Saturday, May 19, 2012

Science - Space Shuttle, NASA's Gamble on Safe Re-Entry at 3000 F (30,000 Tiles, $10K Each!)

"Science - Space Shuttle, NASA's Gamble on Safe Re-Entry at 3000 F (30,000 Tiles, $10K Each!)"," To insulate the Orbiter from the searing heat of reentry, the idealized solution is a ""vacuum"", which blocks all heat transference.
 Idealizing again, this "package" (tile - containing all functioning elements to achieve optimized thermal insulation) would be as thin as practical (and small in horizontal dimensions).
 Finally, the tile would be bonded (the cool - insulated bottom) to the vehicle's basic aluminum structure.
 As every aspect theoretically feasible, the challenge was the smallest practical tile size that was producible in volume.
 The tiles are bonded to the Orbiter structure by standard RTV (Room Temperature Vulcanizing) adhesive.
 There are 30,000 black tiles (seen in all photos of a Space Shuttle).
 The TPS tile system has proved its reliability, taming reentry heat (temperatures of from 2200 to 3000 degrees Fahrenheit).
 As the Orbiter speeds down (18,000 mph) into Earth's atmosphere, air molecules are impacted by the Orbiter, causing tiny pulses of heat and drag; this causes wing leading-edge temperatures to rise to from 2200°F to 3000°F (depending upon reentry angle) - during approximately a six minute speed-altitude transition period, and gradually slows the Orbiter down, eventually reaching ground level and landing speeds of a typical aircraft.

The voice over the loudspeaker was concluding, "So congratulations to all of us on the Shuttle team, STS-2 appears to have been a great success, and - ", Another voice abruptly cut in, "Rockwell Space, Will Mr.

At mention of my name, I rose from the conference table, looking at my boss, Chief Engineer, and his boss, president of Rockwell Space Division.
 She nodded to me and pointed to a phone.
 Our greetings were terse - Moser spoke for about five minutes, I asked a few questions.
" I said I'd be up at Edwards (Air Force Base) in about two hours.
 No indication of a TPS malfunction during reentry, but the tile damage looks unusual - Dr.
" The Chief Engineer nodded.

I drove automatically, knowing well the freeway route - my mind reviewing what I'd been told.
 The damage looked like chunks of the tile's insides, an inch or two, was missing.
 There was also other typical tile damage, the pits and break-throughs of the thin black glass, as after the STS-1 flight - undoubtedly due to stray bits of gravel, churned up from the concrete launch pad (despite careful vacuuming before each flight).
 The cost of the TPS was almost unbelievable, but their function, protecting against fiery reentry, as well as their compactness, permitting the Orbiter to function like an airplane - was what made viable the potential of the Space Shuttle program.
 Chris Kraft and the near-disaster of Apollo 13.
 There was a degree of satisfaction in his asking for me - but then NASA had given me the chore of presenting the TPS briefings at all NASA Flight Readiness Reviews for two years.

I turned into Edwards Air Force Base, parked my car, then saw a jeep speeding towards me.
 I climbed in and we took off.
 I got out of the jeep and walked quickly to it.

"So, what do you think?" The voice was familiar.
 "Kraft" We shook hands.
" The engineer handed me a set of photos of the damaged tiles.
 As we walked around the vehicle seeing whatever else looked unusual, Dr.
 Send us a top tile engineer to be at the Cape day after tomorrow - we'll get a NASA man also, then, plus you and Moser, I want an internal layout of possible causes in a week.
 The investigation became a "detective" scenario, puzzling out clues, conjecturing what could have happened, verification by test.

A week later, a briefing was given to the NASA Base Directors and Administrator:

The rainstorm was from a direction which caused a platform on the work-assembly structure to spill overflowing rain-water onto the left wing - Columbia standing vertically in the launch mode.

Occasionally hairline cracks were known to develop through the thin glass outer (black) coating of the tiles: either during manufacture; during the bonding process of attaching each tile to the airframe structure; when stuffing "gap-fillers"; or possibly even during the prior STS-1 flight (close packing of tiles causing occasional excess pressure on the thin glass walls during the vibration of landing).

During the flight mission, the left wing was pointed to deep outer space for many hours, the temperatures of the wing tiles therefore dropping to extremely low values, approaching absolute zero.

The ice-filamentary clump could therefore crack the glass casing and be ejected from the tile - occurring during one of the following events: upon freezing due to the significant volumetric expansion from fluid to ice; during reentry, when the ice began to melt, becoming a gas, the drastic volume increase bursting the glass casing; when the vehicle went through the sonic boom, the surface jolt of air pressure causing any remaining chunk of solidified filaments to be ejected from the top of the tile; or when the vehicle landed, the vibration shaking any remaining ice-quartz chunks loose.

Recommendation: when rain precedes a launch, a tarpaulin should be used to protect the tiles.

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