PH307 Disasters Essay Space Flight Disasters, Smith, October 2009 Essay title: Challenger and Columbus. What are the known risks and unknown risks of manned spaceflight? Can we assess the risk? Should we take the risk?

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STS-51L: The Challenger Accident
Correcting some misconceptions...
Copyright ©2002
Roger Balettiehrust differential between the two boosters, which was as predictabMr. Maxson claims that the cause of the Challenger Accident was not an O-ring burnthrough on the starboard (right) Solid Rocket Booster (SRB) as has been proven by photographic, telemetric, and video evidence as well as examination of recovered flight hardware. To the contrary, Mr. Maxson lists several technical errors and several sinister motives assigned to many different people in both government and private sector walks of life. Given my experience as a Flight Dynamics Officer in the Space Shuttle Mission Control Center, I will center my attention on those theories with which I have the most experience. I will leave the other theories to the reader to examine.

The majority of Mr. Maxson's claims are based on a perception of certain events leading up to the launch (most, if not all, without any documented evidence presented in the book) or based on visual examination of photographs and/or videos. The former perceptions are described from a first-person point-of-view, with Mr. Maxson being in the midst of, or having direct access to, a surprising number of events and personnel related to this historic event (á la Tom Hanks in the movie "Forrest Gump"). The latter examinations are subjective analyses of photographs that sometimes present blurry or fuzzy artifacts that are interpreted to be something sinister or at other times a description of events that can only be described as "a far stretch".

Given that, Mr. Maxson's theories, outlined in his book, which I will be discussing are:

  • A cryogenic cold-soaking of the port (left) SRB caused the left SRB to burn through, not the right. This led to a fracture in the External Tank (ET) at launch, resulting in a hydrogen fire ignited on the pad.

  • The Shuttle Reaction Control System (RCS) was used during ascent, enhancing the ET hydrogen fire.

  • An abort was being initiated by the Shuttle crew.

  • The Inertial Upper Stage (IUS) was ignited during the conflagration.

  • The SRBs switched sides (i.e., "crossed") during the conflagration.

However, given the narrative style of and lack of cohesive explanations in Mr. Maxson's book, I will address the shortcomings of the above-stated theories in a different manner. Anecdotal reflection of events and speculative analyses of photographic and video evidence do not always equal a factual presentation of theory.

I. Anecdotal evidence

The first chapter of Mr. Maxson's book is titled "Prima Facie Evidence". It is important to this discussion to understand the definition (from of "prima facie":

prima facie \PRY-muh-FAY-shee; -shuh\,

    At first view; on the first appearance.
    1) True, valid, or adequate at first sight; as it seems at first sight; ostensible.
    2) Self-evident; obvious.
    3) (Law) Sufficient to establish a fact or a case unless disproved.

Most, if not all, of the evidence presented as "prima facie" in this first chapter are the result of either mis-interpretation of photographic and video evidence or the speculative extrapolation of statements made during a time in which facts were not known.

None of it meets the definition of "prima facie", as above.

Among the first mistaken claims is that "a disturbing problem occurred prior to lift-off" ("The Betrayal of Mission 51-L", page 1). A long-range video taken from the Vehicle Assembly Building showed a shadow at the end of the crew access arm. Mr. Maxson, without any evidence, sensor readings, or other corroboration, decided that this was "dense black smoke" (ibid, page 1, Figures 1 and 2). Curiously, this claim was never repeated throughout the book, nor was it ever explained why this may have been important... had it actually occurred.

Photographs and videos of Shuttle launches both before and since STS-51L have shown the creation and growth of the trans-sonic shock wave forming on the stack as it passes through Mach 1.

Mr. Maxson's narrative attempts (incorrectly) to interpret this relatively regular visual display as "passage through Mach 1 was not routine" (ibid, page 1) and that the "particular effects were unique to 51L" (ibid, page 45).

The image here shows a recent (STS-106) ascent exhibiting the same effects. It is critical to note that this effect occurs on every Shuttle launch. It is visible to the human eye when condensation effects occur due to localized humidity, etc.

It is also at this point that Mr. Maxson's "proof" of trouble relies on visual observation of rather fuzzy or grainy images and applying an absolute definition of events to them. For instance, a photograph (ibid, page 1, Figure 4) claims to show that "flame bursts sporadically appeared on the right side of the tail" (ibid, page 1). Given that the video camera was looking through the downstream plume of both the SRBs and the Space Shuttle Main Engines (SSMEs), it is nearly impossible to assign any origin of such a faint visual event based solely on this evidence. Even Mr. Maxson claims that he can see a plume "despite the view through the bright gases from the main engine exhaust" (ibid, page 2).

Without any supporting evidence, Mr. Maxson further claims that "it seemed evident to me that Mission Control had been apprehensive about something" (ibid, page 2). Given my professional experience and personal friendships with a number of Flight Controllers who were present in the Mission Control Center (MCC) for the STS-51L ascent, this is an incorrect statement. There were no real-time indicators (certainly at the point where Mr. Maxson makes his claim) that the Accident was about to occur.

Some of the most spectacular and obvious evidence of the cause of the STS-51L Accident (namely the starboard SRB burnthrough) was completely dismissed by Mr. Maxson in a single statement regarding Recording Optical Tracking Instrument (ROTI) video.

Specifically, a claim that "there was no sign of a 'burnthrough in the right booster' later fictionalized by NASA and memorialized in the media" (ibid, page 3).

The photographic and video evidence of the starboard SRB burnthrough, as well as the telemetric readings showing that the right SRB was 24 psi (approximately 6 sigma) lower than the left SRB, provides a useful counterpoint to the sensational claim made that no burnthrough on the right booster had occurred.

A significant statement, attributed to a Mr. Leo Krupp, is used to provide some backing to Mr. Maxson's claim of the left SRB being the significant cause of the Accident. Mr. Krup (sic) is identified as a "former Enterprise pilot" (ibid, page 4), when Mr. Krupp is easily identified as a former Supervisor of Pilot Technology at Rockwell International.

At any rate, Mr. Maxson uses a quote from Mr. Krupp during a CBS network interview shortly after the Accident where Mr. Krupp speculates "I assume it was the right one, because it looked like the left one was the one that exploded" (ibid, page 4). A transcript of the conversation has Mr. Krupp stating "Well Dan, first of all I don't think anyone can really say for sure until NASA has a chance to analyze all the data and look at their telemetry downlinks and try to put this thing together". By stating up front that he was speculating on cause without a thorough engineering review, Mr. Krupp's statement can not be considered as "prima facie evidence."

Without spending significantly more effort on providing individual counterpoints to each of Mr. Maxson's claims, it is seen that the hypotheses promoted in "Betrayal" as "prima facie evidence" are based more on speculation than on evidence.

II. Speculation

Mr. Maxson claims that the condition of launch pad 39B prior to STS-51L (first Shuttle usage of this launch facility) contained serious hydrogen leaks that were neither detected by nor reported to NASA. Mr. Maxson claims that intentional launch delays and subsequent ET refuelings "ensured that the left solid rocket was adequately cold-soaked for disaster" (ibid, page 26).

The only rationale for this apparently intentional sabotage was blamed on "(President) Reagan's plans for militarizing space" (ibid, page 81). Claims of "organized crime at KSC" (ibid, page 19) were also made (without any attempt at providing proof) in an attempt to assign sinister motives and a willing intent to cause the destruction of Challenger and the deaths of the seven crewmembers.

NASA's launch facilities have a large number of sensors at various locations. For a hydrogen leak of this magnitude to have gone undetected or left other obvious visual signatures belies the historical evidence of past hydrogen leaks of significantly less magnitude being detected and holding launch.

Much speculation was also attached to video artifacts claimed to be RCS usage during ascent. Without any evidence to back up these claims, statements like "undisclosed to the public, NASA began to make limited use of the (RCS) jets at altitudes below 70,000 feet" (ibid, page 8)and "NASA Select and the (STS) 41-C telemetry recorded unmistakable evidence of first-stage RCS activity" (ibid, page 13).

There is no telemetry evidence available within Mr. Maxson's book, nor any of which I am aware at all, that would back up these fantastic claims. Ascent guidance does not rely on RCS for attitude control. The claim that "the Air Force had begun a policy of using the RCS jets to maintain center of gravity for certain payloads" (ibid, page 38) shows a lack of basic understanding of the flight dynamics of the Space Shuttle, especially in the ascent regime.

Several times within the book, Mr. Maxson makes claims to a more northeast trajectory for Challenger. Telemetry evidence does not support this as fact.

A claim that "an uplink to select Casablanca, made at the last minute, would explain Challenger's northeast trajectory" (ibid, page 109) implies that Transoceanic Abort Landing (TAL) site selection has any bearing on ascent guidance. In fact, TAL site selection has no bearing whatsoever!

The groundtrack produced by the ascent guidance is a direct function of the targeted orbital inclination, unless yaw-steering is enabled, as would be the case for very high-inclination (i.e., 57° or higher) missions. STS-51L was a "due East" or 28.5° inclination mission.

During another discussion, Mr. Maxson claims that the selection of Casablanca was made at the behest of CIA Director Bill Casey so that "an extremely cold left booster would force the shuttle south from its advertised due east trajectory, causing public alarm" (ibid, page 32). In reality, Dakar, Senegal, was the TAL site selected for the launch of STS-51L on the morning of January 28, 1986. Casablanca was declared "NO GO" due to forecast rain and low ceilings violating Flight Rules.

Mr. Maxson further claims that the crew was in the middle of performing an ascent abort during the last few seconds of the ascent. There is no evidence for this claim, either.

A claim that Scobee (CDR) and Smith (PLT) "had been receiving special training for an abort" (ibid, page 52) is presented in an attempt to convince the reader that this training was somehow unusual. Standard crew training flow concentrates on ascent procedures, including abort scenarios, intensely prior to launch.

Speculative examination of very fuzzy images from camera E204 (ibid, page 53, figures 88 and 89) claims that a "fast-sep" abort was in progress. Given that there was no telemetry evidence to support this, the crew was not aware of the events leading up to the Accident, and their training would not have had them perform this sort of drastic action without clear indication of a problem, it is safe to say that the conclusions reached concerning an ascent abort are incorrect.

During the conflagration that resulted and the aerodynamic breakup of Challenger, Mr. Maxson makes the claim that the Inertial Upper Stage (IUS) booster, attached to the Tracking and Data Relay Satellite (TDRS) and contained in Challenger's payload bay, was somehow responsible for further destruction.

A claim that "the guidance thrusters on this payload missle had ignited" (ibid, page 57) leads to the statement that "the IUS hurtled forward into the crew cabin" (ibid, page 57). By claiming the IUS RCS thrusters had "burst into flame" (ibid, page 57), Mr. Maxson overlooks the key point that the IUS thruster is actually a solid rocket motor. The IUS RCS thrusters are quite small and incapable of providing the thrust to which he attributes them.

For some reason, an attempt is made to convince the reader that the SRBs crossed within the conflagration fireball. No telemetric evidence is available to support this.

An excellent review of "Betrayal", "STS-51L: The Challenger Accident -- Conspiracy Theories, Challenger, and Solid Rocket Boosters" (written by Jon Berndt), addresses this point extremely well, and I don't feel the need to re-invent the wheel. Please refer to Jon's review for more information.

III. Open Questions for Mr. Maxson

  1. Why is there no mention of the 8 smoke puffs clearly seen exiting from the same area where the flare on the right SRB was to be seen later? The frequency of these puffs approximated the 4 times/second frequency of the structural load dynamics and SRB joint flexing.

  2. If an ET fracture occurred at launch (ibid, page 34), why was there no LH2 pressure drop detected until approximately T+65 seconds?

  3. Why does the right SRB rate gyro telemetry show an angular velocity difference with respect to the Orbiter when the left SRB does not?

  4. If the assumption of a right aft RCS firing is to be considered, how can the distance from the right OMS pod (where the RCS jets are mounted) to the ET be resolved without a complete loss of heat energy in the near-to-supersonic airflow about the stack configuration?

  5. What job titles, specifically, did you hold between "mid October 1985" and February 1986?

    • You mention at least three job transfers between KSC and Vandenberg during that time with a myriad of vague job descriptions ranging from being "in charge of operating system software" (ibid, page 13) to writing "computer procurement orders" (ibid, page 13) to "prioritizing all Category 1 work scheduled for completion prior to 51-L" (ibid, page 19). At some point in your story, you claim to be "essentially a software expert" (ibid, page 19), but never provide a clear educational or professional background that shows proof of that claim. Can you provide that proof?

    • In addition, a claim of "experience in controlling the flow of gaseous hydrogen" (ibid, page 19) was made. At what point during your career were you engaged in this hardware activity?

differential at lift-off.

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