Baikonur) launch site. But the higher inclination alternative, 51 degs instead of 49 degs, must have the red object coming from the north towards the Skylab, whereas, from the testimony of the astronauts, it appears that the red object was west of the Skylab. But Russian space objects are carefully tracked by both US and Russian observers as well as others. NASA signed an agreement with NORAD for NORAD to provide NASA with continually updated computer projections warning of potentially dangerous close approaches of any and all space objects during a manned space mission. These projections are generated with a NORAD/USAF computer program called COMBO (Computation for Miss Between Orbits). The COMBO program does not require that the satellites be directly in view of NORAD radars and other sensors at the moment of close approach -- the projections are made to any point in the satellite orbits anywhere in the world using the principle that manmade satellites follow predictable flight paths. As of 1973, according to NORAD/ADC, "NASA has not had to maneuver a manned spacecraft to avoid a collision with another satellite" based on the COMBO warnings. See the article by Major Samuel C. Beamer, Commander, Det 8, 14th Missile Warning Squadron, ADC, Laredo, Texas, "Nerve Center for Space Defense," Air University Review, September-October 1973 (online at The point of the above calculations and discussion is this: had it been another satellite in an elliptical orbit that was only a few kilometers or so from Skylab at its closest point, then it should have been known to the organizations that keep track of all satellites. It probably would have been within a few tens of kilometers of Skylab when Skylab went through the areas of the world where there were NASA and NORAD radars and sensors operating. There was no report that NASA or NORAD detected any object near Skylab, and a near-miss of only a few kilometers would have been an extremely dangerous situation as tracking radars often have errors of that magnitude (meaning it could have been at 0-distance, i.e., a direct and fatal collision).


Whatever the object was, it traveled a long distance with the Skylab. They saw it for about 10 or more minutes. During that time it and the Skylab traveled 4,600km (2,800 miles) or more. The big question, then, is this: is it possible to prove that there was, or at least could have been, a (manmade) earth satellite which either reflected sunlight as red light (in the absence of atmospheric reddening of sunlight) or which had several bright red lights and which could have been within a few miles of Skylab for many minutes without NORAD/NASA detecting it? If it was a manmade satellite, then its orbit was "uncomfortably" close to the Skylab orbit and it certainly should have been picked up by NORAD at some time during its orbit. Based on the available information, these authors conclude that there was not a manmade satellite that could explain this sighting and hence the object was truly anomalous. Further data are being sought. We thank James Smith for helpful comments and the above-listed web sites for NASA data on Skylab 3.