Sunday, April 8, 2012

Reflections on Deflections

A side flame deflector stored in the Launch Complex 39B parking lot. Image source:

I was driving Sunday past Launch Complex 39B when I noticed two side flame deflectors parked in the lot. I don't know if they're from 39A or 39B.

Looking for more information on the flame deflectors, I found on the Internet a January 2011 document by United Space Alliance looking at damage to the LC-39A flame trench during the STS-124 launch on May 31, 2008.

Click the arrow to watch the STS-124 launch.

As detailed in the report, "over 3,500 of the 22,000 interlocking refractory bricks that line the east wall of the SRB Flame Trench were liberated from Pad 39A."

"Liberated" is a polite way of saying they got blown out the Solid Rocket Booster flame trench about 1,800 feet at a velocity of 680 miles per hour.

One shudders contemplating what might have happened if those bricks had been blown upwards into a booster or the external tank.

The report notes that the "flame trench refractory brick system was designed for the Saturn Apollo program, which had a liquid fuel propulsion system, and was grandfathered into use in the Shuttle program, which has a solid fuel propulsion system." Apparently no one did a "detailed definition of the loads and environments" of the trench comparing the Space Shuttle to the Saturn V.

The north trench was designed for Saturn's liquid fuel, but during Shuttle it was used for SRB exhaust. "With the solid fuel propulsion system the overall environment is worse," the report concluded.

  • Materials are heated, then cooled with the sound suppression water
  • The solid propellant residue (aluminum oxide) is abrasive
  • Another of its byproducts (hydrogen chloride) subjects the materials in the launch environment to a hydrochloric acid bath
  • The released water acts like a blanket to trap the acoustic energy of the SRB ignition below it, thus subjecting the materials and equipment below it to a more intense acoustic environment

The "Lessons Learned" at the end of the report sound suspiciously like warnings issued after the Challenger and Columbia accidents:

  • The fact that a legacy system has never failed catastrophically does not guarantee that it will not fail in the future
  • Detailed loads and environments need to be defined for design of new launch vehicle [Ground Support Equipment] and facilities
  • More comprehensive inspection methods should have been used in order to detect material erosion when it was first becoming noticeable in the flame trench

A July 2008 image of repairs to the LC-39A flame trench after it was damaged by the STS-124 launch. Image source: NASA.

Once the flame trench was repaired, to my knowledge no further incidents of damage occurred. But these conclusions suggest that, five years after Columbia, NASA was still assuming that just because something hasn't failed in the past means it won't fail in the future.

UPDATE April 9, 2012 — It tuns out that the booster flame trench did fail again, with STS-125 on May 11, 2009. According to Florida Today, "Monday's launch of shuttle Atlantis blew a 25-square-foot section of material off a flame trench deflector at Kennedy Space Center's launch pad 39A ... The damage was located on the north side of the solid rocket booster flame deflector, near an area that was repaired after the launch of Discovery's STS-120 mission on Oct. 23, 2007." reported on July 14, 2008 that some of the bricks dislodged on STS-124 did travel vertically, creating the risk of damaging the Shuttle during launch.

As observed on an infrared video of the launch – which pointed to several items of debris rising above the pad and appearing to follow Discovery – the radar also noted debris tracks which appeared to be travelling in a vertical path.

‘Indications of discrete, near vertical, debris tracks can be seen in one pass of the vertical radar. These cannot be rendered at heights lower than the 295′ level of the FSS due to sector blanking for that sensor.

‘This signature is consistent with infrared camera indications of particles reaching high apparent altitudes around the pad near lift-off' ...

Managers have previously noted that it would be impossible for the bricks from the flame trench to threaten the vehicle – which is based on analysis of the bricks finding a path upwards through the MLP. This is indeed impossible.

While analysis of the infrared footage is inconclusive, and requires further evaluation, engineers concur with management and conclude the debris has to be throat plugs and water baggie debris – at least for the events observed next to the SRB exhaust.

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