Comparison of the Timing of a Course Change Made by an Object in a STS-102 Video with Orbiter Thruster Firings




For several years, Jeff Challender has been recording space shuttle video from NASA Select television. When he or one of his correspondents finds potentially anomalous objects in a video he posts the images and descriptions of them on his Project Prove web site.


What he refers to as the “STS-102 Washington Sequence[1]” caught my attention because of certain similarities to the more well known STS-48 video. Namely, one of the objects that had entered the video frame at the upper left is seen to accelerate abruptly at nearly the same moment that a bright flash of light occurs. While there were several objects in the STS-48 video that changed course in response to a light flash, the similarity is still striking. A second similarity to the STS-48 video is the appearance of a fast-moving object shortly after the light flash that seems to pursue and almost overtake the object that accelerated in response to the light flash. These objects are shown in the “time exposure” overlay of Figure 1. This video sequence was taken on March 19, 2001 around 12:30 GMT.




Figure 1 Time exposure overlay of frames at 1-second intervals from STS-102 video0.

Video sequence courtesy of Jeff Challender


Presumably, the “mundane” interpretation for this STS-102 sequence is the same as that which was first proposed for the STS-48 video: A reaction control system (RCS) thruster on the space shuttle fires and its exhaust plume impinges on nearby debris particles, causing them to move abruptly.


Another similarity between this STS-102 sequence and the STS-48 sequence that should be noted here is that the objects appear shortly after orbital sunrise – a situation, it has been argued, that indicates the objects are “close” to the shuttle and therefore are orbiter debris. However, objects many kilometers from the orbiter would also be sufficiently close to it that they would become illuminated by the sun at around the same time as the shuttle. This coincidence, then, does not seem so compelling an indicator for the orbiter debris hypothesis as has been claimed, particularly when Jeff has captured video and posted images of several objects before sunrise and long after sunrise[2].


What the STS-102 video offers that the STS-48 video did not is the opportunity to directly compare the time of the light flash with thruster firing times listed in RCS telemetry records for the mission. This is possible because the video Jeff captured includes a view of the mission status display board in the JSC Mission Control Center. That display shows the current time both as Greenwich Mean Time (GMT) and as Mission Elapsed Time (MET). The GMT for the light flash in the video can be calculated simply from the elapsed video time (what I will refer to as EVT) for a frame displaying the GMT and the EVT for the frame showing the light flash. Expressed as an equation the GMT of the flash is then:


GMTflash = GMTdisplayed – (EVTdisplayed – EVTflash)


The EVT values can be obtained from the Quicktime movie information window. This sort of straightforward time check was not possible with the STS-48 video I obtained from NASA because that video showed only footage taken from the space shuttle and none from the MCC. The more indirect (and vastly more complex) method of time comparison I described in a 2003 article[3] suffered from uncertainties in the altitude of the Earth’s nightglow layer, which was used to determine the times of star transits. There may also have been some errors in the shuttle’s position in orbit due to the cumulative effects between thruster firings. The simple method used here for the time of the STS-102 event depends primarily upon the assumption of accurate time keeping by NASA.


Interpreting Displayed Video Times


Unfortunately, there is a practical complication to this simple method of time determination from the MCC time display. The size of the time display as it appears in the video frames is so small that some of the numerals are barely readable and ambiguous.  The numerals 0, 6, 8, and 9 are difficult to distinguish from each other. However, the numerals 1, 2, 3, 4, 5, and 7 are sufficiently distinct that they can often be used to resolve the ambiguous numerals by eliminating values that would produce an unreasonable time. The known difference between GMT and MET is especially useful for verifying the interpretation of the ambiguous numerals; any interpretation of numerals in the GMT cannot be correct if subtracting the known GMT-MET difference produces a MET to which the less ambiguous digits in the displayed MET cannot belong.  For the STS-102 mission the value of GMT minus MET is 67 days, 11 hours, 42 minutes and 9 seconds[4]. This difference can be represented in a less wordy notation as 67:11:42:09.


The first video frame displaying the times on the MCC status board is shown in Figure 2. After watching the video, Jeff determined that the GMT time on this frame was 078:12:30:43. As shown in the image, subtraction of the GMT-MET difference from his GMT time value produces a MET value in conformance with all of the unambiguous MET numerals, which indicates his reading of the GMT was correct.



Figure 2  First frame in STS-102 video showing Greenwich Mean Time and Mission Elapsed Time.



Event Time versus Orbiter RCS Thruster Firing Times


While the fractional parts of seconds are not shown on the mission status board display, all times can be narrowed down to a fraction of a second in precision using two adjacent frames for which the ones digit (the right-most digit) in the time display changes from 9 to 0 as the tens digit simultaneously increments going from one frame to the next. Two such frames are shown in

Figure 3. While the “9” in the ones place in the first GMT value and the “0” in the subsequent frame are difficult to distinguish from each other by appearance alone, they can have no other value since 50 must follow 49.


Figure 3 Time displays from two adjacent frames showing the seconds part of the GMT

changing from 49 to 50 seconds.



According to the QuickTime information display, the EVT of the 49-second frame of  Figure 3 is 1 minute 54+4/30 seconds, or 1:54+4/30. The EVT of the 50-second frame is 1:54+11/30, so the GMT changed to 12:30:50 at some point in the time interval of 7/30 second between those two frames.


The EVT for the light flash and subsequent course change of the “main” object was 1:39+19/30. Using the second frame of Figure 3 as the time reference, the GMT for this event was therefore 12:30:35.27. Table 1 shows the telemetry data obtained from the Johnson Space Center Freedom of Information Office for Space Shuttle Discovery’s RCS thruster firings between 12:15:00 and 12:35:00 GMT on the 78th day (March 19) of 2001 on the STS-102 mission. The RCS thruster firing that most closely coincides in time with the light flash was R5D (is the designation for the downward-pointing vernier thruster on the right side of the Orbiter’s tail). The time of the firing was at 12:30:39.068 GMT, which is approximately 3.8 seconds after the light flash occurred. This effectively rules out this RCS firing as the cause of the flash, assuming the time data is correct. Further, there is an additional time delay between when a signal is transmitted by the orbiter and when it is received on the ground. A “round trip” time delay (a signal from the ground to the shuttle and back to ground again) can be as much as 6 seconds[5]. A one-way delay could thus be as long as 3 seconds. Taking this time lag into account, the thruster firing actually could have occurred 6 or 7 seconds after the light flash event.


The RCS firing preceding the light flash event ended at 12:29:48.748, which is 46 seconds before the light flash. The rapidly moving thruster exhaust gases were many kilometers away from the orbiter by the time of the light flash and could have had no effect on anything near the orbiter.




Only one of two conclusions seems possible: Either the light flash event in the STS-102 video was a truly anomalous event unrelated to shuttle operations or there was a serious error in the displayed time on the MCC mission status board. While most people may get by with their wrist watches off by several seconds from the correct time, it seems highly unlikely that NASA mission controllers would consider an error of more than 6 seconds acceptable. It seems much more likely that the displayed time is accurate to the millisecond.


While the timing of the light flash seen in the earlier STS-48 video sequence could not be determined with great confidence, the spatial distribution of flash brightness over the video frame and the duration of the light flash were found to be inconsistent with a thruster firing[6]. The examination of the STS-102 video presented here provides further evidence that such flashes are not the product of shuttle thruster firings.


Table 1 STS-102 RCS firings for a time period from 12:15:00 to 12:35:00 GMT.

Source:  Johnson Space Center Freedom of Information Office


GMT               Jet  Value

078:12:16:21.948  F5R  ON

078:12:16:23.388  F5R  OFF

078:12:16:57.068  R5D  ON

078:12:16:58.108  L5D  ON

078:12:16:59.068  R5D  OFF

078:12:16:59.148  L5D  OFF

078:12:17:17.948  R5D  ON

078:12:17:18.028  L5D  ON

078:12:17:18.188  R5D  OFF

078:12:17:18.268  L5D  OFF

078:12:21:49.628  F5R  ON

                  R5D  ON

                  R5R  ON

078:12:21:50.588  F5R  OFF

                  R5D  OFF

                  R5R  OFF

078:12:26:01.228  R5D  ON

078:12:26:01.788  L5D  ON

                  R5D  OFF

078:12:26:01.868  L5D  OFF

078:12:26:26.588  R5D  ON

078:12:26:26.668  L5D  ON

                  R5D  OFF

078:12:26:26.748  L5D  OFF

078:12:29:47.708  F5R  ON

                  R5D  ON

                  R5R  ON

078:12:29:48.748  F5R  OFF

                  R5D  OFF

                  R5R  OFF

078:12:30:39.068  R5D  ON

078:12:30:39.148  L5D  ON

078:12:30:39.548  R5D  OFF

078:12:30:39.628  L5D  OFF

078:12:30:40.348  R5D  ON

078:12:30:40.428  L5D  ON

078:12:30:40.508  R5D  OFF

078:12:30:40.588  L5D  OFF


[1] “STS-102 The Washington Sequence”

[2] For an object during another mission that appears during orbital night, see

[3] A New Look at the Evidence Supporting a Prosaic Explanation of  the STS-48 “UFO” Video

[4] The corresponding METs and GMTs for several events in the STS-102 mission are given in a NASA mission status report at URL:

[5] Space Robot Dynamics and Control: To Orbit, From Orbit, and Future

Kazuya Yoshida

Department of Aeronautics and Space Engineering, Tohoku University


[6] Analysis of the Light Flash in the STS-48 Video.