Wednesday, August 28, 2013

Fifteen Years and Counting

August 26, 1998 ... A Delta III explodes shortly after launch from Pad 17B at Cape Canaveral Air Force Station.

August 26 of this week marked the fifteenth anniversary of the last rocket launch explosion at Cape Canaveral Air Force Station.

It was the maiden launch of the Boeing Delta III from Pad 17B on August 26, 1998. The payload was the Galaxy X commercial communications satellite.

According to Delta II & III Space Operations at Cape Canaveral, 1989-2009 by Mark C. Cleary:

Between 55 and 65 seconds into the flight, roll oscillations around 4 Hertz (4 Hz) prompted the launch vehicle's control system to gimbal its three swiveling GEMs to compensate for the oscillations until the hydraulic system ran out of fluid. At 65 seconds, the GEMs ceased to swivel, and two of them were stuck in positions that helped overturn the vehicle. The DELTA III's main engine gimbaled to correct the overturning movement, but, as it fought against its big, 13.1-foot-diameter fairing and its GEMs, it quickly lost the battle. The vehicle yawed about 35 degrees, and it began to disintegrate at an estimated altitude of 60,000 feet about 71 seconds after lift-off. In accordance with safety guidelines, the Mission Flight Control Officer on duty sent destruct functions 75 seconds into the flight, and that action completed the destruction of the vehicle. All debris fell into the Atlantic Ocean between 10 and 15 miles east of Cape Canaveral.

Amateur video of the Delta III launch and explosion.

Fourteen days earlier on August 12, a Titan IV-A blew up after launch from Pad 41. The payload was a satellite for the National Reconnaissance Office. It was the last Titan IV-A to be launched.

To quote from Mr. Cleary's Atlas and Titan Space Operations at Cape Canaveral, 1993-2006:

At T plus 39.463 seconds, an alarm issued — input voltage to the Missile Guidance Computer (MGC) had fallen, causing the start of a "power down" sequence for the MGC. At T plus 39.650 seconds, the MGC recovered power and reinitiated the timing reference signal to the IMU, but the IMU came back with a false indication, prompting the MGC to command the TITAN IVA into a full pitch down with a yaw to the right at T plus 39.818 seconds. In less than two seconds, the disaster ensued. When the TITAN IVA’s pitch drifted 13 degrees off the planned trajectory, the vehicle started coming apart. At T plus 41.545 seconds, SRM #1 separated from the core vehicle and triggered the Inadvertent Separation Destruct System (ISDS). The explosion destroyed the core, and SRM #2 was destroyed by its ISDS at T plus 41.709 seconds. At T plus 45.529 seconds, flight controllers sent command destruct signals to the vehicle to ensure its destruction. Based on telemetry, the TITAN IVA reached an altitude of 17,047 feet when it exploded. It was 4,422 feet downrange, and it was traveling at 1,007 feet per second when it disintegrated. Several thousand pieces of propellant and vehicle fragments scattered themselves over a five-mile by three-mile area, but no debris impacted land. No one was in any danger from the mishap, and a 20-knot wind took the cloud of unspent rocket propellant harmlessly out to sea.

August 12, 1998 ... A Titan IV-A is destroyed 45 seconds after launch from Launch Complex 41.

One of the more infamous explosions occurred more than a year earlier. On January 17, 1997, a Delta II exploded thirteen seconds after launch from Pad 17A. The payload was an Air Force NAVSTAR GPS IIR-1 satellite.

According to Mr. Cleary's Delta II & III history:

Approximately 7.2 seconds after ignition, GEM #2 developed a 71-inch-long split in its casing. The split grew to 254 inches before the motor failed catastrophically about five seconds later (e.g., T plus 12.6 seconds). The casing failure prompted the first stage automatic destruct system, which destroyed the vehicle's first stage. The second stage, third stage and payload remained largely intact.

Observing those developments, Mission Flight Control Officers (MFCOs) sent command destruct functions to control the disintegration of the vehicle at approximately T plus 22.3 seconds. Their actions destroyed the second and third stages, which, in turn, released the payload fairing and payload. Unfortunately, the payload and fairing exploded on impact with the ground.

According to McDonnell Douglas' subsequent analysis of the mishap, there were no telemetry or visual indications of the explosion prior to the actual event. Weather was not a factor, and the cause of the explosion was unknown. Regarding events immediately after the mishap, the vehicle was about 1,590 feet above the ground and 100 feet downrange when the explosion occurred. The detonation of GEM #2 destroyed a GEM next to it, and the automatic destruct system took out the remaining GEMs and the first stage. Between 2,000 and 2,500 "firebrands" were released by the exploding GEMs and another 2,100 fragments were released by the disintegrated vehicle.44 Many of those firebrands left craters, and four fragments (e.g., the payload/PAM-D motor and three large GEM pieces) caused secondary explosions estimated at between 1,250 and 2,000 pounds of TNT. Workers found small fragments and unburned pieces of solid propellant as far away as the USAF Space & Missile Museum and the north end of Complexes 31 and 32, but all debris fell well within the Flight Hazard Area, up to 6,500 feet from the launch pad. The toxic cloud from the explosion drifted quickly out to sea.

No one was killed or injured as a result of the accident, but 26 vehicles, including a tractor trailer and a golf cart, were totally destroyed. Forty-six other vehicles were damaged. Four modular trailers were destroyed, and seven others received some degree of damage. The launch pad was not seriously damaged, and the Mobile Service Tower and Umbilical Tower sustained no more damage than they experienced during a normal DELTA II launch. Private property damage (including the leased trailers and the vehicles mentioned above) came to approximately $429,000.

There were 73 people in the blockhouse when the accident occurred. A large piece from one of the GEMs landed on the northeast corner of the blockhouse. The explosion caused damage to the protective berm, but it did not penetrate the blockhouse.47 The occupants were shielded from the fire caused by the explosion, though an appreciable amount of smoke filtered in via a cableway. As one observer noted, the inside the blockhouse took on the appearance of a "smoky bar." All occupants donned breathing apparatus, and firefighters and emergency response teams escorted them out of the area. There were no injuries due to smoke inhalation.

A documentary showing the Delta II explosion. The producers unfortunately added a lot of phony sound effects.

The proximity of the blockhouse to the LC-17 pads led to the construction of the Delta Operations Building the year before just inside the station's Gate 1 to the southwest, but it was not yet operational at the time of the explosion.

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