Posted on 02/21/2003 4:34:05 PM PST by yonif
WASHINGTON - A NASA safety engineer warned days before Columbia broke apart that he feared the shuttle was at risk for a devastating breach near its left wheel, and he suggested people in the U.S. space agency weren't adequately considering the threat.
"We can't imagine why getting information is being treated like the plague," the engineer wrote in one of a number of e-mails released Friday that describe greater concerns about Columbia's safety in the days before its breakup.
Other documents NASA released show that Columbia may have been struck by as many as three large chunks of foam that smashed against delicate insulating tiles as it took off, not just the one previously acknowledged.
Robert Daugherty, an engineer at NASA's Langley research facility, Va., did not indicate that he believed the breach would cause Columbia to break apart during its fiery descent. "No way to know, of course," he wrote.
But Daugherty warned in his e-mail on Jan. 29 about a possible breach near the seal of Columbia's wheel compartment that could have been caused by damage to the shuttle's thermal tiles there. He seemed mostly worried about the risks of pilots struggling to land Columbia with one or more tires damaged by extreme heat.
"It seems to me that if mission operations were to see both tire pressure indicators go to zero during entry, they would sure as hell want to know whether they should land with gear up, try to deploy the gear or go bailout," Daugherty wrote.
Senior NASA officials have steadfastly supported assurances by The Boeing Co., a contractor, since the accident that Columbia was expected to be return safely despite possible tile damage along its left wing. They also have maintained that concerns expressed in e-mails among mid-level engineers such as Daugherty were part of a "what-if" analysis, and that even these engineers were satisfied with Boeing's conclusions.
"During the flight, no one involved in the analysis or the management team or the flight team raised any concerns," NASA spokesman James Hartsfield said Friday.
But the e-mails disclosed in Washington raise important issues about those safety assurances by Boeing, including underlying assumptions about the likelihood of damage from a large chunk of breakaway foam and whether damage to Columbia might have been caused by falling ice.
They also include references by Daugherty and another Langley employee, Mark J. Shuart, about the secrecy within National Aeronautics and Space Administration of the ongoing study of risks to Columbia. Shuart wrote Jan. 28 to two other employees that, "I am advised that the fact that this incident occurred is not being widely discussed."
The e-mails, which never were passed during Columbia's flight to senior mission controllers in Houston, will be turned over to the board investigating the accident, board spokeswoman Laura Brown said. All seven astronauts died in the breakup.
The e-mails were sought since last week by news organizations under the Freedom of Information Act.
Employees at NASA's headquarters here published them Friday with little fanfare on the agency's Web site.
Among the e-mails disclosed Friday were two written after the breakup. Daniel D. Mazanek of the Spacecraft and Sensors Branch at Langley wrote Feb. 7 wrote that the debris that struck Columbia might have been ice, not foam from its external fuel tank.
Boeing had calculated that a chunk of foam weighing 2.67 pounds (1 kilogram) pounds was responsible. But Mazanek estimated that a chunk of ice the same size would have been more damaging because it weighs 63.4 pounds (28.5 kilomgrams) "the equivalent of a 500-pound (225 kilogram) safe hitting the wing at 365 mph (582 kph)
Last week, NASA disclosed a similar e-mail by Daugherty. He wrote two days before Columbia's breakup about risks to the shuttle from "catastrophic" failures caused by tires possibly bursting inside the spacecraft's wheel compartment from extreme heat.
Daugherty was responding in that e-mail to a telephone call Jan. 27 from officials at the Johnson Space Center asking what might happen if Columbia's tires were not inflated when it attempted to land.
Daugherty cautioned in his e-mail disclosed earlier that damage to delicate tiles near Columbia's landing gear door could permit dangerous temperatures causing one or more tires inside to burst, perhaps ending with catastrophic failures that would place the astronauts "in a world of hurt."
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The operative equation for kinetic energy is 0.5*M*V^2, where M = mass, and V = Velocity. In this case the velocity term of interest is actually the "relative velocity" of the debris when it struck the wing. Use of this operative equation suggests that Mazenek thought that the relative velocity of the postulated ice chunk would have been about 1025 mph, which is higher that previous estimates that have been discussed (510 mph). One suspects that this much kinetic energy would have caused immediate and extensive damage to the wing itself.
A 63.4 pound block of ice would have had a much greater "ballistic coefficient" than a 2.67 pound block of foam, since the mass is much greater (a factor of 24x), while the drag would be approximately the same. It is very unlikely that a block of ice decelerated to a relative velocity of 510 mph, let alone 1025 mph.
However, an intermediate scenario would be if the debris was a combination of foam + ice. This combination could scale up the kinetic energy proportionally to the total mass, without drastically altering the ballistic coefficient by a factor of 24x. For example, what if the debris what mostly foam with a small ice content? It is conceivable that a 4 pound chuck of water / ice could decelerate to a relative velocity of 400-500 mph, which would still be a devastating amount of kinetic energy.
If this is truly the case then this would be the opposite of what we typically see after a disaster.
The signal was recorded at about 14:30 GMT. It shows a gradual ramp up of signal followed by a series of sharp events that appear to be explosions, somewhere between 7 and 12 separate events, with one widely spaced small event near the end. It took the sound wave about 30 minutes to arrive at the infrasound array in Lajitas, Texas. Best estimate of real-time for the first large peak is 13:59, within a minute of when NASA lost the telemetry signal.
Calculation of the azimuth (angle to the source) of the peaks of the signal recorded at TXAR by the SMU team show that, though the peaks are spread across about 11 minutes, during which time the shuttle would have traversed a few thousand kilometers, the azimuths all came from the same direction, within plus or minus one degree. This indicates to the seismologists that these are not separate explosions, but rather multiple paths, more properly 'refractions,' of a single explosive event. That event appears to have occurred at about 13:59 over west Texas between Lubbock and Amarillo, at an altitude of about 62 kilometers. Previous simulations of infrasound signals done by researchers at the Los Alamos National Laboratory ("Modeling Study of Infrasonic Detection of 1 kT Atmospheric Blast" by K.A. Dighe, R.W.Whitaker, and W.T.Armstrong) of the stratospheric and thermospheric infrasonic returns from a single explosion show striking similarity to the multi-peak infrasound signals recorded for the breakup of the Columbia at TXAR. SMU analysts compute the signals as most likely a single decompressive event.
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