Some Insights from an Expert

[dcman]

...concerning anomalous objects as seen in space, by orbiter.

Summary

In a discussion with a NASA aerospace engineer familiar with the space shuttle reaction control system, I learned that the thrusters never generate any light while operating, but they always emit a small cloud of unburned propellant just before the thruster fires and a much larger cloud immediately after the thruster shuts down. The post-burn cloud may be visible, but only when reflecting sunlight. The pre-burn cloud is never visible to the human eye but might be detected by a light-sensitive camera. Any light flashes seen in space shuttle videos cannot be from a thruster unless they coincide with the beginning or end of a rocket burn. The consequences of this information in regard to two videos of apparently anomalous objects taken by shuttle video cameras are described.

...

Read the link at bottom of page for body.

Conclusion

There are only two cases that I know of in which objects in a space shuttle video react to a light flash with a radical change in course: STS-48 and STS-102. The information I've received from an expert in the shuttle's RCS propulsion system provides a compelling refutation of Oberg's argument that thruster firings were the cause of the objects' behavior in both cases.

Another assertion by Oberg that is incorrect is that propellant seeping out of propellant lines and freezing in the nozzle is a routine occurrence on the orbiter. To the contrary, it is an indication of a potentially serious leak according to the NASA engineer. If such a leak is detected the caution and warning system notifies the crew that a "Fail-Leak" condition has occurred. The leaking thruster is then isolated by shutting valves upstream of the leak. There is no record that I know of that any such failure occurred during either STS-48 or STS-102, at least during the time when the videos were taken. Based on Oberg's statements, it had seemed to me that in both the STS-48 and STS-102 videos the high-speed "projectiles" seemingly pursuing slower-moving objects might be explained as ice chunks expelled from the nozzle during the rocket burn. But as the presence of such ice in the thruster would indicate a possibly serious problem with the shuttle propulsion system, this explanation no longer seems feasible.

Finally, Oberg stated that the speed of the RCS rocket exhaust gases is about 1000 feet per second. Their actual speed is 3500 meters or 11,482 feet per second.[9] That is ten times faster than the speed he cited. This error is of no great importance to the question of apparent anomalous objects in shuttle videos. But it is one more indication that while Oberg may well be an expert on many aspects of space flight, he evidently has no particular expertise or experience with the RCS propulsion system.

While the NASA engineer I spoke with was a legitimate authority on the space shuttle's RCS rockets, it should be apparent from reading this article that I have not simply made an appeal to authority here just because what he said severely undermines the "prosaic" explanations for these space shuttle videos. Instead, I've tried to verify his assertions to the extent feasible by checking independent references and data sources such as the RCS combustion chamber pressure records for STS-48. Everything I've found was consistent with what he told me.

The brightness curves for both the STS-48 and the STS-102 videos do not match what would be expected for reflected light from unburned RCS propellant if it is assumed that the light flash comes only at the end of a thruster burn as asserted by the NASA engineer I discussed the question with. Even if it is assumed that a light flash can be detected at the beginning of a thruster firing by a light-sensitive camera, the brightness curves in both videos still do not match what would be expected for a thruster burn.

Source: http://www.vgl.org/webfiles/STS-48/RCS/RCS.htm

[dcman]

I guess there isn't a "prosaic explanation" for everything.

Edited November 12, 2007 by dcman

[JimOberg]

Well done for performing some investigations. I'm warning you, this may lead you to discover some things about your favorite cases that you don't want to know -- but that can be liberating. Anyhow, good for you for stepping out from the herd and looking around on your own.

In a discussion with a NASA aerospace engineer familiar with the space shuttle reaction control system, I learned that the thrusters never generate any light while operating, but they always emit a small cloud of unburned propellant just before the thruster fires and a much larger cloud immediately after the thruster shuts down. The post-burn cloud may be visible, but only when reflecting sunlight. The pre-burn cloud is never visible to the human eye but might be detected by a light-sensitive camera. Any light flashes seen in space shuttle videos cannot be from a thruster unless they coincide with the beginning or end of a rocket burn. The consequences of this information in regard to two videos of apparently anomalous objects taken by shuttle video cameras are described.

Right, a thruster plume is not visible except to an IR camera (we did deliberate plume generation on STS-39 to test AF anti-missile sensors), and the prop ratio mismatch at start anbd stop are what usually show up. But I'm baffled by the claim that the bursts are only visible from reflected sunlight -- the combustion products are HOT and glow very nicely, as seen routinely on every shuttle mission (especially during the plume hotfire tests on the day before entry). When I was a flight controller for the OMS/RCS console for STS-1 and STS-2, and later as a flight controller for the Rendezvous group, sitting in the front row in the Mission control Center's MOCR (Mission Operations Control Room), we'd see the plume bursts best at night when the cameras were most light-sensitive. This might also be a candidate for putting some typical video of this onto youtube. But as to plume nighttime visibility, your source is in the dark.

There are only two cases that I know of in which objects in a space shuttle video react to a light flash with a radical change in course: STS-48 and STS-102. The information I've received from an expert in the shuttle's RCS propulsion system provides a compelling refutation of Oberg's argument that thruster firings were the cause of the objects' behavior in both cases.

We saw objects change direction all the time when too close to a thruster plume. I can get testimony from other members of the flight control team. Your source must not have been in those positions at those times.

Another assertion by Oberg that is incorrect is that propellant seeping out of propellant lines and freezing in the nozzle is a routine occurrence on the orbiter. To the contrary, it is an indication of a potentially serious leak according to the NASA engineer.

There would be a major leak every few missions, and a minor leak or two or more every mission. These are all in the mission anomaly logs.

If such a leak is detected the caution and warning system notifies the crew that a "Fail-Leak" condition has occurred. The leaking thruster is then isolated by shutting valves upstream of the leak. There is no record that I know of that any such failure occurred during either STS-48 or STS-102, at least during the time when the videos were taken.

It is impossible to isolate a single thruster by shutting upstream valves -- check out the plumbing diagrams available on line. You could shut off an entire manifold of several thrusters together (either ALL thrusters in line 1 and 2, or ALL thrusters in lines 3,4, and 5), thus sacrificing them all, so it was a serious step. Usually you just fired the thruster again to see if the valve seal set istelf better, or blew out the grit in the line causing the leak. Or just fed the leak.

Besides, it's irrelevant to 48, for example -- here are the comments of two of the crewmen:

STS-48 co-pilot Reightler, when asked, told me: “We saw a lot of this on STS-48 because we had a dump nozzle that was leaking.” This same nozzle leaked on the next ‘Discovery’ mission as well and “created the same shower of ice particles – but apparently this time no one misinterpreted them as UFOs.”

Mission specialist Mark Brown added: “When illuminated by sunlight they looked like small diamonds floating in space, disturbed only when the maneuvering rockets fired – the plumes from the rockets would hit them and send them off in different directions.”

(continued next message)

[JimOberg]

Based on Oberg's statements, it had seemed to me that in both the STS-48 and STS-102 videos the high-speed "projectiles" seemingly pursuing slower-moving objects might be explained as ice chunks expelled from the nozzle during the rocket burn. But as the presence of such ice in the thruster would indicate a possibly serious problem with the shuttle propulsion system, this explanation no longer seems feasible.

You're over your head here. Especially if the 'expert' you're quoting is Lan Fleming. Is it?

The prosaic explanation does not require the dots to be coming from a leaking RCS thruster. There are also several water dump nozzles, plus the nozzles of the flash evaporator ('water spray boiler' system), and earlier in missions, ice from the main engine bells. And that doesn't even count particulate sources such as thermal protection system gap fillers, payload bay detritus, explosive bolt and guillotine fragments, thermal blanket fragments, including buttons, etc etc. The variety of sources of shuttle-derived debris is pretty extensive.

Finally, Oberg stated that the speed of the RCS rocket exhaust gases is about 1000 feet per second. Their actual speed is 3500 meters or 11,482 feet per second.[9] That is ten times faster than the speed he cited. This error is of no great importance to the question of apparent anomalous objects in shuttle videos. But it is one more indication that while Oberg may well be an expert on many aspects of space flight, he evidently has no particular expertise or experience with the RCS propulsion system.

If I typed 1,000 ft/sec it is an obvious error (I could claim a typo, and would appreciate a citation so if it is on my home page I can correct it), but my on-line reports ought to say "approx 10,000 ft/sec" because I know that exhaust velocity is the product of a thruster's "specific impulse" times the acceleration of gravity ('g'), which for RCS engines is about 290 seconds times 32.2 ft/sec/sec, or 9338 ft/sec. The OMS engines have a specific impulse ("i sub sp") of 312 seconds, so their exhaust velocity is about 10,046 ft/sec.

Since 1 ft = 0.3048 meters, the RCS exhaust velocity in metric is 2846 m/sec, and for the OMS, is 3062 ft sec.

To achieve an exhaust velocity of 3500 meters per second, you'd need a specific impulse of 357 seconds. That's actually in the range of efficiency of the space shuttle main engines, which use liquid hydrogen fuel to get that extra oomph during ascent.

What may have happened is the source DCMAN talked to just used the specific impulse of the 'shuttle rocket engine', the main engines, and assumed that all rocket engines on the shuttle were equally efficient. It's a reasonable assumption for an outsider.

The reason I have these numbers memorized is because I was certified as a console operator of these OMS/RCS engines (not the main engines -- they sat in another row) early in the shuttle program, and the rockets haven't changed.

DCMAN, please check back with your source on these numbers. Let us know his/her response.

While the NASA engineer I spoke with was a legitimate authority on the space shuttle's RCS rockets,

...well, this may not be so clear-cut. Ask them what certificates they ever got for Mission Control work or for mission design products, or as a trainer for flight crews -- any real expert would have such documentation. Or did they just read about the engines in some manual? Please be a little more specific. Because if the above math is any clue, your source misrepresented himself/herself to you.

it should be apparent from reading this article that I have not simply made an appeal to authority here just because what he said severely undermines the "prosaic" explanations for these space shuttle videos. Instead, I've tried to verify his assertions to the extent feasible by checking independent references and data sources such as the RCS combustion chamber pressure records for STS-48. Everything I've found was consistent with what he told me.

And just where did you find that information on line?

[JimOberg]

You're over your head here. Especially if the 'expert' you're quoting is Lan Fleming. Is it?

Ahh, I checked the footnotes you gave, and it was a post by Fleming. HE claims he talked with some anonymous expert.

Sorry that I misinterpreted your post to say that YOU had gone and done original research.

Congratulations were premature, you were just cutting-and-pasting again.

The footnote to the 'RCS plume velocity' figure that you posted here does not work.

You'll have to do better.

What a waste of time.

Edited November 12, 2007 by JimOberg

[SkepticalEd]

...concerning anomalous objects as seen in space, by orbiter.

Summary

In a discussion with a NASA aerospace engineer familiar with the space shuttle reaction control system, I learned that the thrusters never generate any light while operating, but they always emit a small cloud of unburned propellant just before the thruster fires and a much larger cloud immediately after the thruster shuts down. The post-burn cloud may be visible, but only when reflecting sunlight. The pre-burn cloud is never visible to the human eye but might be detected by a light-sensitive camera. Any light flashes seen in space shuttle videos cannot be from a thruster unless they coincide with the beginning or end of a rocket burn. The consequences of this information in regard to two videos of apparently anomalous objects taken by shuttle video cameras are described.

SkepticalEd: "I have stated this over and over, just a short while ago while "dueling" with Jim Oberg about what one sees in the STS-48 video. It is my opinion that after seeing this footage over and over during the years it was first released that the flash one sees SEEMS to have nothing to do with a thruster firing from the shuttle. Shuttle thruster firings have been shown on TV many times and at no time did any of them resemble the flash on STS-48. I can't explain what the flash is the result of but if the shuttle had fired a thruster then it goes without saying that an action produces a reaction. In this case, the shuttle should have moved, even infinitesimally and you would have seen the reaction by the slight movement of the camera's view. After all, don't they fire the thrusters to change the attitude of the vehicle? Isn't a thruster firing a "violent" action? Shouldn't a reaction to a violent action be visible via the camera's view?"

[JimOberg]

DCMAN, are you going to ask Fleming about his silly errors in the posting you passed on, or are you going to just pretend you didn't try to foist off another 'UFO buff' as some sort of real 'NASA expert'. Don't you feel even a little chagrined by how quickly this latest attempt at evidence collapsed?

[lost_shaman]

It is impossible to isolate a single thruster by shutting upstream valves -- check out the plumbing diagrams available on line. You could shut off an entire manifold of several thrusters together (either ALL thrusters in line 1 and 2, or ALL thrusters in lines 3,4, and 5), thus sacrificing them all, so it was a serious step. Usually you just fired the thruster again to see if the valve seal set istelf better, or blew out the grit in the line causing the leak. Or just fed the leak.

Besides, it's irrelevant to 48, for example -- here are the comments of two of the crewmen:

STS-48 co-pilot Reightler, when asked, told me: “We saw a lot of this on STS-48 because we had a dump nozzle that was leaking.” This same nozzle leaked on the next ‘Discovery’ mission as well and “created the same shower of ice particles – but apparently this time no one misinterpreted them as UFOs.”

Jim that quote is irrelevant to your point about potential RCS thruster valve leaks. Reightler was referencing a leaking water dump nozzle (Supply Water Dump Valve) not an RCS jet.

Incidentally that is exactly how the fix was made, by closing an 'isolation valve' "upstream" and then 'purging' the line. The supply dump line, valve and nozzle were not used again for the remainder of the mission.

That was done because NASA doesn't just sit around dumbfounded watching the 'pretty ice crystals' when even a water dump valve "leaks" ("Burps") on a Shuttle Flight!!! In fact NASA has been quite interested in every minor "leak" ("Burp") in the water dump valves and nozzles that can be documented. RCS valve "leaks" on the other hand are quite major in comparison as these are potentially catastrophic failures for spacecraft that could potentially result in a loss of life. So watching the 'pretty ice crystals' isn't an official NASA response in that case either!

Edited November 13, 2007 by lost_shaman

[lost_shaman]

The footnote to the 'RCS plume velocity' figure that you posted here does not work.

You'll have to do better.

What a waste of time.

If I typed 1,000 ft/sec it is an obvious error (I could claim a typo, and would appreciate a citation so if it is on my home page I can correct it)

Jim before you start throwing such LARGE stones around in your own glass house let me quote you from your own 1992 article NASA STS-48 "UFO" VIDEO Subject: Actual explanation for the notorious STS-48 "UFOs" on videotape 1992.

"The ejected burn byproducts travel at about 1000 ft/sec." - http://www.debunker.com/texts/sts48_ufo.html

Jim the figure cited (1000 ft/sec) clearly comes from the reading of your own 1992 article on this video. I mean you're literally telling someone who's quoted your own 1992 article, telling them, "You'll have to do better"!!! OUCH!!!

[JimOberg]

Jim before you start throwing such LARGE stones around in your own glass house let me quote you from your own 1992 article NASA STS-48 "UFO" VIDEO Subject: Actual explanation for the notorious STS-48 "UFOs" on videotape 1992.

"The ejected burn byproducts travel at about 1000 ft/sec." - http://www.debunker.com/texts/sts48_ufo.html

Jim the figure cited (1000 ft/sec) clearly comes from the reading of your own 1992 article on this video. I mean you're literally telling someone who's quoted your own 1992 article, telling them, "You'll have to do better"!!! OUCH!!!

Yep, I better fix it....

That's the difference between my errors and DCMAN's.

[dcman]

Yep, I better fix it....

That's the difference between my errors and DCMAN's.

Jim the purpose for me bringing this up, is to point out that you clearly make errors. That article you wrote is from 1992; you wrote "The ejected burn byproducts travel at about 1000 ft/sec." AN ERROR!! You had 15 years to correct it...now you want us to believe it was just a typo? What else are you wrong about?

You'll have to do better!

What a waste of time!

I should have called this thread "Debunking the Debunker"

Edited November 13, 2007 by dcman

[JimOberg]

Jim the purpose for me bringing this up, is to point out that you clearly make errors. That article you wrote is from 1992; you wrote "The ejected burn byproducts travel at about 1000 ft/sec." AN ERROR!! You had 15 years to correct it...now you want us to believe it was just a typo? What else are you wrong about?

You'll have to do better!

What a waste of time!

I should have called this thread "Debunking the Debunker"

I'm fixing it.

Your turn.

[dcman]

I'm fixing it.

Your turn.

Are you still smarting from the embarrassment??

Edited November 13, 2007 by dcman

[JimOberg]

Are you still smarting from the embarrassment??

On a scale of 1 to 10, about 3....

mainly because it WAS my professional specialty

and I should have noticed. In the fifteen years

AFTER that piece was written, whenever I

mentioned exhaust velocity, I got it correct... but

not that time.

[lost_shaman]

Yep, I better fix it....

We're all Human. I make mistakes everyday.

It's supprizing how many people these day's actually think they don't make them!

[dcman]

DCMAN, are you going to ask Fleming about his silly errors in the posting you passed on, or are you going to just pretend you didn't try to foist off another 'UFO buff' as some sort of real 'NASA expert'. Don't you feel even a little chagrined by how quickly this latest attempt at evidence collapsed?

I believe he is going to be responding here shortly...this ought to be very interesting. I wrote him an email to inform him of the conversation we had and to give him the opportunity to defend himself. He did respond and said "I'll make some comments when I get a chance."

Edited November 22, 2007 by dcman

[dcman]

On a scale of 1 to 10, about 3....

mainly because it WAS my professional specialty

and I should have noticed. In the fifteen years

AFTER that piece was written, whenever I

mentioned exhaust velocity, I got it correct... but

not that time.

Personally, I would expect better of you then this...as one of my engineering profs used to say to me "there are no part marks in the real world." When you make a scientific statement such as you did, and considering the the position you held at NASA, I would expect that you would not make such an obvious error. Anyway, at least you were able to admit it...I'll give you that. I'll go even further and say the same thing about you that you said about Clark McClelland: "James Oberg certainly did serious, significant, and capable service for the US space program, and rubbed shoulders with the biggies, and take justifiable pride in. No disputing that."

Edited November 22, 2007 by dcman

[Magnatude]

DC, Jim, I dont find this a waste of time.

Its very informative!

At least for me, if it counts for anything.

I glean a lot for my own writing from everyones posts, and you each contribute much to understanding both sides of the debate.

[Lan Fleming]

Ahh, I checked the footnotes you gave, and it was a post by Fleming. HE claims he talked with some anonymous expert.

Sorry that I misinterpreted your post to say that YOU had gone and done original research.

Congratulations were premature, you were just cutting-and-pasting again.

The footnote to the 'RCS plume velocity' figure that you posted here does not work.

You'll have to do better.

What a waste of time.

I can see Oberg is still his usual cheery self.

Yep. That's what I claim since that's what happened. The project I was working on required information on a propellant transfer system that was supposed to move fuel and oxidizer from the shuttle's own tanks to the International Space Station. The propellant transfer system was cancelled and the hardware was never built. We just built a computer model of it as a test case for modeling software we were developing. Since the transfer system involved the shuttle's reaction control system, I talked at length to an engineer at JSC who had been involved in some of the design and testing of the RCS. The main subject we were interested in was how the helium used to pressurize the propellant tanks was kept out of the lines that feed the thrusters. He showed me a piece of the mesh material and a few other odds and ends from the RCS he kept in his office (I don't think he's actively involved with the RCS work anymore, though).

In the course of the discussions, I asked him about how frequently light flashes were produced by the vernier thrusters. He said it happened every time they are fired, but the light isn't produced by the rocket exhaust plume, which is invisible. According to this engineer, the light is sunlight reflected off a cloud of ice particles from the thruster nozzle shortly after the rocket shuts down. This "snow" is a product of evaporative cooling of liquid propellant trapped in the tubing between the fuel valve and and the vacuum of space.

This engineer was also unfamiliar with Oberg's notion that imbalances in the fuel/oxidizer ratio would cause the rocket exhaust plume to be visible. Like myself, he was under the impression that, since the fuel and oxidizer combine chemically at a fixed stoichiometric ratio, any excess fuel or oxidizer would be expelled in the stream of the hot exhaust plume as unburned and invisible gas.

The main point with respect to the STS-48 video is this: Some of the objects change course abruptly at almost the same moment that the light flash occurred. If it is assumed that the objects moved when hit by the exhaust plume and the light flash was from a "snow" cloud at the end of the 1.2-second burn, then the objects would have to be over 4 kilometers away from the shuttle because that's the distance the exhaust plume would travel in 1.2 seconds before impinging on the objects. That distance, of course, would be just a tad too large for the space shuttle's camera to detect small ice particles if that's what the objects were.

I'm not going to give out the engineer's name since he didn't give his permission and I didn't tell him my questions had to do with UFOs, which is a naughty word at NASA not spoken in polite society during business hours. Oberg should be able to check with one of his NASA friends if he wants to verify this, but I think this engineer knew what he was talking about and his explanation of how the verniers emit ice clouds seems to make sense physically. Oberg's "imbalanced" propellants explanation does not seem to make sense.

In any event, the light flash in the video is clealy NOT from a rocket at all for reasons I've explained before: the flash of light is lens flare. It originates in the upper left corner of the video frame and expands downward toward the lower right corner. The L5D thruster to which Oberg attributes the light flash is below and to the left of the lower left corner of the video frame. Plus, the line of sight at the camera's upper left corner was elevated 62 degrees above the plane of the shuttle's wings. Any plume of gas or "snow" from the thruster seen at that position would be about 30 feet above the thruster's location. That's quite a distance for stuff escaping from the nozzle of a small, downward-pointing vernier thruster to travel and still be visible. But if "eager believers" want to believe the light flash is rocket exhaust because it fits their pet theories, there's nothing I can do to stop them.

By the way, I was able to calculate the camera elevation at the corners of the image because I had first calculated the camera's line of sight at the center of the image, which turned out to be about 55 degrees above the plane of the space shuttle's wings and 65 degrees to the left of the spacecraft's nose. That I know because I figured it out the hard way: using the identifiable stars in the image to get the camera's orientation and the quaternion data describing the spacecraft's orientation, which I got from the NASA FOIA office. Then I did it the easy way by writing to the FOIA people and just asking them directly which way the camera was pointed. The coordinates they sent me were within 1 degree of what I had calculated. That sort of confirmation is nice to get once in a while. It almost makes it worth getting attacked personally by self-styled "skeptics." But not quite.

[Lan Fleming]

The footnote to the 'RCS plume velocity' figure that you posted here does not work.

Public access to the link Oberg is complaining about may have been blocked since I wrote that article. Or maybe it's always been restricted to on-site. But here's the original reference with the table showing the thruster exhaust velocities:

NSTS 07700, Volume XIV Space Shuttle System Payload Accommodations.

Appendix 1: System Description and Design Data - Contamination Environment

I copied the velocity from document and I didn't make a typo, though the difference between the 3500 m/s velocity it cites and the 2846m/s Oberg now says it's supposed to be is inconsequential. The exhaust plume goes a LONG way in 1.2 seconds at either speed.

[SkepticalEd]

I can see Oberg is still his usual cheery self.

In any event, the light flash in the video is clealy NOT from a rocket at all for reasons I've explained before: the flash of light is lens flare. It originates in the upper left corner of the video frame and expands downward toward the lower right corner. The L5D thruster to which Oberg attributes the light flash is below and to the left of the lower left corner of the video frame. Plus, the line of sight at the camera's upper left corner was elevated 62 degrees above the plane of the shuttle's wings. Any plume of gas or "snow" from the thruster seen at that position would be about 30 feet above the thruster's location. That's quite a distance for stuff escaping from the nozzle of a small, downward-pointing vernier thruster to travel and still be visible. But if "eager believers" want to believe the light flash is rocket exhaust because it fits their pet theories, there's nothing I can do to stop them.

If this boring conversation is about the popular STS-48 footage it validates my claim that the flash that is seen is not from a shuttle thruster. I'm not an expert on space matters but I go with what I see. However, for Fleming to say that it is lens flare is about as silly an explanation as I've ever heard. I've never seen "lens flare" without a source for the flare, and the "flare" appear and dissipate in a flash (pun intended). Usually lens flare appears proportianately as the camera lens is rotated towards the light source, strengthen, and either stay if the camera is fixed in that position, or disappear proportionately as the camera continues to move away from the light source that created the lens flare in the first place. The flash on STS-48 is neither a shuttle thruster nor lens flare. Someone will have to do better.

Edited November 24, 2007 by SkepticalEd

[JimOberg]

Oberg's "imbalanced" propellants explanation does not seem to make sense.

The English of which is, "MY brain can't make sense of that explanation."

Welcome to the discussion. I'll dig up some REAL expert testimony, for our colleagues here.

As to how the engines behave, as seen on downlink television, that's the way it is --

physical explanations have to conform to eyewitness reports. In MANY fields of study, for sure...

Edited November 25, 2007 by JimOberg

[Lan Fleming]

The English of which is, "MY brain can't make sense of that explanation."

Welcome to the discussion. I'll dig up some REAL expert testimony, for our colleagues here.

As to how the engines behavem, as seen on downlink television, that's the way it is --

physical explanations have to conform to eyewitness reports. In MANY fields of study, for sure...

Thanks. If I've misinterpreted your explanation, I apologize. But I thought that this statement you made implied the cause of the light flash was due to an imbalance in the proportion of fuel versus oxidizer:

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.

If that's not the case, I'd like to know why unstable flow would lead to flashes of light. As I mentioned, the main topic of my discussion with the NASA engineer was the helium pressurant. The piece of mesh material he showed me is the material that is placed inside the propellant tank to prevent helium bubbles from getting into the propellant stream to the thrusters. Such bubbles, if large enough, can produce unstable propellant flow. I don't know if that would generate any light, but I was told that such instabilities can cause large-amplitude vibrations in the combustion chamber that can rupture the thruster, resulting in an explosion. That's certainly not something that would be considered routine. I didn't ask whether any such anomaly had ever occurred on a shuttle flight, but I would think it could render the entire RCS system inoperable.

[Lan Fleming]

If this boring conversation is about the popular STS-48 footage it validates my claim that the flash that is seen is not from a shuttle thruster. I'm not an expert on space matters but I go with what I see. However, for Fleming to say that it is lens flare is about as silly an explanation as I've ever heard. I've never seen "lens flare" without a source for the flare, and the "flare" appear and dissipate in a flash (pun intended). Usually lens flare appears proportianately as the camera lens is rotated towards the light source, strengthen, and either stay if the camera is fixed in that position, or disappear proportionately as the camera continues to move away from the light source that created the lens flare in the first place. The flash on STS-48 is neither a shuttle thruster nor lens flare. Someone will have to do better.

Perhaps my terminology is not accurate, but what I would consider to be lens flare doesn't require the light source to be visible in the image. Light from an unseen source could reflect off the inside of the rim of the enclosure holding the lens and then be visible in the image. That's exactly what can be seen to happen as the sun rises at the beginning of the video sequence: the bright patch in upper left corner gradually gets larger and expands toward the lower-right corner of the frame until the entire image becomes washed out. The sun is in the opposite direction of the lens flare: somewhere below the lower right corner of the image. The "flash" is a sudden increase of brightness in the same upper left corner that expands in the same direction, almost as if the sun is having a sudden flare up.

Bruce Maccabee, who's got a PhD in optical physics, suggested that the flash was caused by a momentary specular reflection off some surface of the shuttle that was oriented relative to the sun in such a way that more sunlight suddenly entered the camera for a short time. Maccabee is a UFO researcher, but he's not enamored of this shuttle video. His suggestion was that the occurrence of the specular reflection at the moment the objects change course was just a random coincidence, leaving the prosaic explanation more or less in tact, but minus the light flash playing any role at all. A more exotic explanation would be that the flash was some big off-camera event in the same general direction as the sun but something else entirely. What that something might be I'll leave to your imagination.

[lost_shaman]

Well if it was just a thruster firing as Jim advocates, you'd think we'd see this same type of flash happen all the time on Shuttle flights but we don't. If it was an RCS thruster firing we should see a similar flash everytime the same thruster fires from the same camera during daylight, and I don't think that is the case.

Edited November 24, 2007 by lost_shaman